Reaction of selected common bean genotypes to physiological races of Phaeoisariopsis griseola occurring in Kenya

The wide pathogenic variability occurring in Phaeoisariopsis griseola , the causal agent of angular leaf spot of common bean ( Phaseolus vulgaris L.), dictates that new sources of resistance be continuously identified. This study was undertaken to determine the reaction of selected bean genotypes to different races of P. griseola in order to identify potential sources of resistance to angular leaf spot. Selected bean genotypes from Eastern and Central Africa Bean Research Network (ECABREN) and National Dryland Farming Research Centre (NDFRC), Katumani in Kenya were separately inoculated with forty-four races of P. griseola and evaluated for disease development under greenhouse conditions. The genotypes included small- and large-seeded types. None of the genotypes was resistant to all the races, indicating a high complexity of the pathogen population. Thirteen genotypes were resistant (disease score 1 to 3) or moderately resistant (score 4 to 6) to at least 40 of the races. Small-seeded bean genotypes ECAB 0754 and ECAB 0617 were resistant or moderately resistant to all races except Mesoamerican race 33-39 and Afro-Andean race 58-18, respectively. Genotype ECAB 0754 exhibited the highest level of resistance, with an average disease severity of 1.1%. All the resistant or moderately resistant genotypes were of the small-seeded bean types which are commercially less popular. The commonly grown large-seeded genotypes were generally susceptible. Among the bean genotypes evaluated, the small-seeded pintos and browns/yellows possessed high levels of resistance. The results of this study indicate that different bean genotypes have varying levels of resistance to angular leaf spot that can be pyramided into appropriate background to provide durable resistance.Une large variabilité pathogénique du Phaeoisariopsis griseola , l’agent causal de la tâche angulaire de feuilles du haricot commun ( Phaseolus vulgaris L.), suggère qu’il y’ait une identification continue de nouvelles sources de résistance. Cette étude était entreprise pour déterminer la réaction des génotypes de haricot sélectionnés aux différentes races de P. griseola afin d’identifier de sources potentielles de résistance à la maladie de tâche angulaire de la feuille. Les génotypes de haricot fournis par l’Eastern and Central Africa Bean Research Network (ECABREN) et le National Dryland Farming Research Centre (NDFRC), Katumani au Kenya étaient séparément inoculés avec quarante-quatre races de P. griseola pour l’évaluation en serre du développement de maladies. Les génotypes comprenaient de petits et gros grains de semences. Aucune des génotypes n’était résistant à toutes les races de maladies, indicant ainsi une complexité élevée de la population des pathogènes. Treize génotypes étaient résistants (échelle de cotation: 1 à 3) ou modérément résistants (échelle de cotation: 4 à 6) sur au moins quarante de toutes les races. Les génotypes de haricot à petits grains ECAB 0754 et ECAB 0617 étaient résistants ou modérément résistants à toutes les races à l’exception de Mesoamerican race 33-39 et Afro-Andean race 58-18, respectivement. Le Génotype ECAB 0754 avait manifesté un niveau élevé de résistance, avec un taux moyen de séverité de 1.1%. Tous les génotypes résistants ou modérément résistants étaient de ceux à petits grains commercialement moins populaires. Les génotypes à gros grains communément cultivés étaient généralement susceptibles. Parmi les génotypes évalués, ceux à petits grains "pintos" et bruns/jaunes étaient dotés des niveaux élevés de résistance. Les résultats de cette étude montrent que différents génotypes de haricot possèdent de niveaux différents de résistance à la maladie de tâche angulaire de la feuille pouvant être combinés par pyramidage pour développer une variété de haricot à résistance durable

Disease surveillance and farmers’ knowledge of Brachiaria (Syn. Urochloa) grass diseases in Rwanda

Brachiaria (syn. Urochloa) is one of the most important tropical forages grass of African origin. Its performance is affected by different constraints, including diseases. This study assessed the distribution, incidence and severity of Brachiaria diseases and documented farmers’ knowledge on Brachiaria diseases in Rwanda. Surveys were conducted in five districts in the dry and wet seasons of 2018 and 2019. Fungi associated with major diseases were isolated and identified based on internal transcribed spacer sequences. The demographic information and farmers’ knowledge of Brachiaria diseases and yield loss were collected using structured questionnaire. Surveys revealed widespread distribution of leaf blight, leaf rust and leaf spot diseases in Rwanda. Incidence and severity of these diseases differed significantly by districts, seasons and district × season interactions; the exception was the non-significant effect of season and district × season interactions on rust incidence in 2018. Molecular identification revealed Phakopsora apoda as a provisional leaf rust pathogen, and frequent association of fungi Epicoccum spp. and Nigrospora spp. with leaf blight, and Bipolaris secalis and Fusarium spp. with leaf spot symptoms. This study provides baseline information for future studies on Brachiaria diseases and recognises diseases as a major challenge to sustainable production of Brachiaria grass in Rwanda and East Africa

Response of improved Brachiaria (Urochloa) grass cultivars to foliar diseases and their agronomic performances in Rwanda

Diseases have emerged as one of the major challenges of Brachiaria production in Africa. Nine Brachiaria cultivars were evaluated for leaf rust, leaf spot and leaf blight diseases and agronomic performances in two agro-ecological zones of Rwanda. The relationships between agronomic traits and area under diseases progress curve (AUDPC) were determined using Pearson correlation analysis. Cultivars differed significantly (p ≤ 0.05) for their response to these three diseases. Basilisk, Marandu, MG4, and Xaraes exhibited moderately resistant to resistant response to all three diseases, but Cayman and Cobra were susceptible to leaf rust. Site × cultivar × harvest interaction was significant for diseases and agronomic parameters (p ≤ 0.05). Cultivars also differed significantly for biomass production and dry matter content (p ≤ 0.05). The highest biomass producers were Marandu and Xaraes, and Cayman, Cobra and Piata had highest dry matter content. The AUDPC for leaf rust and leaf spot had negative and significant correlation with biomass yield. Our study concludes a satisfactory level of resistance in Basilisk, Marandu, MG4 and Xaraes to all three foliar disease in Rwanda. We recommend routine surveys for emerging and re-emerging Brachiaria diseases and studies to develop effective management measures against Brachiaria diseases

Constraints of rehabilitating degraded semi-arid lands of Kenya using indigenous perennial grasses

Land degradation which among others include loss of vegetation is rampant in Kenya, destroying both the fragile arid and semiarid lands and the non-arid areas. Efforts to rehabilitate semiarid areas by re-vegetation has often failed. This study was carried out to determine factors responsible for these failures. The study was conducted in the semi-arid district of Kibwezi. Three (3) grass species Cenchrus ciliaris, Enteropogon macrostachyus and Eragrostis superba were used for revegetating the land, while agro-pastoralists in the area were interviewed through questionnaires to get their perceptions on the failures of reseeding. Low rainfall, poor seed quality, lack of enough seed, flush floods, destruction by grazing animals were found to be factors limiting the success of reseeding

The Challenges Posed by Ipomoea kituensis and the Grass-Weed Interaction in a reseeded semi-arid environment in Kenya

Rehabilitation of denuded patches using perennial grasses has been used extensively in semi-arid environments of Kenya. However, weeds continue to pose an enormous challenge to the success of many rehabilitation programmes. The aim of this study was to identify the common weeds that pose a challenge to rehabilitation success and establish the grass-weed interactions in rehabilitated areas of a semiarid environment in Kenya. A survey questionnaire was administered to capture the farmers’ perception on the most problematic weeds and the challenge they pose to rehabilitation programmes. Experimental plots were laid out under simulated rainfall (sprinkler system). Three perennial grasses; Cenchrus ciliaris, Eragrostis superba, and Enteropogon macrostachyus, were used. These grasses were sown along ox-ploughed micro-catchments as pure stands and two grass mixtures and monitored at three phenological stages; early vegetative (15cm), elongation (30cm) and reproduction (60cm) representing high, medium and low grazing intensities respectively. Results from this survey showed Ipomoea kituensis posed the greatest challenge to rehabilitation programmes. Results also showed an inverse relationship in biomass yields between the weeds and established grasses across the three phenological stages. These results strongly suggest that selective weeding of rehabilitated semi-arid environments is critical for the success of rehabilitation programmes in semi-arid Kenya.http://erepository.uonbi.ac.ke/handle/11295/85400https://www.academia.edu/23682665/The_Challenges_Posed_by_Ipomoea_kituensis_and_the_Grass-Weed_Interaction_in_a_reseeded_semi-arid_environment_in_Kenyahttps://pdfs.semanticscholar.org/986f/211cfd44136979d0f0fd02e939c0ba503f91.pd