Polygenic Heritability of Rose Root Rot Disease Resistance in Offspring of Rosa multiflora.

Rose root rot disease caused by Pythium helicoides Dreehsler has brought heavy damage to cut rose production in Japan, and il has became apparent that Rosa mullijlora showed resistance to this disease. Hoses have been bred by interspecies crossing with Rosa species including of R. mullijlora, and many progenies of R. mullijlora have been bred as determined cluster-flowered roses. However, the genetic architecture of this resistance remains. So, in this study, four kinds of R. mullijlora and 21 rose cultivars that have been clarified in the cross-fertilization genealogy with R. mullijlora were used as plant materials, and ihe inheritability of resistance to root rot disease was investigated. Four kinds of R. mullijlora had all high resistance, and ihe resistance to root rot disease in R. mullijlora was inherent eliaraeteristic of species. Five varieties not less tlian 50% in relatedness with R. mullijlora were shown as varied ' resistant' and 'moderately resistant. Therefore, ihe inherent resistant characteristic in R. mullijlora was not controlled by single major gene, and ihe resislibility in R. mullijlora was not cytoplasmic but nuclear heredity. Although there was significant neUive relation between relative root rot severity and relatedness with R. mullijlora, the variance of relative root rot severity had tendency to expand as relatedness with R. mullijlora reduced. This result, therefore, indicated that the contingency of resistance expression increased as the relaledness with R. mullijlora was reduced. The varieties having low degree of relaledness with R. mullijlora had similar relative root rot severity with R. mullijlora. These results indicated llial we would be able to select resistant roses from progenies crossed with R. mullijlora. [ABSTRACT FROM AUTHOR]