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Iris yellow spot virus (IYSV, genus Tospovirus) is a viral disease of bulb and seed onion crops and is transmitted by Thrips tabaci. Foliage damage of up to 75% has been reported in Kenya and Uganda. In this study, the rate of IYSV replication in the larva, pupa and adult stages of T. tabaci and other non-vector thrips species and colour forms such as Frankliniella occidentalis, F. schultzei (dark) and F. schultzei (pale) was evaluated by monitoring relative levels of nucleocapsid (N) and non-structural (NSs) proteins using N-and NSs-specific antibodies. The effect of IYSV replication on mortality of thrips was also determined. N protein levels increased in all three stages of IYSV-fed T. tabaci, indicating replication of IYSV. In IYSV-fed non-vector thrips, the increase of N protein levels in the larval stage was lower than IYSV-fed T. tabaci but higher than their healthy counterparts. The N protein levels did not increase at pupal and adult stages. NSs protein was not detected in first instar of either vector or non-vector thrips species. After a 4 h postacquisition period, a significant increase in NSs proteins was only observed in IYSV-fed T. tabaci, clearly differentiating vectors and non-vectors of IYSV. IYSV replication did not influence the survival of the vector thrips species, T. tabaci populations or the non-vector thrips species. This study indicates the effectiveness of monitoring non-structural proteins such as NSs, compared to nucleocapsid proteins, for differentiating vectors and non-vectors of IYSV.

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Determination of yield stability is critical in identifying new common bean cultivars with either specific or broad adaptation in target environments. This study aimed to assess genotype by environment (G x E) effects on agronomic performance of 78 F 1.7 lines selected with molecular markers for multiple disease resistance from 16 inter-racial bean populations. Field trials were conducted in low-, medium-and high altitude conditions in Kenya. Data collected on seed yield were subjected to additive main-effects and multiplicative interaction (AMMI) model to separate additive variance from the G x E interaction and to determine the stability of genotypes across locations. Results showed that G x E effects were highly significant (P<0.001), implying that tested lines behaved differently across the three locations. Better yields were recorded from high altitude Tigoni site while the lowest were from low altitude Mwea site. Yield across sites ranged from 1,518 to 2,748; 1,324 to 3,860; 1,537 to 3,722 and 1,010 to 3,718 kg ha-1 for pinto, red mottled, red kidney and mixed color bean lines, respectively. Number of pods plant-1 was the most strongly correlated to seed yield and could be, therefore, used as an indirect selection criterion for seed yield. The environment was responsible for the largest part of yield variability (86.4%, 84.8%, 82.3% and 49.5% for pinto, red kidney, red mottled and mixed color bean lines, respectively). KMA13-22-21 and KMA13-29-21 were the most stable high yielding lines across locations. Higher yielding lines were the most unstable across sites. Two pinto, four red kidney, 15 red mottled, and two mixed color lines did better than their corresponding checks with yield advantages of 7.6, 14.3, 71.5, and 34.9%, respectively. These lines should, therefore, be selected for further testing and release.

Indiscriminate use of synthetic pesticides has resulted in loss of access to niche markets due to presence of chemical residues in fresh vegetable produce. There is need for safe alternatives to synthetic pesticides in management of pests and diseases in horticultural production. The objective of this study was to evaluate effectiveness of plant extracts in suppressing growth of plant pathogenic fungi in vitro. Mature plant tissue samples were finely blended, extracted with 95% (v/v) ethanol and the extracts were concentrated by evaporation under vacuum at 60 0 C to remove the ethanol. Antifungal activity of the extracts was tested by incorporating the extract into the culture media onto which fungal pathogens were then cultured. Sensitivity of the fungal pathogens was determined by measuring the pathogen colony radial growth of the treatments compared to controls. Extracts from different plants varied in activity, with turmeric extracts being the most active. Turmeric extracts inhibited fungal colony radial growth by 30 to 73 % while mint was the least active. Alternaria solani was the most susceptible pathogen while Pythium ultimum was the most sensitive to extracts from all the plants evaluated. Fusarium oxysporum f. sp. lycopersici was tolerant to most of the plant extracts tested. Sensitivity of all the pathogens tested was found to decrease with the age of the cultures. The study showed that plants extracts contain compounds that inhibit growth of plant pathogenic fungi. Such compounds could be exploited as biopesticides to manage plant diseases thereby reducing the chemical residues in horticultural production.

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.