Abstract
The resistance breaking population (RB population) of Meloidogyne incognita that damages resistant tomato cultivars grown in greenhouse was confirmed in southern Hokkaido in 1996. In this report, the emergence and factor analysis of the RB population of M. incognita occurred in Hokkaido are described, with the following results:(1) The RB population of M. incognita was detected in the production regions where resistant tomato cultivars were cultivated in greenhouse with successive cropping or at a high frequency.(2) The degrees of root gall of 29 resistant tomato cultivars grown in soil inhabited by the RB population were as high as those of the susceptible cultivars. No cultivars resistant to the RB population were found.(3) The degrees of root gall of resistant tomato cultivar grown in soil inhabited by the RB population, was formed from 22°C to 33°C the same as that in the case of the susceptible cultivar. On the other hand, no root gall was formed below 28°C in the resistant cultivar grown in soil inhabited by a common population of M. incognita, but the resistance was lost above 30°C.
