Comparison of mass selection and S₁ selection for improving resistance to sorghum downy mildew (Peronosclerospora sorghi (Weston & Uppal) C.G. Shaw) in corn (Zea mays L.)

Vita.Percent infection and gain per cycle of selection were compared after two cycles of mass selection with progeny test, mass selection without progeny test and S1 selection in breeding for resistance to sorghum downy mildew (Peronosclerospora sorghi (Weston & Uppal) C.G. Shaw) in Corn (Zea mays L.). All populations were derived from the base population from 1976-1978 at College Station with selection intensity of 20%. Selection was practiced primarily for disease resistant plants with mature grain, without particular regard to plant and ear types. The base population and derived populations were subjected to conidial inoculation in the greenhouse and natural field inoculation in two locations, Robstown and College Station, Texas in 1979. S1 selection was the most effective selection method for reduction of susceptibility to P. sorghi in this study. Gains per cycle for the first and second cycle of S1 progeny selection were 9.35 and 2.12%, respectively with the average gain of increasing resistance of 5.74% per cycle. Gains per cycle were significantly different for mass selection with and without progeny test. Gains of 6.11 and 1.68% were observed from first and second cycle of mass selection with progeny test. The average gain for this selection method was 3.89% per cycle. Lowest average gain of 2.80% per cycle was observed from mass selection without progeny test. Gains in reducing infection were 4.27 and 1.33% from first and second cycle of this latter selection method. Higher gains were observed in first than in the second cycle of selection in all three methods used in this study due to decreasing in genetic variability. Gains for each cycle were significantly higher under greenhouse inoculation method than in two locations of natural infection except gain from second cycle of selection at Robstown. Infection percentages were significantly different among the base population and six derived populations. Highest infection of 14.41% was observed from base population. The lowest infection was from second cycle of selection, 2.94%. Greenhouse conidial inoculation induced significantly higher percentages of infection than natural infection in the field at both locations. The highest infection percentages was 15.51% under greenhouse condition..