Yams (Dioscorea spp.) possess the potential to contribute to food security and poverty alleviation in DR Congo; however, yam production is limited by several constraints, including the lack of yam improvement programs to address challenges relating to yield improvement, resistance to foliar diseases, and post-harvest tuber quality. Identification of a superior genotype for these traits and reservoirs of genes for improvement would guide yams’ improvement. This study aims to evaluate and identify landraces with superior performance for farmers and consumers. We evaluated 191 accessions from six yam species, and significant variation in the performances was observed at p < 0.05. Accessions of D. alata were superior for tuber oxidative browning (−0.01), D. cayenensis for high yield potential (29 t/ha), D. bulbifera for yam mosaic virus (YMV) tolerance (AUDPC = 3.88), and D. rotundata for tuber dry matter content (37%). A high genotypic and phenotypic coefficient of variation (>40) was observed for tuber yield, number of tubers per plots, tuber flesh oxidative browning, and tuber flesh texture. High broad-sense heritability estimates (>60) were similarly observed for all the assessed parameters except number of tubers per plot. Tuber size was identified as the best predictor for tuber yield (b = 2.64, p < 0.001) and tuber dry matter content (b = 2.21, p < 0.001). The study identified twenty stable landrace accessions from three Dioscorea species (D. alata (7); D. cayenensis (2); D. rotundata (11)). These accessions combined high yield potential, high tuber dry matter, high tolerance to YMV and YAD, and low tuber flesh oxidation. The accessions could be considered for the establishment of a yam improvement program in DR Congo.

Background: Yam (Dioscorea spp.) is multiple species with various ploidy level and considered as cash crop in many producing areas. Selection based phenotyping for yield and its related traits such as mosaic virus and anthracnose diseases resistance and plant vigor in multiple species of yam is lengthy however, marker information has proven to enhance selection efficiency. Methodology: In this study, a panel of 182 yam accessions distributed across six yam species were assessed for diversity and marker-traits association study using SNP markers generated from Diversity Array Technology platform. For the traits association analysis, the relation matrix alongside the population structure were used as co-factor to avoid false discovery using Multiple random Mixed Linear Model (MrMLM) followed by gene annotation. Results: Accessions performance were significantly different (p < 0.001) across all the traits with high broad-sense heritability (H²). Phenotypic and genotypic correlations showed positive relationships between yield and vigor but negative for yield and yam mosaic disease severity. Population structure revealed k = 6 as optimal clusters-based species. A total of 22 SNP markers were identified to be associated with yield, vigor, mosaic and anthracnose diseases resistance. Gene annotation for the significant SNP loci identified some putative genes associated with primary metabolism, pest and resistance to anthracnose disease, maintenance of NADPH in biosynthetic reaction especially those involving nitro-oxidative stress for resistance to mosaic virus, and seed development, photosynthesis, nutrition use efficiency, stress tolerance, vegetative and reproductive development for tuber yield. Conclusion: This study provides valuable insights into the genetic control of plant vigor, anthracnose, mosaic virus resistance, and tuber yield in yam and thus, opens an avenue for developing additional genomic resources for markers-assisted selection focusing on multiple yam species.

Purpose: The present study evaluates the antifungal activity of essential oils of Curcuma longa and Eucalyptus globulus on strains of Lasiodiplodia theobromae and Pseudocercospora fijiensis in the Kisangani region (DR Congo). Methods: The essential oils were obtained after extraction by the hydro distillation method. The isolation of strains of L. theobromae was made from the fragments of mesocarp taken from the diseased cocoa, previously cut with a Scarpel and then disinfected with bleach water, while the strains of P. fijiensis were obtained by the method of discharging ascospores on agar medium (H₂O Agar) and then transplanting on potato dextrose agar (PDA). In addition, inhibition of mycelial growth on a PDA was used as a method to assess the sensitivity of strains to the essential oils of the medicinal plants studied. Results: The results obtained show that the essential oils of the rhizomes of C. longa and the leaves of E. globulus showed a low yield of essential oils (EOs) of 0.50% and 0.48% respectively. However, the EOs of the rhizomes of C. longa and the leaves of E. globulus exhibited inhibitory action on the mycelial growth of strains of L. theobromae and P. fijiensis. Conclusion: The ANOVA test applied to the mean mycelial growth values of these two strains (L. theobromae and P. fijiensis) on the Eos of C. longa showed that the difference is not significant (p-value = 0.47). In addition, there is also no significant difference (p-value = 0.51) between the mean mycelial growth values of these two fungal strains on the essential oil of E. globulus.

The cocoa tree (Theobroma cacao L) is a persistent perennial crop in tropical regions whose production period is sufficiently spread out over the whole year. As a result, it offers pathogens conditions for survival without real disruption of their life cycle. Symptoms of cocoa pod black rot disease have been observed in both the Bengamisa cocoa growing area and the Yangambi area in the Democratic Republic of Congo (DRC). This study aimed to characterize the strains of Lasiodiplodia theobromae on cocoa trees in the Kisangani region. Macroscopic and microscopic observations were made on the pods while the identification of the species was confirmed by a molecular approach based on the sequencing of part of the ribosomal DNA including the ITS regions (internal transcribed spacers) and the 5.8S gene. The results of this study showed that the phenotypic characteristics of the strains isolated in the two cocoa growing areas were typical of the L. Theobromae species. These are in particular the spots of soft rot, initially brown, gradually evolving into soot-black which subsequently produced a sort of whitish powder on the surface of the diseased pod. However, the fruiting of the fungus in the PDA medium gave rise to the latter's mycelia, initially whitish, which darkened as they matured. In addition, PCR amplification followed by sequencing of the fungal strain was beneficial by removing any doubt about the nature of the fungal species isolated in the two cocoa-growing areas.