G. L. Teetes

Molecular analysis of sorghum resistance to the greenbug (Homoptera: Aphididae).

Abstract Chromosomal regions of sorghum, Sorghum bicolor (L.) Moench, conferring resistance to greenbug, Schizaphis graminum (Rondani), biotypes C, E, I, and K from four resistance sources were evaluated by restriction fragment-length polymorphism (RFLP) analysis. At least nine loci, dispersed on eight linkage groups, were implicated in affecting sorghum resistance to greenbug. The nine loci were named according to the genus of the host plant (Sorghum) and greenbug (Schizaphis graminum). Most resistance loci were additive or incompletely dominant. Several digenic interactions were identified, and in each case, these nonadditive interactions accounted for a greater portion of the resistance phenotype than did independently acting loci. One locus in three of the four sorghum crosses appeared responsible for a large portion of resistance to greenbug biotypes C and E. None of the loci identified were effective against all biotypes studied. Correspondingly, the RFLP results indicated resistance from disparate sorghums may be a consequence of allelic variation at particular loci. To prove this, it will be necessary to fine map and clone genes for resistance to greenbug from various sorghum sources.

Photoperiod and temperature as factors controlling the diapause of the sunflower moth, Homoeosoma electellum☆

Abstract Induction of larval diapause of the sunflower moth, Homoeosoma electellum (Hulst), was found to be dependent upon both temperature and photoperiod. Diapause was induced more readily at 21 than at 27°C, but only in photoperiods having 11 hr or less of light/day. Greatest percentages of diapausing larvae occurred among larvae subjected to 10 hr or less light time/day at 21°C, regardless of the photoperiodic exposure of the parents and eggs. The incidence of diapause was extremely low when larvae were subjected to periodic reductions in either temperature or day-length. A concomitant reduction of temperature and day-length increased the percentage of diapausing larvae to some degree, but this was small compared to percentages obtained among larvae maintained in days of 11 hr or less at 21°C. Diapause termination may be influenced by temperature and photoperiod. Diapause termination required less time at 27° than 21°C. Also, larvae which were subjected to photoperiods having 11 hr or more light/day resumed development more rapidly than larvae held in shorter light periods.