Cataloguing, Documentation and Management of fungal diseases of strawberry (Fragaria x ananassa Duch.)
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Date
2017
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Department of Plant Pathology, College of Horticulture, Vellanikkara
Abstract
Strawberry (Fragaria x ananassa Duch.), hybrid species of genus Fragaria, cherished for its characteristic flavour, colour and tentalizing aroma, is becoming an important table fruit of millions of people around the world. However, the crop is inflicted by several fungal diseases that reduce its commercial value. Hence, the present investigation was carried out to identify and catalogue the major fungal diseases of strawberry growing in Kerala.
Purposive sampling surveys were carried out in strawberry growing tracts of Kerala viz., Wayanad, Idukki and Malappuram to collect infected samples and also to assess the incidence of fungal diseases during different periods viz., December-January, March-April and July-August. During the survey, four leaf spots (LSW-1, LSI-1, LSM-1 and LSI-2), four leaf blights (LBW-1, LBI-1, LBI-2 and LBM-1), one fruit rot (FRW-1) and two crown and root rots (CRI-1 and CRM-1) were noticed. Among the crown and root rot diseases, CRM-1 recorded the highest per cent disease incidence (PDI) of 82 per cent. Leaf blight (LBW-1) recorded maximum severity of 25.2 per cent among foliage diseases. Correlation studies were carried out to elucidate the influence of weather parameters on disease development.
Symptomatology of different diseases was studied both under natural and field conditions. Pathogenicity was proved by mycelial bit inoculation and spore suspension method. Cultural and morphological characterisation of the isolates were carried out and for further confirmation of the identity upto species level, the isolates were sent to National Centre for Fungal Taxonomy (NCFT), New Delhi. The pathogens causing LSW-1, LSI-1 and LSM-1 were identified as Colletotrichum gloeosporioides, LSI-2 as Alternaria alternata, LBW-1 as Rhizoctonia solani, LBI-1 as Phoma exigua, LBI-2 as Curvularia lunata, LBM-1 as Pestalotiopsis longisetula and FRW-1 as Rhizoctonia solani. The two crown and root rot pathogens, CRI-1 and CRM-1 were confirmed as Fusarium oxysporum and Lasiodiplodia theobromae respectively.
In order to recommend an appropriate management strategy for the aforesaid diseases, in vitro and in vivo evaluation were carried out using fungicides, biocontrol agents and organic formulations. Fungicides viz., carbendazim 12% + mancozeb 63%, propineb 70 WP, Bordeaux mixture, cymoxanil 8% + mancozeb 64%, difenoconazole 25EC and carbendazim 50WP were found effective against various foliage diseases. Carbendazim 12% + mancozeb 63%, cymoxanil 8% + mancozeb 64%, copper hydroxide 77WP and carbendazim 50 WP recorded cent per cent reduction in mycelial growth of Fusarium oxysporum (CRI-1). Similarly, carbendazim 12% + mancozeb 63%, copper hydroxide 77WP, cymoxanil 8% + mancozeb 64% recorded 93-100 per cent reduction of Lasiodiplodia theobromae (CRM-1). Results of dual culture studies with Trichoderma asperellum and Pseudomonas fluorescens against pathogens revealed 66.67 to 100 and 0 to 70.55 per cent control respectively. Likewise, organic formulations like Calphomil recorded an inhibition ranging from 13.3 to 75.33 per cent, whereas neem oil, panchagavya and baking powder + vegetable oil mixture could restrict the growth of pathogen only upto 34 per cent.
In vivo experiment was conducted to study the efficacy of fungicides and biocontrol agents under natural conditions also. Accordingly, four major selected pathogens viz., C. gloeosporioides, P. longisetula, F. oxysporum and L. theobromae were subjected to molecular characterisation prior to in vivo studies. The sequence homology on molecular studies revealed that the isolates showed similarity to C. gloeosporioides, Neopestalotiopsis clavispora, F. oxysporum and L. theobromae. Results of the pot culture experiment revealed that Trichoderma asperellum showed better control against C. gloeosporioides compared to other treatments followed by carbendazim 12% + mancozeb 63%. Propineb 70 WP, T. asperellum and carbendazim 12% + mancozeb 63% reduced the severity caused by Neopestalotiopsis leaf blight disease. The combination fungicide carbendazim 12% + mancozeb 63% (0.2%) was found equally efficient against F. oxysporum and L. theobromae.
Thus, the study has enlightened our knowledge on the various fungal diseases inflicting strawberry as well as the role of weather in disease development and the management practices using plant protection chemicals and bioagents both under in vitro and in vivo conditions. Hence, further studies should be focused to carry out multilocational trials in strawberry growing tracts of Kerala.
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