An application of DNA diagnosis method for preservation of the susceptible strain to densonucleosis virus type-1 of the silkworm, Bombyx mori.

Abstract

The nonsusceptibility (complete resistance) to Bombyx mori densonucleosis virus type-1 (BmDNV-1) of the silkworm is controlled by a recessive gene, nsd-1, in the 21st linkage group. The +nsd-1is a dominant DNV-1 susceptibility gene. We constructed the CSD-1 strain, congenic strain of the C137 (nsd-1/nsd-1) for the 21st linkage group, starting with a female of the C137 and a male of the J137 ( +nsd-1+nsd-1). Since crossing over is restricted to males in the silkworm, the CSD-1 strain is maintained by repeated backcrossing of the males of C137 to the nsd-1/ + females. CSD-1 strain contains susceptible (nsd-1/ + ) and nonsusceptible (nsd-1 /nsd-1) larvae at a 1 : 1 ratio. Some random amplified polymorphic DNAs (RAPDs) in the 21st linkage group of the J137 have been found previously. In order to develop the diagnosis method for the susceptibility of the CSD-1 larvae without virus inoculation and killing, we used these RAPD markers. DNAs extracted from the abdominal legs of 4th instar larvae after ligation, or legs of moths, were individually used as templates for polymerase chain reaction (PCR). We could distinguish the susceptible individuals from the nonsusceptible ones. This diagnosis method is useful for detecting the DNV-1 susceptible individuals without virus inoculation and for obtaining the next generation of diagnosed ones. © 1996, The Japanese Society of Sericultural Science. All rights reserved.