Founder parents have played an important role for the development of wheat in China, which have produced many large-grown varieties or important breeding lines. But all founder parents in different crops were found as a result of summation of the pedigrees. How are founder parents produced from various germplasm? Why can many important varieties be bred through using them? The answers for the two questions are not clear.In order to understand the formation of founder parent Bima 4, explore the evolution law of founder parents and find new founder parents in future, the founder parent Bima 4, its 80 progeny, 17 intermediate parents in the pedigree derived from Bima 4, its 5 sister varieties and the parents (total 105 accessions) were analyzed in this study using agronomic traits and SSR markers.1. Phenotypic trait of founder parent Bima 4. Total accessions were grown in five ecological areas including Yangling in Shaanxi, Taian in Shandong, Shijiazhuang in Hebei, Chengdou in Sichuan and Yangzhou in Jiangsu in 2006-2007 and 2007-2008 seasons with 3 repeats per site and analyzed for seven important agronomic traits. The result indicated that the founder parent Bima 4 was attractive for plant height, spikelet number, grain number, 1000-grain weight and spike number per plant, and had produced prominent contribution to its progeny in main agronomic traits. With the increasing of the generations, there was an enhancement trend for 1000-grain weight. When comparing the change among Bima 4, intermediate parents and the accessions in different generations, transgressive inheritance was found for the agronomic traits, which might result from the interaction among different genes of QTL.2. Important chromosomal loci in founder parent Bima 4. Total ninety-eight varieties in the pedigree derived from Bima 4 were analyzed using 434 SSR markers which are distributed across eighteen chromosomes with the exception of 2A, 1B and 1D with average genetic distances of 5.92 cM among adjacent markers according to the reported literature by Somers et al., of which, 368 (84.2%) were polymorphic. Total 448 alleles were amplified in Bima 4 using the polymorphic markers, of which, 12 alleles could be found in its total progeny, 7 alleles could not be detected in any of them, and the remaining alleles were transmitted to the progeny with the frequencies of 0.0125 to 0.9875. One hundred and eighty alleles were amplified at 157 SSR loci in Bima 4 and could be found in equal or over 60% of the progeny. On the other hand, when compared with intermediate parents in different generations of the pedigree respectively, 43 alleles which were amplified in Bima 4 but absent in 16 intermediate parents could be tracked in the accessions from the first to third generation. If expected parental contribution with Mendelian inheritance is 0.5 for a F2 -derived inbred, the unique alleles of Bima 4 at 10 SSR loci could be tracked from the first to third generation with higher frequencies than theoretical varlues in each generation. This indicated that the chromosomal loci in Bima 4 underwent certain selection pressure during the breeding.3. Important chromosomal regions in founder parent Bima 4. Of 157 SSR markers, where the alleles of Bima 4 were inherited in equal or over 60% of the progeny, 56 markers which distribute 15 chromosomes with the exception of 3B, 4D and 7A formed 20 important chromosomal regions, whose genetic distance was less than 11 cM between adjacent markers, and most of them were round the centromere. The range of genetic distance in the chromosomal regions were from 0 to 16 cM, of which, the distance between Xgwm456 and Xgwm341 on the chromosome 3D is 0 cM, and Xgwm5~Xbarc67~Xcfa2234~Xwmc264 on the chromosome 3A had the longest genetic distance. On the other hand, of 43 markers which amplified unique alleles in Bima 4 and they could be tracked from the first to third generation, 6 markers formed three important chromosomal regions, namely Xgwm120~Xgwm47 on chromosome 2B, Xgwm371~Xgwm499 on chromosome 5B and Xgwm645~Xcfd49 on chromosome 3D with 4, 2 and 1 cM, respectively.4. Association between important chromosomal loci, regions and agronomic traits. Association were tested betweem 228 SSR markers and important agronomic traits (including spike length, spikelet number, grain number, 1000-grain weight, spike number per plant, yield and plant height). At q<0.20, 93 markers were found to connect with agronomic traits using association mapping, and the contribution rate of the markers for agronomic traits was from 0.0125 to 0.2672 with the average of 0.1219. Thirty-eitht markers which amplified the same alleles as Bima 4 in more than 60% of the progeny were connect with agronomic traits, and when comparing the means of agronomic traits among different alleles amplified by the same marker, we found that the values across total varieties which had the same alleles as Bima 4 were equeal or higher than those with other alleles at each of 13 SSR markers, that is to say, the alleles of Bima 4 increased the production of wheat. On the other hand, 11 markers, which amplified unique alleles in Bima 4 and the alleles could be tracked from the first to third generation, were connected with agronomic traits, of which, the allele of Bima 4 at the locus Xbarc18 was correlated with higher 1000-grain weight than other alleles amplified at the same locus. Nineteen markers which were connected with agronomic traits located on the important chromosomal regions mentioned above. The markers on 5 chromosomal regions were related with different traits. The alleles of Bima 4 presented positive or negative effects between different loci or on the same regions for different traits, which might result from certain interaction among different loci or traits in order to reach coordinated development in the breeding.5. Important chromosomal loci or regions in 6 founder parents. Six founder parents including Bima 4, Beijing 8, Orofen, Abbordanze, Early Piemium and Lovrin 10, which were in the pedigree from Bima 4, had 40 common alleles. Of them, the frequencies of 38 alleles were more than 86% in total progeny, and the markers were included in the 157 ones mentioned above.6. Important chromosomal loci or regions in Bima 4 compared with other 5 sister varieties. Through comparing the polymorphic patterns among the 6 sister varieties, we found that Bima 4 had 13 unique alleles, Bima 1 and Bima 4 had 5 common alleles which were different from the remaining 4 sister accessions. Moreover, the genetic distances between Xgwm425 and Xgwm95 on the chromosome 2A and between Xcfd42 and Xgwm469 on the chromosome 6D were 1 cM, respectively. The alleles, which were amplified only in Bima 4 or were common in Bima 4 and Bima 1 but absent in other sister varieties, were tracked in the progeny from Bima 4, and the result indicated that the alleles amplified in Bima 4 by 7 SSR markers accurred in over 60% progeny. What′s more, association test indicated that ten of these special SSR loci were connected with plant height, spike length, spikelet number, grain number, 1000-grain weight, spike number per plant or yield.7. Genetic features of Bima 4 as a founder parent. Through the analysis of this work, we found that Bima 4 had produced prominent contribution to its progeny in main agronomic traits. With the increasing of the generations, there was an enhancement trend for 1000-grain weight. When comparing the change among Bima 4, intermediate parents and the progeny in different generations, transgressive inheritance was found for the agronomic traits, which might result from the interaction among different genes of QTL; on the other hand, there existed important chromosomal loci and regions which were connected with important agronomic traits in Bima 4. This might be basic genetic features of Bima 4 as a founder parent. |