Pyramiding of alleles with different rust resistance specificities in Linum usitatissimum L.

Abstract

Transgenic flax plants expressing flax rust resistance specificities conferred by L2 and L10 alleles of L locus were produced through Agrobacterium tumefaciens-mediated transformation of hypocotyl segments or anther culture derived-calli. Transgenic plants were characterized by PCR amplification and Southern hybridization. Homozygous transgenic lines containing a single locus of effective transgene were isolated by consecutive progeny analyses of transgenic plants. In addition, homozygous lines were directly obtained from transformation of haploid cells followed by spontaneous or artificial chromosome doubling when anther culture derived-calli were used as the explants. All transgenic plants containing L2 transgene expressed L2 flax rust resistance specificity and had unambiguous infection type (IT) “0” (immune) reactions to flax rust race 22, which is virulent to endogenous L6 and K1 genes present in the untransformed Linola™1084. Transgenic plants containing L10 transgene exhibited various levels of resistance to flax rust race 191. Five plants had IT “fleck” (immune) reactions, similar to the reactions with the L10 rust differential line, Bolley Golden Selection. The enhanced resistance to rust race 191 in these transgenic plants was attributed to the expression of L10 rust resistance specificity. Further evaluation of the transgenic plants containing L2 or L10 transgene to flax rust race 258 and race 247 respectively showed that the endogenous rust resistance specificities were not modified. The implication of this study in producing transgenic flax plants with multiple resistance specificities and for crop improvement using molecular breeding strategy is discussed.