Browsing by Author "Arunga, Esther E."

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    Characterization of Kenyan French Bean genotypes into gene pool affiliations using allele specific markers
    (ACADEMIC JOURNALS, 2020-07) Arunga, Esther E.; Odikara, Shadrack O.
    French bean (Phaseolus vulgaris L.) is a major export crop in Kenya where it serves as a cash crop for smallholder farmers and a source of employment. However, there is limited information on characterization of available germplasm which is essential in genetic improvement of this crop. The present study was therefore aimed to identify the gene pool affiliations of Kenyan French bean germplasm using specific molecular markers in order to understand the available germplasm for future use in breeding programs. The germplasm panel consisted of 46 accessions, comprising 40 French bean and six dry bean genotypes. The accessions were characterized using four gel-based molecular markers: SHP1-A, SHP1-B, SHP1-C and phaseolin protein marker. The most informative marker was the phaseolin protein marker which indicated that 82% of the French bean genotypes are of Andean origin, while 18% are of the Mesoamerican origin. Low polymorphism was observed for the SHP1 markers and the data from the three SHP1 markers did not correspond to the phaseolin protein marker for the French bean germplasm although SHP1-A and SHP1-B were able to differentiate the Andean from the Mesoamerican differential cultivars. The information on the gene pool affiliations of Kenyan French bean accessions is important for breeders to harness the divergence between the two gene pools in order to broaden the genetic base of the crop.
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    Genetic diversity of determinate French beans grown in Kenya based on morpho-agronomic and simple sequence repeat variation
    (Academic Journals, 2015-08) Arunga, Esther E.; Kinyua, Miriam; Ochuodho, Julius; Owuoche, James; Chepkoech, Emy
    French bean (Phaseolus vulgaris L.) in Kenya is cultivated predominantly in the Central, Eastern and Rift Valley provinces. Despite its importance as an export commodity, there has been little breeding effort devoted to its improvement and no much focus on gaining an understanding of the genetic diversity of the germplasm used in cultivation. The present objective was to evaluate the genetic diversity of a set of 36 Kenyan French bean accessions, based on a combination of morpho-agronomic and simple sequence repeat markers (SSRs). For the former, 20 morpho-agronomic traits were measured in two growing seasons, while for the latter; the germplasm was genotyped at 26 SSR loci. The accessions varied significantly (P≤ 0.05) with respect to pod diameter, pod length, pod number per plant, pod weight per plant and seed weight, but not with respect to the number of days taken to reach flowering, leaf length, leaf width or plant height. There was a large influence of season over flowering time, pod diameter, pod length, plant height and seed weight, and a significant (P≤ 0.05) interaction between accession and season for pod diameter, pod length, pod weight per plant, number of pods per plant and seed weight. The variation in the morpho-agronomic traits split the 36 accessions into four clusters. Shannon-Weaver diversity indices for qualitative, pseudo-qualitative and four selected quantitative traits ranged from 0.23 to 0.88. Of the 26 SSR primer pairs, which successfully amplified all 36 DNAs, 18 were informative, producing a mean of 2.17 alleles per SSR locus and a PIC value between 0.17 and 0.41. The level of gene diversity ranged from 0.19-0.50 (mean 0.36). The low observed mean heterozygosity reflected the predominantly autogamous habit of French bean. The modest amount of genotypic variation uncovered can be attributed to the effect of intensive selection for pod quality. A phylogeny based on the informative SSR loci revealed three major clusters, each representing a different pod diameter class. Combining the morpho-agronomic and DNA-based markers in this assessment of germplasm provides a way of taking advantage of the best features of both marker types that can be useful for identification of French bean varieties and applications of molecular markers to breeding.
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    Inoculum sources and management of bean scab caused by Elsinoë phaseoli
    (UoEm, 2024-06-24) Masheti, Yona; Muthomi, James W.; Muiru, William M; Arunga, Esther E.; Gepts, Paul
    Bean scab caused by Elsinoë phaseoli is a major challenge to common bean cultivationin Kenya. However, knowledge about its epidemiology and management is limited.This study conducted three experiments in Kakamega, Kenya, evaluating scab inocu-lum sources and control options. The first experiment evaluated three different inoc-ulum sources over two seasons; bean crop residue caused the highest scab incidencein both the 2021 (62.1%) and 2022 (81.1%) seasons. The second experiment assessedthe effect of rotation history on scab over three seasons. Scab incidence consist-ently surpassed 90% within the first 30 days after planting in half-yearly rotated fieldsacross all seasons, while the disease was absent after planting in fields with no recenthistory of legumes. Fields rotated out of legumes consistently had the highest grainyield, averaging 1.5 t ha−1 over the seasons. Additionally, the rotation land treatmentdisplayed significantly more pods per plant during the 2021 (9.7), 2022a (9.8), and2022b (12.5) seasons. In the third experiment, the impact of five fungicides and fourcropping systems on bean scab was investigated over two seasons. Neither fungicidetreatments nor cropping systems had an effect on bean scab incidence even whenonly severe symptoms were considered. Carbendazim had the highest yield (1.9 t ha−1)outperforming the unsprayed control only in the 2022 season while none of the otherfungicides outperformed the control treatment in yield parameters in either season.This study emphasizes the challenge of managing bean scab without proper crop rota-tion and underscores the role of crop residue as a critical inoculum source.
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    Loss of pod strings in common bean is associated with gene duplication, retrotransposon insertion and overexpression of PvIND
    (2022-06) Parker, Travis A.; Cetz, Jose; Lopes de Sousa, Lorenna; Kuzay, Saarah; Lo, Sassoum; Floriani, Talissa de Oliveira; Njau, Serah; Arunga, Esther E.; Duitama, Jorge; Jernstedt, Judy; Myers, James R.; Llaca, Victor
    Fruit development has been central in the evolution and domestication of flowering plants. In common bean (Phaseolus vulgaris), the principal global grain legume staple, two main production categories are distinguished by fibre deposition in pods: dry beans, with fibrous, stringy pods; and stringless snap/green beans, with reduced fibre deposition, which frequently revert to the ancestral stringy state. Here, we identify genetic and developmental patterns associated with pod fibre deposition. Transcriptional, anatomical, epigenetic and genetic regulation of pod strings were explored through RNA-seq, RT-qPCR, fluorescence microscopy, bisulfite sequencing and whole-genome sequencing. Overexpression of the INDEHISCENT (‘PvIND’) orthologue was observed in stringless types compared with isogenic stringy lines, associated with overspecification of weak dehiscence-zone cells throughout the pod vascular sheath. No differences in DNA methylation were correlated with this phenotype. Nonstringy varieties showed a tandemly direct duplicated PvIND and a Ty1-copia retrotransposon inserted between the two repeats. These sequence features are lost during pod reversion and are predictive of pod phenotype in diverse materials, supporting their role in PvIND overexpression and reversible string phenotype. Our results give insight into reversible gain-of-function mutations and possible genetic solutions to the reversion problem, of considerable economic value for green bean production.
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    Resistance to Pythium root rot and anthracnose among Kenyan common bean genotypes and marker-assisted introgression of resistance genes
    (Taylor and Francis, 2022-12) Misango, Shamir; Otsyula, Reuben; Arunga, Esther E.
    ABSTRACT Common bean (Phaseolus vulgaris L.) is an important food legume crop and major protein source in Kenya and many parts of the world. However, the yields are low due to the diseases like anthracnose caused by Colletotrichum lindemunthianum and Pythium root rots. The study, therefore, sought to screen Kenyan common bean genotypes for anthracnose and Pythium resistance and to improve the resistance of local landraces to the two diseases. Local landraces and commercial cultivars were screened for resistance under greenhouse conditions for Pythium and in vitro for anthracnose. The results showed that majority of the landraces were moderately resistant to anthracnose and Pythium root rot. The study further utilized molecular markers linked to anthracnose and Pythium resistance, respectively, to determine their potential to detect specific resistance genes among the test genotypes. None of the markers amplified the test genotypes except the control genotypes pointing toward different resistance genes. Further, cultivars G2333 and KK8 were used as donor parents for anthracnose and Pythium resistance, respectively, in a marker-assisted backcross breeding program involving three high-yielding farmer-preferred landraces. A number of lines were developed that carry both resistance genes. These lines can be advanced for release as new cultivars to enhance common bean production in Kenya.