Quantifying and Modelling the Mobilisation of Inoculum from Diseased Leaves and Infected Defoliated Tissues in Epidemics of Angular Leaf Spot of Bean |
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Authors: | Delphine?Allorent Laetitia?Willocquet Aloisio?Sartorato Email author" target="_blank">Serge?SavaryEmail author |
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Institution: | 1.IRD-CBGP,St-Gély-du Fesc cedex,France;2.Centre INRA,Le Rheu cedex,France;3.EMBRAPA Arroz e Feij?o C,Santo Antonio de Gioas,Brazil;4.UMR Santé Végétale Centre INRA de Bordeaux,Villenave d’Ornon,France |
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Abstract: | Daily multiplication factor (number of daughter lesions per mother lesion per day) values were experimentally measured in
four replications of a monocyclic experiment on angular leaf spot (ALS) of bean, where sources of inoculum were artificially
established within a bean canopy, on the ground (defoliated infected leaves), or both. Daily multiplication factor of lesions
in the canopy (DMFRc) was higher than that of infectious, defoliated tissues (DMFRd) in all replications. Both DMFRc and DMFRd
were strongly reduced under dry compared to rainy conditions. Under rainy conditions for spore dispersal DMFRd was about two
to three times smaller than DMFRc. Defoliated leaves may nevertheless represent a significant source of infection, depending
on the amount of infectious tissues. Mother lesions within the canopy generated more daughter lesions in the medium (or lower)
layers of the canopy than at its upper level (DMFRc higher at the medium and lower layers of a canopy), whereas DMFRd values
seemed to decrease with height in the canopy. A mechanistic simulation model that combines host growth and disease-induced
defoliation was designed to simulate the respective contributions of the two components of the dual inoculum source of a diseased
canopy (infected foliage and defoliated infectious tissues), and varying infectious periods in both sources. Simulations suggest
that higher DMFRc values have a large polycyclic effect on epidemics whereas that of DMFRd is small, and that large effects
of the infectious period of lesions in the canopy are found when DMFRc is high. Simulations using experimentally measured
DMFRc and DMFRd values indicated much stronger epidemics in rainy compared to dry conditions for spore dispersal, but disease
persistence in the latter. The implications of considering a dual source of inoculum in the course of a polycyclic process
are discussed with respect to epidemic thresholds. |
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Keywords: | corrected basic rate of infection daily multiplication factor defoliation epidemic threshold Phaeoisariopsis griseola progeny/parent ratio |
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