Ranking of partial resistance to common rust (Puccinia sorghi Schr.) in 30 sweet corn (Zea mays) hybrids

Thirty sweet corn (Zea mays) hybrids were evaluated for resistance to rust (Puccinia sorghi Schr.) for 3 years in an artificially inoculated field plot at St Paul, Minnesota. On the basis of visual determinations of rust severity, these cultivars were ranked according to level of resistance. All of them allowed at least some rust to develop, but the degree of final rust severity varied considerably. Correlation coefficients between the rust severity scores recorded for the hybrids in all three pairs of years were 0·68 (1978–1979), 0·79 (1978–1980) and 0·86 (1979–1980). Spearman's rank correlation coefficients were 0·76, 0·89 and 0·82, respectively, for the same comparisons.