Abstract
Brassica juncea is a major oilseed crop in tropical and subtropical countries, especially in south-east Asia like India, China, Bangladesh, and Pakistan. The widespread cultivation of genetically similar varieties tends to attract fungal pathogens which cause heavy yield losses in the absence of resistant sources. The conventional disease management techniques are often expensive, have limited efficacy, and cause additional harm to the environment. A substantial approach is to identify and use of resistance sources within the Brassica hosts and other non-hosts to ensure sustainable oilseed crop production. In the present review, we discuss six major fungal pathogens of B. juncea: Sclerotinia stem rot (Sclerotinia sclerotiorum), Alternaria blight (Alternaria brassicae), White rust (Albugo candida), Downy mildew (Hyaloperonospora parasitica), Powdery mildew (Erysiphe cruciferarum), and Blackleg (Leptoshaeria maculans). From discussing studies on pathogen prevalence in B. juncea, the review then focuses on highlighting the resistance sources and quantitative trait loci/gene identified so far from Brassicaceae and non-filial sources against these fungal pathogens. The problems in the identification of resistance sources for B. juncea concerning genome complexity in host subpopulation and pathotypes were addressed. Emphasis has been laid on more elaborate and coordinated research to identify and deploy R genes, robust techniques, and research materials. Examples of fully characterized genes conferring resistance have been discussed that can be transformed into B. juncea using advanced genomics tools. Lastly, effective strategies for B. juncea improvement through introgression of novel R genes, development of pre-breeding resistant lines, characterization of pathotypes, and defense-related secondary metabolites have been provided suggesting the plan for the development of resistant B. juncea.
Highlights
The Brassicaceae family has about 3709 species and 338 genera, displaying enormous diversity and used as a source of oil, vegetables, mustard condiments, and fodder (Warwick et al, 2006)
It is presumed that this species originated approximately 0.039-0.055 million years ago (Yang et al, 2016) and the present B. juncea species evolved through chromosomal triplications and other re-arrangements (Lysak et al, 2005)
The identification and introgression of resistant gene sources into B. juncea against major fungal pathogens is a difficult procedure owing to the close association of R genes with other agronomic traits, variations in host resistance-response against pathogenic races, the polygenic inheritance of resistance, and gene interactions
Summary
The Brassicaceae family has about 3709 species and 338 genera, displaying enormous diversity and used as a source of oil, vegetables, mustard condiments, and fodder (Warwick et al, 2006). The major biotic diseases and pathogens of mustard that cause a serious threat to B. juncea worldwide are Alternaria blight [Alternaria brassicae (Berk.) Sacc.; A. brassicicola (Schwein.) Wiltshire; A. raphani Groves & Skolko], Sclerotinia stem rot [Sclerotinia sclerotiorum (Lib.) deBary], White rust [Albugo candida (Pers.) Kunze], Clubroot [Plasmodiophora brassicae Woronin], Powdery mildew [Erysiphe polygoni DC.], Blackleg [Leptosphaeria maculans (Desmaz.) Ces.& De Not.], and Downy mildew [Hyaloperonospora parasitica (Pers.: Fr.) Fr.] (Williams and Saha, 1993) These diseases cause serious damage to mustard production worldwide owing to the lack of vertical and horizontal resistance against pathogens in current cultivating varieties. Phosphatidic acid acts as a signaling molecule by binding to target proteins altering their subcellular localization and enzymatic activity
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