不同光周期处理对大豆开花结荚进程的影响

通过长日照（１６ｈ光／８ｈ暗）和短日照（９ｈ光／１５ｈ暗）相互转换处理，证明大豆品种“早１２”为相对短日植物，９个短日就可完成其成花的光周期诱导过程。大豆感受光周期效应的株龄在真叶期。短日诱导处理不仅促进花序产生的速度及数量，还有利于荚的发育；长日处理的结果恰相反。     

不同品种大豆耐盐性的比较研究

通过对中黄13号和科丰6号2个大豆品种进行不同浓度的盐处理(01、002、00 mmol/L NaCl)后,测定其干重、脯氨酸、丙二醛、叶绿素含量以及根系活力和过氧化物酶活性等相关生理指标,通过其生长及生理指标变化,比较2个大豆品种的耐盐性并探讨其耐盐机理。结果表明:随着盐浓度的增加,2个大豆品种幼苗叶绿素含量、根系活力以及过氧化物酶活性均降低,脯氨酸、丙二醛含量均增加,最终导致幼苗干重的下降,但品种间生理指标变化趋势不同,科丰6号较中黄13号变化缓慢,说明前者耐盐性较强。     

大豆吡哆醇生物合成蛋白基因(PDX)的电子克隆和进化分析

电子克隆(In silicocloning)是随着基因组计划和EST计划实施而发展起来的利用生物信息学手段进行基因克隆的新方法。根据物种间同源基因相对保守的特点,以拟南芥(Arabidopsis thaliana)吡哆醇生物合成蛋白cDNA序列为信息探针,对大豆(Glycine max)EST数据库进行同源搜索和序列拼接,获得了1 280 bp长的大豆吡哆醇生物合成蛋白的基因序列(GenBank登陆号为DQ139265)。经过RT-PCR扩增、基因组PCR扩增、分子克隆和序列分析验证,结果表明与电子克隆序列完全一致。该基因具有完整的开放阅读框架(ORF,20~955 bp),编码311个氨基酸。通过与水稻、日本百脉根、烟草、截形苜蓿等物种的吡哆醇生物合成蛋白序列比对,发现该基因具有高度的保守性。表明根据物种间同源基因序列,对跨物种间EST数据库进行同源检索、筛选、拼接,是克隆基因的有效途径。     

Establishment of Chinese soybean Glycine max core collections with agronomic traits and SSR markers

It is very important to efficiently study and use genetic diversity resources in crop breeding and sustainable agriculture. In this study, different sampling methods and sample sizes were compared in order to optimize the strategies for building a rationally sized core collection of Chinese soybean (Glycine max). The diversity in the core collection captured more than 70% of that in the pre-core collection, no matter what sampling methods were used, at a sampling proportion of 1%. Core collections established with both simple sequence repeat (SSR) marker data and agronomic traits were more representative than those chosen on an independent basis. An optimal sampling method for a soybean core collection was determined, in which strategy ‘S’ (allocating accessions to clusters according to the proportion of square root of the original sample size within each ecotype) was used based on SSR and agronomic data. Curve estimation was used to estimate the allelic richness of the entire Chinese soybean germplasm and a minimum sample size for a core collection, on which a sampling proportion of about 2% was determined to be optimal for a core collection. Further analysis on the core collection with fourteen agronomic traits and allelic constitution at 60 SSR loci suggested that it highly represented the entire collections both on genetic structure and diversity distribution. This core collection would provide an effective platform in proper exploitation of soybean germplasm resources for the study of complex traits and discovering important novel traits for crop genetic development.     

Effect of Inoculant Rate on Nodulation and Various Agronomic Traits of Soybean

In a soil lacking indigenous Bradyrhizobium japonicum , soybean ( Glycine max [L.] Merr.) nodulation depends upon the number of rhizobia applied with the inoculum. This field study reports the effect of different rates of applied rhizobia on nodulation, dry matter and nitrogen content in soybean in a Mediterranean soil lacking B. japonicum.
Treatments included six rates of B. japonicum , ranging from 2.5 × 10⁴ to 6.075 × 10⁶ rhizobia cells per seed applied to the seed as peat inoculant at planting, 100 kg N ha⁻¹ and an uninoculated control. The experiment was conducted in an Entisol soil. Regression analysis showed linear relationship between the rate of applied rhizobia and the number of the nodules per plant or the dry weight per nodule. In early stages of development (32 and 68 days after planting) plant dry weight was not affected by inoculation rate. At harvest a rate of 7.5 × 10⁴ rhizobia cells per seed was necessary for maximum total and stover dry weight. A higher rate, 6.75 × 10⁵ rhizobia cells per seed, was required to obtain maximum grain yield, total N content in plant tops and grain N content. Grain percentage N was increased up to 2.025 × 10⁶ rhizobia cells per seed. Nitrogen application increased grain yield, total N content and grain N content at the same level as the lower inoculation rate.     

Sensitivity to Drought Stress of Three Soybean Cultivars During Different Growth Stages

Three soybean ( Glycine max L.) culivars, Lee-74, Wright , and Ra 401 , were subjected to 100 % (control), 75 %, and 50 % of field capacity during vegetative (VI), flowering (R2), and pod-filling (R4) stages in greenhouse and field studies. Stress applied at R2 significantly reduced the yield in the greenhouse, while in the field, the maximum reduction was observed when the plants were subjected to stress at R4. Stress during VI reduced the yield components less than stress applied during R2 or R4 stages in both studies. The pod number and seed weight were the yield components most affected by drought stress, and the number of seeds per pod the least affected. Yield stress index was significantly correlated with the yield and its components. The reproductive stage was clearly more sensitive to drought than the vegetative stage. The cultivar Lee 74 had the highest yield and the second highest yield stress index whereas the cultivar Ra 401 had the lowest yield.     

Discovery of new male-sterile cytoplasm sources and development of a new cytoplasmic-nuclear male-sterile line NJCMS3A in soybean

Most of the cytoplasmic-nuclear male-sterile (CMS) lines of soybean were developed only from a limited cytoplasm sources and performed not as good as required in hybrid seed production, therefore, to explore new male-sterile cytoplasm sources should be one of the effective ways to improve the pollination and hybridization for a better pod-set in utilization of heterosis of soybeans. In the present study, total 80 crosses between 70 cultivated and annual wild soybean accessions and three maintainers (N2899, N21249, and N23998) of NJCMS1A were made for detecting potential new sources with male-sterile cytoplasm. The results showed that in addition to the crosses with N8855.1 (the cytoplasm donor parent of NJCMS1A) and its derived line NG99-893 as cytoplasm parent, there appeared three crosses, including N21566 × N21249 and N23168 × N21249, with male-sterile plants in their progenies. According to the male fertility performance of backcrosses and reciprocal crosses with the tester N21249, the landrace N21566 and annual wild soybean accession N23168 were further confirmed to have male-sterile cytoplasm. Accordingly, it was understood that the source with male-sterile cytoplasm in soybean gene pool might be not occasional. The results also showed that the genetic system of male sterility of the newly found cytoplasm source N21566 was different from the old cytoplasm source N8855.1, while N23168 was to be further studied. Based on the above results, the derived male-sterile plants from [(N21566 × N21249) F₁ × N21249] BC₁F₁ were back-crossed with the recurrent parent N21249 for five successive times, and a new CMS line and its maintainer line, designated as NJCMS3A and NJCMS3B, respectively, were obtained. NJCMS3A had normal female fertility and stable male sterility. Its microspore abortion was mainly at middle uninucleate stage, earlier than that of NJCMS1A and NJCMS2A. The male fertility of F₁s between NJCMS3A and 20 pollen parents showed that 7 accessions could restore its male fertility and other 13 could maintain its male sterility. The male sterility of NJCMS3A and its restoration were controlled by one pair of gametophyte male-sterile gene according to male fertility segregation of crosses between NJCMS3A and three restorers. The nuclear gene(s) of male sterility in NJCMS3A appeared different from the previously reported CMS lines, NJCMS1A and NJCMS2A. The development of NJCMS3A demonstrated the feasibility to discover new CMS system through choosing maintainers with suitable nuclear background.     

Identification of soybean strains resistant to Xanthomonas campestris pv. glycines

Summary Soybean germplasm was screened for resistance to bacterial pustule disease. The etiological agent, Xanthomonas campestris pv. glycines, was isolated from the leaves of field grown soybean in Maharashtra, India. The screening of soybean stocks was carried out by excised leaf inoculation method. A differential susceptibility to the pathogen was observed in the tested stocks. Two stocks P-4-2 and P-169-3 were found to be completely resistant to the pathogen and displayed an incompatible reaction. Four cultivars, EC-34160, Bragg, Kalitur and PK-472 displayed moderate resistance and the remaining stocks were susceptible to the attack of the pathogen. The stocks P-4-2 and P-169-3 remained resistant even to a high concentration of 10⁹ colony forming units (cfu)/ml of the pathogen.     

Genetic diversity in soybean as determined by RAPD and microsatellite analysis

The random amplified polymorphic DNA (RAPD) and microsatellite techniques were used to evaluate the genetic diversity among 18 soybean genotypes selected for a breeding programme to increase the protein content of varieties adapted for central European growing conditions. Out of 33 random primers used in RAPD reactions, only 12 showed polymorphism useful for characterization of these genotypes. In contrast, all 12 microsatellite primer pairs used in this study detected polymorphism with 2–6 alleles per locus. Similarity measures and cluster analysis were made using RAPD and simple sequence repeat (SSR) data, separately and together. The resulting dendrograms were compared with each other and with the available pedigree information as a control. The dendrogram derived from RAPD data showed some divergence from the pedigree information available for the lines. The dendrograms based on SSR data and SSR data combined with RAPD gave very good agreement with pedigree information. It can be concluded that the combined use of a limited number of RAPD and SSR markers is a useful and reliable means of evaluating genetic relationships of genotypes in the absence of pedigree data.