Screening and identification of salt tolerance soybean varieties and germplasms

Soil salinization is a globally prevalent abiotic environmental stress.The imbalance of ions caused by high concentrations of sodium chloride results in a 40%reduction in soybean yield.Soybean,as an important crop for soil quality improvement,necessitates the identification of salt-tolerant varieties and germplasms to effectively utilize and enhance saline-alkali land.In this study,we assessed the salt tolerance of 435 soybean varieties and germplasms during the seedling stage.Among them,Qihuang34,You2104,Hongzhudou,Pamanheidou,and Osage exhibited grade 1 salt tolerance rates surpassing other tested materials.Furthermore,Hongzhudou and Qihuang34 demonstrated higher salt tolerance during germination and emergence stages based on their elevated rates of emergence,salt tolerance index,chlorophyll content,and shoot fresh weights.Overall findings provide valuable resources for molecular breeding efforts aimed at developing salt-tolerant soybean varieties suitable for cultivation in saline-alkali soils.

High efficient broad-spectrum Bradyrhizobium elkanii Y63-1

Soybean(Glycine max),the primary source of high-quality plant protein,plays a crucial role as a grain and oil crop in China.Harnessing the full potential of symbiotic nitrogen fixation in soybean production holds immense significance for agriculture and ecology alike.Zhongdou 63,a newly developed early-maturing summer soybean cultivar in 2021,exhibits remarkable traits such as high yield,superior quality,multi-resistance,and wide adaptability.In this study,eight distinct rhizobia strains from diverse regions were meticulously screened to identify highly effective strains specifically suited for Zhongdou 63.The aboveground biomass,plant height,chlorophyll content,root length,nodule number,and nodule dry weight of Zhongdou 63 were measured and the data were subjected to statistical analysis.The results demonstrated that Y63-1 is a predominant strain of Zhongdou 63.Subsequently,we conducted further investigations on the broad-spectrum nodulation characteristics of Y63-1.Ten representative soybean cultivars were individually inoculated with Y63-1 and subsequently analyzed for nodule numbers and nodule dry weight in their symbiotic systems with rhizobia.The findings revealed that Y63-1 effectively formed nodules with all ten soybean varieties tested.In summary,our current study identified highly efficient broad-spectrum Bradyrhizobium elkanii strain Y63-1 as the predominant strain in Zhongdou 63 and provided a theoretical foundation for enhancing yield potential not only in Zhongdou 63 but also in other varieties through inoculation with highly efficient rhizobia in production.

Herbivore defense responses and associated herbivore defense mechanism as revealed by comparing a resistant wild soybean with a susceptible cultivar

Plants have evolved sophisticated defense mechanisms against herbivores to help them adapt to the environment. Understanding the defense mechanisms in plants can help us control insects in a more effective manner. In this study, we found that compared with Tianlong 2(a cultivated soybean with insect susceptibility), ED059(a wild soybean line with insect resistance)contains sharper pubescence tips, as well as lower transcript levels of wound-induced protein kinase(WIPK) and salicylic acid-induced protein kinase(SIPK), which are important mitogen-activated protein kinases involved in early defense response to herbivores. The observed lower transcript levels of WIPK and SIPK induced higher levels of jasmonic acid(JA), JA biosynthesis enzymes(AOC3) and some secondary metabolites in ED059. Functional analysis of the KTI1 gene via Agrobacterium-mediated transformation in Arabidopsis thaliana indicated that it plays an important role in herbivore defense in ED059. We further investigated the molecular response of third-instar Helicoverpa armigera(Hübner) larvae to Tianlong 2 and ED059. We found apoptotic cells only in the midguts of larvae that fed on ED059. Compared with larvae reared on the susceptible cultivar Tianlong 2, transcript levels of catalase(CAT) and glutathione S-transferase(GST) were up-regulated, whereas those of CAR, CHSB, and TRY were down-regulated in larvae that fed on the highly resistant variety ED059. We propose that these differences underlie the different herbivore defense responses of ED059 and Tianlong 2.

Comparative analysis of symbiotic phenotypes of soybean ’’Tianlong 1’’ with two different rhizobia and co-inoculation at different developmental stages

Symbiotic nitrogen fixation between soybean and rhizobia, which directly catalyze reduction of atmospheric nitrogen into ammonia, has critical importance in agricultural economy and environment. However, soybean symbiotic nitrogen efficiency, which changes with growth stage, largely relies on symbiotic host-specificity and nodule development. In this report, symbiotic phenotypes of soybean ‘Tianlong 1’ with different inoculation (inoculated with Bradyrhizobium japonicum strain 113-2, Sinorhizobium fredii USDA205 and co-inoculated with 113-2 and USDA205) were comparatively studied at different developmental stages. Without additional nitrogen, chlorophyll content, above ground fresh weight,plant height, nodule number and nodule dry weight changed with different rhizobia at various developmental stages. 113-2 had more advantages than USDA205 in promoting plant growth and nodulation. Nodulation morphology of co-inoculation was more similar to 113-2 than USDA205. Competitive nodulation between two rhizobia promoted plant growth, which had significant agricultural application prospect. For the first time, this study provided evidence for co-inoculation with different rhizobia having positive effect on plant growth, and shed new light on the competitive relationship between different rhizobia.

Symbiotic matching between soybean ‘Tianlong 1’ and rhizobia

‘Tianlong 1’ is widely popularized and applied with good comprehensive characters and is also good receptor for genetic transformation. However, little is known about symbiotic nitrogen fixation of ‘Tianlong 1’. In this report, 10 soybean rhizobia from different areas were selected to perform symbiotic matching test with ‘Tianlong 1’ in chamber. Two aboveground indicators (fresh weight aboveground and plant height) and 4 underground indicators (length of root, number of nodules, dry weight of root nodules per plant and morphology of nodules) were measured and data were statistically analyzed. Results showed that ‘Tianlong 1’ was a broad-hosted soybean which has different symbiotic matching abilities with these 10 rhizobia. Bradyrhizobium japonicum has more advantages than Sinorhizobium fredii in promoting plant growth and nodulation. 113-2 and 5036 were high effective strains. 113-2 was regarded as the most effective rhizobium matching to ‘Tianlong 1’ due to geographical advantages and adaptability. This research will promote symbiotic fixation of ‘Tianlong 1’ in agricultural industry for the first time.

Expression pattern of GmLAX genes under different stresses in soybean drought sensitive cultivar and tolerant cultivar

Auxin has been reported to regulate plant growth and development,as well as to mediate plant adaption to abiotic stresses,including drought.AUX/LAX family displays auxin uptake functions and comprises four highly conserved genes AUX1 and LIKE AUX1(LAX1,LAX2,and LAX3)in Arabidopsis.There are fifteen GmLAX family genes in the soybean genomes and several members were regulated by dehydration stress.In this study,the sequence differences and expression pattern of GmLAXs-I were analyzed under stress treatment between the soybean droughttolerant Jindou 21 and drought-sensitive varieties Zhongdou 33.Five homologous genes of AUX1 were all responsive to PEG,salt,ABA and IAA stimuli.There were two SNPs in the promoter region of GmLAX4 gene,and this gene was differentially expressed in two cultivars.Moreover,our results showed YFP-GmLAXs are predominantly localized in plasma membrane.Taken together,our results suggest that GmLAXs are involved in abiotic response,which can provide theoretical and technical support for the genetic improvement of soybean drought tolerance.

Evaluation of seed vigor in soybean germplasms from different eco-regions

Seed vigor plays an essential role in soybean production.Soybean seed is sensitive to environment and easy to get seed deterioration.Generally soybean seed vigor can be maintained for less than one year and have to be multiplied every year.Varieties with good seed vigor are essential for maintaining planting population and stable yield.In this research,419 germplasms from three eco-regions,South China,Huanghuai region and Northeast China,were evaluated for seed vigor by assessing germination ratio,germination potential and germination index.About 34.8%of tested germplasm had germination ratio equal or more than 85%,suggested by the national soybean seed quality standard of China.Only 9 from 82 tested cultivars met the seed standard.Seed germination ratio distribution had obvious regional feature.Landraces performed better seed vigor than cultivars.Germplasms from South China had stronger seed vigor compared to those from Huanghuai and Northeast regions.Seed vigor has no significant relationship with maturity and 100-seed weight.Totally 21 germplasms with strong seed vigor,favor maturation and seed size were identified and can be used in future breeding program.

Pedigree analysis of nationally approved soybean cultivars from 1984 to 2013 and implications for breeding

To reveal origins of 316 state authorized varieties from 1984 to 2013, rules of their parentsJ selection including types and hybrid configurations of direct parents, geo-graphical sources and types of their ancestors were analyzed. Various important direct parents and ancestors were summarized and nuclear contribution of ancestors was also estimated by pedigree analysis. Among 316 registered cultivars, 298 （94.3%） were bred by hybridization, and most of their direct parents were cultivars or breeding lines （65.5%）. Cultivars and breeding lines were mostly used as female parents, with 53.0% and 38.7% respectively. The 316 released cultivars were traced to 373 final ancestors, mainly com-posed of landraces （55.5%） and breeding lines （36.7%）. The 373 final ancestors came from different regions, including 121 from northern area, 110 from Huang-Huai-Hai area, 53 from southern area and 76 from abroad. These ancestors were mainly from the same ecologic zone as the approved cultivars. Newly approved cultivars always have more ancestors and a broader genetic base. However, distribution of these ancestors was unbalanced, and a few ancestors provided significant genetic contributions to later generations, such as the most concentrated final ancestors from Huang-Huai-Hai region followed by northern and southern regions. These results offer more information regarding their important parents and provide valuable references to soybean breeding. We should increase soybean germplasm exchanges with different regions and make use of elite lines, foreign cultivars and wild soybean germplasm to broaden the genetic background.

Screening and evaluation for soybean resistance to Phakopsora pachyrhyzi in Glycine soja

Soybean rust caused by Phakopsora pachyrhizy is an important disease of soybean, and yield losses are very common in humid growing regions. Most commercial cultivars are susceptible and the disease is usually managed with fungicides. Resistance breeding is the most effective in controlling the disease. In this study, detached - leaf assay and greenhouse inoculation were used to screen 200 Glycine soja accessions for resistance to Phakopsora pachyrhizi in China. Most of the accessions were susceptible, and W8214 was the only accession that demonstrated RB resistance to Phakopsora pachyrhizy. The further repeated tests confirmed the resistance in W8214.