Tomato Management Practices and Diseases Occurrence in Mwea West Sub County

Tomato is an important crop in Mwea West Sub County, Kirinyaga County, Kenya. A survey was carried out in the area to investigate tomato management practices, diseases and pests that hinder tomato production. The study endeavoured to establish farmers’ knowledge on fusarium wilt disease and root-knot nematodes and the methods used to control them. Data was collected from two hundred and eighteen randomly selected small holder producers who were equally distributed in the study area. Data collected included tomato management practices, diseases and pests that hinder production. Majority (85.3%) of the respondents were males while a few (14.7%) were female. The respondents (71.6%) indicated that tomato was the most important crop grown for income generation in the area. Most important varieties grown were cultivars, Safari, Kilele F1, Prosta F1 and Rio- Grande. Most important diseases affecting tomato crop were; early blight (Alternaria solani) and late blight (Phytophthora infestans), fungal wilts (Fusarium sp. Verticillium sp. Rhizoctonia sp.) and bacterial wilt (Ralstonia solanacearum). Plant parasitic nematodes and pests (thrips, aphids, spider mites) were also reported in the study area. There was a significant(P<0.05) association between the following variables; type of land owner and major use of land, type of land owner and cropping system, source of agricultural information and whether or not to apply pesticides into the soil. Farmers were quite knowledgeable about tomato farming as they had access to information from various sources; however there are still major gaps in knowledge especially on diseases and pests. Keywords: Tomato, diseases, pests, nematodes, managemen

Evaluation of resistance reaction of maize germplasm to common foliar diseases in Kenya

Use of resistance varieties is the most practical method of managing crop diseases. There is a great variation in terms of resistance reaction to diseases among the various maize germplasm and with the liberization of seed market, the sector has witnessed proliferation of massive introduction of new varieties whose reaction to diseases cannot be ascertained. This study was conducted to evaluate the reaction of maize varieties to northern leaf blight (NLB), common maize rust, gray leaf spot (GLS) and maize streak disease (MSD). The experiment was conducted at Kabete Field Station, University of Nairobi for two seasons namely short rains and long rains. The germplasm was bought from the commercial seed stockists and the landraces obtained from KARI Katumani and from farmers. The diseases were assessed by monitoring and scoring for disease incidence and severity. The appropriate scoring keys were used for determination of disease severity. All the varieties showed symptoms of the four diseases in both seasons but the intensity of the diseases differed significantly among the different varieties. Disease incidence was highest for common rust with a mean of 14.29% for the variety DH04, while disease incidence was highest (19.21%) for northern leaf blight in season two for Kinyanya which is a landrace. Gray leaf spot and the common smuts had the lowest mean incidence ranging from 0 to 0.25% for common smut and 0 to 2.6% for gray leaf spot. Season two had comparatively higher disease incidence means compared to season one. Meteorological data showed that season two had more rains and this explains the reasons behind this. Though all the varieties screened were found to be affected by the diseases to various levels, the varieties displayed significant differences in the disease incidence and severity. This shows that use of resistance varieties should be considered in the management of maize diseases. Focus should also be on pyramiding genes for resistance in the breeding programmes to develop varieties with multiple resistance to different diseases. Key words: Disease incidence and severity, disease score, symptoms, varietie

Reaction of Selected Coffee Germplasm to Root-Knot Nematodes in Kenya

Coffee is one of the most important cash crops in Kenya and a leading export earner. Nematodes are among the most important biotic constraint in coffee production in Kenya and crop improvement work has mainly been breeding for resistance to diseases such as coffee berry disease and coffee leaf rust. However resistance has been used successfully in other coffee producing countries and it is one of the most economical and practical nematode management strategies. A greenhouse study was conducted to test the response of local and exotic coffee germplasm to root knot nematodes (RKNs). Ten (10) cultivars provided by Coffee Research Foundation (CRF) were tested for resistance to Meloidogyne incognita under greenhouse conditions (25±2oC). Nematodes were extracted from the roots using Modified Baermann Technique and enumerated using Cobbs slide. After 90 days of plant growth, the disease severity was evaluated and the experiment repeated twice. Galling indices (GI), egg mass indices (EMI) and nematode populations recovered from soil samples indicated a range of responses from resistant to highly susceptible.  Three breeder’s lines including Robusta tree 1, Robusta tree 2 and Robusta tree 3 were rated resistant with galling indices of 1.2-3.0. This study has demonstrated the potential of host resistance as a strategy in the management of nematodes in coffee for increased productivity. Field evaluation needs to be conducted to confirm these findings. The identified resistance sources can be utilized to deploy resistance genes to improve existing varieties that have high commercial value but lack resistance to nematodes.   Key words: Resistance, susceptible, galling indices, nematode population, cultivar

Plant Parasitic Nematodes Associated With Coffee in Kenya and Factors Influencing their Occurrence, Abundance and Diversity

Frequent detection of galls on coffee roots has raised concerns of nematodes in coffee production systems in Kenya. This study aimed at determining the occurrence of nematodes associated with coffee in Kenya and the role of crop management, cultivars, soil properties and agro ecological zones on the abundance and frequency of nematodes. A survey was conducted in the prime coffee growing areas in 10 counties namely; Machakos, Makueni, Kiambu, Embu, Kirinyanga, Nyeri, Meru, Kisii, Nandi and Trans-Nzoia. Nematodes were extracted using a combination of centrifugal floatation and Modified Baermann techniques and identified to genera level.  Nutrient analysis was carried out using the Double Mehlich method. Results showed that nematodes belonging to 30 genera were recovered from coffee agro-ecosystems. Plant parasitic nematodes were the most prevalent with 64% frequency (19 genera) of occurrence followed by bacterial feeders at 24%. The genus Tylenchulus, Meloidogyne and Pratylenchus were the most dominant across all the coffee growing areas. Coffee farms in the coffee-tea zones (Upper Midland 1) harbored the highest numbers of plant parasitic nematodes, followed by Upper Midland 2 and least in the marginal coffee growing zones (Upper Midland 3). Well managed farms had less plant parasitic nematodes compared to neglected farms. K and P significantly contributed to the variation in the nematode community composition. This study demonstrated the prevalence of plant parasitic nematodes, factors that influence their abundance and distribution and justifies need for further management of nematodes in coffee production. Key words: Abundance, agro-ecologial zones, diversity, nematode genera, nutrient

Evaluation of Verticillium chlamydosporium and Arthrobotrys oligospora for biological control of Meloidogyne incognita in celery and tomato

The ability of nematode trapping fungi and egg-parasitising fungi to colonize and persist in the rhizosphere of crop plants is thought to be an important factor influencing the success of biological control of root infecting nematodes. In this study, two strains of an egg parasitic fungus Verticillium chlamydosporium (Vc- 10 and Vc-2M) and one isolate of the nematode-trapping fungus Arthrobotrys oligospora were evaluated to determine their pathogenicity to Meloidogyne incognita and persistence in the rhizosphere of celery (Apium graveolus L.) and tomato(Lycopersicon esculentum L.) plants in a greenhouse experiment. The isolates tested differed significantly (P≤0.05) in their pathogenicity to M. incognita and survival in the rhizosphere. Isolate Vc-10 of V. chlamydosporium was the most virulent pathogen of the nematode. Root galling was lowest (P≤0.05) in tomato plants treated with the isolate Vc-10 (2.2); pots treated with this isolate had the lowest final soil population of infective juveniles; there was a 62.2% and 98.5% infections of eggs and egg-masses respectively by Vc-10 on tomato plants. Isolates Vc-10 and Vc-2M of V. chlamydosporium persisted in the soil and could be re-isolated from the rhizosphere and roots of tomato plants at least 16 weeks after soil infestation. The final inoculum density was, however, higher (P≤0.05) for Vc-10 (1.35×105 cfu/g soil) than Vc-2M (9.25×104 cfu/g soil). A. oligospora on the other hand did not give any significant (P≤0.05) control of the nematode on both crops, there was severe galling on the roots of celery plants (7.4) and tomato plants (6.3) treated with this biological control agent. A. oligospora could not be re-isolated from the plant rhizosphere sixteen weeks after soil infestation. Lack of nematode control on both crops by A. oligospora was attributed to its poor or no establishment in the plant rhizosphere. The fact that it could not be reisolated from the rhizosphere may imply that the fungus did not survive in the rhizosphere of the test plants. Keywords: Verticillium, Arthrobotrys, Meloidogyne, rhizosphere, persistence, root-knots, chlamydospores. J. Trop. Microbiol. Biotechnol. Vol. 3 (2) 2007: pp. 51-5

Reaction of potato cultivars to Ralstonia solanacearum in Kenya

A survey of bacterial wilt (BW) incidence was carried out in three potato producing districts of Kenya, namely, Nyeri, Nyandarua, and Meru in 1997. The survey was carried out in 30 randomly selected farms in each district. Incidence of BW was highest (18.8%) in Nyeri district, intermediate (16.7%) in Meru and lowest (10.4%) in Nyandarua. A significant and negative correlation (P=0.05; r = -0.34) between bacterial wilt incidence and altitude was observed. Fifteen potato cultivars, Nyayo, Desiree CIP-800048, Roslin Tana, Kerrs pink LB-5, Golof (Dutch Robjin), B53, Tigoni CIP-381381.13, Rutuku CIP-720097, Asante CIP-381381.20, Kenya Dhamana CIP-800228, Mauritius Clone (89016), KP93739.26, KP92633.26, and Cruza148 CIP-72011 were subsequently evaluated for their reaction to Ralstonia solanacearum in artificial and natural infections in the greenhouse and in the field. Although none of the cultivars appeared resistant, there were significant (P=0.05) differences in bacterial wilt incidence and severity among the cultivars. Cultivars Kenya Dhamana, Mauritius and Cruza (CIP-720118) had low bacterial wilt severity and incidence and were rated tolerant, whereas the other cultivars were rated moderately susceptible or very susceptible. Key Words: Bacterial wilt, incidence, Kenya, Solanum tuberosum, tolerance (African Crop Science Journal 2001 9(1): 251-256

Studies on the interaction between Ralstonia solanacearum (Smith) and Meloidogyne Spp. in potato

A survey was undertaken to determine population density of Meloidogyne   juveniles (J2) in 90 fields randomly selected from three potato-producing districts in Kenya namely Nyeri, Meru and Nyandarua. Mean nematode densities were highest (45) in samples collected from Nyeri and Nyandarua and lowest (31) in soil samples collected from Meru. The reaction of 15 potato cultivars to Meloidogyne incognita   was determined under greenhouse conditions. Plants were inoculated with 6000 eggs and second-stage juveniles each. Highly significant (P=0.01) differences were observed between the cultivars. Galling index was highest (5.5) in cv. KP93739.26 and lowest (1.9) in cv. Nyayo. All cultivars supported nematode reproduction with the highest (5.0) egg mass index being recorded in cultivars KP93739.26, Kerr's Pink, Desiree CIP-800048, KP92633.26 and B53. No cultivar exhibited immunity. The relationship between infection by root-knot nematodes and severity of bacterial wilt in three potato cultivars with varying levels of resistance to bacterial wilt namely Asante CIP 381381.20 (susceptible), B53 (moderately susceptible), and Kenya Dhamana (resistant), was investigated in a greenhouse experiment. Bacterial wilt was more severe in plants infected with both pathogens as compared to plants infected with R. solanacearum   alone

Plant parasitic nematodes associated with common bean in Kenya and the effect of Meloidogyne infection on bean nodulation

(African Crop Science Journal 1999 7(4): 503-510