Abstract
Heavy losses by dark leaf spot disease in oilseed Brassica have incited research towards identifying sources of genetic tolerance against causal pathogen, Alternaria brassicicola. Several morpho-molecular parameters were evaluated to test the performance of field mustard and rapeseed genotypes under artificial inoculation with this pathogen. During Brassica-Alternaria interaction, physio-biochemical defense response was witnessed in tolerant genotypes. Two tolerant genotypes (one for field mustard and one for rapeseed), i.e., EC250407 and EC1494 were identified. However, necrotic lesions were more prominent in susceptible genotypes with minimum chlorophyll (chlorophyll a, chlorophyll b and total chlorophyll) and carotenoids contents. Contrary to photosynthetic pigments, increase in total soluble protein (TSP) contents was observed with disease progression in susceptible genotypes. Tolerant genotypes of field mustard and rapeseed displayed remarkable increase in the activities of redox enzyme in infected leaves with least yield loss (6.47% and 5.74%) and disease severity index (DSI) of 2.9 and 2.1, respectively. However, yield/plant showed close association with other morpho-yield parameters, photosynthetic pigments and redox enzymes (superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) activities except silique length and TSP. Based on the results of morpho-biochemical analyses, redox enzymes and morphological parameters; their interplay is proposed to determine the tolerance outcome of the Brassica-A. brassicicola interaction.
Highlights
Brassica (Brassica napus, B. juncea and B. rapa) ranks second among oilseed crops after soybean [1]
Most prominent symptoms were observed in highly susceptible genotype EC1333 (Fig 2), the highest disease severity index (DSI) was observed in EC1333 (9.5) followed by EC24181 (5) and least in genotypes EC250407 and EC1494 (2.9 and 2.1)
Our results showed that CAT activity was higher and more obvious in tolerant genotypes as compared to susceptible genotypes depicting the role of CAT in tolerance mechanism; as reported by Meena et al [17] and Debona et al [50]
Summary
Brassica (Brassica napus, B. juncea and B. rapa) ranks second among oilseed crops after soybean [1]. The genus Brassica consists of members rich in nutritional and economical values [2]. In spite of substantial crop production in oilseed Brassica, immense inconsistency remains between actual and potential yield due to exposure to various stresses (biotic/abiotic) [3]. Alternaria fungi are well-known among biotic stresses for their damaging behavior [4].
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