Effects of the plant growth regulator prohexadione-calcium and the SAR-inducer acibenzolar-S-methyl on the quality of apples at harvest

An experiment was conducted over two consecutive years (2002 and 2003) in an apple orchard planted with Malus X domestica cv. 'Mitcligla' to study the impact of treatments with acibenzolar-S-methyl or prohexadione-calcium on different characteristics of fruit quality at harvest. Parameters measured included: quantity of marketable apples, harvest maturity, organoleptic attributes, and amount of PR-10 gene products encoding potential allergens. Our results highlighted the fact that application of acibenzolar-S-methyl during the 2003 growing season led to a reduction in the red colour of the skin and to a reduction in the sugar content of the apples, whereas prohexadione-calcium had no measurable effect on these parameters. The application of prohexadione-calcium induced an increase in the accumulation of PR-10 transcripts in fruits compared to control or acibenzolar-S-methyl treatments. An analysis of the expression of two members of the APb gene sub-class, AP2 (Ypr10*Md.a) and AP3 (Ypr10*Md.c),. which are homologous to the major apple allergen Mal d 1, revealed a higher abundance of transcripts in apples after the application of prohexadione-calcium compared to the acibenzolar-S-methyl treatment. These experimental data have implications for the quality attributes of marketable fruits, since the use of acibenzolar-S-methyl may modify some harvest maturity parameters related to consumer preferences, while prohexadione-calcium could increase the major allergen content of apples.