SIMPLE LINEAR RELATIONSHIP BETWEEN DRY-MATTER, SPECIFIC-GRAVITY, AND TISSUE SPECIFIC-GRAVITY IN A DIPLOID POTATO BREEDING POPULATION

Two hundred clones were randomly selected in 1988 and in 1989 from a hybrid population of Solanum phureja and Solanum stenotomum to determine the relationship between specific gravity (SG) and percent dry matter (%DM), and between tissue specific gravity (TSG) and %DM. The objectives were: (1) to determine the dry matter prediction equation for a diploid potato population, (2) to determine whether estimates of %DM and efficiency of selection for %DM could be improved by measuring TSG, and (3) to determine the influence of year on the estimates. In 1988 the prediction equation for the relationship between %DM and SG was %DM = 198.71(SG)-191.30, r= 0.85. Ranges and means for the variables were: (1) %DM: 16.99 - 32.67, mean 25.16; (2) SG: 1.054 - 1.122, mean 1.089. In 1989 the relationship of %DM and SG was predicted as %DM = 194.46(SG)-187.53, r = 0.87; whereas the relationship of %DM and TSG was predicted as %DM = 196.77(TSG)-192.91, r = 0.87. Ranges and means for the variables were: (1) % DM: 10.68 - 34.57, mean 21.32; (2) SG: 1.030 - 1.122, mean 1.074; (3) TSG: 1.046 - 1.141, mean 1.089. Slopes were not significantly different between any of the prediction equations, but intercepts were significantly different. Estimates of %DM were not improved by measuring TSG. Year did influence the relationship between %DM and SG.