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 r esistance in maize (Zea mays) to northern leaf blight (caused by Exser ohilum turcicum) are well documented. However, their effects on the ex pression of partial resistance to the disease have not been studied. S ix maize inbred lines, representing a wide range in levels of partial resistance to northern leaf blight, were evaluated for three component s of partial resistance (incubation period, latent period, and sporula tion intensity) in controlled environmental chambers representing a fa ctorial arrangement of three temperature regimes (22/18 C, 26/22 C, an d 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 period s of inbred lines were consistently correlated, regardless of environm ental conditions, and reflected the lines' levels of partial resistanc e. Although there was some relationship with partial resistance, sporu lation intensity on inbred lines was highly variable, interacting with both temperature and light, and was greatly reduced at the 30/26 C te mperature regime. Incubation or latent period length could be a useful measure of partial resistance of maize genotypes in greenhouse or gro wth chamber screenings of seedlings. Unlike major gene resistance, par tial resistance expressed as an increased latent period appears to be a stable trait expressed over a wide range of temperature and light co nditions, although higher temperatures tended to increase the differen ces among genotypes.