Difference In Growing Development And Genetic Analysis Of Soybeans With Different Tolerance To Low-Potassium Stress

Soybean is the main oil crops in China. The plant needs more potassium than other crops. However, both available potassium and potash fertilizer resource are deficient in China, which limits the improvement of soybean yield. Base on the plant genetic diversity to environmental stress, discovering the germplasm resources and breeding soybean varieties with tolerance to low potassium stress is an effective ways to solve the above problem. In this experiment, total of 72 soybean varieties (lines) from three northeast provinces in China were screened through the field experiment in low potassium soil, and typical varieties (lines) with different tolerance to low potassium stress were obtained. Furtherly, growth and development characters of these typical soybean varieties (lines) were compared through the field, potted and hydroponic experiment. Meanwhile, genetic characters of soybean tolerance to low potassium stress were studied. The purpose of this study is to provide technical and theoretical guidelines for better using soybean germplasm resources and breeding soybean varieties with tolerance to low potassium stress in the future. The results were as follows:1. Screening of soybean genotypes with tolerance to low potassium stressDifference of tolerance coefficient and K deficiency symptoms in leaf was obvious among the 72 soybean varieties (lines). In most of soybean varieties (lines), adaptability to low potassium stress was moderate. A few of soybean varieties (lines) showed more sensitive or tolerant phenotype to low potassium stress. According to tolerance coefficient and leaf K deficiency symptoms, these soybean varieties (lines) were divided into three types:sensitive type to low potassium, middle type to potassium and tolerant type to low potassium. Tiedou 36 and T40 as typical tolerant type varieties (lines), and GD2910 and GD8521 as typical sensitive type varieties (lines) were selected for further study.2. Differences in stem and leaf characters of soybeans with different tolerance to low potassium stressGenerally, plant height of soybeans was lower at each stage of growth period under low potassium stress. While, plant height of tolerance line T40 by low potassium stress was less affected.Number of stem nodes on all tested soybean varieties (lines) increased under low potassium stress, especially after blooming period.Number of stem nodes on GD8521, a sensitive type varieties (lines) to low potassium increased most. Moreover, low potassium stress reduced stem diameter of all tested soybean varieties (lines). Decreasing range of stem diameter on sensitive line GD8521 was the largest, but smaller on tolerant line T40.Leaf length of all tested soybean varieties (lines) was also decreased under low potassium stress, especially at blooming period. Decreasing range in tolerant varieties (lines) to low potassium was smaller than that in sensitive varieties (lines). Similarly, petiole length of sensitive line GD8521 was markedly inhibited, while, little effect was presented on tolerant line T40. From the beginning of branching period, ratio of K deficiency symptoms leave in tolerant varieties (lines) gradually reduced or maintained at a low level. On the contrary, the ratio in sensitive varieties (lines) gradually increased or maintained at a high level.Under low potassium stress, the number of branch of the sensitive varieties (lines) was seriously decreased, while tolerant line T40 was lightly affected. Low potassium stress increased node number of lowest pod, especially in sensitive varieties (lines).3. Differences in root characters of soybeans with different tolerance to low potassium stressThrough pot experiment, it was showed that taproot length, lateral root length, number of lateral root and root nodules of all tested varieties (strains) were reduced under low potassium stress. The negative effects on sensitive varieties (lines) were stronger than tolerant varieties (lines). Data from water culture experiments showed that low potassium stress reduced total root length, surface area of root, root volume and number of root tips of soybeans. Samely, the negative effects on sensitive varieties (lines) were stronger than tolerant varieties (lines). It was also found that low potassium stress increased root average diameter of sensitive varieties (lines) and decreased it in tolerance varieties (lines).4. Differences in flower and pod characters of soybeans with different tolerance to low potassium stressThe time of the first flower and mature of soybeans under low potassium stress were delayed. Low potassium stress reduced the number of pods per plant in sensitive varieties (lines), and increased the number of pods per plant in tolerance varieties (lines). Decreasing ranges in seed number per plant and 100-seed weight in sensitive varieties (lines) were larger than tolerant varieties (lines). There was no significant difference in the number of seeds per pod between sensitive and tolerant varieties (lines). 5. Differences in accumulation and distribution of dry matter in soybeans with different tolerance to low potassium stressAccumulations of dry matter in different organs of tested soybean varieties (lines) were reduced under low potassium stress. The negative effects on sensitive varieties (lines) were stronger than tolerant varieties (lines), such as accumulation of dry matter in stem at the stage of branching period, in roots, leave and stems after blooming period, and in seeds at the maturity stage.Before blooming period, distribution of dry matter in tolerant varieties (lines) was more reasonable than sensitive varieties (lines). The growth among root, stem and leaf was harmonious, and distribution ratio of dry matter in stem was higher in tolerant varieties (lines), which facilitate transport and storage of photosynthate product. After blooming period, decrease in distribution ratio of dry matter in root and leaf was lesser in tolerant varieties (lines), which facilitate yield formation.6. Differences in nutrition characters of potassium in soybeans with different tolerance to low potassium stressUnder low potassium stress, content of potassium in leaf, stem, pod and seed in all tested soybean varieties (lines) decreased, but there was a difference between tolerant and sensitive varieties (lines). Decreasing extent of above indexes was smaller, and K content was higher in tolerant varieties (lines) than in sensitive varieties (lines).K accumulation in all tested soybean varieties (lines) decreased under low potassium stress. Compared with sensitive varieties (lines), the tolerant varieties (lines) were less affected. Moreover, K utilization efficiency of all tested soybean varieties (lines) was significantly improved under low potassium stress, especiall for sensitive varieties (lines).7. Genetic analysis of leaf k deficiency symptom and total root length in soybeans with tolerance to low potassium stressT40 (tolerance to low-potassium stress) as the female parent, two sensitive lines GD8521and GD2910 as the male parent made two cross. Genetic analysis of the number of leaf with low potassium symptom was conducted applying the joint segregation analysis of a mixed genetic model of major gene plus polygene in five generations (P1, P2, F1, F2 and F2:3) derived from two crosses. The results showed that tolerance to low-potassium stress in soybean was dominated by one major gene with additive effects plus poly-genes with additive-dominance effects. Heritability of major geneswas 56.72% and 59.31% in F2 population from two cross, and that of poly-genes in F2 population was 20.28% and 9.19% respectively. Heritability of major genes was50.32% and 40.68% in F2:3 populations from two cross, and that of poly-genes in F2:3 populations was 17.72% and 23.32% respectively. Heritability of major gene in two crosses was more powerful than poly-genes. It indicated that the number of leaf with low potassium symptomthe in soybean was dominated by major genes.T40 (tolerance to low-potassium stress) as the female parent, sensitive lineGD8521 as the male parent made cross.Inheritance of total root length was analyzed applying the joint segregation analysis of a mixed genetic model of major gene plus polygene in five generations (P1, P2, F1, F2 and F2:3). The results showed that total root length was dominated by additive-dominance-epistatic gene. The heritability of poly-genes in F2 and F2:3 was 38.266%和41.884% respectively. In addition, the environmental variance in F2 and F2:3 accounted for 61.734%, and 58.116% of the phenotypic variance respectively, indicating that the environmental factors have some effect on total root length in tolerance to low-potassium soybean.