The Use of Potassium Phosphonate (KHP) for the Control of Major Apple Pests.

Phosphonate-based products have demonstrated diverse abilities to protect crops against pests, with various modes of action proposed. In this article, we specifically investigated potassium phosphonate (KHP) on apple crops. Its performance to control three major apple bioagressors (Venturia inaequalis, Erwinia amylovora, and Dysaphis plantaginea) was evaluated under semicontrolled conditions. The product was able to confer significant protection rates (40 to 75% for apple scab, 40% for fire blight, and 30% for rosy aphid), which can be explained by its more or less efficient biocidal activity against the three pests, and by its ability to induce apple immunity (pathogenesis-related proteins and secondary metabolites genes). A cumulative effect of treatments as well as the systemic behavior of the product was demonstrated. Fields trials against apple scab and the postharvest disease bull's eyes rot (Neofabraea vagabunda) were performed on different apple varieties by applying KHP combined with light pest management programs either reducing (dessert orchards) or suppressing (cider orchards) fungicide applications. KHP was able to reduce apple scab by 70 to 90% on shoots and young and harvested fruit, and bull's eyes rot by 70 to 90% on harvested fruit. Overall, our results indicate that KHP is useful for the protection of apple trees against its major pests by direct effect and by triggering the host defense system.

Pre-harvest climate and post-harvest acclimation to cold prevent from superficial scald development in Granny Smith apples.

Superficial scald is one of the most serious postharvest physiological disorders that can affect apples after a prolonged cold storage period. This study investigated the impact of pre- and post-harvest climatic variations on superficial scald in a susceptible apple cultivar. Fruit batches with contrasting phenotypes for superficial scald incidence were identified among several years of "Granny Smith" fruit production. The "low scald" year pre-harvest climate was characterised by a warm period followed by a sudden decrease in temperature, playing the part of an in vivo acclimation to cold storage. This was associated with many abiotic stress responsive genes which were induced in fruit peel. In particular 48 Heat Shock Proteins (HSPs) and 5 Heat Shock transcription Factors (HSFs) were strongly induced at harvest when scald incidence was low. For "high scald" year, a post-harvest acclimation of 1 week was efficient in reducing scald incidence. Expression profiles of stress related genes were affected by the acclimation treatment and indicate fruit physiological adaptations to cold storage. The identified stress-responsive genes, and in particular HSPs, could be useful indicators of the fruit physiological status to predict the risk of scald occurrence as early as harvest.