Varietal Assessment of Threshold Air Temperatures for Cold Damage in Loquat Fruit

摘要

Shift in locations suitable for loquat [Eriobotrya japonica (Thunb.) Lindl.] due to global warming leads to a high requirement for accurate assessment of suitable locations. This study aimed to develop a technique for using past winter air temperatures to judge whether an area is suitable for loquat production. The relationship between air temperatures and cold damage levels observed in orchards of four main production areas (Chiba, Kagawa, Nagasaki, and Kagoshima prefectures) for some years were analyzed. The survival rates of young fruit of each variety were positively correlated with the annual minimum air temperature. Threshold air temperatures for cold damage (the air temperature at which the survival rate decreased to 80%) of six varieties ('Tanaka', 'Mogi', 'Natsutayorr, 'Nagasakiwase', 'Harutayori', and 'Biwa Nagasaki No. 21') were acquired by using statistically significant linear regressions. 'Tanaka' had excellent cold hardiness, with the lowest threshold air temperature, whereas 'Nagasakiwase' and 'Ilarutayorr tolerated the cold less well, with higher threshold air temperatures. Locations suitable for production of 'Tanaka' and 'Nagasakiwase' were judged based on the upper limit of the threshold air temperature for cold damage. The current production areas agreed with the locations judged to be suitable for the production of each variety. These results suggest that the threshold air temperatures for cold damage obtained in the present study provide a valid assessment of suitable current and future locations for both varieties.