Mapping QTL For Seed Size And Seed-Flooding Tolerance In Two Recombinant Inbreeding Line Populations Of Glycine Max×G. Soja

Annual wild soybean is the ancestor of cultivated soybean, with many elite traits such as good tolerance to stresses, more pods and seeds, and high protein content. It is an important research field to exploit and utilize the elite genes of wild soybean in soybean breeding program. Some loci or alleles for high yield or high protein content in wild soybean have been mapped and used in breeding practices, and some cultivars have also been developed with the pedigree of some Glycine soja accessions. In our previous studies, PI 342618B, a wild soybean accession from Russia was identified as one of the most tolerant lines to waterlogging stress. The objectives of this study are focused on mapping QTL for 100-seed weight, seed shape and seed-flooding tolerance. Two recombinant line populations, i.e. NIRI4P (Nannong 493-1 X PI342618B F6:9) and NJRINP (Nannong 86-4 X PI342618B F6:10), with their parents were used. Field trials were carried out to do the QTL mapping of 100-seed weight and grain shape in Pukou district of Jiangsu province and Fengyang city of Anhui province, and germination experiments were conducted by using the obtained seeds to map QTL of seed-flooding tolerance. The main results were showed as follow.1. ANOVA for seed trait parameters e.g.100 seed weight, length, width, and length to width ratio in both populations was done. The results showed significant difference between the families, environment and line X environment interaction for all the traits. It means that all the traits are under the control of three factors. No obviously transgressive segregation was found and broad sense heritability of>0.70 shows that all the traits of two populations have heritable variation and magnitude of variation is larger. Most traits did not show skewed distribution. In case of the traits of seed-flooding tolerance, four tested traits including germination potential, germination rate, normal seedling rate at third or fifth day after flooding treatment have great ranges and significant differences among lines in both populations, Broad sense heritability of>0.75 shows that all the traits have high heritable variation. However, the heritability values of four relative rate of treatment to control of germination rate, germination potential, normal seedling rate at third or fifth day after flooding treatment were found to be lower. Since these relative values could reflected the tolerance performance of each line based on the control level, these four traits were also used in the subsequent QTL analysis.2. By using the linkage map of two populations and software of WinQTLCart2.5 for QTL mapping analysis, QTL for 100-seed weight, seed length, width, seed length-to-width ratio and degree of seed smoothness were detected. In NIRI4P population, total 33 QTL of 4 traits were found. These were located on the 19 chromosomes excluding the chromosome No.18. Twelve of them controlled 100-seed weight. Among them, locus qIswtt02-2 was found on chromosome No.2 in confidence interval 54.1 cM-59.7 cM and 56.2 cM-59.2 cM was repeatedly detected in both planting sites. The QTL qIswtO4-2 was found on chromosome No.4 in confidence interval 50.2 cM-52.5 cM was also repeatedly detected. Total 4,6 and 1 QTL controlled seed length, seed width and seed length-to-width ratio, respectively. In NJRTNP population 29 QTL of 4 traits were found. These were located on the 16 chromosomes. Out of 29,21 controlled 100-seed weight. The QTL qNswt15-1 on chromosome No.15 in confidence interval 63.7-66.3 cM was repeatedly detected in both planting sites. Out of 29 QTL,2,1 and 5 QTL controlled seed length, seed width and seed length-to-width ratio respectively. One QTL on chromosome No.2 was detected controlling grain shape, including seed length, width and seed length-to-width ratio. In general, grain size and grain traits are controlled by many QTL with minor effects in two RIL populations, there are big differences of genetic constitutions for 100-seed weight and seed shape between the two parental cultivated soybeans.3. QTL mapping results of seed-flooding tolerance in NIRI4P population showed that, under flooded conditions,8 QTL of 4 traits which are germination potential, germination rate, normal seedling rate at third or fifth day after flooding treatment, were discovered. The QTL qlg2-1 on chromosome No.2 (near 88 cM position) was detected conferring for the germination potential and normal seedling rate at third day after flooding treatment. The QTL qIg2-2 of chromosome No.2 (94.9 cM position) controlled germination potential, germination rate and normal seedling rate at third day after flooding treatment. The QTL qlg6-1 of chromosome No.6 (30.9 cM position) was detected controlling the germination potential, germination rate and normal seedling rate at fifth day after flooding treatment. The QTL qIg10-1 of chromosome No.10 (0.8 cM position) was also detected controlling the germination potential and normal seedling rate at fifth day. The QTL qIrgr10-1 of chromosome No.10 in confidence interval 0 cM-0.5 cM controlling the relative germination rate and relative normal seedling rate at third day was repeatedly detected.QTL mapping results in NJRINP population showed that under flooded conditions,7 QTL of four traits were detected. The QTL qNg8-1 of chromosome No.8 (51.0 cM position) controlling the germination potential, germination rate, normal seedling rate at both third and fifth day was repeatedly detected. Six QTL of four relative value traits were detected. The QTL qNg8-3 of chromosome No.8 was also detected in 49.6 cM position controlling the relative value of germination potential and normal seedling rate at third day after flooding treatment. The seed-flooding tolerance of two populations is controlled by several minor QTL, and many tolerant alleles are originated from the wild soybean. The genetic basis of the seed submergence tolerance is different between the two tested populations.