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Epidemiology of Fusarium agave wilt in Agave tequilana Weber var. Azul

March 2017
Plant Protection Science 53(3)

DOI:10.17221/142/2016-PPS

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CC BY-NC 4.0

Authors:

Norma Alejandra Mancilla Margalli

Tecnológico Nacional de México/Instituto Tecnológico de Tlajomulco

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Fusarium oxysporum is reported as the principal causal agent limiting production of Agave tequilana Weber var. azul, but frequent isolation of F. solani, and symptoms typical of F. solani as a pathogen like severe reddish coloured root rot and loss of soil anchorage are frequently associated with diseased agaves. Inoculations of agave plantlets with F. solani induced typical agave root rot symptoms in greenhouse trials. The incidence of both pathogens was determined molecularly with specific primers in the ITS2 sequence. Dispersion patterns of agave wilt, determined in plantations of different age, indicated a tendency to produce aggregated patterns over time as the disease spread from the initial symptomatic plant to adjacent plants. Although both fungi were isolated from agave diseased plants, and in spite of the higher percentage of detection and root rot symptoms, it is concluded that F. solani may have a greater impact in agave wilt.

Relation of the relative yield loss of sugar beet to relative weed cover in all experimental locations and years IHO-Ihinger Hof, Germany; DOK-Lipetsk region, Russia

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Relation of the relative yield loss of sugar beet to weed biomass in all experimental locations and years IHO-Ihinger Hof, Germany; DOK-Lipetsk region, Russia

…

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Vol. 53, 2017, No. 2: 118–125 Plant Protect. Sci.

doi: 10.17221/57/2016-PPS

Sugar Beet Yield Loss Predicted by Relative Weed Cover,

Weed Biomass and Weed Density

R GERHARDS*, K BEZHIN and H-J SANTEL

Department of Weed Science, Institute of Phytomedicine,

University of Hohenheim, Stuttgart, Germany

*Corresponding author: roland.gerhards@uni-hohenheim.de

Abstract

Gerhards R., Bezhin K., Santel H.-J. (2017): Sugar beet yield loss predicted by relative weed cover, weed biomass

and weed density. Plant Protect. Sci., 53: 118–125.

Sugar beet yield loss was predicted from early observations of weed density, relative weed cover, and weed biomass

using non-linear regression models. Six field experiments were conducted in Germany and in the Russian Federation

in 2012, 2013 and 2014. Average weed densities varied from 20 to 131 with typical weed species compositions for

sugar beet fields at both locations. Sugar beet yielded higher in Germany and relative yield losses were lower than in

Russia. Data of weed density, relative weed cover, weed biomass and relative yield loss fitted well to the non-linear

regression models. Competitive weed species such as Chenopodium album and Amaranthus retroflexus caused more

than 80% yield loss. Relative weed cover regression models provided more accurate predictions of sugar beet yield

losses than weed biomass and weed density.

Keywords: crop-weed interaction; weed competition; yield loss function

Weed management plays an important role in

sugar beet production. Wide row spacing and slow

development in early growth stages result in late

canopy closure. Up to 100% of the crop yield may be

lost because of weed competition if weed control is

poor or is not performed at all (K & S

1991). Effective weed control is needed mainly during

the critical period of sugar beet development, which

is approximately the period during the first 60 days

after emergence. Then, sugar beet does not tolerate

co-existence with weeds without losing yield (M

& W 2006; J & S 2013). Weeds

need to be removed until the 8-leaf stage of sugar

beet. Emerging weeds after the 8-leaf stage did not

cause any significant sugar beet yield losses (J

et al. 2008). In European sugar beet production,

Chenopodium album L., Amaranthus retroflexus

L., Galium aparine L., Matricaria chamomilla L.,

M.inodora L., Stellaria media (L.) Vill., and Po-

lygonum convolvulus L. are the most abundant weed

species (P 2008).

Multiple (3–4) applications of selective herbicides

are the common practice in European sugar beet weed

control programs. Herbicides are sprayed after every

weed emergence wave to keep the crop weed-free.

Alternatively, post-emergent inter-row hoeing in

combination with herbicide band applications within

the row have successfully been practiced to control

weeds in sugar beet (K et al. 2015).

Precise estimations of sugar beet yield loss due

to weed competition are needed for decisions on

integrated weed management strategies. Usually,

empirical models are used to estimate the crop yield

loss by weed competition from early observations

of weed density (C 1985) and relative weed

cover (K & S 1991; L et al. 1996).

Models fitted better for relative weed cover than for

weed density (A et al. 2013), because relative weed

cover accounts for the size of the crop and weeds and

relative time of emergence (C et al. 1987).

However, tall and upright growing weed species such

as Echninochloa crus-galli L. and C. album were still

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underestimated in their competitive effect on crops

when relative weed cover was measured. Therefore,

M and H (2004) suggested relating

weed biomass to crop yield loss. Still, the problem

remains comparing competitive effects of mixed

weed populations. B and Z (1994) used

a density equivalent to determine the competitive

effects of each weed species.

Estimated crop yield losses may vary consider-

ably between different sugar beet production areas

and years due to different climatic conditions, soil

types, weed populations, productivity, and crop-

ping practices. Results of the relation between sugar

beet yield loss and weed competition have so far

been derived from field studies in Western Europe

(K & S 1991; L et al. 1996) and in

the USA (N et al. 2013). However, sugar

beet yields and summer precipitation have been re-

ported to be lower in the sugar beet production area

in the Russian Federation on Chernozem soils than

in Western Europe and in the USA (V

& I 2013). Therefore, predicted yield losses

may vary between the experimental sites in Germany

and in the Russian Federation.

The objective of this study was to predict sugar

beet yield losses from early observations of weed

density, relative weed cover and weed biomass us-

ing non-linear regression models. The following

hypotheses have been tested:

–Early assessments of weed biomass result in more

accurate predictions of sugar beet yield loss than

those of weed density and relative weed cover.

–Relative yield losses of sugar beet are higher in the

Russian experiments than at the German site due

to weed competition and the competitive ability

of weed species.

MATERIAL AND METHODS

Experimental sites. Six field studies were con-

ducted in typical sugar beet growing areas of Germany

and the Russian Federation. Three field experiments

were conducted at the experimental station of the

University of Hohenheim – Ihinger Hof (IHO), Baden

Württemberg, Germany (48°74'03''N, 8°91'56''E) in

2012, 2013 and 2014. The soil at IHO is classified

as Haplic Luvisol, the soil type is a silty clay loam

with high fertility and good water retention capacity.

Three experiments were carried out in the Rus-

sian Federation, two in 2013 and one in 2014 at an

experimental station located at Doktorovo (DOK)

in the Lipetsk region (52°78'47''N, 39°02'72''E). The

soil at the Russian locations is a typical Voronic

Chernozem with high content of organic matter and

high biological activity.

Environmental conditions and cropping prac-

tices. The climate at IHO is temperate cool with

average yearly temperatures of 9.2°C in 2012, 8.7°C

in 2013, and 10.4°C in 2014. The cumulative annual

precipitation was favourable for sugar beet growth

with 727mm in 2012, 923 mm in 2013, and 763 mm

in 2014 except for two short periods of drought in

spring in 2012 and 2014. The sites in the Russian

Federation at DOC are characterised by a temperate

continental climate with average yearly temperatures

of 7.0°C in 2013 and 6.6°C in 2014 and annual pre-

cipitation totals of 462 mm in 2013 and 340 mm in

2014. All three summer periods were hot and dry.

Experimental design. The trials were arranged

as completely randomized block design with four

replications. All experimental plots were 8 m long

and 3 m wide with a row distance of 0.5 m. Sugar

beets were sown at a density of 110 000 seeds/ha af-

ter strip tillage in April (IHO) and early May (DOK).

The previous crop was winter wheat at all locations.

The experimental design includes four treatments.

Treatment 1 is an untreated control. Treatment 2

was kept weed-free by continuous hand-weeding. In

treatment 3 and 4, weed infestation was manipulated

to achieve a wide range of infestation levels over the

experiment. This facilitates modelling the relation-

ship between weed competition and yield loss. At

IHO, a relatively low weed pressure of approximately

20–40weeds/m2 was expected in the untreated control

plots. Therefore, 400 and 800seeds/m2 of C. album

were sown in treatments 3 and 4 to increase weed

density by approximately 50 and 100%. At DOK, a

higher natural weed infestation of 100–150 weeds/m2

was expected. Therefore, 35 and 70% of the emerged

plants of C. album and A. retroflexus were removed

by hand in treatments 3 and 4 to establish targeted

weed densities.

Data collection and analysis. The number of

emerged sugar beets (n/ha) was counted at the

BBCH12 (H et al. 1997) development stage of the

crop and averaged over all plots in all experiments.

All weed infestation measurements were carried

out at the BBCH 18 growth stage of the crop. Weed

density per species was counted within a 1 m2 frame

in the centre of each plot. Relative weed cover was

calculated by digital image analysis. RGB images of

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1 m2 were taken in the sampling areas where weeds

were counted before. The images were processed

with the computer program ImageJ Version 1.47a.

Green colour of weeds and sugar beet was separated

from soil using the Colour Threshold procedure. To

distinguish between crop and weed, an interactive

graphic editing program was utilised to eliminate

the leaf area of weeds and only to display the crop

leaf area. Crop and weed biomass was also meas-

ured in the same sampling area where weeds were

counted before. Entire crop and weed plants were

dug out, washed and underground and aboveground

plant parts were collected separately and dried in a

hot-air oven at 80°C for 72 h until the weight was

constant. Dry weight was recorded. In autumn, sugar

beets were harvested manually in an area of 2.5 m2

per plot. Fresh mass of sugar beets was recorded.

For the analysis of extractable sugar content, beets

were washed and processed to measure their sugar

content. At DOK, a portable refractometer was used

to determine the %Brix value of the sugar juice and

at IHO, the laboratory polarimetric method was

applied. Both methods correspond to the ICUMSA

standards (ICUMSA 2013) and provided equal results.

Statistical analysis. e relation of weed density and

weed biomass to the relative yield loss of sugar beet

was estimated by ﬁtting both parameters into the non-

linear regression model proposed by C (1985):

YL = q × d (1)

1 + q × d/a

where: YL – relative yield loss; d – weed density or weed bio-

mass; q – yield loss per unit of weed parameter; a – maxi-

mum yield loss

The effect of weed cover on the relative yield loss

of sugar beet was estimated by fitting the same two

parameters into a non-linear regression model pro-

posed by K and S (1991):

YL = q × LW (2)

1 +

[(

)

– 1

]

× LW

where: YL – relative yield loss; LW – relative weed cover;

q – yield loss per unit of weed parameter; a – maximum

incurred yield loss

The relative yield loss was calculated using the

following function:

YL = Ywf – Yw (3)

Ywf

where: YL – relative yield loss; Ywf – weed-free yield;

Yw–yield in weedy plots

The relative weed cover was calculated according

to the equation:

LW = Lweed (4)

Lweed + Lcrop

where: LW – relative weed cover; Lweed – weed cover;

Lcrop–crop cover

The fit to the model was tested by plotting normal

QQ plots and residuals distribution plots. For model-

ling weed-crop interaction, the statistical programR,

Version 2.15.0 (2015) was used.

RESULTS

Crop and weed densities, crop yields. In all ex-

periments, the sugar beet emerged, established and

normally developed further (Table 1).

Weed densities were higher at DOK with a to-

tal density of 58–131 weeds/m2 than at IHO with

20–86weeds/m2 (Table 2). The composition of weed

infestations was also different in both regions. Warm-

season weeds A. retroflexus and E. crus-galli occurred

only in the Russian Federation. S. media, C. album,

and M. inodora dominated at IHO (Table 2). Weed

compositions were representative of sugar beet pro-

duction areas at both locations.

On average, yields were roughly 45% lower at the

Russian site than at IHO in all treatments, likely

caused by low precipitation and shorter growing

season there (Table 3).

Modelling weed-crop interactions. All datasets

show a positive correlation between weed density

and sugar beet yield loss. Even low weed densities

already caused significant yield reductions. At DOK

2013, 2014 and IHO 2013, 50% of the maximum weed

density caused about 80% yield reduction. Weed

competition and maximum yield losses on average

Table 1. e number of emerged sugar beets (number/ha) in all experiments

DOK 1 2013 DOK 2 2013 DOK 2014 IHO 2012 IHO 2013 IHO 2014

Crop density 102 800 104 400 97 200 90 000 100 000 107 200

IHO – Ihinger Hof, Germany; DOK – Lipetsk region, Russia

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were higher at DOK than at IHO. The weed density

model shows a satisfactory fit to the data with regres-

sion coefficients ranging from 0.95 to 0.98 (Figure 1).

Relative weed cover data were distributed less ho-

mogeneously than weed densities (Figure 2). Hence,

at DOK and IHO most values of relative weed cover

ranged between 0.5 and 1 and similar as for weed

density, only very few data were in the range of the

economic weed threshold. At DOK 2 2013, the most

abundant weed species was A. retroflexus L. regard-

less of the high variation in weed density (from 25to

110plants/m2), relative weed cover ranged from

0.75 to 1. A similar situation was observed at DOK1

2013, where Chenopodium album L. was the most

abundant species. Relative weed cover regression

graphs look less steep compared to the lines for weed

density. Therefore, the weed cover model predicted

a lower yield reduction at lower relative weed cover,

which is not in line with the weed density analysis.

As it was expected, the relative yield loss of sugar

beet was correlated positively with weed biomass.

However, the estimated yield loss was less accurate

than for relative weed cover. The site with the highest

density of A. retroflexus showed a 95% sugar beet yield

reduction caused by only 10 g/m2 of weed biomass

at BBCH 18, which was 1.8% of the maximum weed

biomass (Figure 3). The graphs of weed biomass

and weed cover models look very similar. Like the

relative weed cover ‒ sugar beet yield regression

model, the weed biomass model predicted the lowest

relative yield loss for IHO 2014. This complies with

the output of the weed cover model.

Table 2. Density (number/m2) of the most abundant weed species in all experiments measured at the BBCH 18 growth

stage of the crop (H et al. 1997) in untreated control plots using a 1 m2 frame in the centre of each plot

Weed species DOK 1 2013 DOK 2 2013 DOK 2014 IHO 2012 IHO 2013 IHO 2014

Amaranthus retroﬂexus 21.2 43.7 4.0 –––

Chenopodium album 39.1 2.8 28.9 5.8 27.6 7.5

Cirsium arvense – – 0.4 –––

Echinochloa crus-galli 1.4 1.3 1.3 –––

Fumaria oﬃcinalis 4.2 2.0 ––––

Galium aparine – – 0.2 –––

Galeopsis tetrahit 8.8 1.5 0.4 –––

Lamium purpureum 7.8 2.7 18.6 – 1.5 –

Matricaria inodora 1.0 – – 1 43.1 13.7

Poa annua – – – – 3 –

Polygonum aviculare – 1.5 2.2 –––

Polygonum convolvulus 17.1 2.3 46.2 8.2 3 –

Polygonum lapathifolium 3.3 – 9.2 –––

Setaria glauca 1.0 –––––

Sonchus arvensis –––3.0 2.5 –

Stellaria media –––– 5.2 –

laspi arvense 1.9 – 1.2 –––

Veronica persica –––0.7 – 4.9

Viola arvensis – – 18.5 1.0 – –

Total weed density 106.8 57.8 131.1 19.7 85.9 26.1

IHO – Ihinger Hof, Germany; DOK – Lipetsk region, Russia

Table 3. Average sugar beet yield (t/ha) and white sugar yield (t/ha) of the weed-free control at all experimental locations

DOK 1 2013 DOK 2 2013 DOK 2014 IHO 2012 IHO 2013 IHO 2014

Sugar beet yield 45.2 54.6 37.9 83.3 82.9 95.0

White sugar yield 7.2 10.2 8.6 15.0 12.8 16.8

IHO – Ihinger Hof, Germany; DOK – Lipetsk region, Russia

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Figure 1. Relation of the relative yield loss of sugar beet to weed density in all experimental locations and years

IHO – Ihinger Hof, Germany; DOK – Lipetsk region, Russia

Table 4. Regression parameters calculated for the two-parameter model of relative (A) sugar beet yield loss–weed

density interaction modiﬁed according to C (1985), (B) sugar beet yield loss-relative weed cover interaction

according to K and S (1991), and (C) sugar beet yield loss-weed biomass interaction modiﬁed according

to C (1985)

Environment A B C

q ± SE a ± SE q ± SE a ± SE q ± SE a ± SE

DOK 1 2013 0.06 ± 0.06 1.07 ± 0.17 1.78 ± 1.38 0.97 ± 0.05 0.08 ± 0.12 0.96 ± 0.09

DOK 2 2013 0.44 ± 0.48 0.86 ± 0.04 11.01 ± 16.89 0.83 ± 0.02 1.41 ± 1.77 0.83 ± 0.01

DOK 2014 0.06 ± 0.03 0.99 ± 0.07 10.76 ± 7.11 0.90 ± 0.02 0.09 ± 0.06 0.95 ± 0.05

IHO 2012 0.22 ± 0.17 0.80 ± 0.15 1.77 ± 1.44 0.72 ± 0.08 0.01 ± 0.01 0.77 ± 0.18

IHO 2013 0.05 ± 0.02 1.02 ± 0.12 1.01 ± 0.34 0.93 ± 0.05 0.01 ± 0.001 1.15 ± 0.21

IHO 2014 0.01 ± 0.003 1.37 ± 0.95 0.13 ± 0.03 0.43 ± 0.03 0.01 ± 0.001 0.58 ± 0.07

q – competitive ability of the weeds ± standard error (SE); a – maximum yield loss ± SE; IHO – Ihinger Hof, Germany;

DOK–Lipetsk region, Russia

Relative weed cover provided the best estimator

of sugar beet yield loss, followed by weed biomass

and weed density (Table 4). The weed density regres-

sion model showed no strong correlation between

relative damage coefficient and relative yield loss

and the standard errors for q and a in the data set

were higher than for relative weed cover and weed

biomass.

Relative yield loss of sugar beet

1.0

0.8

0.6

0.4

0.2

0 50 100 150 200 250

Weed density (number/m2)

1.0

0.8

0.6

0.4

0.2

1.0

0.8

0.6

0.4

0.2

Relative yield loss of sugar beet

1.0

0.8

0.6

0.4

0.2

1.0

0.8

0.6

0.4

0.2

1.0

0.8

0.6

0.4

0.2

0 50 100 150 200 250

Weed density (number/m2)

0 50 100 150 200 250

DOK 1 2013

DOK 2 2013

DOK 2014

IHO 2012

IHO 2013

IHO 2014

y = 0.44x/[1 + (0.44x/0.86)] y = 0.05x/[1 + (0.09x/1.02)]

y = 0.01x/[1 + (0.01x/1.37)]

y = 0.22x/[1 + (0.22x/0.80)]

y = 0.06x/[1 + (0.06x/1.06)]

y = 0.06x/[1 + (0.06x/0.99)]

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DISCUSSION

Over all seasons, A. retroflexus and E. crus-galli

were among the most abundant weed species at the

DOK trial site, located in the central Chernozem

region of the Russian Federation. Continental cli-

mate at DOK characterised by hot summers and

water shortage gives a competitive advantage to C-4

plants over C-3 plants (Z & R 2007). Cool-

season weed species such as S. media and M.inodora

were abundant only at IHO, located in southwest-

ern Germany in an area with the more maritime

type of climate. Therefore, the results of the study

confirm the hypothesis that warm and dry growing

conditions in the Russian Federation favour more

warm-season weed species than in the temperate

region of Germany.

One reason for the higher weed infestation in

the experiments at the Russian site than at IHO in

Germany are large soil weed seed banks, which are

yearly replenished by the seeds dropping from un-

controlled weeds (K 2012). A second reason

for higher weed infestations at DOK in the Russian

Federation is the high soil organic matter content,

which strongly reduces the availability of soil active

herbicides in the soil water (M & W 2006)

due to adsorption and enhanced breakdown. A third

reason could be the lower competitive ability of the

crop due to water deficiency.

The hypothesis that the relative yield loss due to

weed competition and the competitive ability of weed

species are higher under Russian growing conditions

than in Germany is confirmed. The regression esti-

mates of weed cover and weed biomass gave higher

maximum yield losses and relative damage coeﬃcients

for the Russian site than for the German experiments.

At DOK, the relative weed cover model estimate of

qparameter ranged between 1.8 and 11.0. At IHO,

q-values ranged only from 0.1 to 1.8. e highest value

of q was calculated for DOK 2 in 2013 and 2014, where

A. retroﬂexus, C. album, and P. convolvulus were the

most abundant weed species. is corresponds with

Figure 2. Relation of the relative yield loss of sugar beet to relative weed cover in all experimental locations and years

IHO – Ihinger Hof, Germany; DOK – Lipetsk region, Russia

Relative yield loss of sugar beet

1.0

0.8

0.6

0.4

0.2

0 0.2 0.4 0.6 0.8 1.0

Relative weed cover

1.0

0.8

0.6

0.4

0.2

1.0

0.8

0.6

0.4

0.2

0 0.2 0.4 0.6 0.8 1.0

Relative weed cover

0 0.2 0.4 0.6 0.8 1.0

Relative yield loss of sugar beet

1.0

0.8

0.6

0.4

0.2

1.0

0.8

0.6

0.4

0.2

1.0

0.8

0.6

0.4

0.2

y = 0.13x/[1 + ((0.13/0.43) – 1)x]

y = 1.01x/[1 + ((1.01/0.93) – 1)x]

y = 1.76x/[1 + ((1.76/0.72) – 1)x]) – 1)x]

y = 11.01x/[1 + ((11.01/0.83) – 1)x]

y = 1.78x/[1 + ((7.78/0.97) – 1)x]

y = 10.76x/[1 + ((10.76/0.9) – 1)x]

DOK 1 2013

DOK 2 2013

DOK 2014

IHO 2012

IHO 2013

IHO 2014

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the statement that these species are among the most

serious competitors of sugar beets (P 2008;

J & S 2013). Serious yield reductions were

recorded when these species escaped control (P

2008; G et al. 2012; J & S 2013).

e steep regression line at low infestation levels at

DOK could also be a result of severe drought. At DOK

2014, annual precipitation was about 240 mm, which

is less than 50% of the long-term average precipitation

in this region (Hydrometcentre of Russia 2015). L

et al. (1996) also found a strong inﬂuence of climatic

conditions on the crop-weed interaction.

e use of weed biomass in forecast tools of crop

yield loss is very complicated. It requires destructive

sampling and further processing of collected material,

which needs time and equipment. In comparison, scout-

ing for weed density is more feasible. e measurement

of weed cover gave the most accurate prediction of the

sugar beet yield loss in our study. Weed cover seems to

be the most suitable parameter for decision algorithms

for weed management in sugar beets.

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Figure 3. Relation of the relative yield loss of sugar beet to weed biomass in all experimental locations and years

IHO – Ihinger Hof, Germany; DOK – Lipetsk region, Russia

Relative yield loss of sugar beet

1.0

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Relative yield loss of sugar beet

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0 200 400 600 800 1000 1200

y = 0.08x/[1 + (0.08x/0.96)]

y = 1.41x/[1 + (1.41x/0.83)]

y = 0.09x/[1 + (0.09x/0.95)]

y = 0.003x/[1 + (0.003x/1.15)]

y = 0.007x/[1 + (0.007x/0.58)]

y = 0.007x/[1 + (0.007x/0.77)]

DOK 1 2013

DOK 2 2013

DOK 2014

IHO 2012

IHO 2013

IHO 2014

125

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the relative leaf area of weeds. Weed Research, 36: 93–101.

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R., Petersen J. (2003): Environmental situation and yield

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(2013): Yield of glyphosate-resistant sugar beets and ef-

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7–14. (in Russian)

Received: 2016–04–08

Accepted after corrections: 2016–12–04

Publishe online: 2017–01–25

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Agave Wilt Susceptibility by Reduction of Free Hexoses in Root Tissue of Agave tequilana Weber var. azul Commercial Plants in the Fructan Accumulation Process

Article

Full-text available

Jul 2024
INT J MOL SCI

Agave tequilana stems store fructan polymers, the main carbon source for tequila production. This crop takes six or more years for industrial maturity. In conducive conditions, agave wilt disease increases the incidence of dead plants after the fourth year. Plant susceptibility induced for limited photosynthates for defense is recognized in many crops and is known as “sink-induced loss of resistance”. To establish whether A. tequilana is more prone to agave wilt as it ages, because the reduction of water-soluble carbohydrates in roots, as a consequence of greater assembly of highly polymerized fructans, were quantified roots sucrose, fructose, and glucose, as well as fructans in stems of agave plants of different ages. The damage induced by inoculation with Fusarium solani or F. oxysporum in the roots or xylem bundles, respectively, was recorded. As the agave plant accumulated fructans in the stem as the main sink, the amount of these hexoses diminished in the roots of older plants, and root rot severity increased when plants were inoculated with F. solani, as evidence of more susceptibility. This knowledge could help to structure disease management that reduces the dispersion of agave wilt, dead plants, and economic losses at the end of agave’s long crop cycle.

Inoculación de bulbilos de Agave tequilana con hongos micorrízicos arbusculares: efecto en el crecimiento y biocontrol contra Fusarium oxysporum

Article

Full-text available

Mar 2023

El uso de microorganismos ha sido una alternativa para promover el crecimiento y biocontrol de plagas y enfermedades en diversos cultivos y agave. En este trabajo se estudió la inoculación de bulbilos de Agave tequilana con distintas micorrizas arbusculares sobre el crecimiento y control de la marchitez causada por Fusarium oxysporum. En invernadero, se inocularon bulbilos de Agave con el consorcio nativo “Barranca de las Nueces”, un inóculo comercial de esporas de Rhizofagus y un control sin micorriza. Después de cuatro meses de micorrización, se registró un incremento del 31 % en biomasa fresca y 61 % en altura de bulbilos micorrizados respecto al tratamiento sin micorrizar; además, de un 28 % de colonización micorrízica en los tratamientos micorrizados. A los 120 días después de la micorrización, un grupo de plantas se infectó con Fusarium oxysporum y cien días después se registró el crecimiento y el control de la enfermedad. Los resultados mostraron solo efecto significativo de la micorrización sobre el crecimiento de los bulbilos y aquellos con el inóculo comercial presentaron el mayor crecimiento. Respecto al control contra Fusarium oxysporum, todas las plantas infectadas mostraron un nivel de medio a severo de acuerdo con la escala generada. Los resultados mostraron una promoción en crecimiento de los bulbilos por la micorrización; sin embargo, no se logró evidenciar algún tipo de control contra la enfermedad, al menos a nivel foliar. Los hongos micorrízicos arbusculares promueven el crecimiento de bulbilos de agave y podrían aminorar el daño de enfermedades en esta especie.

Asexually propagated Agave tequilana Weber var. azul exhibits variation in genetic markers and defence responses to Fusarium solani

Article

Full-text available

Jun 2022

Agave (Agave tequilana Weber var. azul) is considered a crop with low genetic diversity because it has been propagated vegetatively for centuries for commercial purposes, and consequently, it could be equally susceptible to pests and diseases. However, the present study employs plant material derived from field grown plants exhibiting phenotypic variability in susceptibility to agave wilt. The offshoots from rhizomes of these plants were reproduced in vitro and classified as potentially resistant or susceptible. Amplified fragment length polymorphism (AFLP) analysis confirmed wide genetic differences among individuals, but these differences were not correlated with the observed phenotypic variability in resistance. Propagated plantlets were inoculated with Fusarium solani in two time-lapse confrontations for 72 h and 30 days. The early biochemical response showed statistically superior levels in the accumulation of shikimic acid, phenolic compounds, and chitinase activity in potentially resistant plantlets. There was an inverse correlation of these early biochemical responses and salicylic acid and the incidence of diseased root cells in isogenic plantlets in the 30-day confrontation with F. solani, suggesting that these activities and accumulation of molecules were primordial in the defence against this pathogen.

IDENTIFICATION OF CAUSAL AGENTS OF DRY ROT OF Agave potatorum Zucc IN NURSERY

Article

Full-text available

Jun 2024

Currently, the causal agents associated with dry rot of Agave potatorumZucc at the nursery stage have not been identified. Fungal strains of the genera Fusarium, Alternaria, Colletotrichum, Phoma, Botryodiplodia, Cercospora, Aspergillusand the bacterium Dickeya chrysanthemihave been identified in various species of Agavecausing various diseases. Due to the importance of the species in the state of Oaxaca and its high demand, the objective of the present work was to carry out a phytosanitary diagnosis ofdry rot of A. potatorumat the nursery stage in the district of Sola de Vega, and to identify the main damages and the causal agents associated with morphological bases. Incidence, severity and mortality of the plants were measured, and the causal agents were isolated and purified by the monosporic culture method.Data were analyzed by analysis of variance and mean tests (Duncan,α=0.05). Incidence was similar in the diagnosed nurseries; however, severity and mortality had higher values in the nursery located in Santa María Sola, the lowest mortality values were found in the community of Quialela. Five strains associated with the disease were isolated, three of which showed morphological characteristics of the genus Fusariumand two of the genus Alternaria. Strain 2 CRCH belonging to the genus Fusariumhad a greater presence in root and stem tissues of diseased plants and strain 4 CRCH had a greater presence in foliar damage.

A new agaveculture: genetic resources for the bioeconomy era

Thesis

Full-text available

Jul 2023

Fabio Raya

For centuries, agaves have played a crucial role in semiarid regions worldwide, often serving as the only viable crop option in these challenging environments. As we transition into a bioeconomy era, agaveculture emerges as a crucial component of sustainable development strategies worldwide. The vast genetic diversity within this genus offers immense potential for bioenergy, bioproducts, and climate-resilient agriculture. Brazil has a long tradition in producing agaves developed for fiber and can become a leader in this field. However, the market crisis triggered by synthetic fibers has impacted the development of this crop in the country, both from a scientific and technological standpoint. Long-term projects, like the Agave breeding program, have been discontinued, and the production system has become reliant on agro-extractivism. To restore this crop to its prominent role and unlock the full economic and environmental benefits of agaves, genetic resources must be developed. This thesis, structured into four chapters, explores the significance of genetic resources in shaping a new era of agaveculture. The first chapter highlights the technological challenges that must be overcome to establish agaves as a new bioethanol feedstock, its potential to alleviate land competition and enhance food and energy security. In the second chapter, using transcriptomics, we have identified several molecular mechanisms and targets that breeders can pursue to better understand biomass architecture and abiotic stress responses in Agave. Moving on to the third chapter, we organize a new germplasm bank based on rescued cultivars from the previous Agave breeding program and characterize the plants using molecular markers and morphophysiological traits. Finally, the fourth chapter introduces the development of a molecular diagnostic tool for sisal bole rot disease, the main phytosanitary problem affecting Agave in the country. The molecular epidemiology using this test highlights the fragility of the current production system but also indicates possible correlations between disease symptomatology and nutritional status, as well as potential effects of different cultivars. These genetic resources empower future researchers to develop improved varieties of agaves that are more resilient to climate change, have higher productivity, and possess desired traits for specific applications.

Molecular epidemiology of sisal bole rot disease suggests a potential phytosanitary crisis in Brazilian production areas

Article

Full-text available

Nov 2023

Sisal bole rot disease is the major phytosanitary problem of Agave plantations in Brazil. The disease is caused by a cryptic species of Aspergillus: A. welwitschiae. To date, the only way to diagnose the disease was to observe external symptoms, visible only when the plant is already compromised, or through the isolation and sequencing of the pathogen, which requires cutting the entire plant for bole tissue sampling. We developed a new primer set based on a unique gene region of A. welwitschiae, which can detect the phytopathogenic strains through PCR directly from sisal leaves. Using the new marker to study the main sisal-producing areas in Brazil, we discovered a troublesome situation. The main producing areas of this crop had a pathogen incidence of 78%–88%. The dispersion index indicates a regular spatial pattern for disease distribution, suggesting that the use of contaminated suckers to establish new fields may be the main disease-spreading mechanism. Altogether, the high incidence of the pathogen, the unavailability of clean plants, the unpredictability of disease progression, and the low investment capacity of farmers reveal the vulnerability of this sector to a potential phytosanitary crisis. By correlating the disease symptomatology with soil nutritional traits, we suggest that higher potassium availability might decrease visual symptoms, while phosphorus may have the opposite effect. Also, we observe a potential cultivar effect, suggesting that common sisal may be more susceptible than hybrid cultivars (especially H400). This new molecular tool is a significant advance for understanding the disease, enabling the implementation of a monitoring program and studies that may lead to pathogen control strategies and changes in the Brazilian production model.

Fusarium and Neocosmospora Species Associated with Rot of Cactaceae and Other Succulent Plants

Article

Full-text available

Apr 2022
J. Fungi

Infections by Fusarium and Fusarium-like species on cacti and other succulent plants cause the syndrome known as Fusarium dry rot and soft rot. There are only few records of Fusarium species as pathogens of cacti and other succulent plants from Iran. The objective of this study was the identification and characterization of fusarioid species recovered from ornamental succulents in Shiraz County, Iran. Three fusarioid species, including F. oxysporum, F. proliferatum, and Neocosmospora falciformis (formerly F. falciforme), were recovered from 29 diverse species of cacti and other succulents with symptoms of Fusarium dry rot and soft rot. The three fungal species were identified on the basis of morphological characters and the phylogenetic analysis of the translation elongation factor1-α (tef1) nuclear gene. The F. oxysporum isolates were identified as F. oxysporum f. sp. opuntiarum. The pathogenicity of the three fusarioid species was tested on a range of economically important ornamental succulents, mostly in the Cactaceae family. The three species showed a broad host spectrum and induced different types of symptoms on inoculated plants, including soft and dry rot, chlorosis, necrotic spots, wilt, drying, root and crown rot. This is the first report of N. falciformis as a pathogen of succulent plants worldwide.

BACTERIAL DIVERSITY WITH PLANT GROWTH-PROMOTING POTENTIAL ISOLATED FROM Agave americana RHIZOSPHERE

Article

Full-text available

Sep 2021

Objective: Study the diversity of cultivable rhizospheric bacteria associated to Agave americana, and select native strains with potential as plant growth-promoting bacteria (PGPB). Design/methodology/approach: The isolated bacteria were phenotypically characterized. The genetic diversity and identity of the strains were revealed by genomic fingerprints and by sequencing of 16S rRNA gene. Plant growth promoting ability and plant inoculation assays were evaluated to know the potential as PGPB. Results: A total of 235 strains were isolated from A. americana rhizosphere and were classified within of 10 different bacterial genera. Rhizobium, Pseudomonas, Acinetobacter had high potential as PGPB. Study limitations/implications Cultivable approach was used to study rhizobacteria. A metagenomic study could expand the knowledge about the structure and diversity of bacterial community associated to A. americana. Findings/conclusions Rhizosphere bacteria have potential use as biofertilizer for the cultivation and propagation of A. americana and other agave species.

Agricultural practices and environmental factors drive microbial communities in the mezcal-producing Agave angustifolia Haw.

Preprint

Full-text available

Oct 2024

Mezcal, a traditional Mexican alcoholic beverage, has been a vital source of livelihood for indigenous and rural communities for centuries. However, increasing international demand is exerting pressure on natural resources and encouraging intensive agricultural practices. This study investigates the impact of management practices (wild, traditional, and conventional) and environmental factors on the microbial communities associated with Agave angustifolia, a key species in mezcal production. High-throughput sequencing of the 16S rRNA and ITS2 gene regions revealed distinct prokaryotic and fungal community structures across different plant compartments (endosphere, episphere, and soil), identifying 8,214 prokaryotic and 7,459 fungal ASVs. Core microbial communities were dominated by Proteobacteria, Actinobacteria, Ascomycota, and Basidiomycota. Alpha diversity analyses showed significant increases in prokaryotic diversity from the endosphere to soil, while fungal diversity remained stable. Notably, conventional management practices were associated with reductions in beneficial microbial taxa. Environmental factors such as precipitation and temperature significantly influenced microbial diversity and composition, especially in the rhizosphere. Beta diversity patterns underscored the strong impact of plant compartment, with management practices and aridity further shaping microbial communities. These results reveal the intricate interactions between management practices, environmental conditions, and microbial diversity, providing valuable insights for the sustainable cultivation of A. angustifolia.

The genomic analysis unveils reduced genetic variability but an increased proportion of heterozygote genotypes of the intensively managed mezcal agave, Agave angustifolia Haw

Article

Full-text available

Jul 2023
AM J BOT

Premise: The central Oaxaca Basin has a century-long history of agave cultivation, and it is hypothesized to be the region of origin of other cultivated crops. Widely cultivated for mezcal production, the perennial crop known as "espadín" is putatively derived from wild Agave angustifolia. Nevertheless, little is known about its genetic relationship to the wild A. angustifolia or how the decades-long clonal propagation has affected its genetics. Methods: Using RADseq and over 8,000 SNPs, we studied aspects of the population genomics of wild and cultivated A. angustifolia in Puebla and Oaxaca, Mexico. We assessed patterns of genetic diversity, inbreeding, distribution of genetic variation, and differentiation among and within wild populations and plantations. Results: Genetic differentiation between wild and cultivated plants was strong, and both gene pools harbored multiple unique alleles. Nevertheless, we found several cultivated individuals with high genetic affinity with wild samples. Higher heterozygosity was observed in the cultivated individuals, while in total, they harbored considerably fewer alleles and presented higher linkage disequilibrium compared to the wild plants. Independently of geographic distance among sampled plantations, the genetic relatedness of the cultivated plants was high, suggesting a common origin and prevalent role of clonal propagation. Conclusions: The considerable heterozygosity found in "espadín" is contained within a network of highly related individuals, displaying high linkage disequilibrium generated by decades of clonal propagation and possibly by the accumulation of somatic mutations. Wild A. angustifolia, on the other hand, represents a significant genetic diversity reservoir that should be carefully studied and conserved. This article is protected by copyright. All rights reserved.

Incidencia y severidad de la marchitez del agave tequilana Weber var. azul en la zona sur del Estado de Nayarit, México

Article

Full-text available

Aug 2011

Se determinó la incidencia y severidad de la marchitez del agave (Agave tequilana Weber var. Azul), causada por Fusarium oxysporum en Santa María del Oro, Nayarit. Se realizaron dos muestreos en forma sistemática, uno en agosto de 2006 (temporada de lluvias) y otro en marzo de 2007 (temporada seca). Se realizó un tercer muestreo dirigido a plantas que presentaron un grado 2 de marchitez. Se encontraron diferentes grados de marchitez del agave con valores que van desde 83 a 100 % en todas las localidades. Para la primer fecha de muestreo (agosto 2006) se encontraron valores de incidencia en las diferentes parcelas que van de un 83.5 a 94 %, mientras que en la segunda fecha (Marzo 2007), se observaron valores que van de un 98.5 a 100 %. En el tercer muestreo el patógeno estuvo presente, con grado 2, en un 40 a 75 % de las plantas.

Competitive relationships between sugar beet and weeds in dependence on time of weed control

Article

Full-text available

Mar 2008

Small plot trials were carried out in years 2001-2003 with sugar beet. In the treatment without weed control, dry weight of sugar beet top and LAI of sugar beet were very low (approx. 50 g/m2 and 0.5 m 2/m2, respectively). Yield loss of sugar beet was 80-93%. Dominant weeds were Chenopodium album, Fumaria officinalis and Galium aparine. In the treatments where weeds were removed (by hand) until 4 leaf stage of sugar beet, dry weight of sugar beet top and LAI of sugar beet at first increased normally, but were markedly decreased from the half of the vegetation period. Yield loss of sugar beet was 54-28%. Dominant weed in this treatment was Amaranthus retroflexus. The development of sugar beet top dry weight and LAI of sugar beet was practically identical in the treatments where weeds were removed until 8-10 leaf stage of the crop and in those where weeds were removed during the whole vegetation period (500-900 g/m2, or 4-7 m 2/m2, respectively). No yield loss of sugar beet was recorded. Dry weight of weeds did not exceed 30 g/m2 and LAI 0.1 m2/m2. A. retroflexus and Mercurialis annua were the most frequent weeds in this treatment.

Genetic diversity and vegetative compatibility groups in Fusarium oxysporum cause of wilt symptoms in agave (Agave tequilana Weber var. azul)

Article

Full-text available

Jan 2012

Twenty five strains of Fusarium oxysporum obtained from stems of agave (Agave tequilana Weber var. azul) plants with and without wilt symptoms, where analyzed in their diversity with: ITS1 sequence, DNA molecular marker BOX-PCR and Vegetative Compatibility Groups. ITS1 sequence indicated that in spite of all isolates where previously identified like F. oxysporum, a punctual mutation on fifteen of them make that differ from the most of seventy reports of plant pathogenic F. oxysporum complex reported in the GenBank. On the other hand, the taxonomic report of nine of them where very coincident with more of seventy reports included different formae speciales. The dissimilarity analysis of BOX-PCR finger prints indicted that sixteen teen of them, where very similar included the fifteen with the punctual mutation and the other nine strains conform other similarity group. Two vegetative compatibility groups where conformed with only strains of the fifteen group with the punctual mutation.This work evidence that exists a group of F. oxysporum strains, included two positive to patogenicity test to agave, capable to induce wilt symptoms, that constitute an homogeneous group that could be result of plant-pathogen co-evolution.

Potentials of post-emergent mechanical weed control in sugar beet to reduce herbicide inputs

Article

Full-text available

May 2015

Weed control in sugar beet (Beta vulgaris) is usually performed with herbicides applied across the whole field at several timings in the early growth stage of sugar beet. It was tested if herbicide input could be reduced with a combination of preventive, mechanical and chemical weed control strategies. In field experiments conducted at 6 locations mechanical weeding in the inter-row area was combined with band application of herbicides in the intra-row area. At one location, precision farming technologies including camera steering and GNSS-RTK steering were used. Weed densities of up to 91 plants m-2 were detected in the untreated control plots. Band spraying in combination with inter-row hoeing reduced herbicide input by 50 to 75% compared to uniform herbicide applications. Weed control efficacy was 72% in the conventional herbicide treatments, 87% for the combination of weed hoeing and band spraying, 78% for precision hoeing with camera steering and 84% for precision hoeing with GNSS-RTK steering system. Weed control treatments increased white sugar yield (WSY) by 30% compared to the untreated control. The combination of mechanical weed control, band application of herbicides and precision hoeing have shown promising concepts for integrated weed management resulting in significantly reduced herbicide input and high weed control efficacy.

Fusarium Crown and Root Rot of Tarragon in California Caused by Fusarium solani

Article

Jun 2011
PLANT DIS

S. T. Koike

Tarragon, also known as estragon or dragon's-wort (Artemisia dracunculus), is a perennial plant in the Asteraceae. Tarragon is grown for use in cooking as a fresh and dried herb. In May 2010, commercial tarragon grown in a field on California's central coast was affected by a previously undescribed disease. Initial symptoms consisted of chlorosis of leaves and wilting of shoot tips. As the disease progressed, entire shoots and branches turned brown and died. The plant crown epidermis and cortex and the upper cortex of the main roots turned brown with occasional black streaking. Diseased plants died several weeks after the onset of wilting. A Fusarium species was consistently isolated from symptomatic crown and root tissues. On carnation leaf agar (CLA) incubated under lights, the isolates produced stout, slightly curved macroconidia having blunt apical cells. One- and two-celled oval to cylindrical microconidia were abundant and born in false heads on extremely long monophialides. Chlamydospores were present in 1-month-old cultures. On potato dextrose agar incubated under lights, the isolates produced abundant white aerial mycelium with bluish coloration of the culture surface. The isolates were identified as Fusarium solani (2). Pathogenicity tests were conducted using six isolates, with inoculum produced on CLA. For each isolate, 250 ml of a spore suspension (1 × 10 ⁶ conidia/ml) were poured onto the roots of 10-cm potted tarragon plants. Ten plants were inoculated for each of the six isolates. A control set of tarragon was treated with 250 ml of water. All plants were maintained in a greenhouse set at 24 to 25°C. After 8 weeks, plants inoculated with the spore suspensions began to show wilting and browning of leaves. Crown epidermis and cortex and root cortex tissues were brown; Fusarium solani was reisolated from the crowns and roots. The experiment was repeated and the results were the same. To my knowledge, this is the first report of F. solani causing a crown and root rot disease of tarragon. The disease caused significant damage with approximately 50% of the commercial field affected. The other Fusarium species previously reported on tarragon is an uncharacterized F. oxysporum isolated from roots of plants grown in California (1). References: (1) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , March 8, 2011, (2) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, PA, 1983.

Colonization of the Vascular System of Plants by Fungal Wilt Pathogens: A Basis for Modeling the Interactions between Host and Parasite in Time and Space

Chapter

Jan 1989

C.H. Beckman

When we undertake the study of phenomena as dynamically complex as wilt diseases, we are faced with the problem not only of obtaining the information we seek, but also of organizing many bits of information to show significant relationships. This is true because to understand the dynamics of a phenomenon we must use reductive methods to dissect the processes into finer, more detailed, measurable bits, whereas to understand the complexity we must somehow integrate the resulting information to show the relationships within the whole sweep of events. A system of realistic inter-connected models is required. It is my purpose, first, to propose that we all join together in an ongoing process of modeling wilt diseases of plants, and, second, to propose a basis for modeling that has evolved and that places known events within a framework of interconnected time and space frames. The overall framework is derived from our understanding of the disease cycle involving a soil-borne, fungal, vascular parasite and its host.

Pathogenesis in Vascular Diseases of Plants

Chapter

Jan 1989

G.F. Pegg

Prokaryote and eukaryote vascular pathogens represent a wide but unique range of micro-organisms which exist in the host xylem during the pathogenic phase of the life cycle and from there induce symptoms of wilt and /or necrosis. The major fungal and bacterial species involved are shown in Table 1. The term ‘vascular pathogen’ has tended to be used synonymously with wilt pathogen. Where wilt symptoms represent a transitory phase of the disease however, and foliar necrosis is dominant, the list of organisms can be extended greatly to include species such as Xanthomonas campestris on Brassica olearacea, Erwinia amylovora on Pyrus and other hosts, and Stereum purpureum on Prunus. Several pathogens; Fusariurn formae, Ophiostoma ceratocystis, Clavibacter michiganensis subsp. insidiosus and Erwinia stewartii exhibit specificity in their natural hast range. Verticillium dahliae, V. albo-atrum and Pseudomonas solanacearum by contrast infect over 300 hast plants including many of the main field and plantation crops in temperate and tropical countries.

Biology and Host-Parasite Relations of Fusarium Oxysporum F. Sp. Radicis-Lycopersici

Chapter

Jan 1989

Fusarium crown and root rot (or foot and root rot) was first recognized in tomatoes (Lycopersicon esculentum L.) in plastic-covered greenhouses in the Ono and Kamiiso districts of Japan in 1969, on 25 of 74 farms (33%) surveyed, with complete crop loss in some cases. By 1971, 15 of 30 greenhouses (50%) were affected in Ono (Sato and Araki 1974). In retrospect, Sato and Araki thought that the disease had appeared first in 1963. It then appeared in staked field tomatoes in California in 1971 (Leary and Endo 1971) and the causal agent was identified as a new race of Fusarium oxysporum Schlecht. f. sp. lycopersici Sacc.: Snyder & Hansen (FOL) which attacked cultivars of tomato resistant to races 1 and 2 (races 0 and 1 sensu Gabe 1975) of F. oxysporum f. sp. lycopersici (Sanchez et al 1975). In Japan, the causal organism was also identified as F. oxysporum f. sp. lycopersici (Ogura and Ban 1971, 1971).

The Fusarium Lab Manual

Article

Dec 2007

For the first time in over 20 years, a comprehensive collection of photographs and descriptions of species in the fungal genus Fusarium is available. This laboratory manual provides an overview of the biology of Fusarium and the techniques involved in the isolation, identification and characterization of individual species and the populations in which they occur. It is the first time that genetic, morphological and molecular approaches have been incorporated into a volume devoted to Fusarium identification. The authors include descriptions of species, both new and old, and provide protocols for genetic, morphological and molecular identification techniques. The Fusarium Laboratory Manual also includes some of the evolutionary biology and population genetics thinking that has begun to inform the understanding of agriculturally important fungal pathogens. In addition to practical how-to protocols it also provides guidance in formulating questions and obtaining answers about this very important group of fungi. The need for as many different techniques as possible to be used in the identification and characterization process has never been greater. These approaches have applications to fungi other than those in the genus Fusarium. This volume presents an introduction to the genus Fusarium, the toxins these fungi produce and the diseases they can cause. The Fusarium Laboratory Manual is a milestone in the study of the genus Fusarium and will help bridge the gap between morphological and phylogenetic taxonomy. It will be used by everybody dealing with Fusarium in the Third Millenium. -W.F.O. Marasas, Medical Research Council, South Africa.

Fusarium oxysporum f. sp. radicis-vanillae is the causal agent of root and stem rot of Vanilla.

Article

Aug 2015
PLANT PATHOL

Root and stem rot (RSR) is a very detrimental disease of vanilla worldwide. Fusarium oxysporum is frequently associated with the disease but other Fusarium species are also reported. In this international study, we surveyed 52 vanilla plots in three of the most important vanilla producing countries (Madagascar, Reunion Island and French Polynesia) in order to determine the aetiology of RSR disease. Subsets from the 377 single-spored Fusarium isolates recovered from rotten roots and stems in the surveys were characterised by molecular genotyping (EF1α and IGS gene sequences) and pathogenicity assays on Vanilla planifolia and V. ×tahitensis, the two commercially grown vanilla species. Fusarium oxysporum was shown to be the principal species responsible for the disease since it represented 79% of the isolates recovered from the RSR tissues and 40% of these isolates induced severe symptoms on inoculated plantlets. Fusarium oxysporum isolates were highly polyphyletic regardless of geographic origin or pathogenicity. Fusarium solani, found in 15% of the samples, inducing only mild symptoms on plantlets, was considered a secondary pathogen of vanilla. Three additional Fusarium species were occasionally isolated in the study (F. proliferatum, F. concentricum and F. mangiferae) but were nonpathogenic. Histopathological preparations observed in wide field and confocal microscopy showed that F. oxysporum penetrated the root hair region of roots, then invaded the cortical cells where it induced necrosis in both V. planifolia and V. ×tahitensis. The hyphae never invaded the root vascular system up to 9 days post inoculation. As a whole, our data demonstrated that RSR of vanilla is present worldwide and that its causal agent should be named F. oxysporum f. sp. radicis-vanillae.This article is protected by copyright. All rights reserved.