Resistance of apple and pear rootstocks to <i>Neonectria ditissima</i> and their effect on scion susceptibility
The susceptibility of apple and pear rootstocks to European canker (Neonectria ditissima), and the effect of rootstocks on scion susceptibility are largely unknown. Bioassays were conducted to determine the susceptibility to European canker of selected apple and pear rootstocks, and â€˜Royal Galaâ€™ scions bench-grafted onto four apple rootstocks. Trials were conducted using potted trees in a glasshouse in Havelock North and eld-planted trees in Motueka. Significant differences in susceptibility were observed among rootstocks, but the â€˜Royal Galaâ€™ scions were significantly more susceptible than the rootstocks. Accessions were exposed to a harsher test in the glasshouse, so fewer rootstocks were classified as â€œresistantâ€. Nevertheless, rootstocks â€˜M116â€™, â€˜MM106â€™ and â€˜Quince Câ€™ showed high rates of resistance in both locations. Rootstock effects on the susceptibility of â€˜Royal Galaâ€™ were observed in the field but not in potted trees. In further testing using â€˜Royal Galaâ€™ and â€˜Golden Deliciousâ€™ grafted onto four rootstocks, the rootstock choice affected â€˜Royal Galaâ€™ susceptibility but not â€˜Golden Deliciousâ€™.