Transgenic carrots expressing a thaumatin-like protein display enhanced resistance to several fungal pathogens

Abstract

Two transgenic carrot lines (T-33 and T-47) were developed through Agrobacterium-mediated transformation. Both lines constitutively expressed a rice thaumatin-like protein and the phosphinothricin acetyltransferase protein for herbicide resistance, used as a selectable marker. Both lines were propagated in tissue culture and transferred to soil and maintained under growth-chamber conditions. Detached leaves of the transgenic lines and nontransformed 'Nanco' were inoculated in vitro with eight different fungal pathogens, and the extent of leaf necrosis was assessed. The two transgenic lines both had significantly lower disease (P ≤ 0.05) when compared with the nontransformed 'Nanco' for select pathogens. Line T-33 had significantly lower leaf necrosis when inoculated with Alternaria dauci, Alternaria petroselini, Alternaria radicini, Botrytis cinerea, Rhizoctonia solani, and Sclerotinia sclerotiorum. Line T-47 had significantly lower disease when inoculated with A. dauci, A. radicini, B. cinerea, Sclerotium rolfsii, and Sclerotinia sclerotiorum. The detached leaf method was a rigorous approach for assessing the transgenic carrot lines for resistance to fungal infection. The enhanced resistance observed in this study to fungal pathogens as a consequence of expression of a thaumatin-like protein in carrot tissues is the first to demonstrate efficacy against six different pathogens.