Powdery mildew of Indian mustard (Brassica juncea), caused by Erysiphe cruciferarum, is emerging as major problem in India. All the Indian mustard cultivars presently grown in India are highly susceptible to powdery mildew and so far no resistance source has been reported. In this study, with an aim to identify resistant source, 1,020 Indian mustard accessions were evaluated against E. cruciferarum PMN isolate, at Wellington, The Nilgiris, Tamil Nadu, India under natural hot spot conditions. The study identified one accession (RDV 29) with complete resistance against E. cruciferarum PMN isolate for the first time, which was consistent in five independent evaluations. Genetic analysis of F₁, F₂ and backcross populations obtained from the cross RSEJ 775 (highly susceptible) × RDV 29 (highly resistant) for two season revealed that the resistance is governed by two genes with semi-dominant and gene dosage effect. Further, a new disease rating system using six scales (0, 1, 2, 3, 4, and 5) has also been proposed in this study to score powdery mildew based on progress of fungal growth in different plant parts of the F₂ population. The outcome of this study viz. newly identified powdery mildew-resistant Indian mustard accession (RDV 29), information on inheritance of resistance and the newly developed disease rating scale will provide the base for development of powdery mildew-resistant cultivars of Indian mustard.

White rust [Albugo candida (Pers. Ex. Lev) Kuntze] is an important oomycetes disease of Indian mustard [Brassica juncea (L.) Czern & Coss] that causes a drastic reduction in seed yield and quality when the conditions are favorable. A set of 25 Indian mustard genotypes were screened against A. candida Delhi isolate (Ac-Dli) under both controlled and natural epiphytotic conditions. Out of 25, only six genotypes (Pusa Karishma, PDZ-3, Heera, BEC-144, BIO YSR, and Donskaja) were found highly resistant in both environments. To study the inheritance of resistance, four resistant genotypes (BEC-144, BIO YSR, Pusa Karishma, and Donskaja) were crossed with three susceptible genotypes (PM-24, Pusa Vijay, and MSTWR-17-15) in a definite design. The parents, F₁, F_2, and BC₁F₁ (F₁ backcrossed with susceptible parent) generations were screened under both artificially controlled and natural epiphytotic conditions and the results indicated that the resistance in BIO YSR, BEC-144, and Pusa Karishma is governed by a single dominant gene, but more than one dominant gene is responsible for resistance in Donskaja. A test of an allelism conducted on the F₂ population derived by crossing resistant (BEC-144) × resistant (BIO YSR) genotypes indicated that the gene imparting resistance to Ac-Dli isolate in the resistant parents BEC-144 and BIO YSR is the same and they are allelic to each other. Therefore, in broader terms, the information generated in the present study will be useful in Indian mustard breeding programs for the development of durable resistant cultivars.

Estimation of genetic diversity had been carried out in a set of 21 germplasm accessions of Indian mustard for high temperature toler-ance trait using SSR markers. These 21 acces-sions were comprised of 11 high temperature tolerant lines, 6 susceptible and 4 checks, which were obtained after screening of 415 accessions of Indian mustard germplasm for high tempera-ture tolerance at seedling stage. Of the 106 SSR markers evaluated, 54 resulted into amplification products of different sizes, of which 19 were found polymorphic with a total of 52 alleles, at an average of 2.74 alleles per locus. The UPGMA dendrogram revealed the presence of high level of genetic diversity among the accessions evalu-ated. The similarity coefficient ranged between 0.32 and 0.90 with a mean value of 0.61. High temperature tolerant accessions identified in this study along with the information on genetic di-versity provide some useful guides for plant breeders in selecting genetically diverse parents for the crossing program to evolve cultivars pos-sessing high temperature tolerance along with high yielding potential than the existing culti-vars.

In rapeseed and mustard, the major diseases (downy mildew, white rust, Alternaria blight and Sclerotinia stem rot) cause 37–47%loss in pod formation and 17–54% reduction in grain yield. The identification of new sources of resistance is a high priority in breeding programs. About 3000 germplasm accessions of Indian mustard were evaluated under multiple environments (3 seasons) at hot spots (4 locations) and under artificial epiphytophic conditions against insect pests and diseases (aphids, white rust, powdery mildew and Alternaria blight). Accessions IC265495, IC313380, EC766091, EC766133, EC766134, EC766192, EC766230, EC766272 were identified as highly resistant to white rust (A. candida) with disease severity reaction (Percent disease severity Index, PDI = 0) under artificial inoculation. Accession RDV 29 showed the inheritance of resistant source for powdery mildew in Indian mustard. Screening of brassica wild relatives (about 25 species) for white rust found that Brassica fruticulosa, Brassica tournefortii, Camelina sativa, Diplotaxis assurgens, D. catholica, D. cretacia, D. Erucoides, D. Muralis, Lepidium sativum had highly resistance (PDI = 0) to Delhi isolates of white rust. Several traits identified from cultivated and related species will be useful for genetic improvement of rapeseed and mustard.