title: Aspects of the epidemiology of Ditylenchus gigas on faba bean and its interactions with Botrytis fabae
Creators: name: Isadeha, Anthony
Publisher: name: University of Reading
Year: 2022

description: The supply of faba bean in UK is unreliable. This may be linked to many factors, including 
biotic pressure especially from pathogens. The study investigated the interaction between a 
biotrophic nematode (Ditylenchus gigas) and a necrotrophic fungus (Botrytis fabae). In faba 
bean, B. fabae causes chocolate spot disease while D. gigas causes stem lesions. 
D. gigas is the dominant species of Ditylenchus on faba bean in the UK. Its spread is 
controlled in part by certification schemes. To understand how fast isolated infections of D. 
gigas evading certification will spread spatially, field experiments building on the work in
other species of Ditylenchus were conducted over two seasons. These suggest that spatial 
spread of the nematode on beans through the growing season is dependent on distance of 
inoculum from the plant, the orientation of the inoculum from the plant and environmental 
factors in the field. Nematodes spread from a centrally pre-inoculated plant to a distance of 
1.6 m within a season.
B. fabae often co-exists in the presence of D. gigas and therefore glasshouse investigations 
were designed to test the hypothesis that B. fabae (as a necrotroph) will decrease 
susceptibility to D. gigas (a biotroph) and together they will reciprocally affect each other’s 
population density and reduce the productivity of faba bean. An initial experiment involved 
nematodes alone, while a second experiment involved D. gigas and B. fabae co-inoculations. 
Similar data from the two experiments were pooled together for analysis using the mixed 
model for multiple experiments in GenStat. Antagonistic interaction on the population of D. 
gigas was observed, as the number of nematodes extracted from lone inoculation of D. gigas
was more than those from co-inoculation of the two organisms, suggesting an induced 
response. However, a synergistic interaction was observed on grain yield, as the reduction in 
grain yield was more with co-inoculation than lone inoculation of either organism. 
In the light of work on induced defence mechanisms to plant pathogens and pests, the 
hypothesis that the order of infection (i.e., whether D. gigas infects before B. fabae or vice 
versa) will have an effect on induced resistance and affect crop production was then tested.
Potted faba bean (cv. Fuego) were first inoculated with either B. fabae or D. gigas at 2 weeks 
after planting. A second inoculation was done 2 weeks after the first one. The second B. 
fabae inoculation was applied on the upper leaves with protection to prevent spill over to the 
previously inoculated leaves. Inoculation of B. fabae did not induced defence response 
v
against D. gigas. However, pre-inoculation of B. fabae reduced subsequent B. fabae
infection, suggesting an induced defence response specific to this species.
Two successive field trials were conducted to determine whether the glasshouse results 
obtained previously were applicable to the field situation and tested the hypothesis that plant 
nutrition (application of fertilizers) and/or plant variety affect crop production. None of the 
results were significant at the 5 % level. The results from the first season were consistent 
with those from the controlled environment experiment but those from second season 
differed. The trend indicated that cv. Babylon was more resistant to chocolate spot than cv. 
Fuego. Also, potassium sulphate fertilizer very slightly but consistently reduced the severity 
of chocolate spot and rust compared to potassium chloride.
It became increasingly apparent that the methods of monitoring and quantifying D. gigas in 
the studies were time consuming. Therefore, a qPCR assay was developed for the 
simultaneous quantification and identification of D. gigas and B. fabae in faba bean, although 
specificity of the assay at species level was not tested.