Selection of Salicylic Acid Tolerant Epilines in Brassica napus

Two of the major pathways involved in induced defense of plants against pathogens include the salicylic acid (SA)- and jasmonic acid (JA)-mediated pathways that act mainly against biotrophs and necrotrophs, respectively. However, some necrotrophic pathogens, such as Botrytis cinerea, actively induce the SA pathway, resulting in cell death that allows the pathogen to proliferate in the plant. Starting from an isogenic canola (Brassica napus) line, epilines were selected with a reduced sensitivity to SA. The genes belonging to the SA pathway had an altered transcription profile in the SA-tolerant lines, when treated with SA. Besides the already known genes of the SA pathway, new SA target genes were identified, creating possibilities to better understand the plant defense mechanism against pathogens. The SA-tolerant line with the lowest SA-induced gene expression is tolerant to Botrytis cinerea. When treated with SA, this line has also a reduced histone modification (histone H3 lysine 4 trimethylation) at the genes at the start of the SA pathway.

The Dual Role of the Potyvirus P3 Protein of Turnip mosaic virus as a Symptom and Avirulence Determinant in Brassicas

Two isolates of the potyvirus Turnip mosaic virus (TuMV), UK 1 and CDN 1, differ both in their general symptoms on the susceptible propagation host Brassica juncea and in their ability to infect B. napus lines possessing a variety of dominant resistance genes. The isolate CDN 1 produces a more extreme mosaic in infected brassica leaves than UK 1 and is able to overcome the resistance genes TuRB01, TuRB04, and TuRB05. The resistance gene TuRB03, in the B. napus line 22S, is effective against CDN 1 but not UK 1. The nucleic acid sequences of the UK 1 and CDN 1 isolates were 90% identical. The C-terminal half of the P3 protein was identified as being responsible for the differences in symptoms in B. juncea. A single amino acid in the P3 protein was found to be the avirulence determinant for TuRB03. Previous work already has identified the P3 as an avirulence determinant for TuRB04. Our results increase the understanding of the basis of plant-virus recognition, show the importance of the potyviral P3 gene as a symptom determinant, and provide a role in planta for the poorly understood P3 protein in a normal infection cycle.

Pod shatter resistance in the resynthesized Brassica napus line DK142

Resistance to pod shatter was studied within and between populations of the resynthesized Brassica napus line DK142, grown under glass or in the field, at sites in the UK and Belgium. All populations showed similar ranges of resistance that were greater than that of a commercial cultivar (Apex). The increase in range was at least three-fold greater than the range found in Apex. Only sowing time affected the descriptive statistics of shatter resistance of each line, with spring-sown populations more shatter susceptible than winter-sown populations. The partitioning of dry matter to individual tissues of the pod was different for the two lines, with dry matter biased to the seed in Apex and to the receptacle in the more resistant DK142. In DK142 and Apex, as well as F1 and F2 populations derived from crosses between DK142×Apex, correlations for pod shatter resistance and mature pod characters were high, particularly the weight and length of the valves and septum. Shatter resistance increased in plants when pod numbers were reduced by the removal of whole racemes.