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 variabilit\ue9 pathog\ue9nique du Phaeoisariopsis griseola , l\u2019agent causal de la t\ue2che angulaire de feuilles du haricot commun ( Phaseolus vulgaris L.), sugg\ue8re qu\u2019il y\u2019ait une identification continue de nouvelles sources de r\ue9sistance. Cette \ue9tude \ue9tait entreprise pour d\ue9terminer la r\ue9action des g\ue9notypes de haricot s\ue9lectionn\ue9s aux diff\ue9rentes races de P. griseola afin d\u2019identifier de sources potentielles de r\ue9sistance \ue0 la maladie de t\ue2che angulaire de la feuille. Les g\ue9notypes de haricot fournis par l\u2019Eastern and Central Africa Bean Research Network (ECABREN) et le National Dryland Farming Research Centre (NDFRC), Katumani au Kenya \ue9taient s\ue9par\ue9ment inocul\ue9s avec quarante-quatre races de P. griseola pour l\u2019\ue9valuation en serre du d\ue9veloppement de maladies. Les g\ue9notypes comprenaient de petits et gros grains de semences. Aucune des g\ue9notypes n\u2019\ue9tait r\ue9sistant \ue0 toutes les races de maladies, indicant ainsi une complexit\ue9 \ue9lev\ue9e de la population des pathog\ue8nes. Treize g\ue9notypes \ue9taient r\ue9sistants (\ue9chelle de cotation: 1 \ue0 3) ou mod\ue9r\ue9ment r\ue9sistants (\ue9chelle de cotation: 4 \ue0 6) sur au moins quarante de toutes les races. Les g\ue9notypes de haricot \ue0 petits grains ECAB 0754 et ECAB 0617 \ue9taient r\ue9sistants ou mod\ue9r\ue9ment r\ue9sistants \ue0 toutes les races \ue0 l\u2019exception de Mesoamerican race 33-39 et Afro-Andean race 58-18, respectivement. Le G\ue9notype ECAB 0754 avait manifest\ue9 un niveau \ue9lev\ue9 de r\ue9sistance, avec un taux moyen de s\ue9verit\ue9 de 1.1%. Tous les g\ue9notypes r\ue9sistants ou mod\ue9r\ue9ment r\ue9sistants \ue9taient de ceux \ue0 petits grains commercialement moins populaires. Les g\ue9notypes \ue0 gros grains commun\ue9ment cultiv\ue9s \ue9taient g\ue9n\ue9ralement susceptibles. Parmi les g\ue9notypes \ue9valu\ue9s, ceux \ue0 petits grains "pintos" et bruns/jaunes \ue9taient dot\ue9s des niveaux \ue9lev\ue9s de r\ue9sistance. Les r\ue9sultats de cette \ue9tude montrent que diff\ue9rents g\ue9notypes de haricot poss\ue8dent de niveaux diff\ue9rents de r\ue9sistance \ue0 la maladie de t\ue2che angulaire de la feuille pouvant \ueatre combin\ue9s par pyramidage pour d\ue9velopper une vari\ue9t\ue9 de haricot \ue0 r\ue9sistance durable

Plant Parasitic Nematodes Associated with Common Bean In Kenya and the Effect of Meloidogyne Infection On Bean Nodulation

A study to determine the distribution and population densities of plant parasitic nematodes associated with beans was undertaken in Kakamega, Kiambu, Machakos and Siaya districts of Kenya. Soil and root samples were taken from 25 randomly selected farms in each district. Nematodes in the genera Meloidogyne, Pratylenchus, Scutellonema and Helicotylenchus were frequently recovered in the rhizophere of bean plants with varying densities in the different locations of the study. Meloidogyne spp. and Pratylenchus spp. were the most predominant endoparasites occurring in 86 and 61% of the root samples, respectively. Scutellonema and Helicotylenchus species were present in 80 and 59% of the soil samples, respectively. Other nematodes found in association with bean plants were in the genera Tylenchorhynchus, Tylenchus, Criconemella, Aphelenchus, Hemicyliophora, and Trichodorus. Greenhouse tests were conducted to determine the effect of M. incognita infection on nodulation of bean genotypes. With the exception of bean genotype M28, Meloidogyne infection caused significant (P< 0.05) reductions in nodulation. In a second pot experiment, bean cv. GLP-24 was inoculated with Rhizobium leguminosarum bv. phaseoli alone and in various combinations with M. incognita. Both nodulation and the dinitrogen fixation processes were adversely affected especially in plants where nematode inoculation preceded rhizobial inoculation.Une \ue9tude pour d\ue9terminer la distribution et la densit\ue9 de la population de n\ue9matodes parasitaires de plantes associ\ue9s aux haricots a \ue9t\ue9 initi\ue9 dans les districts de Kakamega, Kiambu, Machakos et Siaya au Kenya. Les \ue9chantillons des racines et de sols ont \ue9t\ue9 pris dans 25 fermes s\ue9lectionn\ue9es al\ue9atoirement dans chaque districts. Les n\ue9matodes des genres Meloidogyne, Pratylenchus, Scutellonema et Helicotylenchus ont \ue9t\ue9 fr\ue9quemment trouv\ue9s dans la rhizosph\ue8re des plantes de haricot avec des densit\ue9 vari\ue9es dans differentes parties du pay. Meloidogyne spp. et Pratylenchus spp. \ue9taient des endoparasites les plus dominants apparaissant dans 86 et 67% d\u2019\ue9chantillons de racines, respectivement. Les esp\ue8ces de Scutellonema et Helicotylenchus \ue9taient pr\ue9sents dans 80 et 59% d\u2019\ue9chantillons de sol respectivement. Autres n\ue9matode trouv\ue9s en assoication avec la plante de haricot \ue9taient des genres de Tylenchorhynchus, Tylenchus, Criconemella, Aphelenchus, Hemicyliophora et Trichodorus. Avec exception du g\ue9notype M28, l\u2019infection du Meloidogyne a caus\ue9 de r\ue9duction significative (P<0.05) dans la nodulation. Dans le deuxi\ue8me essai en pots des combinaisons de haricot avec M. incognita ont \ue9t\ue9 consid\ue9r\ue9es. Ensemble les processus de dinitrification et de nodulation ont \ue9t\ue9 d\ue9favorablement affect\ue9s sp\ue9ciallement dans les plantes o\uf9 les n\ue9matodes ont pr\ue9c\ue9d\ue9 l\u2019inoculation du Rhizobium

Mode of inheritance of common bean (Phaseolus vulgaris L.) traits for tolerance to low soil phosphorus (P)

Low soil phosphorus (P) has been singled out as a major constraint leading to perpetually low bean (Phaseolus vulgaris L.) grain yield far below the expected yield potential. In developing countries beans are mainly produced by small-scale farmers who have little capacity to use inorganic fertilizers to replenish their soils. Yet bean production contributes significantly to their income and provides a cheap source of protein to rural and urban populations. The genetics of inheritance of the traits conferring low soil P tolerance is not well understood. The identification and understanding of the mode of inheritance of the traits for P-efficiency in bean will go along way in boosting bean yields through development of varieties adapted to low soil P. The objective of this study was to determine the inheritance of the traits conferring adaptation to low soil P, for the important large seeded red mottled bean market class. Three parents with known tolerance to low soil P were crossed with five adapted but non-tolerant genotypes in an 8 × 8 half diallel mating scheme. The resulting F1 seeds were evaluated under medium and low soil P conditions at two locations. Both general combining ability (GCA) and specific combining ability (SCA) variances were highly significant (P ? 0.01) for all five characters studied except SCA variance for root dry weight at one location. The magnitude of GCA variance was up to twelve times higher than the SCA variance. The GCA:SCA ratio varied from 0.62 to 0.96 for the characters studied. The additive genetic variance was more important than the dominance variance for tolerance to low soil P

Effect of soil fertility management practices and bacillus subtilis on plant parasitic nematodes associated with common bean, Phaseolus vulgaris

On-farm and on-station field experiments were carried out to determine the potential of combining Bacillus subtilis with soil fertility management practices on plant parasitic nematodes and growth of common bean (Phaseolus vulgaris). The treatments were Bacillus subtilis (isolate K194), B. subtilis plus cow manure, B. subtilis plus mavuno, Bacillus subtilis plus farmer practice, manure alone ,mavuno alone with farmer practice as the control. The farmers’ practice entailed application of tripple super phosphate and calcium ammoniun nitrate at the rate of 1000 and 890 kg/ha, respectively. Manure and mavuno were applied at the rate of 10 tons and 890 kg/ha, respectively. The on-farm trial was carried out in 12 different farms. The combination of Bacillus subtilis and cow manure led to a 54% reduction in numbers of plant parasitic nematodes, compared to the untreated control. Consequently, damage by root-knot nematodes was 1.6 and 4.5 in plots treated with the combination (B. subtilis and cow manure) and the untreated control, respectively. Compared to the other treatments, combining B. subtilis and organic amendments resulted in the highest nematode evenness diversity. It can be therefore be concluded that the plant parasitic nematodes associated with common bean can be maintained at levels below economic threshold using B. subtilis combined with cow manure, an integration which also demonstrated conservation of the nematode diversity

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

Distribution Of Lesion Nematodes Associated With Maize In Kenya And Susceptibility Of Maize Cultivars To Pratylenchus Zeae

The distribution and impact of lesion nematodes (Pratylenchus spp.) in Kenyan maize producing areas were evaluated. Soil and root samples were taken from 120 farms in three districts of Kenya, namely Kakamega, Machakos and Trans Nzoia. Mean populations of Pratylenchus spp. (P. zeae and P. brachyurus) in 5 g roots were 280, 131, and 6 in Kakamega, Machakos and Trans Nzoia districts, respectively. Lesion nematodes were recovered from 73.3% of the samples. P. zeae and P. brachyurus had overall incidences of 72.5 and 6.7%, respectively. Greenhouse tests were conducted to determine the effects of P. zeae on growth of seven maize genotypes used in Kenya, Dryland composite 1, Katumani composite, and hybrids 511, 512, 614, 625 and Pwani. Numbers of P. zeae extracted from 5 g roots were significantly (P 64 0.05) different and ranged between 6230 in hybrid 614 and 10970 in Katumani composite. The nematode caused significant (P 64 0.05) reduction in root weight of Katumani composite, Dryland composite 1, hybrid 511 and hybrid 512. Nematode infection significantly (P 64 0.05) reduced shoot weight of Pwani hybrid and height of Dryland composite 1.La distribution et l'impact des n\ue9matodes (Pratylenchus spp) dans les zones de production de ma\uefs au Kenya ont \ue9t\ue9 \ue9valu\ue9s. Le sol et les \ue9chantillons de racines ont \ue9t\ue9 obtenus de 120 fermes dans trois districts du Kenya (Kakamega, Machakos et Trans Nzoia). Les populations moyennes de Pratylenchus spp. (P. Zeae et P. brancyurus) de 5g de racine \ue9taient respectivement de 280, 131, et 6 dans les districts de Kakamega, Machakos et Trans Nzoia. Les l\ue9sions de n\ue9matodes ont \ue9t\ue9 retrouv\ue9es dans 73,3% des \ue9chantillons. Les P. zeae et P. brachyurus ont respectivement d'incidences g\ue9n\ue9rales de 72,5 et 6,7%. Les tests de serre ont \ue9t\ue9 conduits de mani\ue8re \ue0 d\ue9terminer les effets de P. Zeae sur la croissance de sept g\ue9notypes de ma\uefs utilis\ue9s au Kenya; les composites 1 du milieu sec, ceux katumani, et les hybrides 511, 512, 614, 625 et Pwani. Plusieurs P. zeae extraits de 5g de racine \ue9tait d'une fa\ue7on significative (p 640,05) diff\ue9rents et vari\ue9s entre les composites 6230 d'hybride 614 et 10970, de katumani. Les n\ue9matodes ont caus\ue9 une s\ue9rieuse r\ue9duction (p<0,05) du poids de la racine dans le composite Katumani, le composite 1 du milieu sec, l'hybride 511 et l'hybride 512. L'infection de la n\ue9matode a significativement r\ue9duit (p<0,05) le poids de pousse de l'hybride Pwani et la taille du composite 1 du milieu sec

Effect of soil fertility management practices on nematode destroying fungi in Taita, Kenya

The effect of soil fertility management practices on nematode destroying fungi was investigated for three seasons in Taita, Kenya. The study aimed at identifying soil fertility practice that promoted nematode destroying fungi in the soil. Field experiments were established in Taita district, the treatments comprised of Mavuno fertilizer, Triple super- phosphate and calcium ammonium nitrate (TSP+CAN), cow manure and a control where no amendments were applied. This experiment was replicated in ten farms and repeated in three planting seasons. Isolation of nematode destroying fungi carried out was using the soil sprinkle technique and the isolates were identified using the key described by Cooke and Godfrey (1964). There were significant difference (P= 1.705 x 10-06) in occurrence of the nematode destroying fungi between soil fertility treatments. The highest mean (1.6) occurrence of nematode destroying fungi was recorded in soils amended with cow manure and the least (0.7) was recorded in soils from the control plots. A mean of 0.78 was recorded in soils from both TSP+CAN and Mavuno fertilizers. Plots amended with cow manure presented the highest diversity of nematodes followed by the control, then TSP+CAN and least in Mavuno with shannon indices of 0.34, 0.15, 0.13 and 0.11 respectively. Sixty percent of all the isolated nematode destroying fungi genera were from plots treated with cow manure and only twenty percent were from plots amended with the inorganic fertilizer. The control plots recorded higher number of nematode destroying fungi compared to the soils that received inorganic fertilizers