Theor Appl Genet (1992) 83: 720- 726 • + • , :~ 9 ~g,,.e~ ~ /'~;~ , !~j ~j ~ ..~ 9 Springer-Verlag 1992 Inheritance of resistance to Meloidogyne spp. in common bean and the genetic basis of its sensitivity to temperature C.O. Omwega and P.A. Roberts* Department of Nematology, University of California, Riverside, CA 92521, USA Received May 16, 1991; Accepted July 9, 1991 Communicated by G. Wenzel Summary. Bean lines PI 165426, PI 165435, and Ala- bama no. 1, possessing resistance to Meloidogyne incog- nita, and bean lines A315 and A445, possessing gene Mel, were tested against several Meloidogyne incognita and M. javanica isolates. Resistance in bean line PI 165426, PI 165435, and Alabama no. 1 was found to be complementary to resistance conferred by gene Mel. Resistance in PI 165426 was found to be dominant and conditioned by one dominant and one recessive gene at 26 ~ We propose Me2me3 as the genotype symbol for this resistance. Resistance in lines PI 165435 and Ala- bama no. 1 was found to be recessive. Since Alabama no. 1 and PI 165435 were resistant at 26 ~ but suscepti- ble at 29 ~ and segregation of F 2 progeny derived from crosses involving PI 165426 was 13:3 at 26 ~ and 1:2:1 at 28 ~ we concluded that the temperature at which tran- sition from resistance to susceptibility occurs was deter- mined by whether the resistance gene is dominant or recessive. Furthermore, the 1:2:1 segregation of F 2 plants and an intermediate resistance reaction of F 1 plants of crosses involving PI 165426 indicated that allelic dosage of the dominant gene also influenced the transition tem- perature. Key words: Allelic dosage - Dominance - Nematode re- sistance - Phaseolus vulgaris - Temperature sensitivity Introduction Resistance to the root-knot nematode Meloidogyne incognita (Kofoid and White) Chitwood in common bean Phaseolus vulgaris L. has been identified in bean lines * To whom correspondence should be addressed. PI 165426, PI 165435, and Alabama no. 1 (Fassuliotis et al. 1970; Omwega et al. 1989). The inheritance of resis- tance in the first two lines is not known. The resistance in Alabama no. I was reported to be under the control of two (Barrons 1939) or three (Hartmann 1970) recessive genes. Resistance in bean lines PI 165426, PI 165435, and Alabama no. I was found to be effective against the same Meloidogyne spp. isolates (Omwega et al. 1989). From this data it was speculated that resistance in these lines could be under the same genetic control. In contrast, resistance to bean lines A315 and A445 was found to be effective against those Meloidogyne isolates to which the former group of bean lines was susceptible (Omwega et al. 1989). This resistance was found to be under the control of a single dominant gene, Mel (Omwega et al. 1990 a). Although resistance in PI 165426, PI 165435, and Al- abama no. 1 was effective against the same nematode isolates, resistance in PI 165426 was found to be stable at higher temperature than that in PI 165435 and Alabama no. 1 (Omwega et al. 1990b). Influence of temperature on host plant resistance genes has been reported for ne- matode resistance in several interactions, e.g., in tomato (Dropkin 1969; Ammati et al. 1986) and alfalfa (Griffin 1969). This phenomenon also has been reported for other disease or pest plant interactions, e.g., in rust diseases in wheat (Luig and Rajaram 1972) and flax (Islam et al. 1989), and for Hessian fly resistance in wheat (Tyler and Hatchett 1983). As far as we know, no attempt has been made to study the genetic basis of temperature effects on expression of resistance genes in plant-nematode interac- tions. A shift towards susceptibility at 24~ ~ in M. incognita resistant bean line A211 has been reported in an independent study (Mullin et al. 1991). The three bean lines PI 165426, PI 165435, and Alabama no. 1 with re- sistance to M. incognita provided a good model system