Bacterial wilt caused by Ralstonia solanacearum Smith is the most severe potato disease in Rwanda because there is no known pesticide for it and cultural control methods seem almost impossible to implement. Therefore, use of plant extracts with antibacterial activities which are locally available, economically affordable and environmental friendly could be an alternative in the management of the disease. This research focused on in vitro screening of the antibacterial activity of methanol, water and chloroform extracts of ten local plant materials against the pathogen. From this screening, methanol and water extracts of three promising plant species, i.e., tobacco, wild marigold and garlic were also used for determination of minimal inhibitory concentration (MIC). The results showed higher inhibition zone of methanol extracts (16.85 mm) against bacteria followed by water (14.42 mm) and chloroform (14.19 mm) extracts. All ten plant extracts inhibited the growth of the pathogen. Higher antibacterial activity was found in tobacco, wild marigold and garlic extracts (19.61, 18.56, and 18.3 mm inhibition zones, respectively). Minimal inhibitory concentration (MIC) of methanol extracts from tobacco and wild marigold was 6.25 mg mL-1 whereas, garlic methanol extract was 12.5 mg mL-1. Furthermore, MIC of water extract was 12.5 mg/mL-1 in all three plant species. The findings revealed that tobacco, garlic and wild marigold extracts are the best in the control of potato bacterial wilt. Moreover, methanol extracts are the most efficient in management of potato bacterial wilt in comparison to water and chloroform extracts.

Bacterial wilt (Ralstonia solanacearum) is one of the major potato diseases in Rwanda. An in vitro study was carried out to identify and characterize the pathogen isolated from three potato cultivars (Kinigi, Kirundo and Gikungu) in Rwanda. This was achieved by cultural and morphological tests on triphenyl tetrazolium chloride (TTC) and casamino peptone glucose (CPG) agar as well as biochemical tests through Gram staining and biovar test. An in vivo experiment was also performed to assess the pathogenicity of those isolates on potatoes. All isolates showed typical morphological traits of virulent R. solanacearum on TTC and CPG media. The test isolates were Gram-negative bacteria. Biovar test confirmed that all the isolates belonged to race 1 biovar 3 of the pathogen. Furthermore, the highest disease severity (DS=100%) and disease incidence (DI=100%) were observed in Gikungu isolate followed by Kinigi (DS=97.33% and DI=98.25) and Kirundo (DS=94.67% and DI=92.61%). From this study, all three isolates were typical R. solanaceraum belonging to race 1 biovar 3 and were all pathogenic to potato plants. Gikungu and Kinigi isolates were highly virulent than Kirundo isolate. Therefore, Gikungu or Kinigi isolates can be used for further studies in plant protection in management of the disease. Key words: Biovar test, Gram-negative, Gram-positive, pathogenicity test.

The present work evaluated the impact of arbuscular mycorrhizal (AM) fungus on growth. Three species of trees, Tephrosia vogelii , Leucaena leucocephala and Dombeya torrida were treated with fragments of arbuscular mycorrhizae and grown in greenhouse. The aim of the present work was to determine whether arbuscular mycorrhizal symbiotic association with these tree species would enhance their growth. Data on height, stem diameter and number of leaves were taken after every two weeks for a period of three months. Mycorrhizal plants demonstrated higher vigor with Tephrosia vogelii giving a mean height of 57.50 cm, 0.50 cm diameter and 9.33 number of leaves which were significantly different from the control plants at p ≤ 0.05 according to least significant difference (LSD). The biomass was also taken at the end of 90 days of growth and the same trend was exhibited. Mycorrhizal plants also showed root nodules with mycorrhizal arbuscles. This work contributes to our understanding of the effects of AM symbiosis on the accumulation of certain micronutrients in valuable woody tree species. Keywords : arbuscular mycorrhizae, Tephrosia vogelii , Leucaena leucocephala , plant growth

The potato industry in Kenya is threatened by bacterial wilt because most production areas are infested with the wilt-causing Ralstonia solanacearum and over 50% yield losses have been reported. Continuous cultivation causes soil physical and biological constrains that greatly affect the crop performance and increase proliferation of the bacterium. Rotation with non-host or suppressant plant species could contribute to considerable reduction of bacterial wilt in the subsequent potato crops. This study tested the effect of different crop sequences on R. solanacearum population in the soil, wilting incidence and yield of potato. Two season field experiments were conducted at two sites (Egerton University, Njoro and National Agricultural Research Laboratories (NARL), Kabete) with 17 different crop sequences. Rotations involving brassica and legumes with potato gave a higher emergence percentage compared to the other sequences. The bacterial population was significantly influenced by the different environments from the first season to the third season; F (1, 102) =53.2, P<0.001, F (1, 102) =12.5, P< 0.001 and F (1, 102) =236.8, P<0.001 respectively. There was a significant effect F(16,119)=7.063, P<0.001 of the crop rotation sequences on the wilting incidence of potato. Pre cropping potato with spring onion and barley resulted to a significantly lower wilting incidence compared to all the other crop rotation sequences with a mean of 8.3% across sites. The results showed that Potato-Lablab-Potato and Cabbage-Lablab had the highest yield with 19.9 and of 19.7 tons/ha in the one crop rotations and pre crops to potato respectively. A Genotype x Environmental means versus IPCA scores showed that the yield due to barley-spring onion, spring onion-barley and wheat-spring onion as pre crops were more stable in both locations compared to the other cropping sequences. The study indicates that rotations involving spring onion with the locally grown cereals such as barley and wheat can be utilized in curbing bacterial wilt. Rotations involving lablab and cabbage may also be used to increase the yield of potato in bacterial wilt infested fields. These crops should be used in rotations involving more seasons so as to achieve better effects. Key words: Bacterial wilt, crop rotation, potato yield, Ralstonia solanacearum, wilting incidence.

Interest in the extraction of bioactive compounds from natural sources has increased in recent years due to the potential applications of these compounds in food, chemical, and pharmaceutical industries. The methanolic extract of the fungus Engleromyces goetzei was investigated for the presence of phytochemicals and the antibacterial properties. The study shows that the extract has flavonoids, coumarins, saponins, terpenoids and steroids. Engleromyces goetzei has potential as a source of useful antibacterial compounds active against phytopathogenic bacteria. Disk diffusion assay was used to analyze the susceptibility of an organism which help in identifying the proper antibacterial biopesticide. In this experiment, this was done by placing the antimicrobial disks impregnated with E. goetzei on the NA plates swabbed with Xanthomonas campestris, Pseudomonas sryingae pv phaseolicola, Erwinia carotovora and Xanthomonas axonopodis pv. phaseoli . After twenty-four hours of incubation, there were areas around the antimicrobial disks with no bacterial growth. The MIC of E. goetzei against X. axonopodis pv. phaseoli, Ps. syringae pv phaseolicola and X. campestris was found to be 1mg/ml while that of E. carotovora was 10mg/ml. Keywords: Phytochemicals, Engleromyces goetzei , X. axonopodis pv. phaseoli, E. carotovora, Ps. syringae pv phaseolicola, X. campestris

Fusarium wilt caused by Fusarium oxysporum f. sp. ciceris is a soil and seed borne disease affecting chickpea (Cicer arietinum). It is widely distributed where chickpea is grown and it causes variable yield losses depending on the level of resistance of the genotype and suitability of environmental conditions for disease development. Thiram and carbendazim fungicides are used in most crops as seed dress fungicides against a wide variety of pathogens. The impact of the 0%, 50%, 100% and 150% of the recommended 1.5g fungicide/kg seed rates of these two fungicides on plant height, periodic dry matter and number of pods and grain yield of chickpea was evaluated in the field in a split plot design. Two varieties, Chania 1 which is moderately resistant and Chania 2 which is highly susceptible were grown. Plant height, dry matter and pods per plant were significantly higher in Chania 1 moderately resistant variety and when grown under increasing rates of fungicide application. Increasing fungicide application rates significantly increased grain yield of chickpea. The highest Grain yield of 1.4 t/ha was obtained from 150% (2.25g/kg seed) application of either thiram or carbendazim for MR Chania 1 was grown and treated with either thiram or carbendazim at 150% rate of application. Farmers should grow Chania 1 chickpea variety to minimize use of fungicide application rates to range within 1.5 to 2.25 g fungicide/kg seed and obtain high chickpea growth; yield attributes and grain yields ranging between 1.32 to 1.4 t/ha, respectively.

The occurrence of Trichoderma harzianum and T . asperellum in cultivation of oyster mushroom ( Pleurotus ostreatus ) frequently results in serious crop losses and considerable inhibition of growth of mycelium and fruiting bodies of oyster mushroom thus lowering the yield substantially. Bacillus amyloliquefaciens strain isolated from groundnuts proved very effective in antagonizing the oyster mushroom pathogenic T. harzianum and T . asperellum without having a negative effect on P . ostreatus mycelia. The Bacillus amyloliquefaciens was found to produce diffusible and volatile organic compounds. This strain is a potential biocontrol candidate, in addition to the lack of antagonistic activity towards P . ostreatus mycelia. The present study, hence, provides a potential biocontrol agent for Trichoderma green mould. However, field studies of this isolate as substrate inoculant in oyster mushroom are required in order to establish its actual performance. Keywords : Bacillus amyloliquefaciens , Green mould, Mushroom, Biocontrol

A biological survey was carried out in 145 potato farms in nine divisions in Nakuru county, Kenya during the short rains between October and December 2012. The purpose of the survey was to provide comprehensive information on the distribution of bacterial wilt incidence, prevalence and contributing factors in the County. Percentage disease prevalence and incidence, and contributing factors were determined through observation and farmers’ interview respectively. Descriptive statistics were used to determine percentages and frequencies of data collected. Chi-square tests and spearman’s correlation coefficient analysis were used to determine significance of the data and examine relations between different variables respectively. Spot altitudes of the fields were recorded using Geographical Positioning System (GPS). Results showed that besides potatoes, other crops of economic importance in the area are wheat, tea, maize and beans. The average yield of potato in the nine divisions was 14.5 ton/ha. Bacteria wilt prevalence in the County varied from 100% in Bahati sub-County to 35.7% in Mauche and was found to be spread across all the sub Counties surveyed. The incidence also varied form 0 - 41% in the farms surveyed. There was a significant relationship between altitude and bacterial incidence at x 2 (36, N=111) =78.6, p<0.01. The Pearson’s correlation coefficient of r s = -0.30, (n=111, p<0.01) indicated a reduction in bacterial incidence as altitude increased. The disease also reduced with an increase with the number of seasons the field was occupied by other crops besides potatoes as indicated by a chi­­ square test x 2 (20, N=46) =35.235, p<0.05, and the spearman’s correlation r s = -.092, (n=46). Bacterial wilt symptoms on plants were more prevalent from the principal growth stage 6 (2 digit BBCH 60) and this is important in determination of the right stage of positive selection of mother plants for seed purpose. Major contributing factors to bacterial wilt in the region include; seed source, potato variety, lack of seed renewal, etc. Promotion of improved seed development techniques such as positive seed selection, production of mini tubers in the affected areas would improve the seed quality and give high yields. The relevant stakeholders should ensure accessibility of released varieties to all farmers and restrict seed movement to control spread of bacterial wilt. Development of cultural practices that are applicable and affordable in the specific regions and capacity building would contribute in reducing the bacterial wilt spread in the sub-Counties.

GC-MS was used in the investigation of the essential oils chemical composition isolated from the leaves of Lippia javanica. A total of 22 components were identified accounting for 76.85% of the oil composition. The oil is characterized by Monoterpenes as shown by the high percentage of Artemisia ketone (49.52%), m-tert-Butylphenol (8.73%), Linalool (4.43%), beta-myrecene (3.13%), Targetone (2.85%) and Isopiperitenone (2.13%). Sesquiterpenes constituted only 6.06% of the total oil. The oil showed inhibitory effects on the visible growth of Fusarium gramenearum while there was no observable activity of the oil against Fusarium moniliforme. The extent of inhibition of visible fungal growth was dependent on the oil concentration. The oil's Minimum Inhibitory Concentration (MIC) value was found to be 27.07 mg/ml. The results obtained shows that the essential oil from L. Javanica can be used to inhibit the growth of phytopathogenic fungi that causes maize diseases in the farms.

Moulds destroy more than 30% of crop yields in developing countries and produce poisonous mycotoxins like aflatoxins, fumonisins, ochratoxins, deoxynivalenol and zearalenones. The aim of this study was to identify aromatic plants with essential oils that can control the growth of moulds in maize and, therefore inhibit the production of associated mycotoxins in the grains. The assayed mould strains were Fusarium spp and Aspergillus spp. Five essential oils were extracted from aromatic plants (Tarchonanthus camphoratus, Artemisia vulgare, Piper capense, Foeniculium vulgare and Rosmarinus officinalis) using hydro-distillation and screened for antifungal activity against the moulds using the paper disc diffusion inhibition test. The antifungal activity tests showed that all the essential oils screened were active against 14 Aspergillus and 13 Fusarium species. These results show that the essential oils screened have antifungal activities against A. parasiticus, A. flavus, A. wentii, A. ustus, A. nidulans, A. ochraceus, A. tamarii, A. niger, A. versicolor, A. flavipes, A. terreus, A. fumigatus, F. solani, F. proliferatum, F. sporotrichioides, F. moniliforme, F. scirpi, F. chlamydosporum, F. trincinctum, F. oxysporum, F. subglutinans, F. merismoides, F. semitectum, F. nivale, F. avenaceum, F. graminearum, F. culmorum and F. crookwellence species that are the producers of aflatoxins, fumonisins, ochratoxins, deoxynivalenol and zearalenones in maize. These oils can be used in food preservation systems to inhibit the growth of moulds because the inhibitory action involves cytoplasm granulation, cytoplasmic membrane rupturing and inactivation and/or synthesis inhibition of intercellular and extracellular enzymes. This in turn will retard subsequent mycotoxin production. Keywords: Antimould activity, Aspergillus, Fusarium, Inhibition, Mycotoxins.

Hydro-distilled essential oil from Piper capense (L. f.) growing in Kenya was analyzed by gas chromatography mass spectrometry (GC-MS) and evaluated for antifungal activity. The oil was dominated by sesquiterpene hydrocarbons (43.9%) with δ-cadinene (16.82%), b-bisabolene (5.65%) and bicyclogermacrene (3.30%). There was appreciable quantity of monoterpene hydrocarbons (30.64%) including b-pinene (7.24%) and α-phellandrene (4.76%). Arylpropanoids (8.64%) was found in reasonable quantity having myristicin (4.26%) as its major constituent. A total of ten, fourteen and sixteen mycotoxigenic species of Aspergillus, Fusarium and Penicillium respectively were assayed. The oil showed strong antifungal activity against these fungi with Minimum Inhibition Concentration (MIC) ranging from 33.1 to 265 mg/ml. These results show that the oil has antifungal activities against fungi that are producers of poisonous mycotoxins found in foods and therefore can be used in food preservation systems to inhibit the growth of moulds and retard subsequent mycotoxin production. Keywords : Essential oil, inhibition zone, moulds, mycotoxigenic fungi.

Aflatoxin contamination of maize put the health and well-being of Kenyan people at risk, primarily children. Aflatoxigenic fungi can infect grains from pre-harvest stages in the field to post-harvest stages in the stores. The aim of this study was to isolate and characterize aflatoxigenic Aspergillus spp. from maize and soil samples from selected counties of Kenya: Makueni, Nyeri, Bungoma, Uasin Gishu and Siaya. Isolation was done using the direct plating technique of surface-sterilized grains on Czapek Dox Agar medium and plating of serially diluted soil samples. Aspergillus colonies were purified and identified using colony growth characteristics, colony colour on PDA media and microscopic characterisation. In total, 174 Aspergillus isolates were obtained, where 82.3% came from maize samples while 17.7% were from soil samples. Makueni County had the highest number of Aspergillus isolates at 58.1%, Nyeri 12.6%, Uasin Gishu 10.3%, Siaya 10.3% and Bungoma 8.6%. The characterization process identified 10 different Aspergillus spp.; 78.5% were Aspergillus flavus, 8.0% A. versicolor, 3.4% A. parasiticus, 2.3% A. clavatus, 2.3% A. sydowii, 2.3% A. fumigatus, 1.1% A. glaucus, 1.1% A. nidulans, 0.6% A. candidusand 0.6% A. wentii. The results evidence that maize grains and fields in the various counties are highly contaminated with aflatoxigenic Aspergillus species. Key words: Aflatoxin, Aspergillus, maize.