High-density DArTSeq SNP markers revealed wide genetic diversity and structured population in common bean (Phaseolus vulgaris L.) germplasm in Ethiopia.

INTRODUCTION: Common bean is one of the widely consumed food security crop in Africa, Asia, and South America. Understanding genetic diversity and population structure is crucial for designing breeding strategies. MATERIALS: Two hundred and eighty-nine germplasm were recently collected from different regions of Ethiopia and introduced from CIAT to estimate genetic diversity and population structure using 11,480 DArTSeq SNP markers. RESULTS: The overall mean genetic diversity and polymorphic information content (PIC) were 0.38 and 0.30, respectively, suggested the presence of adequate genetic diversity among the genotypes. Among the geographical regions, landraces collected from Oromia showed the highest diversity (0.39) and PIC (0.30). The highest genetic distance was observed between genotypes collected from SNNPR and CIAT (0.49). In addition, genotypes from CIAT were genetically more related to improved varieties than the landraces which could be due to sharing of parents in the improvement process. The analysis of molecular variance revealed that the largest proportion of variation was due to within the population both in geographical region (63.67%) and breeding status (61.3%) based classification. Model-based structure analysis delineated the 289 common bean genotypes into six hypothetical ancestoral populations. CONCLUSIONS: The genotypes were not clustered based on geographical regions and they were not the main drivers for the differentiation. This indicated that selection of the parental lines should be based on systematic assessment of the diversity rather than geographical distance. This article provides new insights into the genetic diversity and population structure of common bean for association studies, designing effective collection and conservation for efficient utilization for the improvement of the crop.

Two Intra-Individual ITS1 rDNA Sequence Variants Identified in the Female and Male Rotylenchulus reniformis Populations of Alabama.

Around 300 different plant species are infected by the plant-parasitic reniform nematode (Rotylenchulus reniformis), including cotton. This is a devasting nematode with a preference for cotton; it is commonly found in Alabama farms and causes severe reduction in yields. Its first internal transcribed spacer (ITS1) region can be sequenced, and potential mutations can be found in order to study the population dynamics of the reniform nematode. The goal of our study was to sequence the ITS1 rDNA region in male and female RNs that were collected from BelleMina, Hamilton, and Lamons locations in Alabama. After separating the single male and female RNs from the samples collected from the three selected listed sites above, the ITS1 region was amplified selectively using specific primers, and the resulting products were cloned and sequenced. Two distinct bands were observed after DNA amplification of male and female nematodes at 550 bp and 730 bp, respectively. The analysis of sequenced fragments among the three populations showed variation in average nucleotide frequencies of female and male RNs. Singletons within the female and male Hamilton populations ranged from 7.8% to 10%, and the variable sites ranged from 13.4% to 26%. However, female and male BelleMina populations had singletons ranging from 7.1% to 19.7% and variable regions in the range of 13.9% to 49.3%. The female and male Lamons populations had singletons ranging from 2.5% to 8.7% and variable regions in the range of 2.9% to 14.2%. Phylogenetic (neighbor-joining) analysis for the two ITS1 fragments (ITS-550 and ITS-730) showed relatively high intra-nematode variability. Different clone sequences from an individual nematode often had greater similarity with other nematodes than with their own sequences. RNA fold analysis of the ITS1 sequences revealed varied stem and loop structures, suggesting both conserved and variable regions in the variants identified from female and male RNs, thus underscoring the presence of significant intra- and inter-nematodal variation among RN populations in Alabama.

Induced variations of ethyl methane sulfonate mutagenized cowpea (Vigna unguiculata L. walp) plants.

Unique variants are desired in the development of genetically improved crops to meet farmer and market needs hence ethyl methane sulfonate (EMS) was used to induce genetic variability in cowpea (Vigna unguiculata cv. Asontem). The main objective of this research was to characterize induced variations in EMS chemically mutagenized population of cowpea (Vigna unguiculata L. Walp Var. Asontem) in the M1 and M2 generations. The optimum concentration (LD50) of EMS for generating the mutagenized population was determined by treating seeds with different concentrations of EMS (0.0, 0.2, 0.4, 0.6, and 0.8% v/v) and observing the germination count after 5 days of planting the seeds in Petri dishes. Three thousand cowpea seeds were treated with the 0.4% EMS to generate the M1 and M2 populations that were evaluated for agronomic and morphological traits with untreated seeds serving as control. Data analysis involved distribution of qualitative and quantitative traits. Germination was significantly reduced in the mutagenized population (17.8%) and compared with that of the wild type (61.6%). Percentage survival was significantly higher in wild type (98.38%) as compared with the M1 population (78.46%). Percentage germination in the M2 population (74.03%) was lower than the wild type (80%). A wide spectrum of agro-morphological abnormalities was observed in the M2 population. Wide variations and uniquely different phenotypic classes were observed in leaf color, leaf shape, growth habit, plant pigmentation, twining tendency, pod curvature, seed shape, and seed coat color. M2 individuals were widely distributed for days to flowering, number of pods per plant, number of seeds per pod, number of locules per pods, percentage seed set, pod length and number of seeds per plant. In conclusion, the EMS mutagenesis was effective in inducing the unique variations that will be useful for breeding and development of new farmer preferred varieties.

Drought Tolerance and Application of Marker-Assisted Selection in Sorghum.

Sorghum is an important staple food crop in drought prone areas of Sub-Saharan Africa, which is characterized by erratic rainfall with poor distribution. Sorghum is a drought-tolerant crop by nature with reasonable yield compared to other cereal crops, but such abiotic stress adversely affects the productivity. Some sorghum varieties maintain green functional leaves under post-anthesis drought stress referred to as stay-green, which makes it an important crop for food and nutritional security. Notwithstanding, it is difficult to maintain consistency of tolerance over time due to climate change, which is caused by human activities. Drought in sorghum is addressed by several approaches, for instance, breeding drought-tolerant sorghum using conventional and molecular technologies. The challenge with conventional methods is that they depend on phenotyping stay-green, which is complex in sorghum, as it is constituted by multiple genes and environmental effects. Marker assisted selection, which involves the use of DNA molecular markers to map QTL associated with stay-green, has been useful to supplement stay-green improvement in sorghum. It involves QTL mapping associated with the stay-green trait for introgression into the senescent sorghum varieties through marker-assisted backcrossing by comparing with phenotypic field data. Therefore, this review discusses mechanisms of drought tolerance in sorghum focusing on physiological, morphological, and biochemical traits. In addition, the review discusses the application of marker-assisted selection techniques, including marker-assisted backcrossing, QTL mapping, and QTL pyramiding for addressing post-flowering drought in sorghum.

Participatory analysis of groundnut (Arachis hypogaea L.) cropping system and production constraints in Burkina Faso.

BACKGROUND: Groundnut is one of the major legume crops grown as food and cash crop across the different agroecological zones of Burkina Faso. It is ranked the 2nd important legume crop for household food, nutrition, and income generation for both rural and urban zones, contributing significantly to food supply and economy of the country. Despite its importance and breeding efforts to develop improved varieties, groundnut productivity remains low. Assessing and describing the present groundnut cropping system and production constraints as well as gender dynamics in the main production areas will help in defining the groundnut breeding priorities. METHODS: A participatory rural appraisal study was conducted in three groundnut production regions (central-eastern, central-northern, and central-western). In each region, 4 villages were selected with a total of 124 farmers interviewed to collect data on socio-demographics, farming systems, cropping practices, and production constraints. Data analysis was carried out for qualitative and quantitative variables using STATA 14. Analysis of variance was conducted across regions and gender, and also between and within regions. Kendall's coefficients were determined for qualitative variables across regions for the constraints using the pairwise rank. Pearson's correlation was carried out to assess the relationship between variables, and the chi-square test was used to assess the difference in farmer preferences. RESULTS: The study revealed a cropping system of groundnut in an environment largely affected by climate change and in a subsistence and extensive agriculture. There is a variation in the groundnut cropping system across the regions. Gender plays a key role in the production of the groundnut, and 48.39% of women are engaged in groundnut cropping with less access to land and production resources. A yield gap between men and women was observed with men achieving more yield than women. There was a strong correlation between the use of improved varieties and technical assistance. A strong correlation was observed between farm size and production, and farm size and sex denoting an extensive production. Production constraints, although similar, were perceived and ranked differently between regions. The lack of improved varieties, absence of agricultural credit, lack of production tools, the high price of seeds, the high price of fertilizer, drought, and disease are some of the important constraints affecting groundnut productivity. CONCLUSION: This study provides a recent view of groundnut cropping, allowing a good understanding of the farmers' situation. The result will contribute to the refining of breeding priorities and guide further activities in groundnut breeding in Burkina Faso.

Integrative genome-wide analysis reveals the role of WIP proteins in inhibition of growth and development.

In cucurbits, CmWIP1 is a master gene controlling sex determination. To bring new insight in the function of CmWIP1, we investigated two Arabidopsis WIP transcription factors, AtWIP1/TT1 and AtWIP2/NTT. Using an inducible system we showed that WIPs are powerful inhibitor of growth and inducer of cell death. Using ChIP-seq and RNA-seq we revealed that most of the up-regulated genes bound by WIPs display a W-box motif, associated with stress signaling. In contrast, the down-regulated genes contain a GAGA motif, a known target of polycomb repressive complex. To validate the role of WIP proteins in inhibition of growth, we expressed AtWIP1/TT1 in carpel primordia and obtained male flowers, mimicking CmWIP1 function in melon. Using other promoters, we further demonstrated that WIPs can trigger growth arrest of both vegetative and reproductive organs. Our data supports an evolutionary conserved role of WIPs in recruiting gene networks controlling growth and adaptation to stress.

The gynoecious CmWIP1 transcription factor interacts with CmbZIP48 to inhibit carpel development.

In angiosperms, sex determination leads to development of unisexual flowers. In Cucumis melo, development of unisexual male flowers results from the expression of the sex determination gene, CmWIP1, in carpel primordia. To bring new insight on the molecular mechanisms through which CmWIP1 leads to carpel abortion in male flowers, we used the yeast two-hybrid approach to look for CmWIP1-interacting proteins. We found that CmWIP1 physically interacts with an S2 bZIP transcription factor, CmbZIP48. We further determined the region mediating the interaction and showed that it involves the N-terminal part of CmWIP1. Using laser capture microdissection coupled with quantitative real-time gene expression analysis, we demonstrated that CmWIP1 and CmbZIP48 share a similar spatiotemporal expression pattern, providing the plant organ context for the CmWIP1-CmbZIP48 protein interaction. Using sex transition mutants, we demonstrated that the expression of the male promoting gene CmWIP1 correlates with the expression of CmbZIP48. Altogether, our data support a model in which the coexpression and the physical interaction of CmWIP1 and CmbZIP48 trigger carpel primordia abortion, leading to the development of unisexual male flowers.

[Sex determination in cucurbits]. / Le déterminisme du sexe chez les cucurbitacées.

Sex determination in plants leads to the development of unisexual flowers from an originally bisexual floral meristem. Cucurbits are not only species of agronomic interest but they also represent model species for the study of plant sex determination, because of their ability to harbor different sexual types. Such sexual forms are controlled by the identity of the alleles at the following loci: andromonoecious (a) and gynoecious (g) in melon, or androecious (a), Female (F), and Monoecious (M) in cucumber. We firstly showed that the andromonoecious a gene in melon encodes for an ACC synthase (CmACS7) and demonstrated that andromonoecy results from a mutation in the active site of the enzyme. Expression of the active enzyme inhibits the development of the male organs and is not required for carpel development. Because the a gene in melon and M gene in cucumber control the same sexual transition, monoecy to andromonoecy, we isolated the andromonoecy M gene in cucumber using a candidate gene approach in combination with genetic and biochemical analysis. We demonstrated the co-segregation of CsACS2, a close ortholog of CmACS7, with the M locus, and showed that the cucumber andromonoecious phenotype is also due to a loss of ACS enzymatic activity. CsACS2 is expressed specifically in carpel primordia of female flowers and should play a similar role to that of CmACS7 in melon in the inhibition of stamina development. Finally, we also showed that the transition from male to female flowers in the gynoecious lines results from epigenetic changes in the promoter of a C(2)H (2) zinc-finger transcription factor, CmWIP1. This epigenetic change is elicited by the insertion of a DNA transposon, which causes the spreading of DNA methylation to the CmWIP1 promoter. Expression of CmWIP1 leads to carpel abortion, resulting in the development of unisexual male flowers. From all these results, we built a model in which CmACS7 and CmWIP1 interact to control the development of male, female and hermaphrodite flowers in melon.