Abstract

Rubus pileatus and its F₁ hybrids with raspberry were resistant to cane blight (L. coniothyrium), but little resistance was obtained in subsequent backcross generations apart from a hybrid identified in the second backcross. Two hybrids from backcrossing R. coreanus to raspberry also showed resistance. R. pileatus and its F₁ hybrids produced hard growth, unlike that of raspberries, which may have been associated with a form of resistance that could not easily be transferred to commercial raspberry cultivars. Some of the genotypes used as parents showed intermediate levels of resistance and it is possible that the highly resistant genotype identified in the second backcross arose from a recombination of genes for resistance. Plants with pubescent canes (gene H) were up to 20% more resistant to mycelial inoculation than those with non-pubescent canes (gene h), and the percentage of machine-harvester inflicted wounds with disease symptoms that resulted from natural infection was also less in genotypes with pubescent canes. Many genotypes with intermediate levels of resistance suffered only limited damage from mycelial inoculation and so there are good prospects for breeding cultivars with an effective resistance, despite the limited value of R. pileatus as a donor species.