Geographic distribution of insect resistance in potatoes

Potato germplasm accessions representing 92 Solanum species and associated with known coordinates of latitude, longitude, and elevation were rated for resistance to one or more of the following potato insect pests: green peach aphid, Myzus persicae (Sulzer); potato aphid, Macrosiphum euphorbiae (Thomas); Colorado potato beetle, Leptinotarsa decemlineata (Say); potato flea beetle, Epitrix cucumeris (Harris); and potato leafhopper, Empoasca fabae (Harris), in Minnesota field trials (1966-1986). Chi-square tests were used to determine if the proportion of resistant accessions differed from expected among altitude classes, small geographic quadrants (4 degrees latitude by 4 degrees longitude), and larger geographic regions (Mexico-USA, Colombia-Ecuador, Peru, Bolivia, and Argentina). Resistant potatoes were not evenly distributed throughout North and South America. Fourteen quadrants were identified that had greater or fewer resistant accessions than expected. The Mexico-USA potatoes as a group had more resistance than expected to all insects except Colorado potato beetle. Potatoes from Colombia and Ecuador were less resistant than expected to all but green peach aphid. Potatoes from Peru were more resistant than expected to green peach aphid. Potatoes from Bolivia were less resistant than expected to potato aphid, but more resistant than expected to Colorado potato beetle, potato flea beetle, and potato leafhopper. Potatoes from Argentina were more resistant than expected to Colorado potato beetle and green peach aphid, but less resistant than expected to potato aphid and potato leafhopper. Potatoes from North America and collected at or below 2,500 m were more resistant than expected to green peach aphid, Colorado potato beetle and potato flea beetle. Potatoes from South America and elevations greater than 3,000 m were more resistant than expected to green peach aphid and potato aphid and those collected at or below 3,000 m were more resistant than expected to Colorado potato beetle, potato flea beetle and potato leafhopper.