Postharvest decay of blueberry fruit in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Horticultural Science at Massey University, Manawatū, New Zealand

Abstract

Postharvest decay limits the storage life of fresh blueberries and is unacceptable in export markets. Currently, no surveys have been conducted to determine the microorganisms causing decay of blueberry fruit during postharvest storage in New Zealand. Identification of the major microorganisms associated with postharvest decay is critical to effective management of decay within the supply chain. This thesis identifies the microorganisms associated with postharvest decay of blueberry fruit with the aim of observing the prevalence and nature of these rots after cold storage. Four combinations of temperature and relative humidity (RH) were used to store blueberry fruit. These treatments were obtained by a factorial combination of two temperatures, 1°C and 15°C, and two relative humidity (RH) conditions of high RH (98-100% RH) or low RH (80% RH). The 1°C storage at either RH was implemented for 42 d, while the 15°C storage had a duration of 14 d. Following storage, the fruit was stored at 20°C for 7 days to simulate shelf life (retail or home use), and decay prevalence evaluated. From the decay signs observed, microorganisms were isolated and identified through morphological and molecular analysis. The major microorganisms isolated from blueberry fruit decay were identified as Botrytis cinerea, Colletotrichum acutatum species complex, and Pestalotiopsis spp. Both B. cinerea and C. acutatum spp. complex are causal agents of decay signs, responsible for grey mould and anthracnose, respectively. Pestalotiopsis spp. was associated with decay of blueberry fruit, but it is unclear whether this is a causal agent of decay. The postharvest storage conditions influenced the prevalence and behaviour of decay. At 1°C, B. cinerea was the dominant causal agent of decay, leading to grey mould sign (extensive grey/tan mycelium) at 98-100% RH. When blueberries were stored at low RH (80%), B. cinerea infections were mostly restricted to the fruit stem scar. During shelf life, after 1°C storage for 42 days, decay showed a higher accumulation rate than when the fruit was stored at 15°C prior to shelf life. In addition, after shelf life, B. cinerea and the C. acutatum spp. complex were the most predominant causal organisms isolated from decayed fruit.