Physical host factors for brown rot resistance in peach fruit

Brown rot in peach fruits caused by the fungi Monilinia sp. is a common disease that can provoke as much as 30 to 40% of crop losses. Little is known about the fruit resistance factors and the infection process. The aim of this study was to investigate the physical factors of resistance of the fruit and their genetic control. This would provide a tool to rationalize genotype x cultural practice combinations in order to reduce brown rot incidence. Mechanical characteristics of fruit skin (conductance, stomatal density, microcracks) potentially linked to Monilinia (M.) resistance were investigated in 27 cultivars. Two cultivars and a segregating population were phenotyped for fruit cuticular conductance and sensitivity was assessed by two independent infection tests. In the microscopy analyses, high diversity of germination and penetration of fungi through stomata and microcracks were observed. Preliminary results show significant differences in the number of stomata among genotypes. However, no obvious relationship was found between stomata number, cuticular conductance and infection at the early stage of fruit development. At maturity, the population displayed high variability in the resistance to M. laxa, giving hope for breeding programs, despite the low stability of results among tests and years. The knowledge gained from these experiments will be integrated into an existing ecophysiological model in order to concurrently optimize fruit characteristics and cultural practices to reduce infection risks.