Stability and fitness of anilinopyrimidine-resistant strains of Botrytis cinerea

The fitness of anilinopyrimidine-resistant isolates of Botrytis cinerea compared with that of sensitive isolates, collected from vegetable crops in Greece during 2005, was investigated. Stability of resistance to anilino-pyrimidine fungicides was determined after consecutive transfers of the fungal isolates on fungicide-free potato dextrose agar for 16 culture cycles or on fungicide-untreated cucumber seedlings for eight disease cycles. Results showed that after the consecutive transfers of the isolates either in vitro or in vivo sensitivity to cyprodinil was not changed significantly compared to the initial sensitivity in all the isolates tested, suggesting a stable genetically controlled trait. Fitness parameters measured were mycelial growth, spore production in vitro, osmotic sensitivity, virulence, spore production in vivo, percentage of spore germination, and competitive ability of the resistant isolates in four pairs with sensitive isolates both on artificial nutrient medium or on cucumber seedling plants. The measurements of the fitness components in individual isolates showed high variability within both sensitivity groups in all, except virulence, fitness components tested. As a group, resistant isolates showed significantly lower (P < 0.05) mycelial growth and virulence, while they were more osmotically sensitive than the sensitive isolates. In addition the resistant isolates showed higher (P < 0.05) spore production in vivo but there was no difference (P > 0.05) between the two sensitivity groups in spore production in vitro and in the percentage of spore germination. However, the correlation to test if there is any relationship between the values of each fitness component tested and the level of cyprodinil sensitivity of each isolate was for all, except the spore production in vivo, fitness components not significant (P > 0.05). This absence of significant correlation coefficient values suggests that the development of resistance to anilinopyrimidine fungicides did not affect the fitness of the resistant isolates. Competition of the resistant versus sensitive isolates was isolates-dependent, since in two of the isolate pairs the resistance frequency decreased significantly after five culture or disease cycles, while in the remaining two pairs resistance frequency increased significantly after five disease cycles or remained stable for one pair after five culture cycles on artificial nutrient media.