Linkage analysis of a dominant resistance gene to the entomopathogenic fungus Beauveria brongniartii in the silkworm, Bombyx mori

Abstract

Resistance to the entomopathogenic fungus Beauveria brongniartii (Sacc.) is controlled by a dominant gene in the silkworm, Bombyx mori (Linnaeus) (Lepidoptera: Bombycidae). We determined the linkage group by which the resistance gene links through linkage analysis with the linkage map of the silkworm based on single nucleotide polymorphisms (SNPs). Taking advantage of the lack of crossing over in females of the silkworm, backcrossed F₁ progenies (BC₁) made by crossing an F₁ female (susceptibility-developed strain AkakoS×resistance-developed strain p50TR) and a male AkakoS were used. The resistant BC₁ individuals were selected by screening of injection with conidial suspension of B. brongniartii. We selected SNP markers that were able to distinguish the genotypes of AkakoS and p50TR on each of the 28 linkage groups and analyzed the genotypes of the resistant BC₁ individuals on each linkage group with the SNP markers. There are two genotypes in BC₁, homo (AkakoS) type and hetero (F₁) type, but only hetero type BC₁ individuals can be resistant to B. brongniartii on the linkage group to which the resistance gene links. All resistant BC₁ individuals showed hetero type only at the 14th linkage group, suggesting that the resistance gene of the silkworm to B. brongniartii exists on the 14th linkage group. We designated this gene as “resistant to B. brongniartii” with the abbreviation Rbbr.