High level resistance to Pseudocercosporella capsellae offers new opportunities to deploy host resistance to effectively manage white leaf spot disease across major cruciferous crops

Field and controlled environment studies were undertaken to define the range and extent of available host resistances to Pseudocercosporella capsellae (white leaf spot) across diverse oilseed, forage and vegetable crucifers, including some wild and/or weedy species, and also within and/or derived from Brassica carinata. In each experiment, there was a wide range in host response from high resistance to high susceptibility as assessed by four disease parameters, viz. in the field for: (i) Area Under Disease Progress Curve (AUDPC) for percent leaves diseased with values ranging from 0 to 375.5; (ii) Percent Leaf Collapse Index (%LCI) for leaf collapse due to disease with values ranging from 0 to 23.0; and (iii), Percent Pod Area Disease Index (%PADI) for pod area affected with values ranging from 0 to 52.1; and (iv) under controlled environmental conditions for Percent Cotyledon Disease Index (%CDI) for cotyledon lesion size with values ranging from 0 to 27.5. At the Crawley field site, B. carinata ATC 94129 was the most resistant genotype with AUDPC = 1.2, followed by Crambe abyssinica (AUDPC 8.7), Eruca sativa Eruc-01 (AUDPC 19.3) and E. vesicaria Yellow rocket (AUDPC 19.4). B. carinata ATC 94129 and B. oleracea var. capitata had the least leaf collapse, with %LCI = 0.2. At the Shenton Park field site, 21 genotypes of B. carinata and B. oleracea var. acephala Tuscan kale showed total resistance, all with AUDPC values of 0. Of the B. napus genotypes carrying one or more B. carinata B genome introgressions, genotypes NC8 (AUDPC 23.0) and NC9-1 (AUDPC 26.2) were the most resistant. Genotypes as assessed on these disease criteria as having high level resistance generally showed no pod infection; in contrast to %PADI values up to 52 on the most susceptible genotypes. Under controlled environmental conditions, the most resistant genotype was B. carinata ATC 94129 with %CDI values of 0 and 0.2, respectively, across two experiments, along with B. napus genotypes Zhongyou 821 and Hyola 42, with a %CDI value of 0 in one of the two experiments. There was a high degree of correlation both within individual experiments across the different disease parameters and also between field and controlled environment experiments. Within both B. napus and B. juncea genotypes tested, the most resistant genotypes were from China, the most susceptible from India, with those from Australia intermediate.