Variation in aggressiveness of Phaeoisariopsis griseola and angular leaf spot development in common bean

Aggressiveness of fifteen isolates of Phaeoisariopsis griseola and variations in angular leaf spot symptom development in common bean were studied. The isolates were selected based on their virulence and genetic differences and represented Andean, Afro-Andean and Mesoamerican groups of P. griseola. Aggressiveness was determined based on length of incubation period, rate of lesion expansion, lesion size and density, rate of sporulation, disease severity and area under disease progress curve (AUDPC). There was a wide variation in aggressiveness and the type of symptoms induced by the different isolates of the pathogen. Incubation period varied significantly (P < 0.05) among isolates and ranged from six to 15 days. Mesoamerican isolates had significantly shorter incubation period than Andean and Afro-Andean isolates. Disease severity, AUDPC and rate of sporulation differed significantly (P < 0.05) among the isolates. Lesions induced by the different isolates varied significantly in size, density and rate of expansion. Mesoamerican isolates induced significantly more lesions than Andean and Afro-Andean isolates. Disease severity was negatively correlated to incubation period and positively correlated to lesion density, lesion size and rate of sporulation. The significant correlations between disease severity, AUDPC, incubation period, lesion density and rate of sporulation indicate that all these parameters are important measures of aggressiveness in P. griseola. The significant variations in aggressiveness between isolates, virulence and genetically defined groups of P. griseola indicate that this parameter can be used to characterise isolates of the pathogen. Symptoms induced by isolates of P. griseola in different bean cultivars varied extensively in size, shape and time of appearance. These variations could, however, not be attributed to any particular cultivar or isolate and can, therefore, not be used to characterise the pathogen. Keywords: Disease severity, incubation period, sporulation, symptom, virulence group J. Trop. Microbiol. Biotechnol. Vol. 3 (2) 2007: pp. 3-1

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

A “win-win” scenario: the use of sustainable land management technologies to improve rural livelihoods and combat desertification in semi-arid lands in Kenya

Dryland ecosystems support over 2 billion people and are major providers of critical ecosystems goods and services globally. However, desertification continues to pose a serious threat to the sustainability of the drylands and livelihoods of communities inhabiting them. The desertification problem is well exemplified in the arid and semi-arid lands (ASALs) in Kenya which cover approximately 80% of the total land area. This study aimed to 1) determine what agropastoralists attribute to be the causes of desertification in a semi-arid land in Kenya, 2) document sustainable land management (SLM) technologies being undertaken to improve livelihoods and combat desertification, and 3) identify the factors that influence the choice of the sustainable land management (SLM) technologies. Results show that agropastoralists inhabiting the semi-arid lands in southeastern Kenya mainly attribute desertification to the recurrent droughts and low amounts of rainfall. Despite the challenges posed by desertification and climate variability, agropastoralists in the study area are using a combination of SLM technologies notably dryland agroforestry using drought tolerant species (indigenous and exotic), grass reseeding using perennial native and drought tolerant grass species (vegetation reestablishment) and in-situ rainwater harvesting to improve livelihoods and by extension combat desertification. Interestingly, the choice and adoption of these SLM technologies is influenced more by the additional benefits the agropastoralists can derive from them. Therefore,it isrationale toconclude that success in dryland restorationand combating desertification lies in programs and technologies that offer a “win-win” scenario to the communities inhabiting the drylands

Different land use types in the semi-arid rangelands of Kenya influence soil properties

Rangelands in semi-arid Kenya have recently witnessed extensive land use changes. These changes can mainly be attributed to increased livestock populations and the response of the increased human population to both local and exogenous opportunities and constraints. This study was carried out in Kibwezi district of Kenya mainly inhabited by agro-pastoralists. The main objective of this study was to establish how different land use types influence soil properties in tropical semi-arid rangelands. Disturbed and undisturbed soil samples from three land use types namely cultivated land (CL), grazing land (GL) and fallow land (FL) at a depth of 15-30cm were collected and analyzed using standard laboratories for soil nutrients and soil physical properties. Results show open grazing lands (CEC 19.59 meq/100g) to be more fertile than cultivated (13.88 meq/100g) and fallow (6.40 meq/100g) lands. This was attributed to the continuous dropping of faecal material by grazing livestock. Higher bulk density in grazing land (1.36 g/cm3) compared to cultivated and fallow lands with 1.29 g/cm3 and 1.33 g/cm3 was attributed to the hoof action of livestock. These results suggest that different land use types in the semi-arid rangelands contribute immensely to soil properties

Improving soil hydrological properties of denuded semi-arid rangeland in southeastern Kenya using reseeding technology

A study was conducted to establish the contribution of Eragrostis superba, Enteropogon macrostachyus and Cenchrus ciliaris in improving soil hydrological properties in semi-arid Kenya. Kamphorst rainfall simulator was used on bare ground and at different grass stubble heights. The experiment was set up under sprinkler irrigation system. Sediment production as a function of runoff and infiltration capacity was significantly different (p<0.05) at different stubble heights. Cenchrus ciliaris had the greatest influence on improving soil hydrological properties followed by Enteropogon macrostachyus and Eragrostis superba respectively. An increase in grass height increased infiltration capacity, reduced runoff and sediment production

Effect of Cattle Manure and Calcium Ammonium Nitrogen on Growth and Leaf Yield of Local Cowpea Accessions in Coastal Kenya

Cowpea is one of the major food crops contributing to food security and poverty alleviation especially among women and resource-poor farmers in marginal areas in Kenya. The effect of different concentrations of cattle manure and inorganic nitrogen (Calcium ammonium nitrate, CAN) application on growth and fresh and dry leaf yields from single and multiple harvest of four local vegetable cowpea accessions, Mnyenze madamada, Sura mbaya, Katsetse and Usimpe mtu mdogo, was studied over two seasons at Mtwapa in coastal Kenya. The research was conducted in a randomized complete block design with three replications with treatments arranged in a factorial arrangement. Analysis of variance was carried out on the data using Genstat Statistical package and means were compared using LSD at 5% level of significance (P=.05). Application of cattle manure and inorganic nitrogen fertilizer CAN had no effect or slightly decreased root length and had no effect on the number of branches per plant irrespective of seasons. The application of organic and inorganic fertilizers increased plant height, canopy width and fresh and dry weights depending on the season. The plants planted during the second and drier second season had lower growth and yield attributes compared to those planted during the first season. Of significance was the significant yield increase from multiple harvests with indications of yield improvements from as low as 1.5-4.0 tons/ha to between 15-20 tons/ha. Calcium ammonium nitrate was more effective compared to cattle manure during the dry season compared to the wet season, when cattle manure significantly increased yields (P&gt;.05). The four select local cowpea accessions responded positively to the organic and inorganic fertilizers over seasons and therefore have the capacity to address food security and income generation in marginal parts of Kenya. &nbsp

Effect of Cattle Manure and Calcium Ammonium Nitrogen on Growth and Leaf Yield of Local Cowpea Accessions in Coastal Kenya

Cowpea is one of the major food crops contributing to food security and poverty alleviation especially among women and resource-poor farmers in marginal areas in Kenya. The effect of different concentrations of cattle manure and inorganic nitrogen (Calcium ammonium nitrate, CAN) application on growth and fresh and dry leaf yields from single and multiple harvest of four local vegetable cowpea accessions, Mnyenze madamada, Sura mbaya, Katsetse and Usimpe mtu mdogo, was studied over two seasons at Mtwapa in coastal Kenya. The research was conducted in a randomized complete block design with three replications with treatments arranged in a factorial arrangement. Analysis of variance was carried out on the data using Genstat Statistical package and means were compared using LSD at 5% level of significance (P=.05). Application of cattle manure and inorganic nitrogen fertilizer CAN had no effect or slightly decreased root length and had no effect on the number of branches per plant irrespective of seasons. The application of organic and inorganic fertilizers increased plant height, canopy width and fresh and dry weights depending on the season. The plants planted during the second and drier second season had lower growth and yield attributes compared to those planted during the first season. Of significance was the significant yield increase from multiple harvests with indications of yield improvements from as low as 1.5-4.0 tons/ha to between 15-20 tons/ha. Calcium ammonium nitrate was more effective compared to cattle manure during the dry season compared to the wet season, when cattle manure significantly increased yields (P&gt;.05). The four select local cowpea accessions responded positively to the organic and inorganic fertilizers over seasons and therefore have the capacity to address food security and income generation in marginal parts of Kenya. &nbsp