Tall fescue (Festuca arundinacea Schreb.) is an open-pollinated, perennial, cool-season turf and forage grass species of great economic importance. It is a major turfgrass species for home lawns in North Carolina and the transition zone states in the US mostly because of its tolerance to the summer heat. Brown patch disease is the most serious and frequently occurring disease of tall fescue, caused by a basidiomycete fungus, Rhizoctonia solani (Kuhn). Gray leaf spot, induced by Pyricularia grisea (Cooke) Sacc., the asexual stage of Magnaporthe grisea (T.T. Hebert) Yaegashi & Udagawa, is becoming another important disease of tall fescue. The objectives of this research were to establish an efficient transformation system for tall fescue using Agrobacterium; to introduce disease resistance genes into tall fescue; and to study the effects of the transgenes in resistance to the two major fungal diseases.
An efficient genetic transformation system, using Agrobacterium tumefaciens-mediated T-DNA delivery, was developed for tall fescue. Thirty four percent of the calli infected with A. tumefaciens were resistant to hygromycin B, the selection agent used to select/identify transformants, and the overall plant transformation frequency (the number of independently transformed plants over the number of calli infected) was about 8%. Southern analysis indicated the integration of transgenes into the plant nuclear genome and simple transgene copy patterns. The high efficiency observed was partly due to an elevated 2,4-D concentration (5 mg L-1) in the culture medium used during callus culture and co-cultivation. Inheritance studies revealed that the transgenes were transmitted to the progenies.
Four genes with potential for fungal disease resistance, including: alfalfa â-1,3 glucanase AGLU1, T4 phage lysozyme, frog dermaseptin, and rice Pi9 genes, were introduced into two cultivars ?Coronado? and ?Matador? of tall fescue through Agrobacterium-mediated transformation. Of 29 T0 transgenic plants examined, six had a higher level of resistance to R. solani and 13 had enhanced resistance to P. grisea. The enhanced levels of resistance in most of these plants was highly significant. Five transgenic plants exhibited enhanced resistance to both fungal pathogens.
