| The narrow genetic base and inbreeding phenomenon in the common potato, Solanum tuberosum L. are serious problems for potato breeding. As rapid expansion in potato industry of China, the demands for high yielding and high quality of potato stock are increasing, and no doubt development of new variety suitable for processing is a good solution to these problems. For breeding the variety suitable for the need of market, exploring useful genes in diploid potatoes and then integrating them into tetraploid potatoes are important. In this research, the variation, relation, and broad-sense heritability of main traits in 70 long-day adapted diploid S. phureja (PHU)-S. stenotomum (STN) hybrid clones were studied and the clones of interest with target traits were selected out using the varieties Atlantic and Kexin 2 as controls. The experiments were carried out in a randomized complete block design with three replications in Jiagedaqi Heilongjiang in 2008 and 2009. The main results were as following.(1) Significant or highly significant difference were found in some PHU-STN hybrid clones compared with the two control varities, Atlantic and Kexin 2, in plant height, main stem number, tuber yield per plant, tuber number per plant, dry matter content,crude protein content (FW and DW) and reducing sugar content, suggesting that large genetic variation exists in the PHU-STN hybrid population.(2) The tuber yield per plant had a highly significant positive correlation to tuber number per plant, plant height and main stem number.Tuber number per plant had a highly significant positive correlation to main stem number, and significant positive correlation to plant height. Plant height and main stem number had a highly significant positive correlation, while crude protein content (FW) and yield had a highly significant negative correlation.(3) The results of partial correlation analysis indicated that tuber yield per plant was highly significantly positively correlated to tube set per plant, significantly positively to plant height; main stem number was highly significantly positively correlated to tuber set per plant and plant height; and crude protein content (FW) was highly significantly negatively correlated to tube yield per plant. However, no significant correlation was found between main stem number and tuber yield per plant, as did in simple correlation analysis.(4) In path analysis, tuber number per plant showed the highest direct effect on yield, crude protein content (FW) had a negative effect on yield, and main stem number had indirect effect on yield via tuber number per plant.(5) Broad-sense heritability for yield per plant, tuber number per plant, plant height, main stem number per plant, dry matter content, crude protein content on the basis of dry weight (DW), crude protein content on the basis of fresh weight (FW) cluster analysis and reducing sugar content were estimated as 0.7305, 0.6789, 0.8050, 0.3722, 0.6622, 0.6486, 0.6621 and 0.4540, respectively. These showed that these traits had a moderately high broad-sense heritability.(6) There were many clones of interested traits that could be selected out of the seventy diploid clones. Clone with high tuber yield per plant but low tuber number per plant BD62-7, clone with high dry matter content BD22-3, high crude protein content (FW) (BD55-3) and clone with low reducing sugar content BD29-3, were among those interested. In addition, clones with various skin color, flesh color, tuber shape, and tuber set could be identified in these diploid potatoes.In short, based on the performance of tuber yield per plant, tube set per plant, dry matter content, crude protein content and reducing sugar, there were large variations in the PHU-STN hybrid population. The estimates of road-sense heritability for tuber yield per plant, tuber set per plant, dry matter content, crude protein content (DW), crude protein content (FW) and reducing sugar content suggested that these traits are heritable. Futhermore, some clones of interest could be identified, which would be used in further breeding program.
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