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.

Laboratory testing and molecular analysis of the resistance of wild and cultivated soybeans to cotton bollworm, Helicoverpa armigera(Hübner)

Identifying a superior soybean variety with high defoliator resistance is important to avoid yield loss. Cotton bollworm(Helicoverpa armigera Hübner) is one of the major defoliators of soybean(Glycine max [L.] Merr.) worldwide. In this study, we evaluated the effect of H. armigera larvae on ED059, a wild soybean(Glycine soja Sieb. et Zucc.), and three cultivated soybean varieties: Tianlong 2, PI 535807, and PI 533604, in choice and no-choice assays. The percentage of ED059 leaflets consumed by H. armigera was lower than that of the three cultivated soybeans. Larvae that fed on ED059 exhibited low weight gain and high mortality rate.Waldbauer nutritional indices suggested that ED059 reduced the growth, consumption, and frass production of H. armigera larvae. Larvae that fed on ED059 showed lower efficiency of conversion of ingested and of digested food than those that fed on Tianlong 2 and PI 533604.However, they showed statistically similar consumption index and approximate digestibility compared with those fed on the three cultivated soybeans. Quantitative real-time PCR analysis revealed that 24 h after insect attack, ED059 had higher transcript levels of Kunitz trypsin inhibitor 3, Cysteine proteinase inhibitor 2, and Nerolidol synthase 1 but a lower transcript level of Pathogenesis-related protein 1 than Tianlong 2. The gene expression results were consistent with the presence of higher levels of jasmonic acid(JA) and transcript levels of the JA biosynthesis enzyme allene oxide cyclase 3 in ED059 than in Tianlong 2. Our findings indicate that ED059 is a superior soybean line with strong insect resistance that may be mediated via the JA pathway.

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.

Research status of soybean symbiosis nitrogen fixation

Soybean(Glycine max)is one of the most important economic legume crops with largest planting area,and is also an important oil crop,as well as food and feed material.Soybean-rhizobia symbiosis plays important roles in plant cultivation and fertilizer application.However,there are many problems in agricultural application of soybean symbiotic nitrogen fixation.In this review,we summarized three restriction factors(host specificity,low nitrogen fixation efficiency and abiotic stress)and discussed research progresses of these factors.Clarification of host specific mechanism will help to select and apply rhizobia inoculants.Both maintaining high nitrogenase activity and delaying nodule senescence can improve the efficiency of symbiotic nitrogen fixation.Abiotic stress-tolerant rhizobia can improve the abiotic stress tolerance of soybean.Breeding stress tolerant genotypes of soybean and rhizobia,obtaining correlated genes are the common strategies to improve soybean symbiotic nitrogen fixation under extreme conditions.Regulatory mechanisms of these restriction factors are still poorly understood and needs further clarification.

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.

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.

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.