Histological and inheritance studies of partial resistance in the Brassica napus–Albugo candida host‐pathogen interaction

Abstract

Traditional and doubled haploid (DH) genotypes of oilseed Brassica spp. resistant, partially resistant, moderately susceptible, and susceptible to Albugo candida were compared for phenotypic development of host-pathogen interaction and histology of host-pathogen interaction. The partially resistant genotype showed pinhead-size pustules, mainly on the upper surface of cotyledonary leaves. Relatively less mycelium was observed in the partially resistant genotype compared with the susceptible genotype. In resistant B. napus genotypes, there was neither pustule development nor any mycelial growth. In the moderately susceptible genotype, the pustules were similar to those in the partially resistant genotype in being of pinhead-size and occasionally coalescing. However, ample mycelial growth in the mesophyll tissue in the moderately susceptible genotype was similar to that in the susceptible control B. rapa cv. ÔTorchÕ. The susceptible genotype B. rapa cv. ÔTorchÕ also showed large coalescing pustules. In the non-host B. juncea cv. ÔCommercial BrownÕ, no pustules were formed although some mycelial growth was observed beneath the epidermal cell layer and in the mesophyll cell layer of the cotyledonary leaf tissue. For inheritance studies, two partially resistant B. napus genotypes were crossed with a resistant B. napus genotype. Various generations viz., F 1 , F 1(reciprocal) , F 2 , and DHs produced from the crosses were inoculated with a zoospore suspension of race 7v of A. candida. The partially resistant phenotype appeared to be controlled by a single recessive gene designated as wpr with variable expression. The simple inheritance of partial resistance has implications for disease resistance breeding against white rust, as this type of resistance can be easily incorporated into elite breeding lines through conventional and DH breeding methods.

Diseases of Edible Oilseed Crops

“…Under controlled conditions, inoculation with three different races of A. candida on F2 population of crosses from resistant × resistant revealed that the resistant genes may be located on the same locus or on different loci. Partial resistance in B. napus to A. candida was controlled by a single recessive gene designated as wpr with a variable expression (Bansal et al 2005). White rust resistance in B. juncea (Somers et al 2002, Manjunath et al 2007) and avirulence in race AC 2 of A. candida to B. rapa cv.…”