Screening for Resistance Sources in Local and Exotic Hot Pepper Genotypes to Fusarium Wilt (Fusarium oxysporium) and Associated Quality Traits in Ethiopia

Abstract

Fifty-four hot pepper germplasm (49 local accessions and 5 AVRDC genotypes) were evaluated for resistance to fusarium wilt in a greenhouse at Melkassa Agricultural Research Centre in Ethiopia. A completely randomized design with three replications was used. Each local accession was also analyzed for associated quality traits of capsaicin and oleoresin content. The overall results indicated that disease incidence ranged from 8 (PBC-731) to 100% for Acc-15. Most local collections exhibited higher disease incidences percent than AVRDC genotypes with an overall mean DI <25% of Fusarium wilt. Among the 49 local accessions, however, only two accessions were found resistant (1-10%) while three were moderately resistant (11-20%). Assessment of the same accessions for resistance to the disease using severity index (SI) showed that 11 accessions and genotypes were found resistant (<10% DSI) whereas nine genotypes moderately resistant (10-20% SI), 10 genotypes were moderately susceptible (21-40% SI), four accessions were found susceptible (41-60%) and the rest 20 accessions were highly susceptible >60%. Based on severity rating (1-5 scale), two accessions (Acc-39 and PBC-731) were highly resistant to wilt with severity ratings of 1 and 14 accessions were found resistant with severity rating scale of 2 whereas 38 accessions were susceptible with severity scale of >3. Capsaicin content percentage ranged from 0.16-0.55%, and heat unit ranged 26372 to 88775 SHU, for Acc-32 and Acc-24, respectively. Oleoresin content in international color unit and ASTA value ranged from 32,800 to 118,840 cu and 82-296 ASTA with an overall mean of 69,704 ICU and 172 ASTA value. The highest color quality colors of greater than 250 ASTA was exhibited by 10 accessions (Acc-4, Acc-5, Acc-6, Acc-7, Acc-24, Acc-27, Acc-33, Acc-34, Acc-39 and Acc-31). This study identified resistance accessions with desirable qualities among the 49 local accessions. These materials also had good wilt resistance potential and could be used as source parents in the future hybridization and for simultaneous selection for Fusarium wilt resistance and high processing quality traits in hot pepper improvement program.

Full text

Screening for Resistance Sources in Local and Exotic Hot Pepper
Genotypes to Fusarium Wilt (
Fusarium oxysporium
) and Associated
Quality Traits in Ethiopia
Shimeles Aklilu1,2*, Getachew Ayana2, Bekele Abebie3 and Tesfaye Abdissa2
1Department of Horticulture, Adama Science and Technology University, Ethiopia
2Ethiopian Institute of Agricultural Research, Melkassa Agricultural Research Center, PO Box No: 436, Adama, Ethiopia
3College of Agriculture, Arsi University, Adama, Ethiopia
*Corresponding author: Shimeles Aklilu, Department of Horticulture, Adama Science and Technology University, Ethiopia, Tel: +251-0911756168;
E-mail: shimiakl@yahoo.com
Rec date: May 05, 2018; Acc date: May 12, 2018; Pub date: May 19, 2018
Copyright: © 2018 Aklilu S, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and source are credited.
Abstract
Fifty-four hot pepper germplasm (49 local accessions and 5 AVRDC genotypes) were evaluated for resistance to
fusarium wilt in a greenhouse at Melkassa Agricultural Research Centre in Ethiopia. A completely randomized
design with three replications was used. Each local accession was also analyzed for associated quality traits of
capsaicin and oleoresin content. The overall results indicated that disease incidence ranged from 8 (PBC-731) to
100% for Acc-15. Most local collections exhibited higher disease incidences percent than AVRDC genotypes with an
overall mean DI <25% of Fusarium wilt. Among the 49 local accessions, however, only two accessions were found
resistant (1-10%) while three were moderately resistant (11-20%). Assessment of the same accessions for
resistance to the disease using severity index (SI) showed that 11 accessions and genotypes were found resistant
(<10% DSI) whereas nine genotypes moderately resistant (10-20% SI), 10 genotypes were moderately susceptible
(21-40% SI), four accessions were found susceptible (41-60%) and the rest 20 accessions were highly susceptible
>60%. Based on severity rating (1-5 scale), two accessions (Acc-39 and PBC-731) were highly resistant to wilt with
severity ratings of 1 and 14 accessions were found resistant with severity rating scale of 2 whereas 38 accessions
were susceptible with severity scale of >3. Capsaicin content percentage ranged from 0.16-0.55%, and heat unit
ranged 26372 to 88775 SHU, for Acc-32 and Acc-24, respectively. Oleoresin content in international color unit and
ASTA value ranged from 32,800 to 118,840 cu and 82-296 ASTA with an overall mean of 69,704 ICU and 172 ASTA
value. The highest color quality colors of greater than 250 ASTA was exhibited by 10 accessions (Acc-4, Acc-5,
Acc-6, Acc-7, Acc-24, Acc-27, Acc-33, Acc-34, Acc-39 and Acc-31). This study identified resistance accessions with
desirable qualities among the 49 local accessions. These materials also had good wilt resistance potential and could
be used as source parents in the future hybridization and for simultaneous selection for Fusarium wilt resistance and
high processing quality traits in hot pepper improvement program.
Keywords: Hot pepper;
Fusarium
wilt; Oleoresin; Capsaicin
Introduction
Hot pepper (
Capsicum annum L.
) is one of the most economically
important vegetable crops in Ethiopia. Cultivars with elongated-fruit
with mildly to highly pungent types are the most preferred. e crop is
widely grown in an altitude ranging from 1400-1900 meters above sea
level under rain fed and irrigated conditions. Its use is primarily as the
main component of daily diet of majority of Ethiopians and also
considered as a high value commodity, which has huge potential for
improving the income and hence the livelihoods of thousands of small
holder farmers [1]. Ethiopia is one of a few African countries that
produce capsaicin and oleoresin for the export market from locally
selected materials that contributed substantially to the national
economy. In spite of tremendous potential use, good scope for
processing, available export market as a spice powder and oleoresin
and a wide range of available genetic resource, little eort has been
made to improve quality and productivity of pepper, in the country [2].
Among biotic factors that aect pepper production in Ethiopia,
Fusarium
wilt that is caused by
F. oxisporium
is one of the most
economically important diseases, and it accounts for yield losses of up
to 80% [3]. In recent years, the importance of the disease has been
increasing and is given considerable attention by hot pepper producers
and other stakeholders.).
Unfortunately, commercially acceptable varieties in Ethiopia are
very susceptible to this disease. It can, however, be hypothesized that
resistant hot pepper germplasm against
Fusarium
wilt could exist
either in the land races that have been cultivated by small scale farmers
for many or exotic accessions imported by dierent research
organizations from dierent countries. In the locally cultivated land
races or in varieties released by local research organizations, gene ow
is expected to be high due to uncontrolled pollination of the crop and
its high rate out-crossing.
erefore, it is imperative to collect, characterize, evaluate and
identify
Fusarium
wilt resistant materials that could be used as sources
of resistance for introgressing resistant traits into commercially
acceptable hot pepper cultivars. On the other hand, most resistant
cultivars lack most important quality attributes of horticultural
characteristics necessary to compete with widely acceptable susceptible
cultivars [4]. erefore, development of new resistant hot pepper
cultivars could also have additional attributes for improving quality of
hot pepper. So far, no systematic research has been conducted on hot
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ISSN: 2329-8863
Advances in Crop Science and
Technology
Aklilu et al., Adv Crop Sci Tech 2018, 6:3
DOI: 10.4172/2329-8863.1000367
Research Article Open Access
Adv Crop Sci Tech, an open access journal
ISSN: 2329-8863
Volume 6 • Issue 3 • 1000367

pepper accessions available in Ethiopia and exotic germplasm
introduced from dierent sources. us, the objective of this study
was, to screen exotic and local genotypes for resistance to
Fusarium
wilt and quality traits (capsaicin and oleoresin contents) and come up
with potential parents that could be used in the future improvement
program.
Materials and Methods
Collection of
Fusarium
disease samples
Field survey was carried out during the 2015 cropping season in the
major pepper growing areas in the central ri valley of Ethiopia. e
major hot-pepper producing areas such as Hawasa, Butajira, Koka,
Ziway, Bishou and Wonji were purposely selected. Farm elds at each
selected area were systematically sampled to collect disease specimens.
Following all accessible roads, every hot pepper farm was selected and
assessed. Highly infected pepper plants showing typical wilting
symptoms (leaf yellowing and dropping and/or partial or complete
plant wilting) were collected for isolation and identication of
F.
oxysporium
. e specimens were up rooted and kept separately in a
polyethylene bag and placed in an ice box with a temperature of about
4°C and brought to Melkassa Agricultural Research Centre (MARC),
Plant Pathology Laboratory.
Isolation and identication
Potato Dextrose Agar (PDA) was prepared by diluting 39 g of PDA
in 1000 ml of distilled water. is was autoclaved for 20 minutes at 120
lb pressure. To restrict bacterial growth, PDA was amended with 100
mg/l streptomycin and then poured into Petri plates. e infected roots
and stems were washed, sterilized, and then placed in the PDA
medium. Aer ve days of incubation at 25 ± 2°C, colonies of fungus
were transferred to fresh PDA media. Sub culturing was done till
distinct/pure culture was obtained. Identication of fungi was done
based on the cultural characteristics and microscopic examination
using the Standard manuals [5].
Acquisition of genotypes and screening for resistance
Fiy-four hot pepper genotypes of 49 locally collected accessions
from dierent agro-ecological zones in Ethiopia described, in Table 1
and 5 AVRDC genotypes (ICPN-916, Melka Shote, Melka Awaze,
Melka Zala and PBC-731 were evaluated for their reaction to
Fusarium
wilt in the green house.
Seedlings of all accessions were raised in the green house in a 52.3
cm × 25.9 cm × 6.1 cm plastic trays, having 12 individual cells with
water draining holes below. A growing media that comprised soil,
compost and sand at a ratio of 2:1:1, respectively. Each media
component was properly sieved in a 0.5 mm sieve size, mixed manually
and autoclaved at 120°C for 90 min and spread on a clean concrete
oor at room temperature. e pepper seeds were carefully drilled in
each cell (2 seeds per cell) and each tray was covered with a thin layer
of dry grass. e trays were watered twice a day using a watering can
with relatively ne nozzles. e experiment was laid out in a Complete
Randomized Design (CRD) with three replications using eight
seedlings per plot. e roots of 45 days old pepper seedlings were
pruned gently 2 hrs prior to inoculation, and trays that contained these
seedlings were placed in water-lled plastic boxes to saturate the roots.
e fungus inoculums were prepared by considering 500 conidia per
ml resulting in a nal concentration of 10,000 conidia per tray. Root
inoculation was performed following procedures described by Black et
al. [6]. Two hundred ml of spore suspension was prepared in which
twenty-ml of spore suspension was poured into each box containing
seedling tray. en immediately placed in a box and incubated for 12
hrs in the green house. en the seedlings were taken from the box and
kept in the green house to evaluate the reaction of accessions with the
control seedlings treated only with distilled water.
Determination of capsaicin and oleoresin content
Mature dry fruits were harvested and dried at an ambient condition
for 3-5 days under shade. en ground to a ne powder with mortar
and pestle. Ten and four gram of pepper powder for capsaicin and
oleoresin respectively was extracted in 100 ml of 96% methanol, in 250
ml Erlenmeyer ask covered with black markings tape and put a
funnel into the neck of the ask. e extraction was performed in 5
hours on temperature of 78°C. en ltered before use and kept in
brown glass bottle. en 2 or 3 ml of ltrate were transferred into 100
ml volumetric ask and the ask was immediately lled up to volume
with methanol. en absorption at the maximum 460 nm was read
against pure solvent in a Spectrophotometer. e apparatus capsaicin
content in Scoville heat unit (SHU) was calculated in (mg/g) of
powder) based the following formula: SHU=Absorbance × IF × 1.61 ×
107
For determination of oleoresins content, the absorption of samples
was read at the maximum 460 nm against pure solvent in a
Spectrophotometer. e oleoresins content in (mg/g of powder)
calculated based the following formula:
ICU=Absorbance × IF × 1.64/weight of sample
ASTA=ICU/weight of sample
Where, IF is the deviation factor of the spectrophotometer (0.60).
Data collection procedures and analysis
e plants were monitored every two weeks for disease symptoms of
(leaf yellowing and chlorosis, shedding from the base, stunting and
total plants wilt and death). en the diseases developments were
evaluated based on dierent criteria.
Disease severity rating scale was rated based on a 5-point scale as
per AVRDC pepper disease compendium [6]. Such as 0=no visible
infection, vigorous, healthy=R; 1=slight leaf yellowing=MR; 2=old
lower leaf yellowing and plant wilting=MS; 3=lower leaves shading and
stunted plants=S; 4=all the leaves shedding and the stem collapsed and
few plants death and HS; 5=Total plant death
Disease incidence (DI) percentage, was calculated as the proportion
of infected plants per plot and expressed as a percentage [7].
Disease Incidence (%)=(Number of infected plants per row/ Total
number of plants per variety) × 100
e incidence was calculated and grading was done on the basis of
wilt incidence (%) as:
• Highly resistant (HR): 0% wilting.
• Resistant (R): 1-10% wilting.
• Moderately Resistant (MR): 11-20% wilting.
• Moderately Susceptible (MS): 21-30% wilting.
• Susceptible (S): 31-50% wilting.
• Highly susceptible: >50% wilting.
Citation: Aklilu S, Ayana G, Abebie B, Abdissa T (2018) Screening for Resistance Sources in Local and Exotic Hot Pepper Genotypes to
Fusarium Wilt (Fusarium oxysporium) and Associated Quality Traits in Ethiopia. Adv Crop Sci Tech 6: 367. doi:
10.4172/2329-8863.1000367
Page 2 of 9
Adv Crop Sci Tech, an open access journal
ISSN: 2329-8863
Volume 6 • Issue 3 • 1000367

e disease severity index (DSI) was calculated according to the
formula given by Galanihe et al. [8].
DSI (%) = Σ{(P × Q)}/(M × N)] × 100
Where P=severity score, Q=number of infected plants having the
same score; M=Total number of plants observed, N=Maximum rating
scale number. e computed Diseases Severity Index (DSI %) of each
material were categorized as: Highly resistant (HR)=0%; Resistant
(R)=DSI% <10%; Moderately resistant (MR)=10-20%; MS=moderately
susceptible, 21-40%; Susceptible (S)=41-60%; highly susceptible (HS)
>60%. Data on wilted plants were recorded every two weeks
throughout the duration of the experiment for 30 days. Disease
incidence and severity (DSI) were transformed using the ARCSIN
function so as to normalize variability. e transformed data were
subjected to analysis of variance using all analysis of variance for
quantitative characters using (SAS 9.2 soware package, 2004). A
probability value of LSD <0.05 was used as a bench mark to examine
variations among the accessions.
Results
Isolation and identication of
Fusarium
Typical characteristics of
F. oxsporium
isolates were recovered from
almost all plants that showed typical symptoms of
Fusarium
wilt. e
isolates were characterized based on morphological characteristics
ranging from cottony white to pink pigmentation on PDA. e
majority of isolates were characterized as white color mycelium and
few isolates showed other pigmentations such as violet, yellow, grey
and color intensity that varies from time to time depending upon the
period of incubation.
Reaction of pepper genotypes to
Fusarium
wilt diseases
Wilt incidence percent: e analysis of variance for
Fusarium
wilt
incidence, severity index and scale showed signicant (P<0.05)
dierences among the genotypes considered in the study. e overall
disease incidence ranged from 8 to 100%, with the lowest values
recorded for pepper genotypes Acc-39 and AVRDC genotypes,
PBC-731, and the highest value registered for Acc-15.
Higher disease incidence was recorded from the locally collected
genotypes than exotic ones. Accordingly, 48% of the local collections
showed greater than 70% DI out of which, nine (18%) genotypes
(Acc-7, Acc-8, Acc-9, Acc-13, Acc-14, Acc-15, Acc-18, Acc-23 and
Acc-24) exhibited high wilt incidence (>90%) level. From the AVRDC
genotypes, PBC-731 was the least infected with
Fusarium
wilt as the
disease incidence level was only 8%, followed by genotypes Melka Zala
and Melka Awaze with 14 and 20% incidences, respectively. However,
from the local genotypes, Acc-39 was not severely infected in the green
house and showed almost equal levels of response to
Fusarium
as that
of the AVRDC genotype PBC-731, which showed <10% incidence level
than all the other local and exotic genotypes. is was followed by
eight local genotypes (Acc-4, Acc-5, Acc-12, Acc-32, Acc-33, Acc-40,
Acc-46 and Acc-49) with incidence levels of <25%, as compared to all
the others that gave incidence levels of >30%. Based on the DI
percentage, only PBC-731 and Acc-39 showed <10% DI and could be
considered to be resistant to
Fusarium
wilt (Table 1).
S No Acc. Disease
Incidence
R Disease
Severity
R S No Acc. Disease
Incidence
R Disease
Severity
1 Acc-1 0.82(0.96) HS 0.66(0.72) HS 28 Acc-28 0.81(0.94) HS 0.65(0.70)
2 Acc-2 0.88(1.1) HS 0.70(0.78) HS 29 Acc-29 0.84(0.99) HS 0.84(1.10)
3 Acc-3 0.74(0.83) HS 0.59(0.63) S 30 Acc-30 0.76(0.86) HS 0.60(0.65)
4 Acc-4 0.23(0.23) MS 0.09(0.09) R 31 Acc-31 0.41(0.41) S 0.24(0.24)
5 Acc-5 0.24(0.24) MS 0.09(0.10) R 32 Acc-32 0.23(0.23) MS 0.09(0.10)
6 Acc-6 0.27(0.27) MS 0.11(0.11) MR 33 Acc-33 0.23(0.23) MS 0.09(0.10)
7 Acc-7 0.94(1.22) HS 0.94(1.22) HS 34 Acc-34 0.41(0.43) S 0.25(0.25)
8 Acc-8 0.91(1.15) HS 0.91(1.14) HS 35 Acc-35 0.41(0.42) S 0.25(0.25)
9 Acc-9 0.92(1.16) HS 0.92(1.17) HS 36 Acc-36 0.28(0.28) MS 0.11(0.11)
10 Acc-10 0.81(0.95) HS 0.81(0.94) HS 37 Acc-37 0.33(0.34) S 0.20(0.20)
11 Acc-11 0.76(0.86) HS 0.61(0.65) HS 38 Acc-38 0.34(0.34) S 0.20(0.21)
12 Acc-12 0.26(0.26) MS 0.09(0.10) R 39 Acc-39 0.09(0.18) R 0.02(0.02)
13 Acc-13 0.90(1.12) HS 0.90(1.12) HS 40 Acc-40 0.25(0.26) MS 0.10(0.08)
14 Acc-14 0.96(1.31) HS 0.96(1.30) HS 41 Acc-41 0.46(0.48) S 0.28(0.31)
15 Acc-15 1.00(1.61) HS 1.10(1.60) HS 42 Acc-42 0.41(0.41) S 0.24(0.25)
16 Acc-16 0.85(1.02) HS 0.85(1.02) HS 43 Acc-43 0.35(0.36) S 0.21(0.22)
17 Acc-17 0.84(1.01) HS 0.84(1.10) HS 44 Acc-44 0.41(0.41) S 0.24(0.24)
Citation: Aklilu S, Ayana G, Abebie B, Abdissa T (2018) Screening for Resistance Sources in Local and Exotic Hot Pepper Genotypes to
Fusarium Wilt (Fusarium oxysporium) and Associated Quality Traits in Ethiopia. Adv Crop Sci Tech 6: 367. doi:
10.4172/2329-8863.1000367
Page 3 of 9
Adv Crop Sci Tech, an open access journal
ISSN: 2329-8863
Volume 6 • Issue 3 • 1000367

18 Acc-18 0.93(1.21) HS 0.93(1.20) HS 45 Acc-45 0.38(0.39) S 0.23(0.23)
19 Acc-19 0.35(0.36) S 0.20(0.21) MR 46 Acc-46 0.20(0.21) MR 0.08(0.09)
20 Acc-20 0.76(0.87) HS 0.60(0.65) HS 47 Acc-47 0.37(0.38) S 0.22(0.22)
21 Acc-21 0.84(1.02) HS 0.84(1.10) HS 48 Acc-48 0.81(0.95) HS 0.81(0.95)
22 Acc-22 0.86(1.04) HS 0.86(1.04) HS 49 Acc-49 0.25(0.25) MS 0.10(0.11)
23 Acc-23 0.94(1.22) HS 0.94(1.22) HS 50 ICPN-916 0.26(0.27) MS 0.10(0.11)
24 Acc-24 0.95(1.25) HS 0.95(1.25) HS 51 Melka Shote 0.26(0.27) MS 0.10(0.11)
25 Acc-25 0.46(0.48) S 0.28(0.28) MS 52 Melka awaz 0.20(0.20) MR 0.08(0.09)
26 Acc-26 0.83(0.99) HS 0.66(0.73) HS 53 Melka zala 0.14(0.14) MR 0.06(0.05)
27 Acc-27 0.78(0.89) HS 0.61(0.67) HS 54 PBC-731 0.08(0.08) R 0.02(0.02)
Mean 0.56 0.45 0.56 0.45
CV (%) 33 35 33 35
LSD (0.05) 0.6 0.7 0.6 0.7
Table 1: Mean diseases incidence and severity index along with resistance levels of 54 hot pepper genotypes to
Fusarium
wilt evaluated at MARC
in, 2015/16. Numbers in parenthesis are transformed values. R=resistance level, HR=highly resistant, R=resistant, MR=moderately resistant,
MS=moderately susceptible, S=susceptible, HS=highly susceptible, CV (%)=coecient of variation in percent and LSD (0.05)=least signicant
dierence at P<0.05.
One local accession, Acc-46 and two AVRDC genotypes Melka
Awaze and Melka Zala which showed 14 to 20% DI could be
considered as moderately resistant. Eleven genotypes (Acc-4, Acc-5,
Acc-6, Acc-12, Acc-32, Acc-33, Acc-36, Acc-40, Acc-49, Melaka
Awaze, Melka Zala with DI of 21- 30% considered as moderately
susceptible. Meanwhile, 13 genotypes (Acc-19, Acc-25, Acc-31, Acc-34,
Acc-35, Acc-37, Acc-38, Acc-41, Acc-42, Acc-43, Acc-44, Acc-45 and
Acc-47) showed DI percent from 31-50% considered as susceptible and
the remaining 25 local genotypes with DI >50% were found to be
highly susceptible (Table 1).
Figure 1: Proportion of 54 hot pepper genotypes in dierent
resistance level to fusarium wilt disease as categorized from disease
incidence (%) evaluated at MARC in 2015/2016.
Considering the two extremes the lowest incidence among local
accession was recorded on Acc-39 (9%), followed by Acc-46 (20%),
while the highest was recorded on genotypes Acc-15 and Acc-14 with
high incidences level of 100% and 96%, respectively. erefore, from
the local genotypes Acc-4, Acc-5, Acc-12, Acc-32, Acc-33, Acc-40,
Acc-46 and Acc-49 and introduced genotypes Melka Awaza, Melka
Zala and PBC-731 had the least wilt incidences in that order. e
overall mean percent DI of (56%) was recorded from local materials
compared to the introduced genotypes (19%). ere was no accession
and genotype without diseases symptom, but high variability existed
within and between genotypes (Figure 1).
Disease severity index: Disease severity indices varied signicantly
(P<0.05) among genotype and local genotypes, based on severity index
rating genotypes were categorized into 5; where, 11 genotypes (Acc-4,
Acc-5, Acc-12, Acc-32, Acc-33, Acc-39, Acc-46, Acc-49, Melaka
Awaze, Melka Zala and PBC-731) were found resistant (<10% DSI)
with the AVRDC lines PBC-731 and local accession, Acc-39, being the
highest resistant with severity index of 2%, whereas nine genotypes
(Acc-6, Acc-19, Acc-36, Acc-37, Acc-38, Acc-40, Acc-49, Melaka
Awaze and Melka Zala) moderately resistant (10-20% SI) and 10
genotypes (Acc-25, Acc-31, Acc-34, Acc-35, Acc-41, Acc-42, Acc-43,
Acc-44, Acc-45, and Acc-47) moderately susceptible (21-40% SI), four
genotypes (Acc-3, Acc-20, Acc-27, and Acc-30) were found susceptible
(41-60%) and the rest 20 genotypes were highly susceptible >60%
(Acc-1, Acc-2, Acc-7, Acc-8, Acc-9, Acc-10, Acc-13, Acc-14, Acc-15,
Acc-16, Acc-17, Acc-18, Acc-21, Acc-22, Acc-23, Acc-24, Acc-26,
Acc-28, Acc-29, and Acc-48) (Figure 2). However, 25 genotypes had
severity index scores above the overall mean of (45%) with Acc-15
(100%) and Acc-14 (96%) found to be severely infected genotypes
followed by genotypes Acc-7, Acc-8, Acc-9, Acc-13, Acc-14, Acc-15,
Acc-18, Acc-23, Acc-24. In general, 24 genotypes and ve exotic
genotypes had severity indices less than the overall mean of 45%, with
four genotypes, PBC-731 and Acc-39, Melka Zala and Acc-46, showing
the least severity index. Nine local genotypes (Acc-39, Acc-46, Acc-32,
Acc-33, Acc-12, Acc-4, Acc-5, Acc-46, Acc-49) and all AVRDC
genotypes registered the lowest severity indices of <10%.
Citation: Aklilu S, Ayana G, Abebie B, Abdissa T (2018) Screening for Resistance Sources in Local and Exotic Hot Pepper Genotypes to
Fusarium Wilt (Fusarium oxysporium) and Associated Quality Traits in Ethiopia. Adv Crop Sci Tech 6: 367. doi:
10.4172/2329-8863.1000367
Page 4 of 9
Adv Crop Sci Tech, an open access journal
ISSN: 2329-8863
Volume 6 • Issue 3 • 1000367

Figure 2: Proportion of 54 hot pepper genotypes in dierent
resistance level to fusarium wilt disease as categorized from
Diseases Severity Index (%) evaluated at MARC in 2015/2016.
Diseases severity scale: Based on disease severity scale (1-5) 54
genotypes categorized in to resistant (1-2), moderate (3) and
susceptible (4-5). us, Acc-39 and AVRDC line PBC-731 were
consistently resistant as their severity score was 1 and with a healthy
plant survival percent ranging from 80 to 95%. Moreover, 14 genotypes
responded within the resistant severity rating scale range of 2. Sixteen
of the 54 genotypes were highly susceptible, with rating scale of 5 while
the rest 13 and nine genotypes had intermediate rating scale of 3 and 4,
respectively. e susceptible control Marko Fana and most other local
genotypes had an average rating scale of 5 with <20% of surviving
plants. us, from 54 genotypes, 14 genotypes (26%) had a mean wilt
severity scale of 2 and were considered resistant, whereas 13 (24%)
genotypes had severity scale of 3 and 9 genotypes (17%) with the rating
scale of 4, whereas 16 genotypes (30%) showed rating scale of 5 (Figure
3).
Figure 3: Reaction of local genotypes and exotic genotypes for
Diseases Severity Rating Scale.
Relationship between disease incidence and severity index of
Fusarium
wilt: Results from linear regression analysis between disease
incidence (%) and disease severity index (%) of
Fusarium
wilt in 54 hot
pepper genotypes showed that the presence of highly signicant
(P<0.000) linear relationship between the two disease parameters. e
coecient of determination (R2) was 0.9692 or 96.92% with near to
perfect correlation (r=0.9845) (Figure 4). is indicated that both
methods are equally important and should be used in evaluation for
resistance to wilt disease.
Figure 4: Linear regression of Disease Incidence (%) (DI) and
Disease Severity Index (%) (DSI) of Fusarium wilt in 54 hot pepper
genotypes evaluated at MARC in 2015/2016.
Capsaicin content: Among the whole genotypes compared, the
capsaicin content ranged from 0.16-0.55% and 26,372 to 88,775 SHU
(Table 2). While the minimum (26,372) SHU was recorded for Acc-32
and the maximum (88,775) SHU for Acc-24. e percent capsaicin
content of 13 genotypes was less than 0.25%. Based on SHU, Weiss [9]
classied pepper cultivars into ve pungency levels, non-pungent
(0-700 SHU), mildly pungent (700-3,000 SHU), moderately pungent
(3,000-25,000 SHU), highly pungent (25,000-70,000 SHU) and very
highly pungent (>80,000 SHU). Accordingly, all of the Ethiopian
pepper genotypes considered in the current study could be categorized
only into highly pungent and very highly pungent types. Having SHU
of >70, 000, only ve of the genotypes (Acc-24, Acc-39, Acc-4, Acc-7
and Acc-9) could be categorized under very highly pungent, whereas
the remaining 44 genotypes with 25,000-70,000 SHU could be
categorized under highly pungent types.
Oleoresin content: e oleoresin content in international color unit
(ICU) and ASTA value ranged from 32,800-118408 ICU and 82-296
ASTA value with overall means of 69,074 ICU and 172 ASTA value
(Table 2). Accordingly, genotypes Acc-39 and Acc-4 had maximum
international color unit of 118,408 ICU and 296 ASTA value, followed
by Acc-24, Acc-33, and, Acc-5 and Acc-34.
Based on the classication method of ASTA [10], all the 49
genotypes were grouped into four categories. us, seven genotypes
gave poor quality of <100 ASTA value (Acc-28, Acc-43, Acc-44,
Acc-48, Acc-14, Acc-18, and Acc-17). Eight genotypes (Acc-2, Acc-6,
Acc-9, Acc-21, Acc-25, Acc-27, Acc-40 and Acc-36) gave very good
quality color within the range of 200 - 250 ASTA value. However, the
highest quality colors of greater than 250 ASTA value was obtained
from ten genotypes (Acc- 4, Acc-5, Acc-6, Acc-7, Acc-24, Acc-27,
Acc-33, Acc-34, Acc-39, and Acc-31), and 24 genotypes gave
intermediate quality colors of within 101-200 ASTA value.
Accessions Fruit weight Powder weight F:P International color unit ASTA value Percent of capsaicin Scoville heat unit
Acc-1 3 2 1.4 59368 148 0.23 37288
Citation: Aklilu S, Ayana G, Abebie B, Abdissa T (2018) Screening for Resistance Sources in Local and Exotic Hot Pepper Genotypes to
Fusarium Wilt (Fusarium oxysporium) and Associated Quality Traits in Ethiopia. Adv Crop Sci Tech 6: 367. doi:
10.4172/2329-8863.1000367
Page 5 of 9
Adv Crop Sci Tech, an open access journal
ISSN: 2329-8863
Volume 6 • Issue 3 • 1000367

Acc-2 3 1.9 1.6 91184 228 0.4 63949
Acc-3 3 1.8 1.7 70192 175 0.27 43663
Acc-4 2.9 1.9 1.5 118408 296 0.46 73319
Acc-5 3 1.7 1.7 110044 275 0.35 55642
Acc-6 2.4 1.4 1.7 99548 250 0.4 64239
Acc-7 2.6 1.5 1.7 101024 253 0.45 71967
Acc-8 2.7 1.7 1.6 55268 138 0.37 58926
Acc-9 3.2 2.1 1.5 98564 246 0.46 74479
Acc-10 2.8 1.7 1.7 61172 153 0.21 33327
Acc-11 3.1 2 1.6 73308 183 0.34 54193
Acc-12 2.9 1.7 1.6 60352 151 0.29 47141
Acc-13 3 1.9 1.6 65108 163 0.22 35645
Acc-14 2.4 1.4 1.7 39688 99 0.22 34873
Acc-15 2.7 1.6 1.7 72816 182 0.31 49459
Acc-16 2.8 1.8 1.6 71996 180 0.34 55062
Acc-17 2.6 1.2 2.1 32800 82 0.35 56221
Acc-18 3 1.7 1.7 39032 98 0.23 37191
Acc-19 2.9 2.2 1.3 73472 184 0.33 52550
Acc-20 3.5 2.3 1.5 72652 182 0.33 52744
Acc-21 3.1 2 1.5 82820 207 0.35 56608
Acc-22 2.9 1.9 1.6 44772 112 0.2 32651
Acc-23 3.4 2.2 1.6 40508 101 0.25 40379
Acc-24 3.2 1.9 1.7 111848 280 0.55 88775
Acc-25 2.8 1.8 1.6 93644 234 0.3 47914
Acc-26 3.2 2.5 1.3 43624 109 0.26 41055
Acc-27 2.9 1.8 1.6 85444 214 0.22 35066
Acc-28 2.8 1.7 1.6 33128 83 0.22 35645
Acc-29 2.4 1.6 1.4 76588 161 0.38 61148
Acc-30 3.4 2.5 1.4 52972 132 0.3 47817
Acc-31 3.2 2.2 1.5 101516 254 0.42 67330
Acc-32 3.1 2.3 1.4 41984 105 0.16 26372
Acc-33 3 2.3 1.3 117752 294 0.38 60568
Acc-34 3.1 1.9 1.7 110864 277 0.38 61824
Acc-35 2.9 1.7 1.7 66092 165 0.28 44533
Acc-36 3.3 2.2 1.5 81344 203 0.36 57863
Acc-37 2.7 1.7 1.6 55104 138 0.19 30719
Citation: Aklilu S, Ayana G, Abebie B, Abdissa T (2018) Screening for Resistance Sources in Local and Exotic Hot Pepper Genotypes to
Fusarium Wilt (Fusarium oxysporium) and Associated Quality Traits in Ethiopia. Adv Crop Sci Tech 6: 367. doi:
10.4172/2329-8863.1000367
Page 6 of 9
Adv Crop Sci Tech, an open access journal
ISSN: 2329-8863
Volume 6 • Issue 3 • 1000367

Acc-38 3.2 2 1.6 71012 178 0.26 41635
Acc-39 2.9 2 1.5 118408 296 0.54 87423
Acc-40 3.3 2 1.6 87904 220 0.36 57960
Acc-41 3.2 2.1 1.5 58876 147 0.25 40186
Acc-42 2.8 1.7 1.6 39852 100 0.22 36128
Acc-43 2.9 1.7 1.8 33292 83 0.3 47914
Acc-44 3 1.8 1.7 38376 96 0.29 46658
Acc-45 2.8 1.8 1.5 53956 135 0.29 47044
Acc-46 2.5 1.4 1.7 40344 101 0.2 32941
Acc-47 2.8 1.4 2 56744 142 0.33 52357
Acc-48 2.7 1.6 1.6 39688 99 0.23 37771
Acc-49 2.6 1.2 2.2 40180 100 0.25 40765
Mean 2.9 1.8 1.6 69074 172 0.32 50141
Table 2: Capsaicin and oleoresin content of 49 local hot pepper genotypes evaluate at MARC, 2014/2015.
Discussion
e study was undertaken to identify wilt resistant local collections
and exotic materials of hot pepper at MARC green house. Signicant
dierences among genotypes were observed and some local materials
equally performed with the exotic genotypes in wilt disease incidences
and severity indices. From the total of 54 hot pepper genotypes
screened, only two genotypes PBC 731 and Acc-39 were found
resistant <10 DI, followed by moderately resistant Acc-46, 52 and 53
with (11-20% DI), whereas, 25 local accessions were rated highly
susceptible (>50% wilting).
Similarly, wide variation in resistance scores rating scale was
observed both between accessions as well as between plants within
genotypes/accessions which is due to their genetic dierences. e
present study is in agreement with the reports of Mamta et al. [11]
which indicated great disease incidence variation within the range of 0
to 78.7% and from thirty varieties screened, only two varieties were
found 100% resistant, against wilt of chilli.
Evaluation of resistance was measured on the basis of total number
of dead to live plants of each genotype, aer inoculation. Grouping of
genotypes on the basis of their reaction to
Fusarium
wilt diseases
facilitated the identication of resistant and susceptible genotypes
based on disease incidence and severity index percent and severity
rating scale. us, based on incidence percent from the total of 54 hot
pepper genotypes screened, 25 local genotypes were found highly
susceptible with DI (>50% wilting), thirteen were moderately
susceptible (31-50%), 11 moderately resistant (21-30% wilting), three
resistant (11-20% wilting) and two genotypes were rated highly
resistant (1-10% wilting).
e practical method to control
Fusarium
wilt is the use of resistant
varieties but there was no exhaustive screening work has been done so
far in local pepper breeding programs. However, this is the rst wide-
scale screening report in large number of local and exotic hot pepper
accessions for resistance to
Fusarium
wilt throughout the country.
Moreover, so far the screening methods have traditionally relied on
eld trials to dierentiate resistance levels and hence this inoculation
technique, when used in the green house as a screening method, reect
the level of resistance that may be expressed under eld conditions.
e variable inoculums densities and uncontrolled environmental
conditions may severely aect the outcome of eld trials that lead to
variable results [12]. However, this screening method demonstrated
the availability of genotypes that are potential sources of resistance to
Ethiopian isolates of
F. oxisporium
which could be incorporated into
commercially acceptable pepper cultivars. From the result of this study
majority of the local materials showed susceptibility response to wilt
diseases and only 10 local genotypes Acc-4, 5, 6, 12, 40, 39, 32, 33, 46
and 49, and three exotic genotypes 54, 50, 53 and 51 scored better in
disease resistance. However, these local genotypes that scored better
disease resistance tend to produce high capsaicin and oleoresin yield.
Moreover, six accessions (Acc-4, Acc-5, Acc-6, Acc-12, Acc-36 and
Acc-40) which scored moderate resistance also gave higher dry pod
yields with good quality fruits. ough all AVRDC genotypes give high
green pod yield and scored better disease resistance but their pod
characters are not acceptable for dry pod production and hence could
be considered as potential parents for improving commercially
acceptable local pepper cultivars in the future crossing program.
Color analysis, based on ASTA method [10] is the most widely used
to measure the commercial quality of cultivars and quanties the total
carotenoid content which has been used as a parameter of quality in
selection, breeding, and cultivar characterization work [13]. High
quality and expensive pepper powders usually show minimum ASTA
values of 100 and as a rule, when the ASTA color value is high the
oleoresin is more expensive [14]. us, according to ASTA [10]
classication theses 49 hot pepper Ethiopian accessions only, 11
accessions (Acc-20, Acc-28, Acc-43, Acc-44, Acc-42, Acc-48, Acc-14,
acc-18, and Acc-17), gave ASTA value lower than 100, whereas, all the
rest 38 accessions are within the acceptable range of (100-296 ASTA)
value. However high color value of greater than 150 ASTA value are
required to compete in the world market and thus accessions of Acc-4,
Acc-5, Acc-6, Acc-7, Acc-24, Acc-27, Acc-33, Acc-34, Acc-39, and
Citation: Aklilu S, Ayana G, Abebie B, Abdissa T (2018) Screening for Resistance Sources in Local and Exotic Hot Pepper Genotypes to
Fusarium Wilt (Fusarium oxysporium) and Associated Quality Traits in Ethiopia. Adv Crop Sci Tech 6: 367. doi:
10.4172/2329-8863.1000367
Page 7 of 9
Adv Crop Sci Tech, an open access journal
ISSN: 2329-8863
Volume 6 • Issue 3 • 1000367

Acc-31 gave high color quality of greater than 250 ASTA unit.
However, Acc-17, 28 and 43 gave the lowest values, in color content as
well as in ASTA value as opposed to the highest values found in
Acc-39, Acc-24, Acc-9, Acc-5, Acc-7 and Acc-4.
e color values recorded in this study are within the ranges
reported by Kim et al., Topuz and Ozdemir and Howard et al. [15-17]
for
C. annum
cultivars. Similar to this study, Zaki et al. [18] reported
maximum color value of (116160 cu) and extractable color of 294.38
ASTA value from pepper. Moreover, Lannes et al. [19] showed a
variation of extractable color from 173-213 ASTA value, Dhali et al.
[20] reported the values within the range of this study 82-190 and
85-1780 ASTA respectively.
Based on heat unit all the peppers accessions classied as highly
pungent 25-70000 SHU and very highly pungent as the Scoville Heat
Unit (SHU) values exceed 70,000. However, two accessions with high
capsaicin and oleoresin content “Acc-24 and 39” can serve as potential
sources of gene for both capsaicin production and oleoresin
production. In line with this study, Kumar et al. [21] reported a range
of capsaicin 0.33-0.49% percent.
However, as opposed to the current study, Deepa et al. [22] reported
the highest range of 12.04-17.06% capsaicin content. e two
accessions which gave the highest color value Acc-24 and 39 also
showed relatively higher capsaicin content and hence according to
Dhalli and Hundai [20] further breeding program should be under
taken in order to lower the capsaicin content of these high color
varieties. As the above analysis indicated, all the accessions which gave
high oleoresin were with the exception of Acc-24 and 39, are within the
preferable pungency limit of (0.2-0.5%) and could directly be
recommended for high oleoresin production content. In this study
these local accessions express a wide range of fruit quality
characteristics, in which all Assossa and West Harareghe and Gojam
accessions had medium fruit size and pungency with low oleoresin
content, whereas most accessions, from Southern region have relatively
large pod size, high pungency and oleoresin yield and showed good
levels of resistance. However, from this study there are, local accessions
that showed high variability in their resistance to wilt, and quality
traits and the best resistant ones could be a primary candidate to
produce breeding lines from a commercial point of view for future
crossing program [23-28].
Conclusion
Signicant dierences were observed among genotypes, with
respect to severity index. When genotypes were partitioned with
respect to their places of origin, local genotypes were more severely
infected and exhibited a relatively higher overall mean severity index of
50% than exotic types (8%). Grouping of the 54 tested genotypes based
on the severity index (SI) showed that 11 genotypes were found highly
resistant (<10% SI), nine were moderately resistant (10-20%), 10
genotypes were moderately susceptible (21-40% SI), four were
susceptible (41-60% SI), while all the rest 20 genotypes were highly
susceptible (>60% SI). In general, from the 54 genotypes tested in the
green house, potential materials were identied from both local
collections and exotic materials. Acc-39 (local) and PBC-731 (exotic)
were found to be the most resistant genotypes. Percent capsaicin
content ranged from 0.16%-0.55%, whereas the capsaicin content in
heat unit (ASHU) varied from 26,372 to 88,775 SHU e oleoresin
content in international color unit (ICU) and ASTA value were ranged
from 32840-118408 color unit and 82-296 ASTA value with an overall
mean value of 69704 ICU and 172 ASTA. Based on the classication of
ASTA (1999) all the 49 genotypes were grouped into four categories;
low extractable color quality (7 genotypes), medium (24 genotypes),
very good color quality (8 accessions) and highest color quality (10
genotypes). In this study, hot pepper genotypes identied with
desirable capsaicin and oleoresin content as well as Fusarium wilt
resistance could be used as source of gene in future hybridization
program for improvement of the crop.
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Volume 6 • Issue 3 • 1000367

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Citation: Aklilu S, Ayana G, Abebie B, Abdissa T (2018) Screening for Resistance Sources in Local and Exotic Hot Pepper Genotypes to
Fusarium Wilt (Fusarium oxysporium) and Associated Quality Traits in Ethiopia. Adv Crop Sci Tech 6: 367. doi:
10.4172/2329-8863.1000367
Page 9 of 9
Adv Crop Sci Tech, an open access journal
ISSN: 2329-8863
Volume 6 • Issue 3 • 1000367