Multivariate statistical analysis of the virulence of Stenocarpella macrospera and host resistance to Stenocarpella gall blight in corn

English. The variability of 119 isolates of Stenocarpella macrospora, collected from different corn-growing areas in the Philippines was studied in culture and in host plants while the expression of host resistance to Stenocarpella leaf blight in corn was determined in 37 corn populations from the Philippines and Indonesia. Various components of virulence and resistance were measured and analyzed using the multivariate statistical method Principal Component Analysis. Variability of S. macrospora indeed existed among the isolates in incubation period, latent period, pycnidal production, lesion size and percent disease severity existed. The most 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 showed that the first component, which accou nted for more than half of the total variance, identified the isolate Sm-14 as the most virulent followed by Sm-13.Host resistance in the populations tested varied in terms of incubation period, latent period, pycnidial production, lesion size and percent disease severity. Populations reistant 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.

English. Conference of the Pest Management Council of the Philippines Cebu City, Philippines 6-9 May 2003