Transgenic approaches to enhance disease resistance in carrot plants to fungal pathogens

Diseases caused by fungi and bacteria are among the most important constraints to carrot production worldwide. These disease afflict the carrots not only during the growing season but also during postharvest storage. In this study, transgenic expression of antifungal genes was investigated to enhance tolerance in carrots to two necrotrophic fungi - Botrytis cinerea and Sclerotinia sclerotiorum. Promoters were evaluated for suitable transgene expression in carrot tissues. The Arabidopsis ubiquitin promoter and Cauliflower mosaic virus 35S promoter showed high-level p-glucuronidase (uidA) gene expression in root tips, leaves and tap roots. Using an Agrobacterium-mediated transformation system, a thaumatin-like protein, chitinase, glucanase and peroxidase genes were expressed in carrot tissues. Transgene expression was confirmed by PCR and by protein expression analysis. Leaf tissues were challenged with the fungal pathogens in vitro. The most significant reduction was observed in the peroxidase-expressing lines, with 75-90% disease reduction. One chitinase-expressing line and 2 TLP-expressing lines had a 15-50% reduction in disease but no glucanase-expressing lines showed significant disease reduction. This is the first report of peroxidase over-expression leading to a significant reduction in disease caused by necrotrophic fungal pathogens.