The effect of Vesicular-Arbusclar Mycorrhiza and Rhizospherepseudomonads on Chickpea Wilt in Zambia
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The effect of vesicular arbuscular mycorrhiza (VAM) and rhizosphere pseudomonads on chickpea (Cicer arietinum L.) wilt caused by Fusarium oxysporum f. sp. ciceri (Matuo and Sato) in Zambia was investigated. Vesicular arbuscular mycorrhiza was isolated from three soils obtained from Kasama area of Lusaka. Rhizosphere pseudomonads were isolated from a chickpea farm in the same area. Physical and chemical characteristics of the soils were analyzed. Both VAM and pseudomonads were characterized and identified. The mycorrhizal flora of the three soils consisted of Glomus etunicatum, Gigaspora nigra and Acaulospora scrobiculata. This composite mycorrhizal flora and rhizosphere pseudomonads were used to determine their effect on fusarium wilt of chickpea. Their effect on growth and productivity of the crop was also investigated. The study was carried out between December 2006 and April 2007 in a greenhouse at the School of Agriculture of the University of Zambia. The VAM flora was amplified for a period of eight weeks by planting surface sterilized seeds of maize variety MMV 600 in heat sterilized soil. Vesicular arbuscular mycorrhiza soil inoculums was mixed in proportions of 3 sterilized soil to 1 VAM soil portion (1 portion equals 1.5kg amplified VAM soil) for use in two of the four treatments. A complete randomized block experimental block design was used with four treatments and four replications. Surface disinfected SPGR-4869 chickpea seeds were planted in the soil mixtures in plastic pots in a greenhouse. The four treatments consisted of the following: A. A combination of fusarium wilts pathogen, sterilized soil and chickpea seeds. B. Fusarium wilt pathogen, pseudomonads, sterilized soil and chickpea seeds. C. Fusarium wilt pathogen, VAM, sterilized soil and chickpea seeds. D. Fusarium wilt pathogen, pseudomonads, VAM, sterilized soil and chickpea seeds. A conidial suspension of 2 cm containing 5.07 x 104 micro conidia of Fusarium oxysporum f.sp. ciceri were inoculated per plant at the time of sowing. For treatments C and D colony forming units (cfu) of 105 of pseudomonad bacterial extract (turbidity 27.20 mg/L at 430nm) was inoculated per plant. The plants were watered with tap water at intervals of 48 hours. Chickpea plants were examined at fifteen days intervals from 15 to 90 days after sowing (DAS) to measure plant height, the number of leaves, flowers and pods per plant. At 90 (DAS) seed weight per plant, fresh shoot weight, fresh root weight and disease incidence were recorded. The results show that there was 52% reduction of fusarium wilt in chickpea inoculated with VAM and pseudomonads (dual inoculation) compared to the control. Single inoculation of VAM showed 50% reduction of fusarium wilt in chickpea plants. The analysis of variance (ANOVA) of the measured parameters indicated that the dual inoculation (VAM and pseudomonads) enhanced growth and development of chickpea plants by 16% compared to the control and produced taller plants with more leaves, flowers and a high shoot and root weight than either of the single inoculation of VAM or pseudomonads. Results of the best subset regression analysis of climatic characteristics (independent variables) on mean numbers of growth, productivity and disease incidence parameters (dependent variables) revealed that the most important climatic characteristic that accounted for most of the observed variation was the photoperiod which was responsible for the high temperature in the greenhouse.
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