Development of tetraploid pure lines in potato toward heterosis breeding

马铃薯是一种高度杂种的四体四倍体。高纯合自交系对杂种优势的研究有重要意义。本研究利用分子标记研究了S位点抑制基因（Sli）在马铃薯高纯合二倍体株系中的适用性和近交过程。通过杂交将Sli基因引入32个二倍体基因型中，并对其在F_1和S_1后代中的表达进行了研究。带有S型或a型叶绿体DNA的F_1杂种产生S_1种子（67.1%），第二次自交时，S_1杂种产生S_2种子的比例为44.2%，而带有W型或t型叶绿体DNA的F_1杂种由于细胞质雄性不育而未能产生S_1种子。一个二倍体无性系97H32-6和一个优秀二倍体无性系97H32-6的杂种分别产生2个S_4科和3个S_5科。使用RFLP和AFLP标记测定的平均杂合度水平分别从S_0的100%下降到S_4的10.7%和S_5的8.6%。每代杂合度降低率分别为38.4%和38.5%，低于理论预期的50%。然而，在晚期自交后代中，没有一个位点或染色体片段是完全杂合的。因此，利用Sli基因进行多次自交，可以获得高度纯合子和种子繁殖的二倍体马铃薯。对S_3家族的51株进行了育性相关性状和杂合度评价。8个染色体切片上至少有9个位点与育性相关的数量性状位点（qtl）相关，其中在杂合子和纯合子中均表现较好。通过进一步的自交，在杂合子中表现较好的qtl很可能被固定在表现第二好的纯合子上，而在纯合子中表现较好的qtl则被固定在最好的基因型上，尽管随着自交代的进行，自交性继续下降。少

Potato is a highly heterotic tetrasomic tetraploid. Highly homozygous inbreds are useful for investigation of heterosis. In this study, applicability of S locus inhibitor gene (Sli) to develop highly homozygous diploid lines of potato and the process of inbreeding were investigated using molecular markers.The Sli gene was introduced by crossing into 32 diploid genotypes and its expression in the F_1 and S_1 progenies was investigated. F_1 hybrids with S- or A-type chloroplast DNA produced S_1 seeds (67.1% of self-pollinated F_1 plants), and by second selfing 44.2% of S_1 plants produced S_2 seeds, whereas those with W- or T-type chloroplast DNA failed to produce S_1 seeds due to cytoplasmic male sterility.A diploid clone 97H32-6 and a hybrid between 97H32-6 and a superior diploid clone produced two S_4 families and three S_5 families, respectively. The average heterozygosity levels measured using RFLP and AFLP markers decreased from the original 100% in S_0 to 10.7% in S_4 and to 8.6% … More in S_5, respectively. The heterozygosity reduction rates per generation were 38.4 and 38.5%, respectively, which were lower than the theoretically expected 50%. However, none of loci or chromosome sections was exclusively heterozygous in the advanced selfed-progenies. Thus, highly homozygous, and seed-propagated diploid potatoes could be obtained by repeated selfing using the Sli gene.Fifty-one plants of an S_3 family were evaluated for fertility-related traits and heterozygosity. At least nine loci on eight chromosome sections were associated with fertility-related quantitative trait loci (QTLs), in which both QTLs performing better in the heterozygotes and in the homozygotes were found for each fertility-related trait. By further continued selfing, QTLs performing better in heterozygotes were likely fixed to homozygotes with secondly better performance, and those performing better in homozygotes were fixed to the best genotypes, although self-fertility continued to decrease as selfed generations proceeded. Less