Prevalence and incidence of postharvest diseases of blueberries in California

Recent establishment of low-chill southern highbush blueberry cultivars in California's warm climate has significantly increased the acreage of blueberry production in the Central Valley of California, which is now a major southern highbush blueberry production region in the United States. The vast majority of blueberries grown in California are destined for the fresh market. As the production continues to grow, the blueberry industry has a need to prolong the storage life of blueberry in order to extend the marketing period. However, the postharvest life of blueberry fruit is limited by fruit rots caused by fungal pathogens. To determine what are the major postharvest diseases affecting blueberries in the region, blueberry fruit were collected at harvest from 42 (27 conventional and 15 organic) and 62 grower lots (49 conventional and 13 organic) in 2013 and 2014, respectively; stored at 0-2°C for 5 weeks; and then evaluated for the presence of fruit rots. Causal agents of rots were isolated from decayed fruit and identified. Incidence of decay ranged from 23 to 74% in 2013 and from 3 to 74% in 2014. One or more than one fungi were isolated from each decayed fruit. On average, Botrytis spp. (mainly B. cinerea), Cladosporium spp., Alternaria spp. (mainly A. alternata and A. arborescens), Aureobasidium pullulans, Rhizopus stolonifer, and Penicillium spp. were isolated from 21-46, 6-13, 25-38, 12-29, 2-26 and 2-8% of the decayed fruit sampled from conventional grower lots, respectively; and from 20-73, 5-18, 11-46, 7-19, 5-25, and 3-4% of the decayed fruit sampled from organic grower lots, respectively. Our results indicated that B. cinerea, Alternaria spp., Aureobasidium pullulans and Cladosporium spp. were the major pathogens as they were consistently isolated from decayed fruit from most grower lots during the 2-year survey and that control measures should target these pathogens.