Sources of Aphid Resistance Mechanisms From the Tuber-Bearing Solanum Germplasm.

Aphids have been a major pest problem to the potato industry for a long time. Potential resistance donors have so far not been identified in the cultivated germplasm. We conducted a survey of the exotic tuber-bearing Solanum germplasm based on possible indicator parameters including known resistance to other insects or pathogens. Our ultimate goal is to develop aphid-resistant donor lines of Solanum tuberosum with resistance genes from exotic species for use in potato breeding. Our survey revealed that Solanum bulbocastanum is highly resistant to both potato (Macrosiphum euphorbiae) and green peach aphids (Myzus persicae) based on aphid survival and aphid reproduction on the host plant and physiological condition of the plant after a period of infestation. Resistance within this species appeared to involve either inducible defenses (Acc. 243510) or avoidance mechanisms (Acc. 283096). Inducible resistance was characterized by the high aphid survival in the first 24 hours while very low aphid reproduction occurs followed by death of the aphids, while avoidance was indicated by immediate death of the aphid within 24 hours and withdrawal from the host plants indicating that the plant was unpalatable to the aphid. Screening of a backcross population (BC₄ to BC₅) of the original S. bulbocastanum (Acc. 243510) x S. tuberosum (Katahdin) somatic hybrid with various potato cultivars identified a number of resistant introgression lines exhibiting inducible defenses. These lines are currently being characterized molecularly by candidate gene approach involving genes functioning in defense signaling as well as by global transcriptome survey via cDNA subtraction.