Journal of Applied Biosciences (J. Appl. Biosci.) [ISSN 1997 - 5902]
Volume 20: 1159 - 1165. Published August 7, 2009.
In vitro growth inhibition of Kenyan Phytophthora cinnamomi isolates by different fungicide formulations
Mbaka J.N*^., Wamocho L.S**., TuroopL** . and Waiganjo M.M.*
*Kenya Agricultural Research Institute, Thika, Kenya; **Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya.
*Corresponding author e-mail: jnmbaka@yahoo.com
ABSTRACT
Objective: To determine the inhibitory effects of locally available fungicides on local strains of Phytophthora cinnamomi causing root rot and stem canker of macadamia in Kenya.
Methodology and results: Pathogen isolates were obtained from soil and diseased macadamia plant parts collected during a survey, carried out from December 2005 to April 2006 in all macadamia growing areas (Central, Eastern, Western, Rift Valley and Coast provinces) of Kenya. Six commercial fungicide formulations commonly used for management of Phytophthora diseases in the horticulture industry in Kenya were evaluated. These were: Melody Duo (Iprovalicarb 55g/kg, Propineb 613 g/kg), Equation Pro (Famoxadone 225 g/kg, Cymoxanil 300 g/ kg) , Nordox 75 WP (Copper oxide 86 % w/w, 75 % metallic copper 14 % w/w), Victory 72 WP (Metalaxyl 80 g/kg, Mancozeb 640 g/kg), Topsin (Thiophanate methyl 50% w/w) and Benovarp 50 WP (Benomyl 50% w/w). Fungicide stocks were prepared in sterile de-ionized water and added to corn meal agar (CMA) at the recommended dosages. Agar discs (5mm diameter) from actively growing CMA cultures of each of the seven isolates of P.cinnamomi were plated on non-amended and fungicide amended CMA media in 90 mm diameter Petri dishes. The Petri dishes were wrapped with parafilm, inverted and incubated at 25 ±2 0C in the dark. Mycelial growth inhibition at the recommended fungicide dose was calculated as the difference between the control and the treatment after 7 days of growth. The growth inhibition data was subjected to General Linear Models (GLM) analysis of variance using SAS version 9.1 for windows. Benovarp, Topsin and Melody duo were lethal to all the P. cinnamomi isolates. Nordox caused a growth inhibition of 95-100 % on all the isolates.
Conclusion and application of findings: The results show that some fungicides recommended for other Phytophthora diseases have an inhibitory effect on P. cinnamomi. These can therefore be incorporated in an integrated management strategy for macadamia root rot. Benovarp, Topsin and Melody Duo are systemic, curative and protective and can be used as soil drench, foliar sprays or trunk injections. Nordox, which is a contact protective fungicide, can be used as paint on stem cankers or wounds caused by mechanical injury, to stop entry of the fungus. However the efficacy of these formulations should be assessed further under field conditions.
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