ArticlePDF Available

On-farm selection for quality and resistance to pest/diseases of cocoa in Sulawesi: (ii) quality and performance of selections against Phytophthora pod rot and vascular-streak dieback

Authors:

Abstract and Figures

The cocoa industry in Sulawesi, the main region of cocoa production in Indonesia, is threatened by destructive diseases, including vascular-streak dieback (VSD) caused by the basidiomycete Oncobasidium theobromae and stem canker and Phytophthora pod rot (PPR) or black pod, caused by Phytophthora palmivora. Using the considerable genetic diversity of cocoa on farms, host resistance was identified and tested with the participation of farmers. Forty-nine local and international cocoa selections with promising resistance characteristics (as well as susceptible controls) were side-grafted onto mature cocoa in a replicated trial with single-tree plots. Developing grafts were assessed in the dry season for severity of VSD infection, scored from 0 (no infection) to 4 (graft death). All of the 49 clones in the trial became infected with VSD in at least some replicates. Average severity varied from 0.2 to 1.6. Potential VSD-resistance was found in eight clones, including DRC 15, KA2 106 and a local Sulawesi selection, VSD2Ldg. Some of the most susceptible clones were local Sulawesi selections from areas with a history of little or no VSD. Thirty-four pod-bearing clones were evaluated over a 2-year period for yield, quality and resistance to natural infections of PPR. Cumulative PPR incidence for all clones was 22% but varied from 8.6 to 43% among clones. Clones with less than 15% PPR incidence were designated as resistant, including DRC 16 and local Sulawesi selections, Aryadi 1, Aryadi 3 and VSD1Ldg. Scavina 12 was moderately resistant in the trial with a PPR incidence of 23%. Cumulative incidences of the mirid, Helopeltis spp., determined in the same evaluation period, indicated that DRC16 was the most susceptible clone with an incidence of 52% in ripe pods and 23% in immature pods. In comparison, KKM4 showed evidence of resistance to Helopeltis spp., with incidences of 34 and 0.8% in ripe and immature pods, respectively. The impact of diseases and pests (including cocoa pod borer) on bean losses and bean quality varied between clones but generally the bean size (or bean count) was affected more than the fat content or shell content.
Content may be subject to copyright.
This article was downloaded by: [University of Sydney]
On: 05 August 2014, At: 16:33
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer
House, 37-41 Mortimer Street, London W1T 3JH, UK
International Journal of Pest Management
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/ttpm20
On-farm selection for quality and resistance to
pest/diseases of cocoa in Sulawesi: (ii) quality and
performance of selections against Phytophthora pod
rot and vascular-streak dieback
Peter McMahon a , Agus Purwantara b , Agung W. Susilo c , Sri Sukamto c , Abdul Wahab
d , Hussin bin Purung e , Muhammad Hidayat e , Darna Ismail e , Tap Taproni d , Smilja
Lambert f , David Guest g & Philip Keane a
a Department of Botany , La Trobe University , Bundoora, 3086, Victoria, Australia
b Biotechnology Research Institute for Estate Crops , Bogor, 16151, Indonesia
c Indonesian Coffee and Cocoa Research Institute , Jember, Indonesia
d BPTP SULTRA , Kendari, Sulawesi Tengarrah, Indonesia
e Mars Symbioscience Indonesia, Jl. Kima , Makassar, Sulawesi Selatan, Indonesia
f Mars Australia , Ring Road, Ballarat, 3350, Victoria, Australia
g Food and Natural Resources, Faculty of Agriculture , The University of Sydney , Sydney,
Australia
Published online: 15 Sep 2010.
To cite this article: Peter McMahon , Agus Purwantara , Agung W. Susilo , Sri Sukamto , Abdul Wahab , Hussin bin
Purung , Muhammad Hidayat , Darna Ismail , Tap Taproni , Smilja Lambert , David Guest & Philip Keane (2010) On-farm
selection for quality and resistance to pest/diseases of cocoa in Sulawesi: (ii) quality and performance of selections
against Phytophthora pod rot and vascular-streak dieback, International Journal of Pest Management, 56:4, 351-361, DOI:
10.1080/09670874.2010.503284
To link to this article: http://dx.doi.org/10.1080/09670874.2010.503284
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of
the Content. Any opinions and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied
upon and should be independently verified with primary sources of information. Taylor and Francis shall
not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other
liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or
arising out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions
On-farm selection for quality and resistance to pest/diseases of cocoa in Sulawesi: (ii) quality and
performance of selections against Phytophthora pod rot and vascular-streak dieback
Peter McMahon
a
*, Agus Purwantara
b
, Agung W. Susilo
c
, Sri Sukamto
c
, Abdul Wahab
d
, Hussin bin Purung
e
,
Muhammad Hidayat
e
, Darna Ismail
e
, Tap Taproni
d
, Smilja Lambert
f
, David Guest
g
and Philip Keane
a
a
Department of Botany, La Trobe University, Bundoora, 3086, Victoria, Australia;
b
Biotechnology Research Institute for Estate
Crops, Bogor 16151, Indonesia;
c
Indonesian Coffee and Cocoa Research Institute, Jember, Indonesia;
d
BPTP SULTRA, Kendari,
Sulawesi Tengarrah, Indonesia;
e
Mars Symbioscience Indonesia, Jl. Kima, Makassar, Sulawesi Selatan, Indonesia;
f
Mars Australia,
Ring Road, Ballarat 3350, Victoria, Australia;
g
Food and Natural Resources, Faculty of Agriculture, The University of Sydney,
Sydney, Australia
(Received 15 October 2008; final version received 18 June 2010)
The cocoa industry in Sulawesi, the main region of cocoa production in Indonesia, is threatened by destructive
diseases, including vascular-streak dieback (VSD) caused by the basidiomycete Oncobasidium theobromae and stem
canker and Phytophthora pod rot (PPR) or black pod, caused by Phytophthora palmivora. Using the considerable
genetic diversity of cocoa on farms, host resistance was identified and tested with the participation of farmers. Forty-
nine local and international cocoa selections with promising resistance characteristics (as well as susceptible controls)
were side-grafted onto mature cocoa in a replicated trial with single-tree plots. Developing grafts were assessed in the
dry season for severity of VSD infection, scored from 0 (no infection) to 4 (graft death). All of the 49 clones in the
trial became infected with VSD in at least some replicates. Average severity varied from 0.2 to 1.6. Potential VSD-
resistance was found in eight clones, including DRC 15, KA2 106 and a local Sulawesi selection, VSD2Ldg. Some of
the most susceptible clones were local Sulawesi selections from areas with a history of little or no VSD. Thirty-four
pod-bearing clones were evaluated over a 2-year period for yield, quality and resistance to natural infections of PPR.
Cumulative PPR incidence for all clones was 22% but varied from 8.6 to 43% among clones. Clones with less than
15% PPR incidence were designated as resistant, including DRC 16 and local Sulawesi selections, Aryadi 1, Aryadi 3
and VSD1Ldg. Scavina 12 was moderately resistant in the trial with a PPR incidence of 23%. Cumulative incidences
of the mirid, Helopeltis spp., determined in the same evaluation period, indicated that DRC16 was the most
susceptible clone with an incidence of 52% in ripe pods and 23% in immature pods. In comparison, KKM4 showed
evidence of resistance to Helopeltis spp., with incidences of 34 and 0.8% in ripe and immature pods, respectively. The
impact of diseases and pests (including cocoa pod borer) on bean losses and bean quality varied between clones but
generally the bean size (or bean count) was affected more than the fat content or shell content.
Keywords: cocoa diseases; Phytophthora pod rot; vascular-streak dieback; on-farm selections; resistance; Sulawesi
smallholders; Helopeltis; bean quality; side-grafted clones
1. Introduction
In Sulawesi, Indonesia, cocoa production has ex-
panded spectacularly beginning from minor produc-
tion in the early 1980s. This expansion has been
overwhelmingly in the hands of smallholders for whom
cocoa provides their main livelihood. As a result,
Indonesia is now the third largest cocoa producer
globally (Directorate General for Estate Crops 1999).
Following two decades of pioneer planting with
minimal problems, the smallholders and the Sulawesi
cocoa industry now face serious losses in production
and impacts on bean quality due to declining soil
fertility and pests and pathogens of which cocoa pod
borer (CPB, the moth Conopomorpha cramerella), the
oomycete Phytophthora palmivora which causes Phy-
tophthora pod rot (PPR) and stem canker, and the
basidiomycete fungus, Oncobasidium theobromae,
which causes vascular-streak dieback (VSD) (Keane
1992; Wardojo 1992) are the most serious. To address
these problems, an Australian Centre for International
Agricultural Research (ACIAR) project was estab-
lished to encourage the use of farmer participatory and
locally applicable methods for the selection, testing and
use of genotypes with better resistance and/or quality
on farms. The project aimed to develop a method of
on-farm selection and clonal testing that could be
adopted by farmers with the help of local extension and
research officers. The possibility of on-farm selection
for superior genotypes was based on the genetic
diversity found on Indonesian cocoa smallholdings as
a result of the several introductions and subsequent
hybridization of diverse cocoa types (original Trinitar-
io types developed during the early 1900s, Amelonado
types introduced from Sabah, Upper Amazon x
*Corresponding author. Email: peter.mcmahon@latrobe.edu.au
International Journal of Pest Management
Vol. 56, No. 4, October–December 2010, 351–361
ISSN 0967-0874 print/ISSN 1366-5863 online
Ó2010 Taylor & Francis
DOI: 10.1080/09670874.2010.503284
http://www.informaworld.com
Downloaded by [University of Sydney] at 16:33 05 August 2014
Trinitario ‘hybrid cocoa’ developed in Java and
including Upper Amazon and Trinitario material
from Malaysia and Papua New Guinea). As well, the
project aimed to build on the particular knowledge
held by farmers about the performance of genotypes on
their farms, the existing and widespread network of
government extension services in Indonesia and the
possibility of using clonal propagation (e.g. side-
grafting of mature trees) methods for farm improve-
ment. To this end, a clone testing trial was established
in Southeast Sulawesi. Clones collected with the
assistance of farmers, as well as international clones,
were propagated by side-grafting onto mature trees on
a working cocoa farm in an area affected seriously by
the major pest/disease problems typically found in
Sulawesi cocoa. Pod-bearing clones in this trial were
evaluated for 2 years (2005–2006). McMahon et al.
(2009) reported on the CPB incidence among the clones
under test during this period and the variability
detected in CPB incidence both between clones and
between seasons. Here we report on results for other
disease or pest problems, especially VSD and PPR.
VSD is a new encounter disease of cocoa, apparently
having transferred repeatedly to cocoa from an
unidentified host in Southeast Asia (Keane 1992) while
PPR occurs on cocoa worldwide. Host resistance to
VSD, at first in Papua New Guinea in the 1960s and
later in Malaysia, proved crucial to overcoming
epidemics that decimated the cocoa industries of those
countries (Zainal Abidin et al. 1984; Keane and Prior
1992). Resistance to VSD is partial, limiting infection
to branch tips thus preventing the fungus from
reaching larger branches and killing trees. Host
resistance to PPR appears to be partial and additive
(Tan and Tan 1990; Saul 1993; Van der Vossen 1997;
Zadocks 1997). Various studies have compared cocoa
genotypes for PPR resistance (e.g. see Blaha 1974;
Soria 1974; Saul 1993; Iwaro et al. 1997, 1998) and
identified resistance in some clones. The clonal testing
trial conducted at Ladongi indicated that the geno-
types, including local farm selections (many of which
were derived from introductions of Amelonado types
from Sabah), varied considerably in incidence and
severity of both PPR and VSD and provided support
to on-farm selection and testing as a promising method
for direct farm improvement and for identifying
promising genotypes for breeding programs.
2. Materials and methods
2.1. Selection, collection and propagation of cocoa
genotypes and trial establishment
Cocoa genotypes were selected on farms in South,
Southeast and Central Sulawesi and East Kalimantan
provinces of Indonesia as budwood sticks, transported
to the farm trial site and side-grafted onto mature
cocoa trees as described in McMahon et al. (2009).
International clones and susceptible local selections
were included in the mixture of genotypes tested. The
clonal testing trial (with a total of 49 clones) was set up
in Ladongi in Kolaka District, Southeast Sulawesi on a
working cocoa farm with the cooperation of the
farmer. The design was single-tree plots, randomised
in 20 replicate blocks (McMahon et al. 2009). Due to
difficulties encountered in side-grafting mature trees,
only 10–18 replicates were achieved for most clones
and 34 clones produced a sufficient number of pods by
the end of 2004 for assessment.
2.2. Severity of vascular-streak dieback (VSD)
The severity of VSD, which infects vegetative shoots,
was assessed during the dry season of 2004 on
developing grafts in the 49 clones established in the
trial. Severity of infection was assessed on a scale 0–4:
0, no infection; 1, signs of chlorosis, little or no leaf
drop; 2, distinctive chlorosis and some leaf drop; 3,
severe leaf loss, dieback; 4, graft death.
2.3. Incidence of Phytophthora pod rot (PPR)
Pods were assessed for PPR twice per month in a 24-
month period from January 2005 to December 2006.
All ripe (harvestable) pods and the immature pods that
were infected with PPR or otherwise infested or
diseased were harvested and separated into healthy
and infected/infested pods. Pods affected by cherelle
wilt could be differentiated from infected/infested
immature pods by their smaller size and were not
included in the assessment. The numbers of immature
and ripe pods infected with PPR were counted.
Harvested ripe pods with PPR infection (but no CPB
infestation) were evaluated for intensity of infection:
either heavily infected (PPR lesion covering over 50%
of the pod surface) or lightly infected (lesion covering
less than 50% of the pod). To estimate the incidence of
PPR on a typical smallholding in the area, a plot of 50
trees was assessed on a farm 0.75 km from the trial site
using the same evaluation method as in the trial, except
that evaluations were conducted monthly.
2.4. Inoculation of detached pods with PPR-infected
pod tissue
Ripe detached pods from a few of the clones in the
Ladongi trial were wound-inoculated with PPR-in-
fected pod tissue. Small discs (5 mm diameter) were
removed from the mesocarp of a PPR-infected pod and
inserted into holes cut with a cork borer in the husks of
healthy pods of the selected clones with three replicate
pods for each clone. The pods were kept in a moist
chamber at room temperature. The length and width
(cm) of the lesion was measured daily for a week
providing an estimate of expansion rate of the lesion
area (cm
2
) for 7 d after inoculation (d.a.i.).
352 P. McMahon et al.
Downloaded by [University of Sydney] at 16:33 05 August 2014
2.5. Determination of actual and potential pod values
for each clone
For each replicate tree, extractable beans were
harvested and separated into two groups: extractable
beans obtained from healthy ripe pods and extractable
beans obtained from infested or diseased ripe pods (see
McMahon et al. 2009). The wet weight for each group
of beans was recorded. For each clone, the collected
beans were pooled, dried and the dry weight recorded.
2.5.1. Actual pod value (no. pods per kg dried beans)
Actual pod value was determined as the number of
ripe, harvestable pods (both healthy and infested/
infected) needed to give 1 kg of dry beans.
2.5.2. Potential pod value and bean losses
The potential pod value was determined from the
beans extracted from healthy pods. Bean losses were
estimated by comparing the bean harvest from all ripe
pods (from which the actual pod value was determined)
with the bean harvest (based on the beans harvested
from healthy pods) expected if all the harvested pods
were free of pest/diseases. Pod values were calculated
for clones producing at least 10 healthy ripe pods.
2.6. Bean quality
For the clones that produced a sufficient quantity of
beans, quality assessments were conducted at the
research laboratory of PT Effem/Mars in Makassar,
Sulawesi. Bean count was determined as the number of
dried beans per 100 g. Shell content and cocoa butter
content were determined. Shell content was evaluated
by deshelling 100 g of beans and weighing the shells to
determine % shell content. To determine cocoa butter
content, bean samples were milled on a Retche
planetary ball mill and the cocoa mass was analysed
for fat content in a Near Infra Red (NIR) high
performance analyser (Foss System II 6500 scanning
spectrophotometer, NIR Systems Inc. Silver Springs
MD) fitted with a transport module in reflectance
mode. Spectra were recorded in the range 400–2500 nm
at 2-nm intervals. Calibrations were developed by
using modified partial least square regression
procedures.
2.7. Statistical analyses
Means for disease incidence (%) were weighted for the
numbers of pods produced by each replicate tree and
subjected to arc-sign transformations (Zar 1996).
Transformed values were subjected to ANOVA fol-
lowed by the Games–Howell test (SPPS Ver 11.5).
Data are presented in their original (untransformed)
form (see McMahon et al. 2009).
3. Results
3.1. VSD severity
Since VSD infects the vegetative shoots of cocoa
plants, all the clones initially established in the trial
were able to be assessed for VSD infection prior to
pod-bearing, when grafts usually still had fewer than
three branches. VSD infections were detected in all of
the clones tested in the trial in at least some replicates.
Table 1 shows the 49 clones in the trial at Ladongi
ranked from lowest to highest average VSD severity.
Clones varied considerably in average severity of
infection and in the range of severity among replicates
and by combining these two measurements, the level of
resistance for each clone was estimated (see Table 1
legend).
Resistant local selections were identified including
VSD2Ldg, selected from a farm in South-East Sulawesi
for potential VSD-resistance. The clones selected as
susceptible controls (VSD1Ldg and VSD4Ldg) were
susceptible or moderately susceptible in the trial. Two
clones known for VSD-resistance, DRC 15 from the
ICCRI collection (Susilo et al. 2009), and KA2 106,
closely related to KA2 101, from Papua New Guinea
(Keane and Prior 1992), proved to be the most
resistant clones in the trial. In addition, PM 1 and
PM 2, originally from an East Kalimantan estate and
Darwis 1, a local farmer selection from East Kaliman-
tan, appeared to be VSD-resistant. Among the most
susceptible of the clones were local selections from
South and Central Sulawesi. This could reflect the
short time that VSD has occurred at detectable levels
on cocoa farms in these areas. For example, VSD was
first reported as a problem in Central Sulawesi in 2000.
3.2. Incidence of PPR among clones
For the 34 pod-bearing clones evaluated over the 2-
year period, the cumulative incidence of PPR in ripe
pods did not exceed 45% in any clone. In two clones,
AA01 and KKM4, over 40% of the pods evaluated
were infected. The average PPR incidence for all the
clones in the trial was 22.3%. However, at a nearby
farm where practices typical of the area were con-
tinued, cumulative PPR incidence was higher at 28.7%
in the same evaluation period. Also, anecdotal reports
from farmers in the area suggest that the PPR
incidence during the wet season was higher in the
surrounding district than at the trial site: on some
farms, the proportion of harvested pods infected with
PPR exceeded 50% during the wet season but only
reached a maximum of 40% in the trial for all the
clones taken together (data not shown).
Figure 1 indicates that the cumulative PPR
incidence in ripe pods varied greatly among clones
from 8.6% in Aryadi 3 to 43.6% in AA01. In ripe pods,
PPR incidence was significantly low in VSD1Ldg,
DRC 16 (a PPR resistant clone from the ICCRI
International Journal of Pest Management 353
Downloaded by [University of Sydney] at 16:33 05 August 2014
collection in Java), Aryadi 3, Aryadi 1, Haris 2 and PM
2 (Table 2). The most susceptible clones were AA01
and KKM 4 while the susceptible controls (Phyt Ldg
and Sugeng) proved to be moderately susceptible in the
trial. (Figure 1, Table 2). Four approximate resistance
groupings were designated based on cumulative PPR
incidence: resistant (515%), moderately resistant
(15–24%), moderately susceptible (25–34%) and sus-
ceptible (434%). According to these criteria, the PPR-
resistant international clone Scavina 12, demonstrated
only moderate resistance in the trial. Figure 2 indicates
changes in PPR incidence with time for relatively
resistant clones compared to susceptible controls.
Generally, in these and other clones (data not shown)
the more resistant clones maintained a lower incidence
in ripe pods compared to susceptible clones during this
period although at times overlap occurred (Figure 2).
Table 2 shows that the proportion of PPR-infected
pods also infested with CPB exceeded 75% in most of
the clones, consistent with the high CPB incidence at
Table 1. VSD infection of clonal grafts in the Ladongi trial ranked from lowest to highest average severity.
Clone No. Clone name Source No. grafts Average severity Range of severity Resistance rating
12 DRC 15 ICCRI, Java 10 0.20 0–1 R
37 KA2 106 Papua New Guinea 11 0.27 0–1 R
18 PM 2 ICCRI, Kalimantan 17 0.29 0–1 R
1 Darwis 1 E. Kalimantan 10 0.30 0–1 R
36 KKM 4 Malaysia 13 0.31 0–1 R
9 PM 1 ICCRI, Kalimantan 11 0.36 0–1 R
16 VSD2Ldg SE Sulawesi 14 0.43 0–1 R
10 K 82 Papua New Guinea 14 0.43 0–2 MR
23 SCA 12 ICCRI collection 10 0.50 0–2 MR
15 AA02 ICCRI collection 18 0.50 0–1 R
29 RCC 71 ICCRI, N. Sumatra 13 0.54 0–1 MR
13 AA01 ICCRI collection 12 0.58 0–1 MR
14 GS 29 Reading, UK 12 0.58 0–1 MR
47 PBK 2 SE Sulawesi 12 0.58 0–1 MR
8 ICS 13 ICCRI collection 16 0.63 0–1 MR
19 KKM 22 Malaysia 16 0.63 0–1 MR
20 NIC 4 ICCRI collection 14 0.64 0–2 MR
22 Bal 209 Malaysia 11 0.64 0–1 MR
28 Sugeng SE Sulawesi 17 0.65 0–1 MR
7 NIC 7 ICCRI collection 12 0.67 0–1 MR
26 DRC 16 ICCRI, Java 15 0.67 0–2 MR
27 NW 6261 ICCRI collection 12 0.67 0–1 MR
24 RCC 70 ICCRI, N. Sumatra 11 0.73 0–2 MS
41 Baharuddin Central Sulawesi 16 0.75 0–3 S
44 Aryadi 2 South Sulawesi 16 0.75 0–1 MS
21 VSD3Ldg SE Sulawesi 18 0.78 0–2 MS
25 BR25 Malaysia 14 0.79 0–1 MS
46 Amiruddin SE Sulawesi 14 0.79 0–2 MS
30 RCC 72 ICCRI, N. Sumatra 15 0.80 0–2 MS
17 KEE 2 Papua New Guinea 11 0.82 0–1 MS
11 M4 Maluku 11 0.82 0–2 MS
6 VSD1Ldg SE Sulawesi 11 0.82 0–2 MS
40 Asmaun merah South Sulawesi 13 0.85 0–2 MS
48 VSD4Ldg SE Sulawesi 10 0.90 0–2 MS
32 RCC 73 ICCRI, N. Sumatra 13 0.92 0–2 MS
3 Darwis 3 E. Kalimantan 12 0.92 0–3 S
42 Ruslan Central Sulawesi 18 0.94 0–2 MS
2 Darwis 2 E. Kalimantan 12 1.00 0–2 S
31 PBK 1 SE Sulawesi 17 1.00 0–2 S
45 Aryadi 5 South Sulawesi 17 1.00 0–2 S
5 Anshary 2 Central Sulawesi 16 1.06 0–2 S
4 Anshary 1 Central Sulawesi 16 1.25 0–3 S
34 Haris 1 Central Sulawesi 11 1.27 0–2 S
49 PhytLdg SE Sulawesi 11 1.27 0–3 S
35 Haris 2 Central Sulawesi 18 1.39 0–3 S
39 Karmono 2 Central Sulawesi 10 1.40 0–2 S
33 Ridwan Central Sulawesi 15 1.40 0–3 S
43 Aryadi 1 South Sulawesi 14 1.43 0–2 S
38 Karmono 1 Central Sulawesi 11 1.64 0–2 S
Notes: Clones in the collection at ICCRI and local farm selections were included in the trial (see section 2). Individual grafts were assessed during
the dry season for VSD severity by ranking infection as 0, no infection; 1, signs of chlorosis, little or no leaf drop; 2, distinctive chlorosis and some
leaf drop; 3, severe leaf loss, dieback; 4, graft death. The resistance rating of clones incorporates both the average severity score and the range of
severity scores of infection observed among the replicates as follows: R, resistant: 50.50 and 0–1; MR, moderately resistant: 0.50–0.69 and/or 0–
2; MS, moderately susceptible: 0.70–0.99 and 0–2; S, susceptible: 40.99 and/or 0–3.
354 P. McMahon et al.
Downloaded by [University of Sydney] at 16:33 05 August 2014
the trial site (see McMahon et al. 2009). The ratio of
heavy (over 50% of the pod husk infected) to light
infection (less than 50% of the pod husk infected)
varied among the clones, providing evidence of
differential rates of lesion expansion on infected pods.
But there was no correlation between total PPR
incidence in ripe pods and the incidence of heavy
PPR infections (Pearson correlation coefficient,
Table 2. Incidence of PPR in ripe pods, the proportion of PPR-infected pods also infested with CPB and the ratio of heavy to
light infections (assessed only in PPR-infected pods free of CPB) in some of the clones tested at Ladongi (see Figure 1).
Clone no. Clone name
% Ripe pods
with PPR
Proportion infested
with CPB (%)
Ratio of heavy/light
PPR infection
2 Darwis2 11.4
ab
88.5 2.0
6 VSD1Ldg 8.6
ab
75.0 3.0
9 PM 1 31.4
d
85.7 2.7
13 AA01 43.6
e
82.4 2.7
14 GS29 19.3
c
87.1 2.0
18 PM 2 10.5
b
73.9 3.6
19 KKM22 20.3
c
82.5 4.0
21 VSD3Ldg 31.3
d
74.7 4.7
23 SCA12 20.4
c
83.5 4.0
24 RCC70 31.7
d
86.8 1.5
25 BR25 30.1
d
80.0 3.8
26 DRC16 11.0
ab
90.0 1.1
28 Sugeng 30.4
d
85.5 2.6
31 PBK 1 21.0
c
90.2 4.5
34 Haris1 21.9
c
66.7 6.0
35 Haris2 11.1
b
86.8 0.4
36 KKM4 42.3
e
91.5 3.0
40 Asmaun merah 23.3
c
85.7 1.0
41 Baharuddin 23.2
c
91.9 9.0
43 Aryadi1 10.9
ab
100.0 7
45 Aryadi3 8.6
a
86.1 1.5
46 Amiruddin 21.1
c
91.8 1.7
Note: Means within a column followed by the same letter are not significantly different (P0.05, ANOVA, Games-Howell).
Figure 1. Cumulative PPR incidence (%) in ripe pods in the trial at Ladongi, determined over a 2-year period (January 2005 to
December 2006). Ripe pods (both healthy and infected) were harvested twice per month and evaluated individually for presence
or absence of PPR infestation. Each bar represents the mean PPR incidence (with SE bars), weighted for the numbers of ripe pods
harvested, for the 2-year period in an individual clone.
International Journal of Pest Management 355
Downloaded by [University of Sydney] at 16:33 05 August 2014
r¼0.205, P¼0.126). Also, there was no correlation
between PPR incidence in ripe pods and the heavy/
light infection ratio (Table 2) (Pearson correlation
coefficient, r¼0.175, P¼0.224).
Figure 3 indicates that the clones varied in percent
PPR infection at the immature stage of pod develop-
ment. Losses at the immature stage exceeded 20% of
the total harvest in the susceptible controls, PhytLdg
and Sugeng, and also in a number of other clones (e.g.
PM 1, RCC 70). The PPR incidence in ripe pods
(Figure 1) was positively correlated with incidence in
immature pods (Figure 2) (Pearson correlation coeffi-
cient, r¼0.399**, P¼0.01).
3.3. Lesion expansion in pods artificially inoculated
with PPR-infected tissue
Although PPR infections developed in most of the
wound-inoculated pods, the rate of expansion of
lesions (data not shown) proved to be highly variable
between replicates as well as clones. However, con-
sistent with the field results, DRC 16 showed evidence
of resistance with a relatively low average lesion area at
7 d.a.i. (550 cm
2
) compared to Sugeng, a susceptible
control, which had a higher average lesion area
(4130 cm
2
). However, lesion expansion data for other
clones tested were not so consistent with the field data
e.g. the clone VSD1Ldg, resistant in the field trial, had
moderate-large lesions 7 d.a.i. (averaging 92 cm
2
) and
PM 1, was quite resistant in the inoculation trial
(average lesion area at 7 d.a.i. 550 cm
2
) yet moder-
ately susceptible in the field trial (Figure 1).
3.4. Other pests and diseases
The most important pest at the trial site after CPB was
the mirid, Helopeltis spp. Figure 4 shows the cumula-
tive average incidence of this pest on total pods
harvested over the evaluation period. Losses due to
Helopeltis were especially high in DRC 16 with 23%
pods lost at the immature stage and a ripe pod
incidence of 52% (Figure 4). Losses out of the total
harvest at the immature stage of pod development were
between 10 and 20% in Darwis 2, Anshary 1 and PBK
2, while the highest total incidence (88%) occurred in
PBK 1, a CPB-susceptible control (see McMahon et al.
2009). Particularly resistant clones were KKM4 (with
Figure 3. PPR incidence (%) determined from the total pod harvest (immature and ripe pods) at Ladongi from 2005 to 2006.
Ripe pods (healthy and infected) and all infected immature pods were harvested twice per month. Differential shading in bars
indicates PPR incidence in immature pods (lower, darker shading) and in ripe pods (upper, lighter shading) as a proportion of all
the pods harvested. Values shown are means (with SE bars for each category) weighted for the number of pods harvested in each
clone.
Figure 2. Changes in PPR incidence during 2005 and 2006
in the ripe pods of relatively PPR-resistant clones, Aryadi 3
and PM 2 (continuous lines, solid symbols) and susceptible
control clones, Phyt Ldg and Sugeng (broken lines, open
symbols) identified at Ladongi (see Figure 1).
356 P. McMahon et al.
Downloaded by [University of Sydney] at 16:33 05 August 2014
an incidence of 34% in ripe pods and 0.8% in
immature pods) and PM 1, PM 2 and AA01.
Colletotrichum sp. was detected at negligible levels in
ripe pods, and was more common in immature pods.
However, incidence even in immature pods was less
than 1% of the total pod harvest for most of the clones
(data not shown). Damage by rodents (squirrels and
rats) was higher in ripe pods than immature pods. Even
so, incidence of damage (out of the total pod harvest)
at the ripe pod stage were less than 2% for most clones
(data not shown): only in KKM 22 (2.3%) and
Amiruddin (4.6%) were ripe pod losses due to rodent
activity higher.
3.5. Pod values and bean quality
Table 3 shows pod values for all the harvested pods
(actual pod values) as well as pod values determined
from healthy pods only (potential pod values) for
selected clones. Potential pod values were lower than
actual pod values in most clones, as expected, reflecting
the impact of pests and diseases. However, the
potential pod values determined in the Ladongi clones
were generally high and were much higher than
expected in some of the international clones. The small
bean size of Scavina 12 was reflected in its high pod
value but this was exceeded greatly by the Kalimantan
clone, PM 2, which had a remarkably high pod value
(172.5) consistent with the very small pods and beans
of this clone.
Bean losses due to pest/diseases in ripe pods were
calculated by comparing the bean harvest obtained
Figure 4. Incidence of Helopeltis spp. (%) determined from the total pod harvest (immature and ripe pods) at Ladongi from
2005 to 2006. Ripe pods (healthy and infested) and all infested immature pods were harvested twice per month. Differential
shading in bars indicates Helopeltis incidence in immature pods (lower, darker shading) and in ripe pods (upper, lighter shading)
as a proportion of all the pods harvested. Values shown are means (with SE bars for each category) weighted for the number of
pods harvested in each clone.
Table 3. Actual pod values (no. ripe pods (infected and
healthy)/kg dry beans), potential pod value (no. healthy pods
per kg dry beans) and bean losses in ripe pods harvested from
some of the cocoa clones in the trial at Ladongi, Southeast
Sulawesi.
Clone no.
Clone
name
Actual
pod value
Potential
pod value
Bean
losses
(%)
2 Darwis 2 47.5 43.6 8.3
6 VSD1Ldg 49.1 34.8 29.2
11 M4 37.1 27.0 27.2
13 AA01 39.0 30.1 22.9
15 AA02 46.0 36.2 21.2
16 VSD2Ld 82.7 55.7 32.6
17 KEE 2 52.0 31.2 40.1
18 PM 2 172.5 152.7 11.5
19 KKM 22 45.2 36.2 20.0
21 VSD3Ldg 45.1 28.7 36.4
22 BAL 209 51.0 40.1 21.3
23 SCA 12 98.8 100.9 72.1
25 BR 25 42.5 35.2 17.1
28 Sugeng 40.3 30.1 25.3
30 RCC 70 50.6 37.0 26.9
31 PBK 1 53.4 44.3 17.1
34 Haris 1 52.1 44.6 14.4
35 Haris 2 53.0 39.9 24.7
41 Baharuddin 46.0 43.1 6.3
42 Ruslan 57.5 44.9 21.8
43 Aryadi 1 38.0 27.0 28.9
44 Aryadi 2 40.6 33.4 17.7
45 Aryadi 3 43.6 37.8 13.4
46 Amiruddin 46.5 22.8 50.9
49 PhytLdg 42.6 45.0 75.5
Notes: Pods were harvested twice per month over a 2-year period.
Beans were collected separately from healthy pods and pods affected
by pest/diseases, dried and weighed. Pod values are given for clones
producing at least 10 healthy ripe pods.
International Journal of Pest Management 357
Downloaded by [University of Sydney] at 16:33 05 August 2014
from all harvested pods with that of healthy pods
(Table 3). Bean losses can be attributed to the
combined effect of pests and diseases, mainly CPB
and PPR. Losses varied considerably among the
clones. Generally, the clones with apparent CPB-
resistance (McMahon et al. 2009) had relatively low
bean losses compared to other clones. For example,
Darwis 2, Aryadi 2, Scavina 12 and PM 2 showed bean
losses of less than 20%. However, clones with low PPR
incidence in the field did not follow this pattern as
PPR-resistant clones such as VSD1Ldg had high bean
losses (29.2%) while some more PPR susceptible clones
(e.g. Baharuddin, Haris 1) had lower losses.
Table 4 presents data on bean quality analyses for
26 of the clones tested in Ladongi. Most of these clones
did not meet the Standard National Indonesia (SNI)
specifications of quality (see Table 4 legend). Few
clones met the minimum fat content of 51% preferred
by industry. Pests or diseases seemed to have no effect
on the fat content of some clones (e.g. KKM 22, GS
29, Aryadi 1) but had a greater effect on others (e.g.
PM 1, Baharuddin). The highest fat content was in
PBK 2, a CPB-susceptible control. Bean count was
affected considerably by pests and diseases in some
clones. Of the 26 clones tested, 9 clones had a bean
count in healthy pods exceeding the industry threshold
requirement of 115, and this increased to 14 clones in
beans from infected pods (Table 4). In most clones,
beans extracted from damaged pods had a higher
proportion of flat beans and placental waste and higher
shell content than beans from healthy pods (Table 5).
4. Discussion
As evaluated in grafts at a relatively early stage of
development, a number of clones in the trial at
Ladongi showed a degree of VSD resistance. Some of
these, e.g. Sugeng and KKM 22, with relatively low
pod values and moderate resistance, could be immedi-
ately useful in VSD-affected areas. However, the VSD-
resistant clones, PM 2 and VSD2Ldg, had very high
pod values. These clones, particularly PM 2 with its
strikingly small pods and beans, would not be useful on
farms. However, the strong resistance characteristics of
these clones could make them valuable parental
material for cocoa breeding. Eight of the 14 clones
assessed as VSD-susceptible at Ladongi (Table 1) were
local selections from Central Sulawesi (see Table 1).
This province was largely unaffected by VSD at the
time the selections were made, and therefore the cocoa
genotypes grown in Central Sulawesi had not been
selected by farmers under pressure from VSD. The
apparently greater level of partial resistance among
genotypes selected from parts of South and Southeast
Table 4. Bean quality characteristics of some of the clones evaluated in the trial in Ladongi, Southeast Sulawesi.
Clone
Bean count Shell content (%) Fat content (%) Water content (%)
Healthy Damaged Healthy Damaged Healthy Damaged Healthy Damaged
Darwis 2 nd 135 nd 16.5 nd 48.9 nd 3.3
Anshary 1 143 86 13.7 13.3 47.9 47.2 2.9 3
VSD1Ldg 86 106 18.9 15.1 50.5 49.1 3.2 3
PM 1 123 151 14.6 16.8 51.4 47.3 2.9 3.1
M4 108 128 12.8 17.4 48 46.4 2.5 2.6
GS 29 79 100 8.4 17 50.5 50.5 2.9 3.1
AA02 91 nd 12.1 nd 50.2 nd 3.1 nd
VSD2Ldg 90 115 12 15.3 49.5 49.6 2.9 2.7
PM 2 178 244 19.2 20.7 47.7 46.8 3.1 3.3
KKM 22 89 108 10.8 14 49.8 51.2 2.8 2.7
VSD3Ldg 119 166 19.2 18.5 48 46.5 2.6 2.8
Bal 209 109 107 11.1 14.2 50.9 51.6 3 2.7
RCC 70 85 128 10.8 14.7 50.9 48.3 2.8 2.1
DRC 16 81 99 10.1 12.6 47.8 45.5 2.9 2.7
Sugeng 94 111 10.9 15.2 50.3 48.5 3.1 2.8
RCC 72 127 117 10.8 16.4 49.5 48.3 2.7 2.7
PBK 1 88 nd 13.8 nd 48.1 nd 3.1 nd
Haris I 98 130 12.6 15.5 48.9 47.8 2.9 2.7
Baharuddin 117 117 14.8 16.9 49.5 45.9 2.6 2.9
Ruslan 1 109 141 11.7 17.2 50.9 49.2 2.6 3.8
Aryadi 1 121 153 11.1 19.6 50.8 52.3 2.7 2.5
Aryadi 2 132 173 12.2 19 49.6 47.9 3.1 2.6
Aryadi 3 124 152 13.2 15.5 49.9 48.5 2.7 2.7
Amiruddin 115 163 13.1 18.8 49.7 48 2.8 3
PBK 2 nd 81 nd 13.6 nd 53 nd 2.8
PhytLdg 92 111 14.7 13.1 49.5 50.1 2.6 2.4
Notes: Beans harvested from healthy pods and pods damaged by pest/diseases were analysed separately and results from each category are shown
in separate columns. SNI specifications: max. bean count (no. dried beans in 100 g) ¼115, max. shell content ¼13% and minimum fat
content ¼51%. nd, not determined.
358 P. McMahon et al.
Downloaded by [University of Sydney] at 16:33 05 August 2014
Sulawesi (e.g. VSD2Ldg), where VSD has been
prevalent at least since the early 1980s, could be
explained by the longer period of time over which they
have possibly been selected under VSD pressure. This
indicates the capacity of the genetically diverse cocoa
in Sulawesi for adaptation to factors in the local
environment (e.g. pest and disease pressure) and the
potential value of employing locally adapted genotypes
for farm improvement, either by selection of resistant
clones or for breeding programs.
In the 2-year evaluation period, the clones tested in
Ladongi, including the on-farm selections, varied
considerably in their cumulative incidence of PPR,
enabling the identification of potential PPR-resistance
in some clones. These results support on-farm selection
as a useful way of identifying potential resistance in
cocoa genotypes but also re-affirm the necessity of
confirming identifications by farmers in systematic
trials (see McMahon et al. 2009). The field trial
indicated that the most PPR-resistant of the clones
were the local Sulawesi selections, Aryadi 3 and
VSD1Ldg. The former selection was identified as
having a low PPR infection rate by a farmer, Aryadi,
while the latter was a VSD-susceptible control. Aryadi
1, selected for CPB-resistance, also demonstrated
potential PPR resistance in the trial. While PPR
incidence fluctuated seasonally, the incidence in the
more resistant clones was generally lower than in
susceptible clones over the 2-year evaluation period
(Figure 2). Saul (1993) also found that lower PPR
incidence was maintained in PPR-resistant clones,
compared to more susceptible clones, during both
wet and dry seasons, and was especially evident during
wet seasons. The maintenance of a low incidence in
resistant types irrespective of the season suggests that
the PPR-resistance observed in the field at Ladongi was
constitutive to pods rather than being a seasonal effect
e.g. rainfall patterns or pod numbers. The PPR-
resistant Trinitario clone developed in Java, DRC 16,
proved to be one of the most PPR-resistant clones at
the ripe pod stage, but not at the immature stage.
Possibly, the high incidence of PPR infection in
immature pods of this clone might have been an
indirect effect of infestation by Helopeltis spp., which
occurred at a particularly high rate in the immature
pods of this clone (Figure 4). Except for DRC 16, PPR
incidence in immature pods was positively correlated
with that in ripe pods, evidence that similar resistance
mechanisms are operating at both stages of pod
development.
Harvested ripe pods infected with PPR (but free of
CPB infestation) were evaluated for intensity of
infection: heavily infected or lightly infected. Since
evaluations were conducted at regular time intervals
Table 5. Bean waste (% dry weight of beans harvested) categorised as flat beans, clustered beans or placental waste from some
of the clones evaluated in the trial at Ladongi.
Clone
Healthy (%)
Total
Damaged (%)
Total
Flat Clustered Placental Flat Clustered Placental
Darwis 2 nd nd nd nd 1.0 0.0 0.8 1.8
Anshary 1 13.7 0.0 0.0 13.7 5.3 0.0 0.0 5.3
VSD1Ldg 2.7 0.0 0.0 2.7 1.1 0.0 0.7 1.8
PM 1 1.0 0.0 0.0 1 3.0 0.0 0.0 3
M4 2.7 0.0 0.0 2.7 3.0 0.0 2.1 5.1
GS 29 0.0 0.0 0.0 0 4.5 0.0 7.6 12.1
AA02 0.2 0.0 0.0 0.2 nd nd nd nd
VSD2Ldg 2.8 0.0 0.0 2.8 8.2 0.0 0.0 8.2
PM 2 1.5 0.0 0.2 1.7 8.0 0.0 2.8 10.8
KKM 22 0.2 0.0 0.0 0.2 0.2 0.0 0.2 0.4
VSD3Ldg 8.8 0.0 0.0 8.8 14.9 0.2 2.0 17.2
Bal 209 0.0 0.0 0.0 0 0.7 0.0 0.6 1.3
RCC 70 0.0 0.0 0.0 0 6.8 0.0 0.3 7.2
DRC 16 0.2 0.0 0.0 0.2 4.1 0.4 1.6 6
Sugeng 2.5 0.0 0.0 2.5 4.7 0.0 0.9 5.5
RCC 72 0.4 0.0 0.0 0.4 1.9 0.0 0.8 2.7
PBK 1 2.6 0.0 0.1 2.7 nd nd nd nd
Haris I 0.0 0.0 0.0 0 4.7 1.4 0.7 6.8
Baharuddin 0.1 0.0 0.0 0.1 4.1 0.3 0.6 5
Ruslan 1 2.7 0.0 0.0 2.7 5.7 0.0 8.6 14.3
Aryadi 1 0.0 0.0 0.0 0 0.0 0.0 0.0 0
Aryadi 2 0.5 0.0 0.0 0.5 5.4 0.0 0.9 6.3
Aryadi 3 19.5 0.0 0.0 19.5 0.0 0.0 0.0 0
Amiruddin 7.8 0.0 0.0 7.8 10.0 0.0 3.5 13.5
PBK 2 nd nd nd nd 0.4 0.0 0.0 0.4
PhytLdg 6.6 5.8 0.1 12.5 7.9 0.9 1.5 10.3
Mean 3.0 0.2 0.0 3.4 4.4 0.1 1.5 6.0
Notes: Beans harvested from healthy pods and pods damaged by pest/diseases were analysed separately and results are shown in separate
columns. nd, not determined.
International Journal of Pest Management 359
Downloaded by [University of Sydney] at 16:33 05 August 2014
(approximately fortnightly) it would be expected that
in cumulative data for the 2-year evaluation period a
low ratio of heavy to light infections would be the
result of a slower expansion rate of pod rot lesions. The
ratio of heavy to light infections did vary between
clones (see Table 2) suggesting that the time taken for
PPR to spread though a pod may vary between clones.
However, these ratios were not correlated with the
incidence of PPR in ripe pods (Figure 1). Undoubtedly
pod size would affect the proportion of the pod affected
by PPR, with small pods being consumed by PPR more
rapidly than larger pods. For example, the resistant/
moderately resistant clones PM 2 and Scavina 12 both
had relatively high heavy/light infection ratios, perhaps
reflecting their small pod size. Evaluation only of PPR-
infected pods that were also free of CPB greatly
decreased the numbers of pods sampled (as most PPR-
infected pods also had CPB) making the data less
reliable. Nevertheless, the lack of correlation between
intensity of infection and incidence could be due to
different types of PPR-resistance mechanisms in pods.
Iwaro et al. (1997) identified two possible mechanisms
of resistance to PPR, the first at the stage of initial pod
infection (pre-penetration) and the second at the stage
of growth and spread of the pathogen following
infection of the pod (post-penetration). Possibly,
pods in the Ladongi trial with high heavy/light ratios
in infected pods, but relatively low PPR incidences (e.g.
Haris 1, PBK 1, KKM22, Scavina 12, Baharuddin),
were susceptible at the post-penetration but not the
pre-penetration stage of infection. Wound-inoculation
results for detached pods were inconsistent with the
field data in most of the clones, as clones that showed
apparent resistance in the field developed relatively
large lesions after artificial inoculation with infected
tissue. DRC 16 proved to be an exception, demonstrat-
ing a high level of resistance both in the field and
inoculation experiment. Possibly, some of the other
clones are resistant at the pre-penetration stage but not
at the post-penetration stage (and are susceptible to
artificial wound-inoculation), while DRC 16 is resistant
at both stages. Also, while PPR-resistance in some
clones might be attributable to a constitutive mechan-
ism (see above), variation in the cropping times of
other clones could account for their low PPR
incidence, especially if the peak crop falls outside the
wettest periods. Such clones might escape high levels of
PPR infection, but still be susceptible to artificial
inoculation. However, the high variability in lesion
expansion rates between replicates means no
strong conclusions can be drawn from the detached
pod tests.
The lower average incidence of PPR in the clones in
the Ladongi trial compared to trees on the nearby farm
plot assessed monthly, could be a result of the frequent
and complete harvesting method of both healthy and
diseased pods in the trial (twice per month in the trial
compared to once a month in the local area). This
observation was supported by anecdotal evidence from
nearby farmers. The higher frequency of harvesting
might have decreased the amount of inoculum avail-
able for new infections. In Cameroon, for example,
Ndoumbe-Nkeng et al. (2004) showed that regular
removal of pods infected with Phytophthora megakarya
at two sites in a 2-year period resulted in substantial
decreases in disease incidence.
Bean losses, estimated from the actual and poten-
tial pod values, would be expected to reflect the impact
of pests and diseases. However, losses varied consider-
ably between the clones and were not necessarily
greater in the more pest/disease susceptible clones
(Table 3). Nevertheless, the data suggest a closer
correspondence of bean losses with cumulative CPB
incidence (see McMahon et al. 2009) than with PPR
incidence. Possibly tolerance to infection/infestation
influenced bean losses. In the case of CPB infestation,
Teh et al. (2006) suggested that some clones, despite
being infested with CPB, exhibit relatively low bean
losses due to tolerance to infestation.
While pest/diseases clearly affected pod values and
bean quality parameters (especially bean counts) in the
Ladongi trial, even the healthy pods of many of the
clones tested had high pod values and bean quality
parameters that were below the industry minimum
standard. This could be a reflection of the condition of
the farm, which was located in an area of generally
poor soils, and also of the age and generally poor
condition of the rootstock trees. The trial at Ladongi
enabled identification of resistance in some clones but
in most cases this was to particular pest/disease
problems. Also, most of the potentially resistant clones
had high pod values or poor bean quality character-
istics. This was also the case for PM 2 and Scavina 12,
which showed evidence of potential resistance to more
than one pest/disease, but had unacceptable pod values
and bean quality characteristics. Clones such as these,
which have valuable resistance characteristics asso-
ciated with poor yield and/or quality, could be used as
parents in a cocoa breeding program to obtain hybrid
progeny with resistance as well as good quality and
yield characteristics.
Acknowledgements
The work presented in this paper was funded by the
Australian Centre for International Agricultural Research
(ACIAR Project CP/2000/102). Yohannes Junianto, formerly
plant pathologist at ICCRI, Jember, East Java, selected the
VSD resistant and susceptible local selections. Many thanks
are due to Pak Suntoro, former head of the Plant Protection
department, Dinas Perkebunan, Kendari, for his help in
facilitating the field trials established at Ladongi, Southeast
Sulawesi.
References
Blaha G. 1974. Methods of testing for resistance. In: Gregory
PH, editor. Phytophthora diseases of cocoa. London:
Longman.
360 P. McMahon et al.
Downloaded by [University of Sydney] at 16:33 05 August 2014
Directorate General for Estate Crops. 1999. Statistik
Perkebunan Indonesia 1995–1997. Kakao: Direktorat
Jenderal Perkebunan, Jakarta. p. 58.
Iwaro AD, Sreenivasan TN, Umaharan P. 1997. Phy-
tophthora resistance in cacao (Theobroma cacao): influ-
ence of pod morphological characteristics. Plant Pathol.
46:557–565.
Iwaro AD, Sreenivasan TN, Umaharan P. 1998. Cacao
resistance to Phytophthora: effect of pathogen species,
inoculation and pod maturity. Eur J Plant Pathol.
104:11–15.
Keane P. 1992. Diseases and pests of cocoa: an overview. In:
Keane PJ, Putter CA, editors. Cocoa pest and disease
management in Southeast Asia and Australasia. FAO
Plant Production and Protection Paper No. 112, FAO,
Rome, p. 1–11.
Keane PJ, Prior C. 1992. Biology of vascular-streak dieback
of cocoa. In: Keane PJ, Putter CA, editors. Cocoa pest
and disease management in Southeast Asia and Austra-
lasia. FAO Plant Production and Protection Paper No.
112, FAO, Rome.
McMahon PJ, Iswanto A, Susilo AW, Sulistyowati E,
Wahab A, Imron M, Purwantara A, Mufrihati E, Dewi
VS, Lambert S, Guest DI, Keane PJ. 2009. On-farm
selection for quality and resistance to pest/diseases of
cocoa in Sulawesi: (i) performance of selections against
cocoa pod borer, Conopomorpha cramerella. Int J Pest
Manage. 55:325–337.
Ndoumbe-Nkeng M, Cilas C, Nyemb E, Nyasse S, Bieysse
Flori A, Sache I. 2004. Impact of removing diseased pods
on cocoa black pod caused by Phytophthora megakarya
and on cocoa production in Cameroon. Crop Protect.
23:415–424.
Saul JY. 1993. Resistance of cocoa genotypes to Phy-
tophthora palmivora in Papua New Guinea [MSc thesis].
Melbourne (Australia): Department of Botany, La Trobe
University.
Soria J. 1974. Sources of resistance to Phytophthora
palmivora. In: Gregory PH, editor. Phytophthora diseases
of cocoa. London: Longman.
Susilo AW, Mawardi S, Sudarsianto. 2009. Keragaan day-
ahasi klon kakao (Theobroma cacoa L.), Sca 6 dan DRC
15, tahan penyakit pembuluh kayu (vascular-streak
dieback). Jurnal Pelita Perkebunan. 15:76–87.
Tan G-Y, Tan W-K. 1990. Additive inheritance of resistance
to pod rot caused by Phytophthora palmivora in cocoa.
Theoretical Appl Genet. 80:258–264.
Teh C-L, Pang J-T-Y, Ho C-T. 2006. Variation of the
response of clonal cocoa to attack by cocoa pod borer
Conopomorpha cramerella (Lepidoptera: Gracillariidae)
in Sabah. Crop Protect. 25:712–717.
Van der Vossen HAM. 1997. Strategies of variety improve-
ment in cocoa with emphasis on durable disease
resistance, INGENIC (International Group for Genetic
Improvement of Cocoa), Reading.
Wardojo S. 1992. Major pests and diseases of cocoa in
Indonesia. In: Keane PJ, Putter CA, editors. Cocoa pest
and disease management in Southeast Asia and Austra-
lasia. FAO Plant Production and Protection Paper No.
112, FAO, Rome. p. 63–67.
Zadocks JC. 1997. Disease resistance in cocoa: a review on
behalf of FAO/INGENCI, INGENIC (International
Group for Genetic Improvement of Cocoa).
Zainal Abidin MA, Varghese G, Mainstone BJ. 1984.
Aspects of the epidemiology of vascular-streak dieback
of cocoa in Malaysia. Proceedings of the 1984 Interna-
tional Conference on Cocoa and Coconuts.
Zar JH. 1996. Biostatistical analysis, 3rd ed. New Jersey:
Prentice-Hall.
International Journal of Pest Management 361
Downloaded by [University of Sydney] at 16:33 05 August 2014
... is, in turn, is expected to have an enduring impact on the long-term commitment of farmers in the production of good-quality cocoa beans (Table 6.3-S). is is definitely a strong point for the cocoa sector. (Buijsse et al. 2006;Crozier et al. 2011;Tzounis et al. 2011) The high susceptibility of the cocoa to different pests hampers the consistent (quantitative and qualitative) supply of cocoa There are difficulties in breeding pest-resistant varieties adapted to different regions and countries, combining both vigor and high bean quality for chocolate manufacturing (Efombagn et al. 2011;McMahon et al. 2010;Micheli et al. 2010) Although new cultivars resistant to major diseases have been identified during the last decades, studies have shown that the resistance may be overcome (Brown et al. 2005;Albuquerque et al. 2010) The cocoa sector faces many challenges derived from aging tree stocks, poor soil fertility management, and widespread difficulty of farmers access to pest control strategies; but also improper use of chemicals and uncontrolled forest conversion (ADM Cocoa 2009; Ayenor et al. 2004;McMahon et al. 2010) In many countries, a successful farm management system for the control of pests and implementation of good postharvest processing practices for cocoa is absent The supply of cocoa beans fluctuates from year to year, which has an influence on the price for farmers (ADM Cocoa 2009) Cocoa bean fermentation relies on the uncontrolled colonization of microorganisms from the environment, which creates difficulty in standardization of quality There is a great dependence of cocoa production from a small number of countries (mainly Ivory Coast followed by Ghana) (ICCO 2011c) ...
... is, in turn, is expected to have an enduring impact on the long-term commitment of farmers in the production of good-quality cocoa beans (Table 6.3-S). is is definitely a strong point for the cocoa sector. (Buijsse et al. 2006;Crozier et al. 2011;Tzounis et al. 2011) The high susceptibility of the cocoa to different pests hampers the consistent (quantitative and qualitative) supply of cocoa There are difficulties in breeding pest-resistant varieties adapted to different regions and countries, combining both vigor and high bean quality for chocolate manufacturing (Efombagn et al. 2011;McMahon et al. 2010;Micheli et al. 2010) Although new cultivars resistant to major diseases have been identified during the last decades, studies have shown that the resistance may be overcome (Brown et al. 2005;Albuquerque et al. 2010) The cocoa sector faces many challenges derived from aging tree stocks, poor soil fertility management, and widespread difficulty of farmers access to pest control strategies; but also improper use of chemicals and uncontrolled forest conversion (ADM Cocoa 2009; Ayenor et al. 2004;McMahon et al. 2010) In many countries, a successful farm management system for the control of pests and implementation of good postharvest processing practices for cocoa is absent The supply of cocoa beans fluctuates from year to year, which has an influence on the price for farmers (ADM Cocoa 2009) Cocoa bean fermentation relies on the uncontrolled colonization of microorganisms from the environment, which creates difficulty in standardization of quality There is a great dependence of cocoa production from a small number of countries (mainly Ivory Coast followed by Ghana) (ICCO 2011c) ...
... Control of IPM involves components of biological agents, resistant planting materials, and environmental management based on the ecological, economic, and sociological considerations to support environmentally friendly farming systems [19,20,21,22,23]. CPB control strategies can be done through technical culture approach, mechanical, chemical, as well as the use of resistant clones [24]. ...
Conference Paper
Full-text available
One of the causes of low productivity of cocoa due to Conopomorpha cramerella known as cocoa pod borer (CPB) and black pod rot (BPR) caused by Phytophthora palmivora. Biopesticides consisted of Beauveria bassiana and kaolin was introduced to protect the surface of cocoa pods from CPB and BPR. The research was conducted in the District of Bacan, South Halmahera Regency, North Maluku from April to December 2017. The research was design using randomized block design (RBD), consisting of four treatments as follows: Bio-K (biopesticides), plastic (0.24 mm transparent plastic), metallaxyl (RG), and farmer technique as a control treatment with five replications and thirty plants per replications. Therefore, in the field were 150 plants. Application of biopesticides performed at two-weeks intervals since the pods measurement from 8-10 cm until harvest time. The observational variables consisted of the symptoms of CPB and BPR, disease incidence, number of CPB infestation, and number of harvested pods. Results showed that biopesticide treatment significantly reduced pod damage by CPB while the disease incidence of BPR was not significantly different from metalaxyl which was the best treatment. The average decreases in the number of cacao pod respectively were Bio-K (7.69%), plastic (14.29%), metalaxyl (27.78%) and control (62.50%). The study implies that Bio-K was effective in protecting cocoa pods from C. cramerella infestation and P. palmivora infection.
... In all locations, these three clones had the lowest disease incidence in the shoots in 2011, 2012 and 2014, indicating stable resistance. Resistance in these clones has been identified in trials located in other districts of Sulawesi, while PBC123 has maintained a high degree of resistance since the 1980s in Malaysia and Sulawesi (Chong and Shepherd 1986;McMahon et al. 2010;2018). In the current study, PBC123 had a relatively high proportion of healthy leaves on the branch 5 months after early stages of infection (Table 7). ...
Article
Full-text available
Vascular streak dieback (VSD), caused by the basidiomycete Ceratobasidium theobromae (syn. Oncobasidium theobromae), is a serious disease of cocoa in Southeast Asia and Melanesia. In the last decade, in many cocoa growing areas in Malaysia and Indonesia, the impact of this disease has increased considerably. In the same period, symptoms of the disease have become dominated by necrotic lesions on infected leaves, in contrast to chlorotic symptoms, characterised by yellowing of the leaf with a typical pattern of remnant green islands, which were formerly ubiquitous. Amplification of basidiomycete ITS and LSU sequences in DNA extracts of VSD-infected plant tissues collected from Sulawesi, Indonesia, and Kerala, India, showing chlorotic symptoms matched previous GenBank accessions (99%). However, neither isolation of an axenic culture nor direct PCR amplification from necrotic leaf tissues was successful. Nevertheless, basidiocarps collected from branches with either necrotic or chlorotic VSD symptom in Sulawesi produced basidiospores and basidia with similar dimensions to those previously documented for C. theobromae suggesting that the same pathogen is associated with both symptoms. Incidence of necrotic symptoms was correlated with disease severity in branches. VSD monitored in a range of resistant and susceptible cocoa clones showed rankings for disease incidence and severity that were consistent for three seasons, confirming that disease resistance was maintained despite the prevalence of necrotic leaf symptoms. A lower proportion of symptomatic leaves on branches 5 months after early symptoms were observed in the resistant Malaysian clone PBC123 (32.6%) compared to the more susceptible M04 (46.9%). Clones common to trials in three different districts in Sulawesi showed a consistently high level of resistance to VSD, including PBC123 and two local selections, M05 and GeniJ.
... These pests can reduce production by up to 30% and cause damage to about 10% of the crop (Acebo- Guerrero et al. 2012). Cocoa bean losses in Ladongi, Southeast Sulawesi can reach 50% due to the main pest and diseases (McMahon et al. 2010a) so that the average cocoa production in Southeast Sulawesi is now 690 kg/ha/year, a decrease of 37% from the 1,100 kg/ha/year in previous years. ...
... In Sulawesi, tests for resistance are also being carried out in high-yielding local cocoa clones and suggest strategies for incorporating VSD resistance. [53,54]. Recently, Marelli et al., [7] highlighted that this pathogen could not move from the vascular tissue to the placenta and colonize the beans. ...
Article
Full-text available
Background: The role of fungi in cocoa crops is mainly associated with plant diseases and contamination of harvest with unwanted metabolites such as mycotoxins that can reach the final consumer. However, in recent years there has been interest in discovering other existing interactions in the environment that may be beneficial, such as antagonism, commensalism, and the production of specific enzymes, among others. Scope and approach: This review summarizes the different fungi species involved in cocoa production and the cocoa supply chain. In particular, it examines the presence of fungal species during cultivation, harvest, fermentation, drying, and storage, emphasizing the factors that possibly influence their prevalence in the different stages of production and the health risks associated with the production of mycotoxins in the light of recent literature. Key findings and conclusion: Fungi associated with the cocoa production chain have many different roles. They have evolved in a varied range of ecosystems in close association with plants and various habitats, affecting nearly all the cocoa chain steps. Reports of the isolation of 60 genera of fungi were found, of which only 19 were involved in several stages. Although endophytic fungi can help control some diseases caused by pathogenic fungi, climate change, with increased rain and temperatures, together with intensified exchanges, can favour most of these fungal infections, and the presence of highly aggressive new fungal genotypes increasing the concern of mycotoxin production. For this reason, mitigation strategies need to be determined to prevent the spread of disease-causing fungi and preserve beneficial ones.
... This is supported by the durability of resistance occurring in resistant genotypes (Prior, 1979;Keane and Prior, 1991). In Sulawesi, a strategy of selecting and testing local cacao genotypes on smallholder farms, which enables the identification of genotypes with promising resistance and other characteristics, demonstrated the potential of a participatory farmer approach to select from genetic resources available on smallholdings (McMahon et al., , 2010. The potential yield, quality characteristics and resistance to cacao pod borer (Conopomorpha cramerella) and Phytophthora palmivora of local clones tested in farm-based trials in three provinces in Sulawesi has been reported previously Purwantara et al., 2015). ...
Article
Vascular streak dieback (VSD) causes serious losses for cacao (or cocoa) smallholders in Sulawesi, Indonesia. The disease is caused by a Cantharellales species, Ceratobasidium theobromae, which colonises the xylem, resulting in leaf chlorosis or necrosis, abscission and eventual branch dieback. The disease is most successfully managed by pruning infected branches and the propagation of resistant genotypes. In participatory trials located in three provinces in Sulawesi, 2.5-year-old trees, which had been clonally propagated from local genotypes or the hybrid progeny of resistant parents, were evaluated for disease severity from 2010 to 2012. Consistent resistance rankings were obtained for clones common to the trials; these were confirmed by re-evaluation in 2014. From plot averages of disease severity, broad-sense heritability was estimated as 0.67-0.92. Two progeny clones, KW617 and ICCRI03, from East Java, had similar levels of resistance in the trials as their respective (resistant) parental clones, PBC123 and Scavina 6. Among four clones monitored for 3 months in West Sulawesi, PBC123 had a higher proportion of healthy leaves on the branch tips and a more restricted spread of infection within the xylem. In contrast, disease symptoms reached the younger leaves in susceptible clones. Individual branches of KW617, monitored from an early stage of symptom development, had a significantly lower number of diseased leaves and higher ratio of new to infected leaves after 9-16 weeks than that in four other clones. Other cacao clones with a relatively high number of diseased leaves during this period overcame infections with the addition of new flushes. Resistance in farm selections did not usually co-exist with yield and bean quality. Deriving new genotypes from crosses between parents with VSD-resistance and high-yield and/or quality traits is required for the production of promising clones with good resistance, yield and quality.
... These pests can reduce production by up to 30% and cause damage to about 10% of the crop (Acebo-Guerrero et al. 2012). Cocoa bean losses in Ladongi, Southeast Sulawesi can reach 50% due to the main pest and diseases (McMahon et al. 2010a) so that the average cocoa production in Southeast Sulawesi is now 690 kg/ha/year, a decrease of 37% from the 1,100 kg/ha/year in previous years. ...
Article
Full-text available
Rubiyo, Dewi YA, Imran, Salim A, Baharudin, Indrawanto C, Ratule MT. 2020. Evaluation of yield and pest and disease resistance of cocoa clones in Kolaka District, Southeast Sulawesi, Indonesia. Biodiversitas 21: 5698-5607. Cocoa is one of the main plantation commodities in Indonesia. It is an important source of foreign exchange and employment. Currently, Indonesian cocoa production and productivity, including in Southeast Sulawesi, are declining due to pests and diseases. In addition, there is a lack of high-quality and high-yielding clones. This study aimed to evaluate the quality of cocoa clones and resistance to cocoa pod borer (CPB) and cocoa pod rot (CPR) disease caused by the fungus Phytophthora palmivora. The study tested 12 cocoa clones, which included four high-yielding clones. The research location was in Lambandia Subdistrict, Kolaka District, Southeast Sulawesi Province, Indonesia. Clonal planting material was propagated by grafting in 2010. The study used a randomized block design and the treatments consisted of 20 plants of each cocoa clone with three replications. The clones were evaluated from 2018 to 2019. The observed variables included resistance to CPB and CPR. The results of the study based on the quality component showed that the clones MT, M04, and M01 had the highest average weight per one dry bean of 1.55 g, 1.64 g, and 1.24 g, respectively. Beans produced by clones MT, M01, and M04 had an average fat content of 53.36%, 52.72%, and 50.76%, respectively. Observations of the average number of pods with CPR showed that the lowest rate of attack (about 6%) was in BAL 209 and PT. Ladongi clones, with attack intensities of 20% and 18%, respectively; therefore, these clones were classified as resistant to CPR. Evaluation of the level of resistance to attack by CPB pests found two resistant clones, PT. Ladongi and Sulawesi 2, with light levels of attack on beans.
... Control of IPM involves components of biological agents, resistant planting materials, and environmental management based on the ecological, economic, and sociological considerations to support environmentally friendly farming systems [19,20,21,22,23]. CPB control strategies can be done through technical culture approach, mechanical, chemical, as well as the use of resistant clones [24]. ...
... In Southeast Sulawesi, VSD disease has become a new problem for cocoa farmers because of its spread to almost all cocoa plantation centers in Southeast Sulawesi. In the report written by McMahon stated that VSD was found to have infected cacao plants since 1980 in District of Ladongi, Kolaka Regency (East Kolaka) [5]. It was also reported to have been found in Kolaka in 1989 [6]. ...
Article
Full-text available
The use of endophytic fungus is one of the effective ways to control Vascular Streak Dieback (VSD)- Ceratobasidium theobromae the in cocoa plants both preventively and curatively. The study aimed to evaluate the potential of several endophytic fungus isolates to reduce the incidence of VSD at the seedling level. This research was carried out in a completely randomized design (CRD) with eight endophytic fungus isolates as treatment, namely 1) Paecilomyces sp. EP1* isolate; 2) Paecilomyces sp. EP1 isolate; 3) Cladosporium sp.; 4) Nigrospora sp.; 5) Paecilomyces sp. EP isolate; 6) Paecilomyces sp. EP8 isolate; 7) Fungicide and 8) distilled water as a control. The results showed that endophytic fungi Paecilomyces Ep1* from cacao petiole was the best inhibitor of VSD disease (0%), and was able to increase the growth of plant height and stem diameter of cocoa plants.
Article
Full-text available
Spatio-temporal variability of soil fertility and cocoa pod borer (CPB) infestation rate provides strategic information about the soil nutrients and CPB population densities at different harvest intervals. This enables the transitioning of cocoa fields (cooca-gliricidia and cocoa-coconut) from conventional to modern precision management. Geostatistical methods were applied to interpolate the data collected from a systematic grid based on a cluster of six cocoa tree stands for both fields and produce maps representing the spatial variability of all soil variables and CPB attack. Cocoa fresh bean weight and CPB infestation data were collected at two week-intervals from cocoa-gliricidia and cocoa-coconut. All field data points were geo-referenced by a differential global positioning system. Data were processed for possible outliers, and analysed by variography and interpolation techniques for quantification of spatial variability. Results showed that both plots exhibited definable spatial structures and were described by exponential models. Precision cocoa management recorded an increase in crop yield by 52.8 and 37.5% at cocoa-gliricidia and cocoa-coconut, respectively. Site-specific nutrient management and integrated pest control in the critical zones showed improvement in cocoa yields, especially during the peak harvest season.
Article
Full-text available
In Sulawesi, Indonesia, cocoa smallholdings are seriously affected by the cocoa pod borer (Conopomorpha cramerella, CPB). CPB is detrimental to both cocoa production and bean quality, and is a major concern to cocoa smallholders, processors, exporters and the international market. An Australian Centre for International Agricultural Research (ACIAR)-funded project was initiated to develop a locally applicable, farmer-participatory methodology for selecting and testing promising cocoa genotypes on farms. In a trial established on a farm in South-East Sulawesi, local Indonesian and international cocoa selections were propagated clonally by side-grafting onto mature trees of mixed genotype and evaluated for 2 years for pod value, quality and resistance to pest/diseases. Local selections were based on the observations of farmers, extension officers or researchers and included a number of clones specifically selected for resistance (or susceptibility, as checks) to CPB. Our results on the CPB-infestation of 34 clones in the trial indicate the potential of employing on-farm selection and testing to improve cocoa farms. Severity of infestation was determined in ripe pods according to whether the proportion of beans damaged by CPB larvae was light (less than 10%), moderate (10–50%) or severe (over 50%). Total CPB incidence in ripe pods for most of the clones was high, exceeding 75%, and was correlated with severe and light incidence, both of which varied more. The data support a model that predicts severe infestation inflicting bean losses occurs above a critical threshold of total CPB incidence. The cumulative CPB incidence in infested pods was significantly lower in a local selection, Aryadi 2, which also had fewer larval entry holes and a low exit/entry ratio indicating a degree of resistance to CPB. The incidence of lightly infested pods was significantly lower in the susceptible controls. Pod hardness was moderately high in Aryadi 2. However, VSD3 (a local selection), Scavina12, KKM22 and BR25, had low levels of severe infestation and/or high incidences of light infestation, but had relatively soft pods. This suggests that factors in addition to pod hardness might be involved in resistance, a possibility also supported by the positive correlation of CPB incidence in ripe pods with that in immature pods and the larger seasonal fluctuations of CPB incidence observed in resistant clones, compared to susceptible clones. In a mixed genotype stand, the lower CPB incidence observed in some clones might be explained partly by pest non-preference.
Article
Full-text available
Black pod rot, caused by Phytophthora megakarya, is the main cause of cocoa harvest losses in Cameroon. Field experiments were carried out over two successive years in two smallholders’ plots of cocoa trees, in order to assess the impact of diseased pod removal (phytosanitary pod removal) on disease progress, total production and final harvest. The generalized linear mixed model proved to be the most appropriate for comparing the two treatments (without and with pod removal) set up in a randomized complete block design. Removing diseased pods helped to reduce the black pod rate by 22% and 31% in the two sites in the first year, and by 9% and 11% in the second year, compared to a plot in which no preventive control measures were taken. The rate of cherelle (very young pod) appearance was also higher when pod removal was carried out. Total production was higher in the plots with pod removal, but the difference between the two treatments was not significant. This study allowed an evaluation of the respective roles of primary and secondary inoculum in the spread of the disease. The cultural practice of phytosanitary pod removal was found to be a potentially efficient control method. However, it would need to be associated with other control methods to establish an integrated management system for cocoa farmers.
Chapter
Full-text available
Article
Eight cocoa clones were examined for variation in resistance to cocoa pod borer (Conopormorpha cramerella Sri) in Sabah, Malaysia. Over a 13 month period up to 1200 ripe pods of each were shaved back to the sclerotic layer and the number of larval entry and exit holes were counted. There were statistically significant differences in the proportion of larvae that were able to exit, with PBC123, a popular commercial clone in Sabah, and IMC23 is more resistant than BAL244 and KKM22. The six more resistant clones were characterized for pod hardness, using a penetrometer. The correlation with the entry/exit ratio suggested that the measurements could be used for screening clones for resistance. The data indicated that at relatively low rates of infestation, the proportion of larvae that can exit from the pods is negatively correlated with the number that enter, which would amplify the effect of partial resistance. The partial resistance of PBC123 may be sufficient to greatly reduce moth populations in a large enough pure stand of the clone. Pod borer resistance should be given a high weighting in an economic index for cocoa clone selection, and should be combined with tolerance of infestation in the form of low damage to the cocoa beans despite infestation. (c) 2005 Elsevier Ltd. All rights reserved.
Article
Quantitative inheritance of resistance to Phytophthora pod rot (Ppr) was studied in cocoa hybrid progeny from 12 Trinitario x Amazonian crosses and their reciprocal crosses. The crossing scheme was similar to a factorial design. Disease was assessed by the number and percentage of infected pods on each tree. Highly significant differences due to general combining abilities (GCA) were obtained for all characters, except for the GCA of Trinitario on total pod production. Differences for specific combining ability (SCA) were not significant for all characters. There were no significant differences between reciprocal crosses. The Trinitario clone K82 provided the only source for the hybrid progenies of strong Ppr resistance to the hybrid progenies, while K20 provided moderate resistance. Other parental clones - KA2-101, KA5-201, KEE 2, KEE 5, and KEE 52 - produced progenies which were susceptible to Ppr. It is evident that resistance to Ppr in cocoa is inherited additively. Maternal and cytoplasmic effects were assumed to have no influence on inheritance of resistance. It is also concluded that resistance to Ppr of the kind shown by K82 is likely to be horizontal resistance. Breeding for high-yielding cultivars combined with Ppr resistance is the most effective way of controlling Ppr of cocoa on the crops of growers with small holdings in Papua New Guinea.
Article
Eight cocoa clones were examined for variation in resistance to cocoa pod borer (Conopormorpha cramerella Sn) in Sabah, Malaysia. Over a 13 month period up to 1200 ripe pods of each were shaved back to the sclerotic layer and the number of larval entry and exit holes were counted. There were statistically significant differences in the proportion of larvae that were able to exit, with PBC123, a popular commercial clone in Sabah, and IMC23 is more resistant than BAL244 and KKM22. The six more resistant clones were characterized for pod hardness, using a penetrometer. The correlation with the entry/exit ratio suggested that the measurements could be used for screening clones for resistance. The data indicated that at relatively low rates of infestation, the proportion of larvae that can exit from the pods is negatively correlated with the number that enter, which would amplify the effect of partial resistance. The partial resistance of PBC123 may be sufficient to greatly reduce moth populations in a large enough pure stand of the clone. Pod borer resistance should be given a high weighting in an economic index for cocoa clone selection, and should be combined with tolerance of infestation in the form of low damage to the cocoa beans despite infestation.
Article
Twelve diverse cacao (Theobroma cacao) genotypes were assessed for pod resistance to Phytophthora palmivora at the penetration and post-penetration stages of infection using two inoculation methods. Correlation analysis between a number of pod characteristics (stomatal frequency, stomatal pore length, surface wax, thickness of exocarp/endocarp, hardness of exocarp/mesocarp, moisture content) and resistance indicated a strong relationship between resistance to lesion establishment (lesion frequency) and the joint effect of stomatal frequency and pore length. The epidermal impressions of the pod surfaces bearing germinating zoospores of P. palmivora provided evidence that penetration occurs through stomata, epidermal hair base, scar and by direct penetration. A poor correlation was obtained between the pod characteristics studied and post-penetration resistance, suggesting that this resistance, assessed by lesion size, is not governed by morphological or physical characteristics of the pod, but probably by biochemical factors. The importance of these findings in breeding of cacao for resistance to P. palmivora is discussed.
Article
Two species of Phytophthora (P. palmivora and P. capsici) and inoculations at two depths (3 mm and 9 mm) were tested each on 10 clones of Theobroma cacao to determine their effects on pod resistance. Ripe and unripe pods were also assessed to determine the influence of physiological status of the pod on the expression of resistance. The two pathogens tested (P. palmivora and P. capsici) differed significantly in their reactions on pods, with P. palmivora being more aggressive than P. capsici. However, the lack of interaction between clones and pathogen species and the similarity in the ranking of clones based on lesion size suggested that selection for resistant clones can be based on one of the two pathogens, preferably the more aggressive one. Pod reactions differed between inoculation depths (3 mm and 9 mm), and between pod maturity stages (ripe and unripe pods) with relatively larger lesions being recorded at 9 mm depth and on unripe pods as compared to those observed at 3 mm depth and on unripe pods, respectively. The magnitude of increase in lesion sizes, however, varied with genotypes, indicating that inoculation depth and pod maturity stage should be standardized in screening cacao germplasm for resistance to Phytophthora.