Postharvest losses by complex of Phytophthora sp. and Botrytis cinerea in long storage pear fruit in the North Patagonia, Argentina

In 2013-2014, severe economic losses caused by postharvest decay of 'Packham's Triumph' pears were recorded in a packinghouse of the Alto Valle de Río Negro. Fruit had been treated with captan and pyrimethanil to control Penicillium spp. and Botrytis cinerea, and stored into carton packets wrapped with nylon in controlled atmosphere. After 9 months, 64 packets with 5500 fruit, corresponding to seven different lots were evaluated. Severe decay symptoms were observed on fruit. The losses were quantified and the aetiology of the disease investigated. Symptoms description, isolation on agarized media and microscopic observation, identified Botrytis cinerea and Phytophthora spp. as the decay incitants. Koch's postulates and inoculation of single or combined pathogens on fruit were performed. Affected fruit came from orchards of two production zones of Rio Negro and Neuquén. Incidence percentage of this decay (% DI) in all fruit reached 13%. The most affected lots showed distributed %DI: (i) 1.3-3% of B. cinerea; (ii) 0.5-1.2% of B. cinerea and Phytophthora spp. and (iii) 1.2-1.6% of Phytophthora spp. Fruit decay caused by concomitant infection of B. cinerea and Phytophthora spp. was firm to touch, mummified the fruit, had two distinct brown colorations and diffuse water soaked margins, and was free from B. cinerea nests. Cultures of B. cinerea in PDA-N and Phytophthora spp. in V-8 media showed typical characteristics of each pathogen. Propagules of Phytophthora spp. were detected by pear bait method in soil samples from the same orchards where the fruit were harvested. Since postharvest diseases are also caused by latent infections occurring during the growing season, analysis of asymptomatic fruit taken 30 days before the harvest revealed 5 and 2% of Phytophthora and 0-2% of B. cinerea. This is the first report of postharvest pear decay caused by B. cinerea associated to Phytophthora spp., with detection of latent infections.