Esther Kahangi

Genetic characterization of cultivated bananas and plantains in Kenya by RAPD markers

Abstract A polymerase chain reaction (PCR)-based approach, namely, random amplified polymorphic DNA (RAPD) was used to estimate the genetic relationships among 20 selected banana cultivars from different regions of Kenya. Nineteen random primers were used. The polymorphisms in PCR amplification products were subjected to the unweighted pair group method for arithmetic averages (UPGMA) and plotted in a phenogram. The dendogram constructed from the similarity data showed that all the 20 cultivars analysed were related. The highly related cultivars included Ng’ombe, Nusu Ng’ombe, Ntobe, Sialamule, Kimuga, Kibuzi, Sibusi, Bukamba, Mfupi and Gitigi whose genome was AAA. The cultivars Manyatta, Mokoya, Murure and Horn plantain whose genome was AAB were less similar while Pekera, Muraru, Spambia, Matumbo, Nyar Sausett and Mtama formed the least related group.

Evaluation of rhizosphere, rhizoplane and phyllosphere bacteria and fungi isolated from rice in Kenya for plant growth promoters

Rice (Oryza sativa L.) is the most important staple food crop in many developing countries, and is ranked third in Kenya after maize and wheat. Continuous cropping without replenishing soil nutrients is a major problem in Kenya resulting to declining soil fertility. The use of chemical fertilizers to avert the problem of low soil fertility is currently limited due to rising costs and environmental concerns. Many soil micro-organisms are able to solubilize the unavailable phosphorus, increase uptake of nitrogen and also synthesize growth promoting hormones including auxin. The aim of this study was to isolate and characterize phyllosphere, rhizoplane and rhizosphere micro-organisms from Kenyan rice with growth promoting habits. In this study whole plant rice samples were collected from different rice growing regions of Kenya. 76.2%, over 80% and 38.5% of the bacterial isolates were positive for phosphate solubilization, nitrogenase activity and IAA production whereas 17.5% and 5% of the fungal isolates were positive for phosphate solubilization and IAA production respectively. Hence these micro-organisms have potential for utilization as bio-fertilizers in rice production.

Effects of chilling and growth regulators on runner production of three strawberry cultivars under tropical conditions

The effect of chilling alone or in combination with gibberellic acid (GA3) and benzyladenine (BA) on runner production in three strawberry cultivars was observed during the warm and cool seasons in a field experiment under tropical conditions in Kenya. Chilling alone promoted a significant production of 18 and 10 runners per mother plant in the cold and warm season respectively in the cultivars tested. When chilling was combined with BA + GA3, runner production per mother plant was raised to 23 and 14 in the cool and warm seasons respectively. Chilled plants provided with exogenous GA3 produced almost the same number of runners as those receiving chilling only, whereas those treated with exogenous BA had significantly more stolons than those of treatments receiving chilling only. Daughter plant production followed a similar pattern as that of stolon production. The control plants produced fewest stolons but most branch crowns. More stolons, daughter plants and branch crowns were produced during the cool t...

Effect of endophytic Fusarium oxysporum on paralysis and mortality of Pratylenchus goodeyi

Three bioassays were conducted to investigate the antagonistic effect of secondary metabolites produced by 5 endophytic Fusarium oxysporum isolates from banana (Musa spp.) plants in Kenya, against Pratylenchus goodeyi. Percentage paralyses were recorded 3, 6 and 24 h after exposure to culture filtrates. Percentage mortality was evaluated after 48 h. All isolates caused significantly higher percentage paralysis (17.5 - 25.9%) and percentage mortality (62.3 - 72.8%) of P. goodeyi motile stages compared to the control (8.4 - 10.9% and 17.3 - 34.6%, respectively). Percentage paralysis of motile stages of P. goodeyi decreased as the length of time exposure to culture filtrates increased, while mortality increased as length of nematodes exposure to culture filtrates increased. Kenyan isolates performed equally as good as the Ugandan isolate (V5W2) in causing paralysis and mortality. Results from this study demonstrated that endophytic F. oxysporum antagonizes P. goodeyi through production of secondary metabolites.

Potential biological control of lesion nematodes on banana using Kenyan strains of endophytic Fusarium oxysporum

The root-lesion nematode Pratylenchus goodeyi is a common pest of banana in Kenya, which results in significant yield losses. An emerging option for the management of banana nematodes includes the use of endophytic fungi, which cause no damage to their hosts but often extend benefits, such as enhanced protection against various biotic and abiotic constraints. In the current study, non-pathogenic Fusarium oxysporum strains originating from banana (Musa spp.) in Kenya (4MOC321 and 11SR23) and Uganda (V5w2) were evaluated for their efficacy against P. goodeyi in tissue culture-derived plantlets (cv. Giant Cavendish and cv. Grand Nain) in pots. Pratylenchus goodeyi densities were 47-60% lower in endophyte-inoculated relative to non-inoculated plants and root necrosis damage was reduced by >30%. Endophyte treatment had no effect on plant growth parameters compared with untreated control plants. The performance of the two Kenyan strains was equally effective as the positive control (V5w2), thus demonstrating their potential as nematode bio-control agents under Kenyan growing conditions.

Effect of natural and artificial chilling in carrot Daucus carota L. at different locations in Kenya. I. Effects on bolting and flowering

SummaryEffect of natural chilling and artificial chilling durations of 2–8 weeks at 9°C on percentage bolting and flowering and on days taken from planting to the two events in carrot cv. Nantes was observed at four locations in Kenya in 1991/92. These were; Juja (1500 m above sea level in a warm Upper Midland (UM) zone) and Molo (2454 m), Kinangop (2558 m) and Marindas (2804 m), all in an Upper Highland (UH) zone. The observation was repeated in 1992/93 but in Juja and Kinangop only. In 1991/92 the lowest bolting and flowering percentage (<25 %) was recorded in carrot plants whose stecklings had received natural chilling at all planted sites while in those whose stecklings had received artificial chilling, bolting and flowering percentage increased with artificial chilling durations within each location. Over 75% flowering was obtained only in those plants grown from carrot stecklings chilled for six and eight weeks within each location and in those given four weeks chilling at Kinangop. In 1992/93, the ...

Effect of natural and artificial chilling in carrotDaucus carotaL. at different locations in Kenya. II. Effect on seed maturity, seedstalk height, umbel number, seed yield and subsequent germination of the harvested seed

Effects of natural and artificial chilling durations of 2–8 weeks at 9°C on seed maturity, seedstalk heights, umbel number, seed yields and subsequent germination of the harvested seed in carrot cv...