Efficacy of seed-dressing and organic amendments against fusarium root-rot of French beans (phaseolus vulgaris l. Cv. Monel.) in Kenya.
Wagichungc., A. G. Richard.
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Laboratory, greenhouse and field tests were conducted to (i) compare relative pathogenicity of Fusarium solani fsp. phaseoli and F oxysporum f.sp. phaseoli on ,french beans (Phaseolus vulgaris L. cv. Monel), (ii) evaluate the efficacy of seed dressing with various fimgicides singly and in combinations against the two pathogens (iii) compare efficacy of organic matter and / or fungicides on root-rot caused by the two' pathogens and (iv) compare effects of delay ~ planting after application of cowdung and Tithonia diversifolia on the root-rot. Laboratory experiments were arranged in a completely randomised block design while greenhouse and field experiments were arranged in a randomised complete block design. Five replicates were used in all tests. In-vitro fimgitoxicity potential offimgicides and fungicide combinations was assessed by computing % inhibition of mycelial growth, % spore germination and number of spores produced on fungicide treated dishes relative to that of controls. Plant growth assessment was based on plant shoot height, dry weights of seeds, shoots and roots, and number of pods produced .. per plant. Disease severity was determined using mean length of discoloured root tissue (MLDRT) and mean.root rot index (MRRl). The plant growth parameters stated above were significantly (p=O.05) lower on plants infected with the two Fusarium spp. than control. However, slightly higher % loss in nw:nber of pods and seed dry weight were realised on those plants infected with F oxysporum fsp. phaseoli than F solani fsp. phaseoli. No statistical differences were noted between the effects of the two Fusarium spp. on bean, growth. Disease severity on plants inoculated with the two pathogens was similar. MLDRT and MRRI, were the same in both cases. However, MLDRT and MRRI were relatively higher on plants infected by F oxysporum fsp. phaseoli than 1'. so/ani fsp. phaseoli. This suggests that F oxysporum fsp. phaseoli may have been more pathogenic than F solani fsp. phaseoli under the prevailing experimental conditions. Fungitoxicity was based on the eTfect of fungicides on mycelial growth, spore germination and sporulation. Fungicide -treatments significantly (P=O.05) inhibited mycelial growth, spore germination and sporulation of both test fungi. However, fungal sporulation was higher in plates treated with fungicides than in controls an indication that fungicides stimulated sporulation. Although no fungicide treatment was seen to be an inhibitor of all the three measures of fungitoxicity, the ranking of the best three fungicide treatments was be, thiram 50 + captan 50 >triforine > metalaxyl mancozeb. Individual fungicide treatments had significantly (P=O.05) better effects on plant growth and disease development than fungicide combination or control. Significantly (P=O.05) higher plant growth parameters and lower MLD RT and MRRl were recorded from single fungicide treatment on both the greenhouse and field grown plants. Significantly (P=O.05) better plant growth, more pods and heavier seed dry weights were recorded from plants obtained from seeds treated with fungicides triforine or metalaxyl. Integration of cowdung and T diversifolia with the fungicide metalaxyl revealed that cowdung or a combination of cowdung with metalaxyl significantly (P=O.05) reduced disease development and increased plant performance more than T diversifolia or a combination of T diversifolia with metalaxyl. Plants harvested in soils treated with T diversifolia or a combination of T diversifolia with metalaxyl or controls had the poorest seed and pod yields. Germination was low and no pods wereharvested from plants grown in these soils. A delay in planting french bean in soil treated with cowdung significantly (P=O.05) decreased development of root rot when compared to untreated controls. The greatest decrease was obtained with 2 and 4 week delay. Shoot and root dry weights of plants infected by F. oxysporum fsp. phaseoli or F solani fsp. phaseoli significantly (P=O.05) increased with delay in planting and were highest where planting was delayed 2 and 4 weeks, respectively. A delay from 0 to 4 weeks in planting french beans in soil treated with crushed leaves of T diversifolia significantly (p=O.05) increaseddisease severity and reduced plant performance when compared to untreated control.