Regional variation in Brassica nigra and other weedy crucifers for diseasereaction to Alternaria brassicicola and Xanthomonas campestris pv. campestris

For Brassica crop breeders, weedy crucifers are potential sources of diseas e resistance and other useful traits. However, few species have been evalua ted or are well represented in germplasm collections. In this study, we eva luated 24 Eurasian crucifer species for disease reaction to North American isolates of the crop pathogens A. brassicicola and X. campestris pv. campes tris. The test array comprised 190 entries (genebank accessions and weed po pulations), including 108 B. nigra entries from four geographic regions and 34 entries of Camelina sativa. Disease reaction was highly variable betwee n species and within some species. Reaction to A. brassicicola was variable between entries of C. sativa, a species reported as highly resistant to Al ternaria pathogens. In B. nigra, disease reaction was variable between geog raphic regions and between entries within some regions. Most of the B. nigr a entries rated as disease resistant were weed populations from North Ameri ca, but disease reaction was not related to the geographic distance between these populations. In summary, disease reaction to two crop pathogens was variable in crucifer weed taxa, including species considered to contain lit tle genetic variation. We identified entries with promising levels of disea se resistance and highlighted the potential value of weedy crucifer genetic resources.