Inheritance of General Resistance in Maize to Puccinia sorghi Schw.1

Abstract

Genetic studies were made of general resistance in maize (Zea mays L.) to common rust, Puccinia sorghi Schw., by means of diallel and generation mean analyses of crosses among 11 inbreds. Most populations were grown under severe natural epiphytotics on Oahu, Hawaii with rust spore burdens from the time of emergence. Susceptible checks averaged 6.8 on the 1 to 7 rust scale, where 7 represented infections covering more than 40% of mature leaf surface. Few inbreds, including Oh545 and CM105 (Cuban Flint origin), displayed effective general resistance under these conditions. The nine parents of a diallel showed high general combining ability (gca) for resistance, and a high coefficient of linear determination (r2 = 0.91) between parental averages and their gca effects. Heterosis was not evident for resistance, and specific combining ability effects were small although statistically significant. Generation mean analysis was made of 20,000 plants from 25 sets of biparental crosses and their F2 and backcross progenies. Heritability estimates were 83.4% (broad‐sense) and 47.0% (narrow‐sense) for the summarized data, and substantially higher for the highly resistant sources Oh545 and CM105. From crosses with the highly susceptible inbreds — B37, CM104 (India) and AA8 (Hawaii) — Oh545 was inferred to carry two major, partially dominant resistance genes.