Inheritance of resistance to fusarium wilt in two common bean races

Fusarium wilt in common bean (Phaseolus vulgaris L.) caused by Fusarium oxy sporum Schlechtend. Fr. forma specialis phaseoli Kendrick and Snyder (Fop) occurs worldwide and can result in severe yield loss. Because cultural meth ods to control disease loss are not completely effective, cultivars with ge netic resistance are needed. The objectives of this study were to determine whether genetic control of resistance to Fop race 4 differs between germpl asm of races Durango and Mesoamerica of common bean and to estimate heritab ility of resistance found in race Mesoamerica. Resistant and susceptible li nes of rates Durango and Mesoamerica were crossed within races to produce F -2 and F-3 progeny. Reaction to Fop was evaluated using a root-dip inoculat ion method and scored using a CIAT disease severity scale from one to nine. F-2 populations derived from race Durango parents shelved a 3:1 (resistant /susceptible) plant segregation ratio, and F-3 progeny tests confirmed that resistance was controlled by a single dominant gene. F-2 data from crosses between parents of race Mesoamerira had continuous distributions for react ion to Fop race 4, suggesting polygenic control of resistance. The narrow-s ense heritability estimate derived from midparent-offspring regression of 1 0 F-2 populations derived from Mesoamerican parents was 0.85 +/- 0.34, and realized heritability estimates ranged from 0.25 +/- 0.19 to 0.60 +/- 0.16 among five populations. The heritability estimates as well as the continuou s variation in disease severity observed support the hypothesis that resist ance to Fop race 4 among parents of rare Mesoamerican is polygenic.