BREEDING OF FUSARIUM WILT-RESISTANT STRAWBERRY CULTIVAR SUITABLE FOR FIELD CULTURE IN NORTHERN JAPAN

Abstract

Fusarium wilt of strawberry, which is caused by Fusarium oxysporum f. sp. fragariae, is a very serious soilborne disease found in cooler regions such as Akita Prefecture in Northern Japan. The initial infestation of the susceptible cultivars Morioka-16 and Pajaro with the disease in Akita Prefecture was noted at minimum air and soil temperatures of ca. 15°C at the end of May. As the months passed and the high temperature season (the beginning to the middle of July) drew near, the numbers of plants that became diseases and died increased rapidly. A way to effectively control this disease has yet to be found. Breeding for new resistance strawberry cultivars suitable for open culture of cooler regions was conducted. A thousand and six F 1 seedlings obtained from the crossing with cv. Pajaro (susceptible resistance) and cv. Belle Rouge (intermediate resistance) were grown until 3-5 leaves had appeared, and were then inoculated with a spore suspension (1 x 10 6 spores/ml) of Fusarium oxysporum f. sp. fragariae (Isolate 91-40). Three resistant lines were then selected. The lines, 'WB-A15', 'WB-B22', and 'WB-B33', were not damaged by the disease when they were cultured in an open field heavily infested with Fusarium oxysporum f. sp. fragariae for three consecutive years (1999 to 2001). These results demonstrate that the lines are resistant enough to Fusarium wilt to be grown under conditions in the regions in question.