Avidan, B., Institute of Horticulture, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Klein, I., Institute of Horticulture, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel

The loquat fruit suffers from russeting, a physiological disorder which severely decreases the marketable value of the fruit. The disorder can be detected as a skin blemish four weeks after fruit set, while the fruit is still green. Toward the phase of fruit color change, the blemish appears as deep brown stripes of ca. 1 mm width the number of fruits affected and the percent skin cover contribute additively to the severity of the disorder. The extent of the damage varies between years and cultivars and it seems to be influenced by microclimate. The objective of the present investigation was to identify some of the conditions contributing to the russeting of the fruit in order to develop means for alleviating the damage. The number of fruits affected by russeting was reduced from 75% to 25 % by growing trees at 30 % reduced light intensity under black net covers. The effects of temperatures and irradiance level during fruit growth were measured in the field by enclosing fruiting shoots in various net and bag covers. An increase in percent russeted fruits was correlated with the increase of air temperature under cover from 17.7°C to 21.6°C, and the deviation from ca. 1000 μmole m-2 s-1 irradiance level, to higher and lower values. Environmental conditions (reduced temperatures and extreme light intensities) which delayed fruit development during the cell division stage (20-60 days after fruit set) were associated with reduced incidence of russeting at the cell enlargement stage.