Variability of Stenocarpella macrospora (Earle) Sutton and expression of host resistance to Stenocarpella leaf blight in corn (Zea mays L.)

Variability of Stenocarpella macrospora was studied in culture and host plants. Isolates of the fungus were collected from 19 corn-growing areas in the Philippines. Variability of S. macrospora indeed existed among isolates studied. In culture, S. macrospora isolates differed in mycelial growth and number of pycnidia produced per plate. In host plants, variability of the isolates in incubation period, latent period, pycnidial production, lesion size and percent disease severity existed. The more virulent isolates produced earlier incubation period and shorter latent period, had more pycnidia, elicited bigger lesion size and higher percent disease severity as well as faster rate of increase in lesion size and apparent infection rate. Principal component analysis on susceptible inbred line showed that the first component, which accounted for more than half of the total variance, sorted Sm-14 as the most virulent followed by Sm-13. The expression of host resistance to Stenocarpella leaf blight in corn was studied in 37 corn populations from the Philippines and Indonesia. Resistance components significantly varied among the populations tested. The variability was exhibited in the differences in incubation period, latent period, pycnidial production, lesion size and percent disease severity. Populations resistant to Stenocarpella leaf blight expressed relatively longer incubation period, longer latent period, less number of pycnidial production, smaller lesion size and lower percent disease severity. Principal component analysis of resistant variables showed that the first component, which accounted for more than half of the total variance, was consecutively dominated by percent disease severity, pycnidial production, latent period, incubation period and lesion size. All of these parameters observed were the main components of resistance to Stenocarpella leaf blight.