Population dynamics of dicarboximide‐resistant strains of Botrytis cinerea on grapevine in New Zealand

Abstract

Changes in the proportion of dicarboximide‐resistant strains of Botrytis cinerea were monitored in two vineyard trials conducted during the period from October 1985 to November 1987. Dicarboximide resistance frequency in samples taken prior to flowering from wood (dead cane‐ends, dead tendrils, old bunch remains) was high (66%) in the first trial, and low (12%) in the second trial. In treatments where resistance frequency was high on wood in spring, it decreased during the phase of disease establishment in new bunches irrespective of whether or not dicarboximide fungicides were applied. In the absence of dicarboximide applications, resistance frequency showed little change during the phase of disease development in bunches. The resistance frequency increased, however, if dicarboximide fungicides were applied, the extent of increase depending on the number and timing of applications and on disease severity at the time of application. Where resistance frequency was high on the wood at harvest, it decreased over the following winter but increased again in spring even though no dicarboximides had been applied. The best disease control in both trials was obtained with a programme in which dicarboximide fungicides were only applied during the period from veraison until harvest.

An hypothesis to account for the behaviour of dicarboximide‐resistant strains of Botrytis cinerea in vineyards

“…The reasons for this decrease are not clear, but we interpret it as reflecting the low er fitness, specifically the lower virulence and competitive ability, of resistant strains (Pak et ai, 1990), During the phase of disease development, the application of dicarboximides leads to a progressive increase in resistance frequency, the extent of which reflects the fitness of the resistant strains. the fungicide programme applied, and disease intensity (Lorenz & Locher, 1988;Pak et <//,, 1990), If disease intensity is low, the resistance frequency will tend to increase less under a given programme than if disease intensity is high. The lower disease severity in the 1987 vintage year, compared with the 1986 year, provides an explanation as to why the resistance of plots that had only received the medium-dicarboximide programme in the 1987 year was lower than that of plots that had received the medium-dicarboximide programme for 2 years.…”

Spatial and temporal characteristics of dicarboximide‐resistant strains of Monilinia fructicola and brown rot incidence in stone fruit

“…Epidemiological studies of fungicide resistance have concentrated on changes over time, such as the demonstration that the frequency of resistant strains changed between samples within a crop season (Cohen & Samoucha, 1989; Kadish & Cohen, 1989). When extended to studies of two or more seasons, persistence of resistant strains in the field was suggested (Pommer & Lorenz, 1987; Pak et al ., 1990). Studies of the spatial pattern of resistant strains, and of disease, may provide new insights into the relative importance of pathogen dispersal mechanisms.…”

Postharvest dipping of kiwifruit in iprodione to control stem‐end rot caused byBotrytis cinerea

“…The population of resistant isolates would be expected to decrease or remain static in the absence of field use of iprodione because the resistant isolates are less fit than the susceptible strains (Beever et al 1989). This also occurs in other B. cinerea host systems (Locher et al 1987;Pak et al 1990). Reduced field use should therefore lead to improved control by postharvest dipping.…”