Evaluation of short postharvest gaseous treatments for inhibition of Alternaria black spot of persimmon 'Rojo Brillante'

Persimmon (Diospyros kaki Thunb.) is an expanding crop in Spain. The most important production area is València (about 90% of total planted area) and astringent 'Rojo Brillante' is by far the most planted cultivar. An increasingly important factor limiting storability of persimmon is postharvest decay due to Alternaria black spot (ABS) caused by the pathogen Alternaria alternata. As in other EU countries, no chemical fungicides are currently approved in Spain for postharvest treatment of persimmon and alternative antifungal treatments are required. The availability of commercial facilities in persimmon packinghouses for fruit deastringency through CO2 treatments opens the door for potential application of antifungal gaseous treatments. 'Rojo Brillante' persimmons were artificially wound-inoculated with A. alternata and exposed 24 h later for 48 h to air at 20°C (ambient atmosphere, control), air at 35°C, 95 kPa CO2 at 20 or 35°C, or 30 kPa O2 + 70 kPa CO2 at 20 or 35°C, all at 90% RH. Incidence (% of infected wounds) and severity (lesion size) of ABS were evaluated after 3, 5, and 10 days of incubation at 20°C and 80% RH. Another lot of treated fruit was cold-stored at 1°C and 90% RH for up to 82 days and fruit quality attributes such as weight loss (WL), firmness, maturity index (MI), and peel color index (CI) were also determined on non-inoculated but treated fruit. After 10 days of incubation at 20°C, none of the gaseous treatments applied at 20 or 35°C significantly reduced ABS incidence and ABS severity was even higher on some gas-treated persimmons than on control fruit. After 40 days at 1°C, ABS incidence was reduced by 30 to 40% on fruit treated with 95 kPa CO2 at both temperatures, but these reductions were not significant after 82 days. ABS severity on cold-stored fruit was also greater on gas-treated persimmons than on control fruit. In general, gas-treated and cold-stored persimmons, especially those treated with 95 kPa CO2, showed lower CI, higher MI and greater firmness than control fruit.