Analysis of diseases affecting winter and spring forms of Brassica napus L. and Brassica juncea L. in the central zone of the Krasnodar region

The purpose of the research was a comparative evaluation of the disease affection of spring and winter forms of Brassica napus and Brassica juncea on the central zone of the Krasnodar region. Phytosanitary monitoring of diseases was carried out from the seedling stage. In 2011-2020, there were identified the diseases affecting winter and spring crops Brassica napus and Brassica juncea to the same extent: the occurrence frequency of downy mildew and powdery mildew was high, of Alternaria blight – from medium to high, of phytoplasma and bacterial blight – low. Differences are established for Sclerotinia disease, Phoma rot, Fusarium blight, white rust, gray rot. The occurrence frequency of Sclerotinia disease on winter form of Brassica napus and Brassica juncea varied in research years from low to medium, of Phoma rot – from medium to high; on spring forms, these diseases were noted in certain years with the low frequency. Fusarium blight affected only sowings of spring forms of Brassica napus and Brassica juncea with medium and high frequency, except for 2018-2019, when it was low. White rust affected only spring from of Brassica napus, gray rot – only winter forms of Brassica napus and Brassica juncea in certain years with the low frequency.

Adult plant resistance to white rust in Lunaria annua

Wild plants produce abundant seeds and seedlings, but most die before reaching maturity, and these premature deaths are often caused by pathogens. Major genes for resistance protect some seedlings or juveniles. These selected individuals can become a resistant, mature cohort. Alternatively, plants can exhibit mature, adult plant resistance. These two explanations can be indistinguishable in the field, when epidemics in natural pathosystems occur regularly resulting in annual selection for resistance. This study included multi-year observations of a biennial plant where the distinction could be made. White rust of Lunaria annua, a pathosystem native to the Mediterranean Basin, took time in its introduced range in Idaho, USA, to generate epidemics. After years of minimal white rust, an epidemic occurred in 2017 in which first-year, juvenile plants had 20 times the sorus density of second-year, adult plants. Since white rust incidence had been minimal for years prior to 2017, the greater resistance of 2017 adults over 2017 juveniles may have been due to adult-plant resistance. This could also be due to phenology: adult plants have mature leaves, and are flowering and maturing seed, by the time that white rust begins to build up on leaves of juveniles. The juvenile-adult difference was maintained in 2018. In white blister rusts, interpretation of resistance can also be complicated by the frequency of asymptomatic infections that adult plants would pass on to the next generation. However, we found no asymptomatic infection of seeds of L. annua in our sampling of the Idaho population.

Impact on Cluster Frontline Demonstrations on the Productivity of Mustard (Brassica juncea)

Cluster frontline demonstrations (CFLDs) are the long-term educational activity conducted in a logical method on partner farmer’s field to show the worth of new technology under micro farming. The present investigation was carried out during the Rabi season (October to March) of respective year 2016-17 to 2019-20 under the National Food Security Mission, Government of India. Four hundred thirteen CFLDs were conducted in 165.2 ha area with the farmers and scientists of KVK. The CFLDs were conducted at adopted fifteen villages of Dholpur district. Cultivation technology was applied under CFLDs included scientific intervention. The highest yield was obtained in demonstrated practices (DP) with an average of 2272.00 kg ha-1 as compared to farmer practice (FP) with an average of 1829.00 kg ha-1. Further, an average additional return (` 16,063.6), effective gain (` 14,335.8), net return (` 64,512.1 ha-1) and benefit-cos ratio (3.49) were found in the DP as compared to farmer practice. An average occurrence of Alternaria blight, white rust, stem rot, aphid were recorded 27.44, 5.93 and 14.85 and 25.05, respectively showed in DP as compared to farmer practice. An average extension gap, technology gap and technology index between and was noted 443.0 kg ha-1, 234.75 kg ha-1 and 10.39%, respectively. The results indicate that the use of scientific intervention under CFLDs to increase the production and profitability of Mustard.

Deciphering the Molecular Architecture of a Candidate R-gene (BjuWRR1) Product Mediating White Rust Resistance in Brassica juncea

In this investigation, a three-dimensional model of a R-gene encoded product BjuWRR1 which is known to play a role in white rust resistance in Brassica juncea was developed to synthesize innovative ways for evolving white rust resistant cultivars. The model was built from the amino acid sequence of BjuWRR1 using structural template information of a disease resistance protein (RPP13-like protein 4 of Arabidopsis thaliana) with the help of homology-based modelling approach. Built models were validated for their stereochemical parameters and structural descriptors using Ramachandran plot analysis, protein structure analysis and ERRAT analysis. Structural analysis of BjuWRR1 model revealed that it is composed of three distinct domains namely a coiled-coil domain, a central NB-ARC nucleotide binding domain and a hypervariable leucine-rich repeat domain. Further, canonical conserved motifs such as P-loop, Kinase2-motif and HD-motif were found in the NB-ARC domain. The built model would help in understanding the molecular basis of plant-immunity against white rust pathogen by understanding the significance of inter-domain interactions in BuWRR1 in triggering the activation of downstream defense response against the white rust pathogen by promoting oligomerization of coiled-coil domains through stabilized hydrophobic interactions and interaction with NB-ARC domain. Presence of patches of charged residues in each domain of BjuWRR1 indicated their possible role in intra-molecular interaction with other domains. Therefore, this model can help in designing functional genomic studies to understand the role of intra-molecular interaction in BjuWRR1 to mediate resistance against white rust pathogen.

Evolutionary trade-offs at the Arabidopsis WRR4A resistance locus underpin alternate Albugo candida recognition specificities

The oomycete Albugo candida causes white rust of Brassicaceae, including vegetable and oilseed crops, and wild relatives such as Arabidopsis thaliana. Novel White Rust Resistance (WRR)-genes from Arabidopsis enable new insights into plant/parasite co-evolution. WRR4A from Arabidopsis accession Col-0 provides resistance to many but not all white rust races, and encodes a nucleotide-binding (NB), leucine-rich repeat (LRR) (NLR) immune receptor protein. Col-0 WRR4A resistance is broken by a Col-0-virulent isolate of A. candida race 4 (AcEx1). We identified an allele of WRR4A in Arabidopsis accession Oy-0 and other accessions that confers full resistance to AcEx1. WRR4AOy-0 carries a C-terminal extension required for recognition of AcEx1, but reduces recognition of several effectors recognized by the WRR4A_Col-0 allele. WRR4A_Oy-0 confers full resistance to AcEx1 when expressed as a transgene in the oilseed crop Camelina sativa.

The Arabidopsis WRR4A and WRR4B paralogous NLR proteins both confer recognition of multiple Albugo candida effectors

The oomycete Albugo candida causes white blister rust, an important disease of Brassica crops. Distinct races of A. candida are defined by their specificity for infecting different host species. The White Rust Resistance 4 (WRR4) locus in Col-0 accession of Arabidopsis thaliana contains three genes that encode TIR-NLR resistance proteins. The Col-0 alleles of WRR4A and WRR4B confer resistance to at least four A. candida races (2, 7 and 9 from B. juncea, B. rapa and B. oleracea, respectively, and Race 4 from Capsella bursa-pastoris). Resistance mediated by both paralogs can be overcome by Col-0-virulent isolates of Race 4. After comparing repertoires of candidate effectors in resisted and resistance-breaking strains, we used transient co-expression in tobacco or Arabidopsis to identify effectors recognized by WRR4A and WRR4B. A library of CCG effectors from four A. candida races was screened for WRR4A- or WRR4B- dependent elicitation of hypersensitive response (HR). These CCG genes were validated for WRR-dependent HR by bombardment assays in wild type Col-0, wrr4A or wrr4B mutants. Our analysis revealed eight WRR4A-recognized CCGs and four WRR4B-recognized CCGs. Remarkably, the N-terminal region of 100 amino acids after the secretion signal is sufficient for WRR4A recognition of these eight recognized effectors. This multiple recognition capacity potentially explains the broad-spectrum resistance to many A. candida races conferred by WRR4 paralogs.