Browsing by Subject "biotic stress"

Plants have evolved mechanisms to cope with various environmental stresses, including abiotic factors like temperature extremes and biotic factors involving the interactions with pathogens and herbivores. Kale (Brassica oleracea var. acephala) is a superfood famous for containing many compounds that are beneficial in the human diet but are primarily produced as specialised metabolites to aid in plant defence. Amongst these are glucosinolates which are defence compounds characteristic of plants in the Brassicaceae family. The aim of this study was to investigate how the diverse metabolic profiles of kale cultivars contribute to postharvest resistance against herbivory and necrotrophy. To assess the resistance of each kale cultivar against herbivory, I used the larvae of the wood tiger moth Arctia plantaginis as a test subject. We used detached leaves from 30 kale cultivars in an overnight feeding experiment with the larvae. The same 30 cultivars were used in a postharvest infection experiment with a generalist necrotroph B. cinerea to investigate the resistance of each kale cultivar against necrotrophy. For a comparative experiment between necrotrophs, we selected 10 kale cultivars to assess the necrosis caused by B. cinerea and a specialist necrotroph A. brassicicola. The A. brassicicola-infected and mock-treated leaves were analysed for their metabolic profiles to observe how these were altered by the infection. The weight gain of the tiger moth larvae was not significantly affected by the kale cultivars or their sugar content. A correlation between sucrose and indole glucosinolates might have reduced the kales’ palatability and potentially deterred the herbivores. In the B. cinerea experiment, we observed a positive correlation between necrotic lesion area and protein, sucrose, and indole GSL contents in kale leaves, even though indole GSLs are generally considered defence molecules against necrotrophic pathogens. When comparing the necrotic damage caused by the two necrotrophs, the specialist A. brassicicola exhibited a statistically significantly more violent infection compared to B. cinerea. Chlorophyll became degraded in the infected leaves compared to the uninfected controls. Amino acid content was high in the aged control and infected leaves, indicating protein degradation either due to senescence or cell wall-degrading enzymes from the pathogen. There was a statistically significant positive correlation between necrotic damage and protein in the infected leaves potentially due to proteins being secreted by the pathogen during infection. Starch levels decreased in the infected leaves compared to the controls. The infected samples also showed decreased glucose amounts potentially being taken up by the necrotroph during infection. Altogether, the study showed that kale cultivars respond to biotic stress factors by triggering metabolic changes that can affect the disease resistance and postharvest quality of the leafy vegetables.