Penicillium expansum Invades Apples Through Stems during Controlled Atmosphere Storage

Empire apples were collected from six orchards in 1997 and 1998 and were then subjected to various inoculation and storage regimes to determine how non-wounded fruit become infected with Penicillium expansum and to determine if decay susceptibility varies with orchard source. Replicated samples of fruit were inoculated within 24 h of harvest either by placing a 10 μl droplet containing 500 conidia of P. expansum onto the end of the apple stems or by placing 500 μl containing 10,000 conidia into the stem basin. Fruit were stored for 7 to 9 months either in cold air (1.1°C) or in controlled-atmosphere (CA) storage (1.1°C, 1.6% oxygen and 2.2% carbon dioxide), and were then evaluated for decay. Twenty-seven to 47% of fruit that had been inoculated by placing spores on the ends of stems developed decay during CA storage whereas less than 1% of similarly inoculated fruit decayed during cold-air storage. Placing spore suspension into the stem basins also resulted in less than 1% decay. Orchard-to-orchard variation in incidence of decay that developed was positively correlated with boron concentrations in both apple leaves (R2 = 0.66) and apple fruit (R2 = 0.62). This is the first report of P. expansum causing commercial losses in apples due to invasion through stems and also the first Accepted for publication 28 September 2006. Published 13 December 2006.