Variance components for yield and specific gravity in a diploid potato population after two cycles of recurrent selection

The potato (Solanum tuberosum L.) processing industry needs cultivars with high tuber specific gravity and acceptable color of processed product. All of the cultivars with high specific gravity currently grown in the U.S. are very closely related, which increases their genetic vulnerability and resu lts in inbreeding as efforts are made to improve these traits. The use of d iploid Solanum sp. in breeding may resolve these problems. The purposes of this study were (1) to estimate narrow-sense heritability for yield and spe cific gravity in random-mating diploid hybrid potato populations of S. phur eja - S. stenotomum (PHU-STN) following two cycles of recurrent selection, (2) to examine phenotypic variances for yield and specific gravity followin g two cycles of recurrent selection within PHU-STN, (3) to compare the yiel d and specific gravity of individual PHU-STN clones with Atlantic, and (4) to screen these PHU-STN clones for the presence of 2n pollen. Four clones h orn each of 72 maternal half-sib families were evaluated for yield and spec ific gravity in replicated field tests in 1990 and 1991. A second selection cycle, using a randomly mated population obtained from the highest specifi c gravity clone in each maternal half-sib family, was similarly evaluated f or yield and specific gravity in replicated field tests in 1995 and 1996. N arrow-sense heritability for specific gravity was estimated as 0.37 +/- 0.2 5 and 0.43 +/- 0.27, in the first and second selection cycles, respectively , with a 27% decrease in phenotypic variance. Narrow-sense heritability for yield was estimated as 0.60 +/- 0.26 and 0.06 +/- 0.24, in the first and s econd selection cycles, respectively, with a 73% decrease in phenotypic var iance. There were significant correlations between yield and specific gravi ty in 1990 (r=0.32) and 1996 (r=0.37), but not 1991 (r=0.08) and 1995 (r=0. 05). These results indicate that additional breeding efforts in this PHU-ST N population could result in improvements in specific gravity. However, the amount of variation for yield in this population is decreasing and may ind icate that the yield potential of this population is rapidly approaching it s limit. In the second selection cycle, many of the 288 clones were signifi cantly higher in specific gravity than the high-specific-gravity cultivar A tlantic, but none were higher yielding. Fifty-eight clones from the second selection cycle produced at least 5% 2n pollen. When used in tetraploid x d iploid hybridizations, this diploid population could furnish new genetic ma terial to the tetraploid potato,germplasm base for simultaneously increasin g specific gravity and yield.