SCREENING OF EXOTIC POTATO GERMPLASM FOR NITROGEN UPTAKE AND BIOMASS PRODUCTION

Exotic potato germplasm may contain useful traits for improving nitrog en CN) use efficiency in cultivated potatoes (Solanum tuberosum L.). T he objective of this study was to evaluate a ''mini'' core collection of wild germplasm for biomass production, N uptake, and N use efficien cy. A field study was conducted during the 1993 growing season on a lo amy sand soil at Becker, Minnesota. Uniform transplants for 39 wild ac cessions and 3 varieties were grown under greenhouse conditions, and a fter 40 days, they were transplanted to the field. Plants were subject ed to two N treatments, 0 and 225 kg N ha(-1), replicated three times in a split-plot design. Plant parts were collected separately 111 days after transplanting, dried, weighed, and analyzed for N concentration . Nitrogen rate and potato species had significant effects on total dr y weight, N content, and tissue N concentration. The regression coeffi cient of N concentration on total dry weight was very low (r=0.22, NS) , whereas the regression coefficient of total N content on total dry w eight was high (r=0.94, P<0.001). At both low and high N environments, Russet Burbank had greater dry weight than all the accessions. Severa l wild accessions, especially S. chacoense, S. commersonii, S. kurtzia num, S. microdontum, and S. phureja, had equal to or greater dry weigh ts than Russet Norkotah or Red Norland. For N uptake efficiency, 2, 7, and 20 accessions were ranked better than Russet Burbank, Russet Nork otah, and Red Norland, respectively. Recovery of soil applied N by the varieties ranged from 16 to 36%; the top seven wild accessions recove red between 27 and 49%. Based on plant growth without added N fertiliz er and relative response to N fertilizer, the species were categorized into four relative N use efficiency groups: good foragers with good r esponse to N, poor foragers with good response to N, good foragers wit h poor response to N, and poor foragers with poor response to N.