Use of reciprocal grafts to elucidate mode of resistance to Colorado potato beetle (Leptinotarsa decemlineata (Say)) and potato aphid (Macrosiphum euphorbiae (Thomas)) in six wild Solanum species

Reciprocal grafts were done between potato (Solanum tuberosum) and six wild Solanum species known to be resistant to the Colorado potato beetle (Leptinotarsa decemlineata (Say)). Potato or wild Solanum foliage from each reciprocal graft was fed to first instar beetles or adult potato aphids (Macrosiphum euphorbiae (Thomas)). The proportion of second instar larvae after 48 h and survival and fecundity (number of nymphs per female) of the aphids were used to estimate the resistance level of the foliage. Survival and fecundity of potato aphid were reduced on wild Solanum foliage (except with S. circaeifolium ssp. capsicibaccatum and S. okadae) used as scion or rootstock, but were not different from the control (potato-potato graft) on potato foliage. Development of Colorado potato beetle on Solanum foliage was reduced. In some cases, potato foliage grafted to wild Solanum became resistant to the beetle. Results suggest that a chemical factor or factors providing resistance to Colorado potato beetle are translocated from foliage of some wild Solanum species to potato foliage. They also indicate that mode of resistance to the two insects differs quantitatively orqualitatively.