Effectiveness of wetlands as reservoirs for integrated water resource management in the Ruzizi plain based on water evaluation and planning (WEAP) approach for a climate-resilient future in eastern D.R. Congo.

It is widely predicted that climate change's adverse effects will intensify in the future, and along with inadequate agricultural practices, settlement development, and other anthropic activities, could contribute to rapid wetland degradation and thus exert significant negative effects on local communities. This study sought to develop an approach based on the Integrated Water Resource Management (IWRM) in the Ruzizi Plain, eastern Democratic Republic of Congo (DRC), where adverse effects of the climate change are increasingly recurrent. Initially, we analyzed the trends of climate data for the last three decades (1990-2022). Subsequently, the Water Evaluation and Planning (WEAP) approach was employed on two contrasting watersheds to estimate current and future water demands in the region and how local wetlands could serve as reservoirs to meeting water demands. Results indicate that the Ruzizi Plain is facing escalating water challenges owing to climate change, rapid population growth, and evolving land-use patterns. These factors are expected to affect water quality and quantity, and thus, increase pressure on wetland ecosystems. The analysis of past data shows recurrence of dry years (SPI ≤ - 1.5), reduced daily low-intensity rainfall (Pmm < 10 mm), and a significant increase in extreme rainfall events (Pmm ≥ 25 mm). The WEAP outcomes revealed significant variations in future water availability, demand, and potential stressors across watersheds. Cropland and livestock are the main water consumers in rural wetlands, while households, cropland (at a lesser extent), and other urban uses exert significant water demands on wetlands located in urban environments. Of three test scenarios, the one presenting wetlands as water reservoirs seemed promising than those considered optimal (based on policies regulating water use) and rational (stationary inputs but with a decrease in daily allocation). These findings highlight the impact of climate change in the Ruzizi plain, emphasizing the urgency of implementing adaptive measures. This study advocates for the necessity of the IWRM approach to enhance water resilience, fostering sustainable development and wetland preservation under changing climate.

Crop calendar optimization for climate change adaptation in yam farming in South-Kivu, eastern D.R. Congo.

The traditional crop calendar for yam (Dioscorea spp.) in South-Kivu, eastern Democratic Republic of Congo (DRC), is becoming increasingly inadequate given the significant climatic variability observed over the last three decades. This study aimed at: (i) assessing trends in weather data across time and space to ascertain climate change, and (ii) optimizing the yam crop calendar for various South-Kivu agro-ecological zones (AEZs) to adapt to the changing climate. The 1990-2022 weather data series were downloaded from the NASA-MERRA platform, bias correction was carried out using local weather stations' records, and analyses were performed using RClimDex 1.9. Local knowledge and CROPWAT 8.0 were used to define planting dates for yam in different AEZs. Results showed the existence of four AEZs in the South-Kivu province, with contrasting altitudes, temperatures, and rainfall patterns. Climate change is real in all these South-Kivu's AEZs, resulting either in rainfall deficits in some areas, or extreme rainfall events in others, with significant temperature increases across all AEZs. Suitable yam planting dates varied with AEZs, September 15th and 20th were recommended for the AEZ 2 while October 15th was optimal for AEZ 1, AEZ 3, and AEZ 4. However, none of the planting date scenarios could meet the yam water requirements in AEZ1, AEZ3, and AEZ4, since the effective rainfall (Pmm) was always inferior to the plant water demand (ETc), meaning that soil water conservation practices are needed for optimum plant growth and yield in these AEZs. This study does not recommend planting yam during the short rainy season owing to prolonged droughts coinciding with critical growth phases of yam, unless supplemental irrigation is envisaged. This study provided insights on the nature of climate change across the past three decades and suggested a yam crop calendar that suits the changing climate of eastern DRC.

Agronomic and hormonal approaches for enhancing flowering intensity in white Guinea yam (Dioscorea rotundata Poir.).

Developing novel white Guinea yam (Dioscorea rotundata) varieties is constrained by the sparse, erratic, and irregular flowering behavior of most genotypes. We tested the effectiveness of nine agronomic and hormonal treatments to enhance flowering on D. rotundata under field conditions. Genotypes responded differently to flower-inducing treatments (p<0.001). Of the test treatments, pruning and silver thiosulfate (STS) were effective in increasing the number of spikes per plant and the flowering intensity on both sparse flowering and monoecious cultivars. STS and tuber removal treatments promoted female flowers on the monoecious variety while pruning and most treatments involving pruning favored male flowers. None of the treatments induced flowering on Danacha, a non-flowering yam landrace. Flower-enhancing treatments had no significant effect on flower fertility translated by the fruit set, since most treatments recorded fruit sets above the species' average crossability rate. Flower-enhancing techniques significantly influenced number of tubers per plant (p = 0.024) and tuber dry matter content (DMC, p = 0.0018) but did not significantly affect plant tuber yield. Nevertheless, treatments that could enhance substantially flowering intensity, such as pruning and STS, reduced tuber yield. DMC had negative associations with all flowering-related traits. This study provided insights into white yam flower induction and suggests promising treatments that can be optimized and used routinely to increase flowering in yam crop, without significantly affecting flower fertility and tuber yield.

Optimization of plant density and fertilizer application to improve biofortified common bean (Phaseolus vulgaris L.) yield on Nitisols of South-Kivu, Eastern D.R. Congo.

Soil nutrient depletion and poor farming practices are serious challenges limiting crop productivity in soils of the eastern Democratic Republic of Congo (D.R. Congo). An experiment was conducted in two cropping seasons to assess the effect of plant density (25 plants m2 and 33 plants m2) and fertilizer application (with and without NPK) on the yield and yield components of three biofortified common bean varieties (HM21-7, RWR2245 and RWR2154). The experiment involved two plant densities, two fertilizer rates and three varieties arranged in a split-split plot design with three replications. Results showed that yield significantly varied with plant density, variety and fertilizer rate (p < 0.05). The best performing variety in terms of grain yield was HM21-7 (1.5 t ha-1) as compared to RWR2154 (1.09 t ha-1) and RWR2245 (1.14 t ha-1). The NPK fertilizer increased the grain yield by 38.2%. Grain yield increased also with the plant density, highest grain yield being recorded on higher plant density (1.37 t ha-1) as compared to low lower plant density (1.25 t ha-1). Agronomic efficiency (AE) was influenced by the variety, with the highest AE obtained on RWR2245 (23.27 kg kg-1) and on high plant density (20.34 kg kg-1). Therefore, we concluded that increasing the plant density by reducing the plant spacing, using NPK fertilizer and high yielding varieties provide with an opportunity to improving common bean yields on Nitisols dominating the highlands of eastern D.R. Congo.

Optimum time for hand pollination in yam (Dioscorea spp.).

Hand pollination success rate is low in yam (Dioscorea spp.), due partly to suboptimal weather conditions. Thus, determining the most suitable time for pollination could improve the pollination success in yam breeding programs. We performed continuous hand pollination within flowering windows of D. rotundata and D. alata for two consecutive years to determine the most appropriate month, week, and hours of the day allowing maximum pollination success. In D. alata crossing block, we observed significant differences among crossing hours for pollination success (p = 0.003); morning hours (8-12 a.m.) being more conducive than afternoons (12-5 p.m.). No significant differences existed between crossing hours in D. rotundata, though the mid-day seemed optimal. For both species, the time interval 11-12 a.m. was more appropriate for crossing while 4-5 p.m. was the poorest. However, in vitro pollen germination tests showed that mid-day pollen collection (12 noon-2 p.m.) had better results than both extremes, though there were strong genotypic effects on outcomes. Pollination success rates differed significantly among months for D. alata (p < 0.001) but not for D. rotundata (p > 0.05). Differences in pollination success existed across weeks within flowering windows of both D. alata (p < 0.001) and D. rotundata (p = 0.004). The seed production efficiency (SPE) had a similar trend as the pollination success rate. No clear pattern existed between the pollination time and the seed setting rate (SSR) or seed viability (SV), though their dynamics varied with weeks and months. This study provided an insight on the dynamics of pollination outcomes under the influence of pollination times and allows detecting months, weeks, and hours of the day when hybridization activities should be focused for better results.

Association mapping of plant sex and cross-compatibility related traits in white Guinea yam (Dioscorea rotundata Poir.) clones.

BACKGROUND: White Guinea yam (Dioscorea rotundata) is primarily a dioecious species with distinct male and female plants. Its breeding is constrained by sexual reproduction abnormalities, resulting in low success rates in cross-pollination. An accurate method for early detection of this plant's sex and compatible fertile parents at the seedling stage would improve levels of cross-pollination success in breeding. We used the genome-wide association studies (GWAS) to dissect the molecular basis of plant sex and cross-compatibility-related traits in a panel of 112 parental clones used in D. rotundata crossing blocks from 2010 to 2020. RESULTS: Population structure and phylogeny analyses using 8326 single nucleotide polymorphism (SNP) markers grouped the 112 white yam clones into three subpopulations. Using Multi-locus random-SNP-effect Mixed Linear Model, we identified three, one, and three SNP markers that were significantly associated with the average crossability rate (ACR), the percentage of high crossability (PHC), and the plant sex, respectively. In addition, five genes considered to be directly linked to sexual reproduction or regulating the balance of sex hormones were annotated from chromosomal regions controlling the assessed traits. This study confirmed the female heterogametic sex determination (ZZ/ZW) system proposed for D. rotundata. CONCLUSIONS: This study provides valuable insights on the genomic control of sex identity and cross-pollination success in D. rotundata. It, therefore, opens an avenue for developing molecular markers for predicting plant sex and cross-pollination success at the early growth stage before field sex expression in this crop.

Cross compatibility in intraspecific and interspecific hybridization in yam (Dioscorea spp.).

Yam (Dioscorea spp.) is a staple crop for millions of people in the tropics and subtropics. Its genetic improvement through breeding is being challenged by pre-zygotic and post-zygotic cross-compatibility barriers within and among species. Studies dissecting hybridization barriers on yam for improving the crossability rates are limited. This study aimed to assess the cross-compatibility, which yielded fruit set, viable seeds and progeny plants in an extensive intraspecific and interspecific crossing combinations in a yam genetic improvement effort to understand the internal and exogenous factors influencing pollination success. Cross-compatability was analyzed at the individual genotype or family level using historical data from crossing blocks and seedling nurseries from 2010 to 2020 at the International Institute of Tropical Agriculture (IITA). The average crossability rate (ACR) was lower in interspecific crossing combinations (6.1%) than intraspecific ones (27.6%). The seed production efficiency (SPE) values were 1.1 and 9.3% for interspecific and intraspecific crosses, respectively. Weather conditions and pollinator's skills are the main contributors to the low success rate in the intraspecific cross combinations in yam breeding. At the same time, genetic distance and heterozygosity played little role. Interspecific cross barriers were both pre-zygotic and post-zygotic, resulting from the evolutionary divergence among the yam species. Dioscorea rotundata had higher interspecific cross-compatibility indices than D. alata. Distant parents produced intraspecific crossbred seeds with higher germination rates compared to closest parents (r = 0.21, p = 0.033). This work provided important insights into interspecific and intraspecific cross-compatibility in yam and suggested actions for improving hybridization practices in yam breeding programs.

Diversity of Water Yam (Dioscorea alata L.) Accessions from Côte d'Ivoire Based on SNP Markers and Agronomic Traits.

Dioscorea alata (L.), also referred to as water, winged, or greater yam, is one of the most economically important staple food crops in tropical and subtropical areas. In Côte d'Ivoire, it represents, along with other yam species, the largest food crop and significantly contributes to food security. However, studies focusing on better understanding the structure and extent of genetic diversity among D. alata accessions, using molecular and phenotypic traits, are limited. This study was, therefore, conducted to assess the pattern of genetic variability in a set of 188 D. alata accessions from the National Agronomic Research Centre (CNRA) genebank using 11,722 SNP markers (generated by the Diversity Arrays Technology) and nine agronomic traits. Phylogenetic analyses using hierarchical clustering, admixture, kinship, and Discriminant analysis of principal component (DAPC) all assigned the accessions into four main clusters. Genetic diversity assessment using molecular-based SNP markers showed a high proportion of polymorphic SNPs (87.81%). The analysis of molecular variance (AMOVA) showed low molecular variability within genetic groups. In addition, the agronomic traits evaluated for two years in field conditions showed a high heritability and high variability among D. alata accessions. This study provides insights into the genetic diversity among accessions in the CNRA genebank and opens an avenue for sustainable resource management and the identification of promising parental clones for water yam breeding programs in Côte d'Ivoire.

Genome-Wide Association Studies for Sex Determination and Cross-Compatibility in Water Yam (Dioscorea alata L.).

Yam (Dioscorea spp.) species are predominantly dioecious, with male and female flowers borne on separate individuals. Cross-pollination is, therefore, essential for gene flow among and within yam species to achieve breeding objectives. Understanding genetic mechanisms underlying sex determination and cross-compatibility is crucial for planning a successful hybridization program. This study used the genome-wide association study (GWAS) approach for identifying genomic regions linked to sex and cross-compatibility in water yam (Dioscorea alata L.). We identified 54 markers linked to flower sex determination, among which 53 markers were on chromosome 6 and one on chromosome 11. Our result ascertained that D. alata is characterized by the male heterogametic sex determination system (XX/XY). The cross-compatibility indices, average crossability rate (ACR) and percentage high crossability (PHC), were controlled by loci on chromosomes 1, 6 and 17. Of the significant loci, SNPs located on chromosomes 1 and 17 were the most promising for ACR and PHC, respectively, and should be validated for use in D. alata hybridization activities to predict cross-compatibility success. A total of 61 putative gene/protein families with direct or indirect influence on plant reproduction were annotated in chromosomic regions controlling the target traits. This study provides valuable insights into the genetic control of D. alata sexual reproduction. It opens an avenue for developing genomic tools for predicting hybridization success in water yam breeding programs.

Optimized Protocol for In Vitro Pollen Germination in Yam (Dioscorea spp.).

Yam (Dioscorea spp.) plants are mostly dioecious and sometimes monoecious. Low, irregular, and asynchronous flowering of the genotypes are critical problems in yam breeding. Selecting suitable pollen parents and preserving yam pollen for future use are potential means of controlling these constraints and optimizing hybridization practice in yam breeding programs. However, implementing such procedures requires a robust protocol for pollen collection and viability testing to monitor pollen quality in the field and in storage. This study, therefore, aimed at optimizing the pollen germination assessment protocol for yam. The standard medium composition was stepwisely modified, the optimal growth condition was tested, and in vivo predictions were made. This study showed that the differences in yam pollen germination percentage are primarily linked to the genotype and growing conditions (i.e., medium viscosity, incubation temperature, and time to use) rather than the medium composition. The inclusion of polyethylene glycol (PEG) in the culture medium caused 67-75% inhibition of germination in D. alata. Although the in vivo fertilization was dependent on female parents, the in vitro germination test predicted the percentage fruit set at 25.2-79.7% and 26.4-59.7% accuracy for D. rotundata and D. alata genotypes, respectively. This study provides a reliable in vitro yam pollen germination protocol to support pollen management and preservation efforts in yam breeding.