Genetic analysis of race-specific resistance to the southern root-knot nematode in sweetpotato II. Inheritance of resistance in the cultivar 'J-Red'.

摘要

Southern root-knot nematode (SRKN), Meloidogyne incognita, causes severe damage to yield and quality in sweetpotato, Ipomoea batatas, production. Resistance against SRKN has been intensively evaluated and enhanced in the sweetpotato breeding programme in Japan. In this study, the genetic basis of multi-race resistance against SRKN in sweetpotato cultivar 'J-Red' was investigated using F< sub>1 progenies derived from the cross between 'J-Red' and the susceptible cultivar 'Choshu'. The two SRKN populations used were those collected from the central part of Kyushu Island (race SP1) and those from the southeastern part of the Kanto plain, Japan (race SP4), both of which showed a differential host reaction against the sweetpotato cultivars 'Norin-2', 'Tanegashimamurasaki-7' and 'Elegant Summer'. The distribution frequency of the progenies, based on the mean numbers of egg-masses was continuous but nearly bimodal, with approximately half of the 57 total progenies having less than 10 egg-masses. Segregation of resistant and susceptible progenies fit the expected ratio of 1:1, based on the assumption that the threshold for SP1 roughly ranged from 5-15 egg-masses per plant and that the threshold for SP4 from 10 to 30. The resistance of 'J-Red' is controlled by multiple genes, including a single gene with a major phenotypic effect. A significant positive correlation was observed between the mean numbers of egg-masses produced by SP1 and by SP4, and a differential reaction to different SRKN races was not obvious among the F< sub>1 progenies. Thus, the genes that control resistance to SP1 and to SP4 in 'J-Red' were considered to be closely linked to one another on the same chromosome or possibly identical.