Salinity is a global challenge to agricultural production. Understanding Na⁺ sensing and transport in plants under salt stress will be of benefit for breeding robustly salt-tolerant crop species. In this review, first, possible salt stress sensor candidates and the root meristem zone as a tissue harboring salt stress-sensing components are proposed. Then, the importance of Na⁺ exclusion and vacuolar Na⁺ sequestration in plant overall salt tolerance is highlighted. Other Na⁺ regulation processes, including xylem Na⁺ loading and unloading, phloem Na⁺ recirculation, and Na⁺ secretion, are discussed and summarized. Along with a summary of Na⁺ transporters and channels, the molecular regulation of Na⁺ transporters and channels in response to salt stress is discussed. Finally, some largely neglected issues in plant salt stress tolerance, including Na⁺ concentration in cytosol and the role of Na⁺ as a nutrient, are reviewed and discussed.

Soybean (Glycine max (L.) Merr.) is a non-native and non-staple crop in sub-Saharan Africa (SSA) with potential to be a commercial crop owing to its wide range of uses as food, feed, and industrial raw material. Soybean was first introduced to SSA by Chinese traders in the 19th century and was cultivated as an economic crop as early as 1903 in South Africa. In the past four decades, soybean cultivation area and production in SSA has increased exponentially, from about 20,000?ha and 13,000?t in the early 1970s to 1,500,000?ha and 2,300,000?t in 2016. Soybean yield has been stagnant in SSA for decades at about 1.1?t?ha⁻¹, much lower than the world average, representing one of the most challenging issues in the soybean industry in SSA. The low soybean yield in SSA can be attributed to the use of poor-performing varieties and to the limited application of fertilizers and rhizobial inoculants in soils with no history of soybean production. South Africa, Nigeria, Zambia, and Uganda are the leading soybean producers in SSA. Soybean research in SSA is conducted by international and national research institutions, including IITA, national soybean improvement programs, universities, and the private sector. Between 1970 and 2011, 195 soybean varieties were released by IITA, private breeders, and national soybean improvement programs in SSA. This paper reviews the history and current state of soybean production and of the utilization and adoption of tropical varieties in SSA, addresses the major soybean yield-limiting factors across the region, and discusses the potential of the soybean industry in SSA. It also highlights soybean improvement efforts and lessons learned from previous soybean improvement efforts and the current progress of some national soybean improvement programs in SSA. Opportunities for scaling up tropical soybean as a major crop across SSA countries are promising.

Leaf senescence is normally the last stage of plant development. Early senescence of functional leaves significantly reduces the photosynthetic time and efficiency, seriously affecting grain yield and quality in wheat. Discovering genes responsible for early leaf senescence (els) are necessary for developing novel germplasms and cultivars with delayed leaf-senescence through molecular manipulation and marker assisted selection. In this study, we identified an early leaf senescence line M114 in a derivative of a wheat breeding population. Genetic analysis indicated that early leaf senescence in M114 is controlled by a single recessive gene, provisionally designated els1. By applying bulked segregant analysis and RNA-Seq (BSR-Seq), seven polymorphic markers linked to els1 were developed and the gene was located on chromosome arm 2BS in a 1.5 cM genetic interval between markers WGGB303 and WGGB305. A co-segregating marker, WGGB302, provide a starting point for fine mapping and map-based cloning of els1.

Soybean isoflavones are essential secondary metabolites synthesized in the phenylpropanoid pathway and benefit human health. In the present study, high-resolution QTL mapping for isoflavone components was performed using specific-locus amplified fragment sequencing (SLAF-seq) with a recombinant inbred line (RIL) population (F_5:7) derived from a cross between two cultivated soybean varieties, Luheidou 2 (LHD2) and Nanhuizao (NHZ). Using a high-density genetic map comprising 3541 SLAF markers and the isoflavone contents of soybean seeds in the 200 lines in four environments, 24 stable QTL were identified for isoflavone components, explaining 4.2%-21.2% of phenotypic variation. Of these QTL, four novel stable QTL (qG8, qMD19, qMG18, and qTIF19) were identified for genistin, malonyldaidzin, malonylgenistin, and total isoflavones, respectively. Gene annotation revealed three genes involved in isoflavone biosynthesis (Gm4CL, GmIFR, and GmCHR) and 13 MYB-like genes within genomic regions corresponding to stable QTL intervals, suggesting candidate genes underlying these loci. Nine epistatic QTL were identified for isoflavone components, explaining 4.7%-15.6% of phenotypic variation. These results will facilitate understanding the genetic basis of isoflavone accumulation in soybean seeds. The stable QTL and tightly linked SLAF markers may be used for marker-assisted selection in soybean breeding programs.

Diseases and health complications caused by mineral deficiencies afflict billions of people globally. Developing pulse crops with elevated seed mineral concentrations can contribute to reducing the incidence of these deficiencies. The objectives of this study were to estimate variance components conditioning seed mineral concentrations of chickpea and lentil grown in Washington and Idaho, determine correlations between different mineral concentrations and between mineral concentrations and yield, 100-seed weight, and days to flowering, and compare seed mineral concentrations between chickpeas and lentils grown in adjacent plots. Genotype effects, although significant in chickpea and lentil for all minerals except selenium, tended to be minimal compared to location, year, and their interaction effects. In both chickpeas and lentils high positive correlations were observed between seed concentrations of phosphorus and potassium, phosphorus and zinc, and potassium and zinc. Correlations between mineral concentration and yield, and mineral concentration and days to 50% flowering were similar for chickpeas and lentils across the majority of minerals. These results may reflect similarities between the two crops in physiological processes for mineral uptake and partitioning. Lentils had higher concentrations of iron and zinc than chickpea when the two crops were grown in adjacent plots, whereas chickpeas had higher concentrations of calcium and manganese. Plant genotypes that are more efficient at obtaining minerals from growing environments will be useful as parental materials to develop improved chickpea and lentil cultivars that have good yield potential coupled with high seed mineral concentrations.

Vitamin B is essential for maintaining normal life activities in humans and animals who have to intake the microelement from the outside, especially from cereal products. In the present study 166 Chinese and foreign wheat cultivars planted in two environments were characterized for variation in vitamin B1 and B2 contents. A genome-wide association study (GWAS) using the wheat 90 K SNP assay identified 17 loci for vitamin B1 and 7 for vitamin B2 contents. Linear regression analysis showed a significantly positive correlation of the number of favorable alleles with vitamin B1 and B2 contents. Marker-trait associations (MTAs) at IWB43809 (6AS, 0 cM) and IWB69903 (6AS, 13 cM) were new and stable, and significantly associated with vitamin B1 content across two environments. The loci identified in this study and associated SNP markers could be used for improvement of vitamin B1 and B2 contents to obtain superior quality along with grain yield in wheat.

Genetic distances between hybrid parents based on phenotypic traits and molecular markers were investigated to assess their relationship with heterosis for grain and stover yield and other traits in pearl millet (Pennisetum glaucum [L.] R. Br.). Fifty-one hybrids developed using 101 hybrid parents (B and R lines) and showing a wide range of genetic distance between their parents based on eight phenotypic traits and 28-38 SSRs were evaluated in two sets for two seasons. The correlation between Euclidean distance (phenotypic distance, ED) and simple matching distance (molecular distance, SM) for parents of both sets was low but positive and significant (r=0.2, P<0.001).The correlation of ED in parents with better-parent heterosis for grain yield was similar in both sets (r=0.38, P<0.05). SM was not correlated with heterosis for grain yield in either set of hybrids. The results showed that phenotypic distance could be a better predictor of heterosis than molecular distance. The correlation between phenotypic distance and heterosis was not strong enough to permit the use of phenotypic diversity among parents as a major selection criterion for selection of parental lines displaying high levels of heterosis for grain and stover yield in pearl millet.

Cigar line Beinhart 1000-1 has effective durable resistance to black shank (BS) and is considered one of the most resistant sources in tobacco (Nicotiana tabacum L.). To investigate the inheritance and identification of stable quantitative trait loci (QTL) for BS response, F₂, BC₁F₂ individuals and BC₁F_2:3 lines were produced from a cross between Beinhart 1000-1 and Xiaohuangjin 1025. Two major quantitative trait loci (M-QTL) named qBS7 and qBS17 were repeatedly detected under different conditions. QTL qBS7 was mapped to the region between PT30174 and PT60621 and explained 17.40%-25.60% of the phenotypic variance under different conditions. The other QTL qBS17 in interval PT61564-PT61538 of linkage group 17 was detected in a BC₁F₂ population in the field and in BC₁F_2:3 in both the field and at the seedling stage, explaining 6.90% to 11.60% of the phenotypic variance. The results improve our understanding of the inheritance of resistance to BS and provide information that can be used in marker-assisted breeding.

Identification of quantitative trait loci (QTL) having small effects on heading date (HD) is important for fine-tuning flowering time in rice (Oryza sativa L.). In this study, minor-effect QTL for HD were identified using five segregating rice populations, including a recombinant inbred line population derived from crosses between indica cultivar Teqing and near isogenic lines of IR24, and four populations derived from residual heterozygotes identified in the original population. HD data from these populations were obtained in multiple years or at two locations with different photoperiods. A total of 11 QTL were detected; they had small additive effects ranging from 0.21 to 1.63 days. The QTL were all detected in different populations, locations and/or years, having consistent allelic effects across experiments and a stable magnitude across years at the same location. These QTL, and other minor-effect QTL that have been cloned or fine-mapped, generally do not have strong photoperiod sensitivity, and thus can be used in a wide range of eco-geographical conditions. Seven of the 11 QTL were different from those that have been cloned or fine-mapped, providing new candidates for gene cloning and marker-assisted breeding. Allelic effects of QTL corresponding to those that had been cloned or fine-mapped, were much smaller in this study than previously reported. The results supported the assumption that qualitative and quantitative genes may be different alleles at the same loci, suggesting that it may be promising to identify minor-effect QTL from major heading date genes/QTL that have been cloned.

Lentil (Lens culinaris Medik) is one of the most important food legumes in the world. The use in lentil of molecular marker-assisted breeding is limited, owing to the low availability of polymorphic markers. In the present study, we developed a set of polymorphic intron-spanning markers (ISMs) using a cross-species mapping approach. In this approach, putative unique transcripts (PUTs) of L. culinaris were mapped onto the Medicago truncatula genome, exploiting its closeness with the lentil genome. Spliced alignment of the PUTs resulted in a total of 25,717 alignments, allowing the development of 1703 ISMs. From these, a subset of 105 ISMs were synthesized and validated with a 51% amplification success rate in 32 lentil genotypes. Of these ISMs, 40 (74%) were polymorphic and generated 2-11 alleles per locus in a genetically diverse panel of 32 lentil genotypes including wild species. This set of polymorphic ISMs along with their functional annotation data will be useful in lentil breeding.

This study determined the effects of genotype-by-environment (G × E) interaction and stability of yield among elite cowpea (Vigna unguiculata L.) selections derived by gamma irradiation. The study was conducted in Namibia at three selected sites: Bagani, Mannheim, and Omahenene, during 2014/2015 and 2015/2016. Thirty-four newly developed mutant genotypes and three local checks were evaluated using a randomized complete block design with three replications. Grain yield data were analyzed using the additive main effects and multiplicative interaction (AMMI) and the genotype main effect plus genotype-by-environment interaction (GGE) biplot methods. The AMMI and GGE biplot models explained 77.49% and 75.57% of total observed genotypic variation, respectively. Bagani and Omahenene were the environments best discriminating the test genotypes during 2014/2015 and 2015/2016, respectively. Four promising mutant genotypes: G9 (ShL3P74), G10 (ShR3P4), G12 (ShR9P5), and G4 (ShL2P4), showed wide adaptation and grain yields of 2.83, 2.06, 1.99, and 1.95 t ha^{− 1}, respectively. The novel mutant lines are useful genetic resources for production or future cowpea breeding programs in Namibia or similar environments.

Single-guide RNA (sgRNA) is one of the two core components of the CRISPR (clustered regularly interspaced short palindromic repeat)/Cas (CRISPR-associated) genome-editing technology. We established an in vitro Traffic Light Reporter (TLR) system, which is designated as the same colors as traffic lights such as green, red and yellow were produced in cells. The TLR can be readily used in maize mesophyll protoplast for a quick test of promoter activity. The TLR assay indicates the variation in transcription activities of the seven Pol III promoters, from 3.4% (U6-1) to over 21.0% (U6-6). The U6-2 promoter, which was constructed to drive sgRNA expression targeting the ZmWx1 gene, yielded mutation efficiencies ranging from 48.5% to 97.1%. Based on the reported and unpublished data, the in vitro TLR assay results were confirmed to be a readily system and may be extended to other plant species amenable to efficient genome editing via CRISPR/Cas. Our efforts provide an efficient method of identifying native Pol III-recognized promoters for RNA guide-based genome-editing systems in maize.