The reactions of five double haploid lines of spring oilseed rape (Brassica napus) to 98 isolates of Leptosphaeria maculans, cause of blackleg, were tested in the greenhouse. The average of lesion lengths measured 3, 4, 5, 6, and 7 weeks after inoculation of stems of 5-week-old plants was used as a measure of virulence of isolates and of resistance of lines. Pearson and Spearman analyses showed that lesion lengths produced by isolates on pairs of lines were significantly correlated. This indicates that the relative virulence of an isolate was similar on all lines and the relative resistance of lines was similar for each isolate. It is concluded that field tests in which canola lines are exposed to natural inoculum of the fungus will generally provide reliable information on the resistance of the plant to naturally occurring populations of the fungus across a wider range of locations.

The development of preemergent and early emergent stages of soybean (Glycine max) and garden pea (Pisum sativum) root nodules has been studied utilizing the superior preservation and resolution obtained by noncoagulative fixatives and subsequent embedding in plastic. In both species, extensive mitotic activity and cytological changes occur in the root cortical cells while the infection thread is restricted to the infected root hair cell. In soybean the central mass of infected tissue is derived mainly from the outer layer of cortical cells whereas the inner cortical cells contribute extensively to the infected tissue of the pea nodules. The temporal and spatial patterns of mitosis differ in the nodules of the two species. Mitotic activity is restricted to a nodule meristem and occurs over a period of many weeks in pea nodules. In soybean nodules, mitotic activity occurs throughout the central zone and before decreasing, persists over a period of a few weeks. The timing and distribution of mitotic activity affects nodule morphogenesis.