Inheritance of Resistance to Yellow Mosaic in Soybean

The inheritance of yellow mosaic resistance in soybean was studied using PI 171443 (UPSM-534) as a resistant source and several susceptible parents including one tolerant line. Susceptibility or tolerance, depending upon the parents used, was observed to be dominant over resistance in F,. The segregation pattern in₂ was erratic and did not fit to any known genetic ratios probably due to varying number of escapes of otherwise susceptible plants. However, the proportion of F₂ plants affected with yellow mosaic was always more than free plants demonstrating further that susceptibility was a dominant trait. In order to avoid the problems due to escapes, the disease rating of each F₂ plant was done on the basis of its F₃ progeny. In crosses involving susceptible & resistant parents, the F₃ progeny tests indicated a 15 susceptible: 1 resistant ratio whereas in crosses involving tolerant and resistant parents a 3 tolerant: 1 resistant ratio was observed. The data indicated that resistance to yellow mosaic is governed by two recessive gene pairs for which gene symbols ryml and rym2 are being assigned.