Quantification of the presence of Botrytis cinerea, Monilinia laxa and Penicillium expansum in blossoms and plums at harvest, and correlation of relative pathogen presence to decay after shelf-life: Potential application of diagnostic information early in the season to use as a management tool of plum decay post storage and shelf life

Post-harvest decay of plums results in significant economic losses to the stone fruit industry. The most prominent fungal species leading to decay is Botrytis cinerea, Monilinia laxa and Penicillium expansum. No method to monitor and quantify inoculum levels exist. The development and implementation of a tool to detect early infections could greatly assist in decay management. The aim of the project was to detect and quantify the levels of the three most prominent fungal species in blossoms and fruit at harvest, and correlate the levels to decay development after storage

Blossoms were harvested from orchards and processed for qPCR analysis. Fruit were harvested from the same orchards and either processed for qPCR analysis for quantification of fungal DNA, or assessed for visual decay development at end of storage

• B cinerea could be detected by multiplex qPCR assay in all blossoms sampled and in some fruit samples prior to storage. The results were repeatable over the two seasons of the trial.
• laxa could be detected by multiplex qPCR assay in some fruit samples, but not P. expansum.
• A strong correlation was found between cinerea DNA in blossoms and decay development after storage. The decay was, however, described as “brown rot”.
• The correlation between cinerea in blossoms and overall decay at the end of storage was not observed in the second season of this trial.

A relatively high correlation was observed between B. cinerea DNA content in blossoms and total decay at the end of storage (R²= 0.75) during the first season of this project. The majority of the decay observed in the fruit was characterised as “brown rot”, caused by M. laxa. M. laxa DNA was not detectable in blossoms, but was detectable in low levels in fruit prior to storage. It needs to be noted that decay development during storage was extremely slow, requiring an extended storage period of almost 60 days before adequate decay was observed. This correlation was not observed in the second season of the study.