Botanical alternatives in management of fungal pathogens of seedling blight of cashew (Anacardium occidentale L.)

Introduction: Cashew (Anacardium occidentale L.) is an important tree crop and seedling survival is pertinent to successful establishment. Cashew seedling is infected by blight pathogens causing more than 60% seedling lost, however pesticides residues related issues and high cost of chemical necessitate efficacy trials of aqueous extracts of Mangifera indica, Azadirachta indica and Hyphtis suaveolens evaluated in-vitro on associated pathogens.

Methods: Flora of blight-infected cashew seedlings was randomly collected from Cocoa Research Institute of Nigeria (CRIN) nursery between July and October, 2019. Mycoflora analysis was carried out in the plant pathology (Mycology) laboratory of CRIN. Antifungal assay of powdered Mangifera indica, Azadirachta indica and Hyphtis suaveolens were screened using aqueous extracts at 1:4 (w/v).  Potato Dextrose Agar (PDA)  amended with 1ml of 100%, 75%, 50%, 25%, and 0% of the extracts and Mancozeb (synthetic fungicide) as standard, 5mm mycelia mat disc of 10day old each of Lasiodiplodia theobromae, Fusarium pallidoroseum and Macrophomina sp. were placed at the centre of the amended media in triplicate and incubated 5-7days using complete randomized design (CRD). Mycelia extension inhibition and percentage growth inhibition (R) obtained.

Results: Aspergillus niger, A. flavus, Fusarium oxysporium, F. pallidoroseum, Lasiodiplodia theobromae., Pythium sp., Rhizopus sp., Macrophomina sp. and  Rhizotonia sp. were isolated. Fusarium pallidoroseum, L. theobromae and Macrophomina sp. screened with the varied concentrations of botanicals showed reduction in mycelia diameter; Mangifera indica (31.50%), A. indica (48.70%) and H. suaveolens (25.86%) on F. pallidoroseum favorably competed with mancozeb (39%) at 25% concentration while only M. indica was significant on L.theobromae(64.12%)and Macrophomina sp.(40.29%)  and significantly different from control (0%).

Conclusion: Aqueous extracts of M. indica, A. indica and H. suaveolens showed fungicidal potential on F. pallidoroseum and M. indica was significant on L. theobromae and Macrophomina sp.