Hairy nightshade undermines resistance of potato breeding lines to Columbia root-knot nematode

Columbia root-knot nematode, Meloidogyne chitwoodi, is a major pest of potato in the Pacific Northwest of the USA and is controlled by costly soil fumigation. Potato breeding lines have been developed with resistance to the predominant race 1 (CRKN-1) of M. chitwoodi. Hairy nightshade, Solanum sarrachoides, is a common weed in potato production in the western USA and a host of CRKN-1. Greenhouse and field studies were conducted with two potato lines with known CRKN-1 resistance (PA95B4-67 and PA99N82-4) and a CRKN-1 susceptible potato cultivar, Russet Burbank. Very little or no CRKN-1 reproduction took place in roots of both resistant breeding lines, and only minor tuber infection occurred when grown in the absence of hairy nightshade. However, when resistant lines were grown in the presence of hairy nightshade, some PA95B4-67 tubers were infected, whereas PA99N82-4 expressed tuber resistance. Hairy nightshade grown with potato maintained CRKN-1 populations prior to potato tuber set, allowing nematodes to infect developing tubers lacking resistance. PA99N82-4 grown in the presence of CRKN-1 and hairy nightshade produced tubers free of CRKN-1 damage, indicating both root and tuber resistance to CRKN-1. Russet Burbank tubers were damaged by CRKN-1 regardless of hairy nightshade presence. These results demonstrate how weed hosts of CRKN-1 may negate the positive impact of growing CRKN-1 resistant potatoes that lack tuber resistance, and the importance of weed control on managing plant parasitic nematode populations.