Maturity Group Classification And Photothermal Comprehensive Response Identihcation Of Chinese Soybean Mini Core Collection

The establishment of Chinese soybean mini core collections facilitated the evaluation andutilization of the rich soybean germplasm resources in China. In this study, the maturity groupclassification of Chinese soybean mini core collections and their photothermal responses wereinvestigated based on planting-of-date experiments in different locations, and further analysis wascarried out to identify their R/V ratio (ratio of the reproductive to the vegetative periods).The mini core collections were sown in Heihe, Harbin, Jining, and Wuhan with the soybeanmaturity group standard varieties from North America as controls. The results showed that the Chinesesoybean mini core collections covered11maturity groups from MG00to MGVIII. Most mini corecollections belonged to MG0to MG VI; The22foreign germplasms in the mini core collections wereclassified into9maturity groups. It indicated that the mini core collections are representative.Based on the differences of flowering time between spring sowing and summer sowing, thephotothermal sensitivity of Chinese soybean mini core collections was calculated. The results indicateda large variation in photothermal responses of Chinese soybean mini core collections, even among thecollections belonging to the same maturity group or from the same province. Significant correlation wasfound between photothermal sensitivity and planting season types in the original sites. Autumn sowingtype soybean is more sensitive to photothermal conditions than summer sowing type soybeans, followedby spring sowing type soybeans. The photothermal sensitivity is significantly correlated with maturitygroup, with increasing sensitivity for longer growth period. According to their photothermal sensitivity,the Chinese soybean mini core collections were classfified into three types: relative insensitive materials(MG000, MG00, MG0and MG Ⅰ),medium sensitive materials (MGII, MGIII, MGIV and MGV) andsensitive materials (MGVI, MGVII, MGVIII, MGVIII and latter ones).According to the data of flowering period (R1) and physiological maturity (R7), we calculated theR/V ratio of Chinese soybean mini core collections in spring sowing conditions. The results showedsignificant differences of R/V ratio among Chinese soybean mini core collections belongting to thesame maturity groups or from the same regions, and the R/V ratio is significantly correlated with theplanting seasons. Considering the R/V ratio, spring-sowing type varieties> summer–sowing typevarieties> autumn-sowing type varieties. Significant correlation was observed between R/V ratio andmaturity group, and the same was true to main stem node number and maturity group. R/V ratiodecreased when maturity groups increased. Main stem node number increased along with the increasingmaturity groups.According to the results, we proposed suggestions to soybean maturity group classification:1) Using the standard soybean maturity group varieties from North America and some Chineserepresentative varieties as controls;2) Sowing the varieties in suitable regions in spring;3) Adoptingstrip or hill planting patterns with low sowing quantity;4) Recording growth period traits of15-30individual plants;5) Determing the maturity.groups of tested varietes by comparing their growth periodtraits with those of standard varieties.Our research provide further insight for the the study, utilization and assesment of Chinesesoybean mini core collections, and is helpful for parent selection, offspring screening, wideadaptability improvement in breeding program and for the prediction of the suitable extension regionsof the new varieties.