R. D. Narla

Current status on production and utilization of spider plant (Cleome gynandra L.) an underutilized leafy vegetable in Kenya

Spider plant exists as semi-cultivated indigenous leafy vegetable with ecological, social and cultural values in most home gardens in Kenya. It plays a significant role in the food and nutrition security of local communities. The tender leaves are usually consumed as a cooked vegetable while the roots, stem and whole leaves are used for medicinal purposes. The importance of spider plant has been discussed in the context of biodiversity conservation and food security because the vegetable is rich in micronutrients and phytochemicals associated with antioxidant, anti-malaria, and anti-microbial properties.

Resistance to Iris yellow spot virus and onion thrips among onion varieties grown in Kenya

Iris yellow spot virus (IYSV) vectored by Thrips tabaci threatens profitable onion production in eastern Africa. Host plant resistance is considered to be the first line of defence against insect-transmitted virus diseases. Hence, information on resistance to IYSV and T. tabaci among common onion cultivars in Kenya is crucial for the development of integrated pest management strategies. This study evaluated the resistance to thrips and IYSV among widely grown onion cultivars in Kenya, viz. Red Pinoy, Red Creole, Bombay Red, Green Bunching and Texas Grano, over two growing seasons. Strawcoloured, diamond-shaped necrotic lesions typical of IYSV infection were observed 2 weeks after transplantation. Observations on thrips numbers per plant, IYSV disease incidence and severity, and virus intensity were undertaken to assess the resistance. Varieties differed significantly with respect to both IYSV disease incidence and thrips numbers per plant from fourth week to physiological maturity. Red Pinoy, Green Bunching and Red Creole were highly susceptible to the virus and thrips, while Texas Grano and Bombay Red were moderately resistant. There were significant differences among the varieties with regard to IYSV intensity, with the highest and the least virus intensity positively correlated with disease severity being recorded in Red Pinoy and Texas Grano, respectively. Among the varieties, Texas Grano produced the highest yield in both seasons, while Red Pinoy produced the least. Hence, Texas Grano and Bombay Red could be recommended as moderately resistant cultivars to thrips and IYSV to be grown in Kenya for markets where pungency is not preferred and preferred, respectively. Regions with high levels of thrips population and IYSV infestation are not suitable for the cultivation of Red Pinoy.

Field transmission efficiency of Alternaria sesami in sesame from infected seed

Four sesame accessions with varying levels of susceptibility to Alternaria sesami were selected from an advanced germplasm collection of the Sesame Improvement Project to determine transmission efficiency of A. sesami from seed under field conditions. Accessions were sown in field plots in Siaya, Kenya, in March and October 1995 during the first and second rainy seasons, respectively. Incidence of Alternaria leaf spot (ALS) following artificial inoculation averaged 85–95% for all accessions in the two seasons. Infection of A. sesami in harvested seed averaged 11.8% for accessions SPS SIK 013, 9.4% for SPS SIK 110, 9.7% for SPS SIK 121 and 6.8% for SPS SIK 130. Three hundred seeds from the harvested seed lots for each accession were sown in disease-free field plots at Kibwezi, Kenya, in March and October 1996 for two seasons. Typical disease symptoms appeared about 5–6 weeks after sowing. Disease progress curves were better described using the Gompertz rather than the logistic model for all the accessions evaluated. Disease onset (Yo) was nearly the same in both seasons but the rate of disease increase (r) was faster in the first season than in the second season. Rate of disease progress was consistently higher for SPS SIK 013 than SPS SIK 130, in both seasons. Area under the disease progress curves for accessions was significantly higher (P<0.01) in the first season compared to the second season. Disease incidence averaged 0.0% for SPS SIK 110, 1.5% for SPS SIK 130, 3.3% for SPS SIK 121, and 3.6% for SPS SIK 013. Transmission efficiency of ALS by seed ranged from 0.0% to 40.7% and was significantly higher for SPS SIK 013 and SPS SIK 121 than for SPS SIK 110 in the two rainy seasons.

Effects of Early and Late Harvest on Agronomic Performance and Stability of Late Blight Resistant (R-gene Free) Potato Genotypes

Late blight is an important constraint to potato production and genotype resistance is an effective disease control mesure. Ten late blight resistant potato genotypes (R-gene free) were assessed for yield performance and stability at early (90 days) and late harvest (120 days) at two locations in Kenya during two years. Significant differences (P ≤ 0.05) in area under disease progress curves (AUDPC) were detected among potato genotypes. Resistant genotypes free of R-genes had significantly (P ≤ 0.05) higher yield at late than early harvest, perhaps due to increased tuber bulking period. The rank of genotypes for AUDPC, late blight resistance, and tuber yield varied across seasons and locations (environment). Additive main effects and multiplicative interaction (AMMI) analysis of tuber yield and late blight resistance resulted in significant (P ≤ 0.05) effects of genotypes (G) and environments (E). The proportion of genotypic variance was larger than the environmental variance and the G × E interactions. For tuber yield, the G, E, and G × E interactions accounted for 42.9, 39.6 and 17.5%; and 53.4, 29.7, and 16.9% at early and late harvests, respectively. For AUDPC, G, E, and G × E accounted for 80.2, 5.0, and 14.8%; as well as 82.3, 4.6, and 13% for early and late harvests, respectively. The resistance of potato genotypes without R-genes varied. Selective deployment of resistant genotypes can improve potato tuber yield.

Seed Potato Production Practices and Quality of Farm Saved Seed Potato in Kiambu and Nyandarua Counties in Kenya

Potato production in Kenya is mainly constrained by limited supply of quality seed potato tubers. The objective of this study was to determine seed potato handling practices and quality of farm saved seed potato. A survey involving 79 farmers was conducted in potato production areas in Kiambu and Nyandarua Counties to collect information on seed potato production practices including sources of seed tubers, seed selection, seed tuber storage, pests and diseases. Samples of seed potato were collected from farmers and evaluated for quality parameters such as tuber size, weight, stout sprout length and infection with diseases. Factors affecting potato production included limited quality seed supply, pests and diseases. Shangi was the main potato variety grown by majority (62.8%) of farmers and all the farmers used own farm saved seed. Most (45.5%) farmers recycled the seed for four seasons and 44.1% of farmers stored seed potato for three months. Freeness from seedborne diseases was the main seed quality preference by farmers. The main pest reported was cutworms (42.6% of farmers) while potato late blight and bacterial wilt were the major diseases reported by 87.1% and 86.7% of the farmers respectively. All farm saved seed potato samples were infected with Fusarium coeruleum, 51.2% with Rhizoctonia solani, 53.3% with Fusarium sambunicum, 33.3% with Fusarium solani and 48.3% with Aspergillus niger. Over 69% of the farm saved seed samples were infected with Ralstonia solanacearum while 40.1% were infected with Potato Virus S, the most dominant. Due to poor post-harvest handling practices, farmers incurred seed quality and quantity losses in storage. Farm saved seed is contaminated with multiple seed borne diseases. Farmers should be sensitized on appropriate seed potato handling practices and there should be increased supply of certified seed potato.

Seasonal dynamics and alternate hosts of thrips transmitted Iris yellow spot virus in Kenya

Thrips-transmitted Iris yellow spot virus (IYSV) (Family Tospoviridae, Genus Orthotospovirus) is a major constraint to onion (Allium cepa L.) production in Kenya. Determining seasonal patterns of the vector and alternate hosts of the virus could help onion farmers plan Integrated Pest Management strategies; while allowing them to move away from calendar-based applications of insecticides. The objective of this study was to determine the distribution, seasonal variations and alternate hosts of vector and IYSV. For distribution, a survey was carried out on a network of farms in all onion growing areas in Kenya; while for seasonality, surveys were done in two areas; Loitoktok and Naivasha. Data were collected on IYSV incidence, thrips population and alternate hosts. Results showed IYSV was widely distributed in all onion growing areas; with incidence varying from 26 to 72%. Highest IYSV incidence was recorded during the cool-dry season, and varied from 56.5 to 71%; while lowest IYSV incidence in onions was observed during the cool and wet season (29.9 to 32.2%). Iris yellow spot disease incidence positively correlated with the number of onion thrips in Loitokitok (r = 0.659; P<0.0001) and Naivasha (r = 0.623; P<0.0001). Identified alternate hosts for IYSV were leeks, chives, shallots, lambsquarters, redroot pigweed, Chinese lantern and black nightshade.Occurrence of thrips on onions, which is grown all year round calls for urgent integrated pest management strategies that includes host plant resistance, field sanitation, forecasting and use of beneficial insects and parasitoids to reduce impact of the pest and disease. Plant health adherence through removal of alternate weeds hosts around the cultivated fields, would be useful in minimising IYSV incidence

Effect of soil sterilisation on biological control of Fusarium oxysporum f. sp. lycopersici and Meloidogyne javanica by antagonistic fungi and organic amendment in tomato crop

ABSTRACT One of the major challenges in the application of biological control agents into the soil is their inability to withstand competition from natural microflora. In this study a management programme involving fungal biological control agents Trichoderma harzianum (TH) and Purpureocillium lilacinium (PL), and the organic amendment neem was carried out for the control of Meloidogyne javanica and Fusarium oxysporum f. sp. lycopersici (FOL). The experiment was carried out in sterile and non-sterile soil in order to test the efficacy of biological control in natural soil conditions. This experiment was repeated twice. A Wilcoxons Signed-Rank test indicated there were no significant (P < 0.05) differences in fusarium wilt control in sterile and non sterile soils in the treatments PL neem and TH neem, but there was significantly (P < 0.05) higher control of M. javanica in the same treatments in sterile soils compared to non sterile soils. The combinations of fungal antagonists and neem were effective in non sterile as in sterile soils in the control of fusarium wilt, while being less effective in the control of M. javanica. Thus the biological control agents can be very effective in the control of fusarium wilt in natural conditions where the soil is not sterilised, but be less effective in the control of M. javanica in the same conditions. There is therefore potential of integrated management of fusarium wilt and root-knot nematodes (RKN) by these biological control agents in natural soil field conditions as an alternative to using chemicals.