EFFECT OF LIGHT AND TEMPERATURE ON EXPRESSION OF PARTIAL RESISTANCE OF MAIZE TO EXSEROHILUM-TURCICUM

The effects of light and temperature on the expression of major gene resistance in maize (Zea mays) to northern leaf blight (caused by Exserohilum turcicum) are well documented. However, their effects on the expression of partial resistance to the disease have not been studied. Six maize inbred lines, representing a wide range in levels of partial resistance to northern leaf blight, were evaluated for three components of partial resistance (incubation period, latent period, and sporulation intensity) in controlled environmental chambers representing a factorial arrangement of three temperature regimes (22/18 C, 26/22 C, and 30/26 C, day/ night) and two light intensities (full light, 639 muE.m-2,s-1, or half light, 320 muE.m-2.s-1). Incubation and latent periods of inbred lines were consistently correlated, regardless of environmental conditions, and reflected the lines' levels of partial resistance. Although there was some relationship with partial resistance, sporulation intensity on inbred lines was highly variable, interacting with both temperature and light, and was greatly reduced at the 30/26 C temperature regime. Incubation or latent period length could be a useful measure of partial resistance of maize genotypes in greenhouse or growth chamber screenings of seedlings. Unlike major gene resistance, partial resistance expressed as an increased latent period appears to be a stable trait expressed over a wide range of temperature and light conditions, although higher temperatures tended to increase the differences among genotypes.