FREEZE INJURY AND PROTECTION OF CITRUS IN JAPAN

Abstract

Japan is one of the major citrus producing countries in the world. The temperature in winter season in Japan is lower than that of other countries for growing citrus, and satsuma mandarin, which is a cold hardy variety, ranks first among leading varieties. Recently, overproduction of satsuma mandarin stimulated the renewal of top working to later maturing varieties which include less cold hardy citrus. Consequently, cold hardiness of citrus becomes one of the more important problems in the citrus industry of Japan. Severe freezes in 1963, 1977, and 1981 severely damaged the fruit and killed many trees. Tree and fruit losses from freeze injury in 1981 were estimated at more than 350 million dollars. Severe losses from freeze have stimulated research on cold hardiness and protection against freeze damage. Recently, breeding and selection of cold hardy citrus and improvement of agricultural techniques against unusual climatic conditions were started at Akitsu Branch, Fruit Tree Research Station and elsewhere (3,4,5,6,10, 11). This report describes recent efforts to develop more cold hardy citrus and protection against freeze damage of citrus in Japan.