FIELD-EVALUATION OF SEED, POD, AND STEM ROT IN WHITE LUPINE GERM PLASM

Disease symptoms were evaluated on 92 accessions of white lupine (Lupi nus albus) grown in replicated field trials in Quebec, New Brunswick, and Nova Scotia. Pod, stem, and seed rot symptoms caused by Phoma sp. were more severe at the Maritime sites than at the Quebec site. At all sites, there were significant differences among accessions. Pod lesio ns were more severe on early-maturing than on late-maturing accessions . Pod lesion ratings taken in the field were not correlated with sever ity of discoloration on harvested seed. Accession means for ratings of seed discoloration from each site were positively correlated with tho se from the other sites, with more similarity between the two Maritime sites than between the Quebec and Maritime sites. The incidence of in fection with Phoma sp. and Pleiochaeta setosa was evaluated on random samples of seed for a subset of nine accessions. Phoma sp. was common in both regions, whereas P. setosa was common in the Maritime region b ut rare in Quebec. Among these nine accessions pooled over all sites, there was no significant correlation between the incidence of infectio n by the two pathogens and severity of seed discoloration, even though inoculation with Phoma sp. at the Quebec site appeared to induce more seed discoloration. At the Quebec site, however, 80% of the samples t hat had low levels of seed discoloration also had low levels of Phoma infection. Thus, it may be possible to use seed discoloration to scree n white lupine germ plasm for resistance to Phoma sp. and other seedbo rne pathogens, at least in environments where conditions do not favor colonization of pods and seeds by other saprophytes that may discolor seeds. Severity of pod symptoms may reflect the physiological age of t he plant at the time of assessment rather than genetic resistance and may not be as useful as seed discoloration in evalution of resistance in the field.