The 2011 ASHS Annual Conference

The possible relationship of seven expansin genes and MdACS1 to maintenance of apple crispness during storage was examined. Expression of expansin genes MdEXPA1, MdEXPA2, MdEXPA3, MdEXPA4, MdEXPA5 and MdEXPA7 was quantified among apple cultivars that remained crisp or lost crispness between harvest and after 8 weeks of cold storage. MdEXPA1 was expressed in low quantities in fresh fruit while MdEXPA4, MdEXPA5 and MdEXPA7 expression was not detected among fresh or cold stored apple cultivars. Among the expansin isoforms studied, MdEXPA2 and MdEXPA3 were the most abundantly expressed. A new expansin isoform, with homology to PcEXPA1, and low expression levels in fresh and cold-stored apples, was isolated in this study and designated MdEXPA8. Two alleles of MdEXPA2 were identified and 41 apple genotypes were allelotyped for this gene to determine to what extent a relationship existed between allelotype and loss of fruit crispness. Paired t-tests suggest that there were no relationship between allelotype and crispness maintenance. However, genotype sample size was small and may have been inadequate to detect any effect.   MdACS1 was also allelotyped in the 41 apple genotypes to determine if there might be an additive effect with MdEXPA2 allelotype, and was found to be unsuitable as a marker for maintenance of apple fruit crispness in the crosses used in this study.