Effect of Legume Cover Crops on Soil Moisture and Orange Root Distribution

Inadequate rain is a major hindrance to soil moisture and crop root growth in arid and semi-arid areas of Kenya. A field study was conducted in Ganda, Vitengeni and Matuga locations within the coastal lowland region of Kenya from May, 2012 to April, 2015 to evaluate the effects of three leguminous cover crops on soil moisture retention and orange tree feeder root distribution. Treatments included mucuna (Mucuna pruriens), cowpea (Vigna unguiculata), dolichos (Lablab purpureus) cover crops and unplowed fallow of natural vegetation as a control. The experiment was laid out in randomized complete block design (RCBD) and each treatment was replicated four times. Data collected were: soil particle size distribution, soil moisture content and orange dry root density. The data collected was subjected to analysis of variance (ANOVA) using procedures of R statistical analysis version 3.3.2. Mean separation was done using the least significant difference (LSD) value at 5% level of significance. Results indicated that mucuna, dolichos and cowpea cover crops significantly (P=.05) increased soil moisture content. The mucuna treated plots recorded an increase in SMC by 39.0% and 33%, dolichos increased by 34.4% and 28.9% and cowpea by 33.6% and 27.3% at soil depth 0-20 and 20-40 cm, respectively, over their own controls. Mucuna and dolichos significantly (P=.05) increased orange feeder root distribution. Mucuna treated plots supported the highest increase in orange root distribution by 36.5% and 31.8%, dolichos increased by 30.2% and 34.1% while cowpea increased by 18.3% and 18.8% in soil depth 0-20 and 20-40 cm respectively compared to their own control. It can be concluded that the three legumes; mucuna, cowpea and dolichos cover crop improved soil moisture and root distribution in orange production. The overall ranking was as follows: mucuna > dolichos > cowpea. From the finding, the use of mucuna and dolichos cover cropping system is recommended as a soil management practice aimed at improving the orange productivity. Further evaluation on the long term (>3 years) effects of cover crops on soil moisture and orange root distribution under different agro ecological zones is suggested

Morphological Characterization And Identification Of Phytophthora Species Causing Citrus Gummosis In Kenya

Frequent outbreaks of citrus gummosis in Kenyan citrus orchards have been reported, yet the identity and distribution of the Phytophthora species causing the disease are unknown. Work was carried out to (i) characterize and identify Phytophthora species associated with citrus gummosis based on cultural and morphological traits and (ii) determine the distribution of these species associated with gummosis in different agroecological zones (AEZ). Some 59 plant and soil samples obtained from symptomatic trees and the rhizosphere were evaluated by direct isolation and baiting, respectively, using Phytophthora semi-selective media. Phytophthora species were identified on the basis of colony morphology, mycelial characteristics, cardinal growth temperatures, morphology and dimensions of sporangia, oogonia and antheridia. For colony morphology and growth temperature studies, a 5 mm diameter mycelial plug of each isolate was transferred to amended cornmeal agar (ACMA) and incubated at 5, 24 and 35°C for 7 days in the dark. Growth rates were evaluated based on daily records of mycelial growth for 7 days. The occurrence and distribution of these species were determined by recording the number of isolates recovered from samples from each AEZ. P. citrophthora was the most prevalent (76.3 %) of all the Phytophthora species identified in all the AEZs, followed by P. nicotianae (22 %). P. syringae was the least (1.7 %) prevalent. P. citrophthora was the only species present in all AEZs sampled whereas P. nicotianae was confined to the coastal lowlands although also present in other zones in a lower scale. P. syringae was present only in low midland zones and was the only species not found in coastal lowland zones. The forty five isolates of P. citrophthora, thirteen isolates of P. nicotianae and one isolate of P. syringae were tested for virulence on fruits of lemon var. rough lemon. The three most virulent isolates of P. citrophthora, two most virulent isolates of P. nicotianae and the only isolate of P. syringae were selected for pathogenicity testing on lemon seedlings. Based on these studies, it may be concluded that P. citrophthora, P. nicotianae (syn. P. parasitica) and P. syringae are the Phytophthora species associated with citrus gummosis in Kenya. Molecular characterization of the pathogens is recommended to confirm true genetic identity of the species

Characterization of isolates that cause black rot of crucifers in East Africa

A study was conducted in the East African countries of Kenya, Tanzania and Uganda in the months of July and August 2009 with the objectives of assessing the status of black rot and race structure of Xanthomonas campestris pv. campestris in the three countries. Samples infected with black rot were collected from farmers’ fields mainly from Brassica oleracea crops (broccoli, cabbage, cauliflower and kales). A total of 399 farms were surveyed of which 260 were from Kenya, 91 from Tanzania and 48 from Uganda. Following successful isolations, a total of 249 isolates of the causal agent, Xanthomonas campestris pv. campestris were recovered. Pathogenicity of all isolates was confirmed on B. oleracea susceptible cultivars Copenhagen Market F1 and Wirosa F1. Sixty of the 250 isolates were race-typed using a differential set Brassica spp. Only two races, 1 (Kenya and Tanzania) and 4 (Kenya, Tanzania and Uganda) were observed however, another race (5) was observed from one isolate recovered from a B. rapa sample obtained from Tanzania in 2003. Genomic fingerprinting with repetitive-PCR revealed clusters that did not depict significant correlations between isolates and geographical location, isolates and host adaptation or isolates and race. However, it did demonstrate existence of genetic differences within the East African X. campestris pv. campestris population indicating that it is not a similar clonal population of the same genetic background

Constraints to commercializing potato in Kenya.

Although potato is an important source of food and income in Kenya, poor yields and erratic returns have constrained profitability and expansion of the crop. The objective of this study was to describe the potato production system, identify constraints, and determine levels of use of inputs; and the profitability of potato as a business in 4 out of the 10 most important potato producing Counties. We used multistage sampling to select 390 farmers from 4 of the 10 most important potato producing Counties. A questionnaire was used to collect information from farmers and means were separated using ANOVA. Results showed that farming was the main source of income for both husband and wife in at least 66% of households and these where fairly young families with the household heads aged 45 years; having 15years of experience in potato production, and having had 13 years of schooling-with significant differences across regions. Potatoes were grown principally by small-holder farmers twice a year on about 0.92 acres in the March/May season and 0.87acres in the September/October season with significant differences across regions. There was uniformity in variety choice with Changi being predominant in three out of the four Counties. Productivity was at a sub-optimal level with yields of 5.6tons/ha compared to an African average of 10.8tons/ha (CIP 2007) - with significant regional differences. The low productivity can be partially explained by the low input use (seed and fertilizer) which was well below what was recommended by the Government extension officers. The quality of the seed used was of doubtful quality as it was not certified seed but sourced mainly from own harvest, from neighbors or from nearby primary markets. Despite all these shortcomings potato production gave farmers a gross income of about $1240 in the March/May season and$1173 in the Oct/Sept and this was above the UN poverty level of $1.5 per day (or approx.$270 per season of 6 months) -with that income differing significantly across regions. Potato thus has the potential to significantly impact the food and income situations of small-holder farmers in Kenya if the identified constraints can be addressed in socially and economically acceptable ways

Foliar diseases and the associated fungi in rice cultivated in Kenya

We conducted a survey to assess the occurrence and severity of rice blast and brown spot diseases on popular cultivars grown in the Busia, Kirinyaga, and Kisumu counties of Kenya in 2019. Working with agricultural extension workers within rice production areas, we interviewed farmers (n = 89) regarding their preferred cultivars and their awareness of blast disease, as this was the major focus of our research. We scored the symptoms of blast and brown spot and assessed the lodging, plant height, and maturity of the crops (days after planting). Furthermore, we collected leaf and neck tissues for the assessment of the prevailing fungal populations. We used specific DNA primers to screen for the prevalence of the causal pathogens of blast, Magnaporthe oryzae, and brown spot, Cochliobolus miyabeanus, on asymptomatic and symptomatic leaf samples. We also conducted fungal isolations and PCR-sequencing to identify the fungal species in these tissues. Busia and Kisumu had a higher diversity of cultivars compared to Kirinyaga. The aromatic Pishori (NIBAM 11) was preferred and widely grown for commercial purposes in Kirinyaga, where 86% of Kenyan rice is produced. NIBAM108 (IR2793-80-1) and BW196 (NIBAM 109) were moderately resistant to blast, while NIBAM110 (ITA310) and Vietnam were susceptible. All the cultivars were susceptible to brown spot except for KEH10005 (Arize Tej Gold), a commercial hybrid cultivar. We also identified diverse pathogenic and non-pathogenic fungi, with a high incidence of Nigrospora oryzae, in the rice fields of Kirinyaga. There was a marginal correlation between disease severity/incidence and the occurrence of causal pathogens. This study provides evidence of the need to strengthen pathogen surveillance through retraining agricultural extension agents and to breed for blast and brown spot resistance in popular rice cultivars in Kenya

Assessment of the virulence spectrum and its association with genetic diversity in Magnaporthe oryzae populations from sub-Saharan Africa

A collection of 122 isolates of Magnaporthe oryzae, from nine sub-Saharan African countries, was assessed for virulence diversity and genetic relatedness. The virulence spectrum was assessed by pathotype analysis with a panel of 43 rice genotypes consisting of differential lines carrying 24 blast resistance genes (R-genes), contemporary African rice cultivars, and susceptible checks. The virulence spectrum among isolates ranged from 5 to 80%. Five isolates were avirulent to the entire rice panel, while two isolates were virulent to similar to 75% of the panel. Overall, cultivar 75-1-127, the Pi9 R-gene donor, was resistant to all isolates (100%), followed by four African rice cultivars (AR105, NERICA 15, 96%; NERICA 4, 91%; and F6-36, 90%). Genetic relatedness of isolates was assessed by single nucleotide polymorphisms derived from genotyping-by-sequencing and by vegetative compatibility tests. Phylogenetic analysis of SNPs of a subset of isolates (n = 78) revealed seven distinct clades that differed in virulence. Principal component analysis showed isolates from East Africa were genetically distinct from those from West Africa. Vegetative compatibility tests of a subset of isolates (n = 65) showed no common groups among countries. This study shows that blast disease could be controlled by pyramiding of Pi9 together with other promising R-genes into rice cultivars that are adapted to East and West African regions