INHERITANCE OF LATENT PERIOD LENGTH IN MAIZE INFECTED WITH EXSEROHILUM-TURCICUM

Extended latent period length is an important component of partial resistance of maize to northern leaf blight (NLB) caused by Exserohilum turcicum. Latent period length is easily measured on seedling plants under both field and greenhouse conditions and has been shown to be a relatively stable trait over a range of temperature and light conditions. The inheritance of latent period length was studied in F-2 and backcross generations of crosses of the experimental inbred line 69-1 (highly resistant, long latent period) and Mo17 (intermediately resistant, intermediate latent period) with the highly susceptible inbred line A632. Studies were conducted under both winter greenhouse conditions and in the field. Differences in mean latent periods between the two parental inbred lines varied from 14.1 days (A632 x 69-1; 1993 field experiment) to 1.8 days (A632 x Mo17; 1993 greenhouse experiment). Analysis of generation means of log-transformed latent periods revealed that over 92% of the variation among generation means could be explained by additive gene action and that dominance and epistatic effects were negligible. Heritability and gene number estimates were in agreement with previously published estimates for partial resistance to NLB measured as reduced disease severity on adult plants. Selection on some sort of progeny mean basis would probably be the most efficient and rapid means of selection for increased latent period and could potentially be more effective than selection for reduced NLB severity after anthesis.