Incidence and Characterization of Major Fungal Pathogens of Strawberry Diseases

Abstract

Strawberry (Fragaria x ananassa Duch.) is a member of family Rosaceae and is among the most widely consumed fruit throughout the world. Its fruit ripens in early spring which gives good economic returns to the farmers. Strawberry crop suffers from numerous diseases and among them, fungal diseases are highly destructive. As no systematic research, so far has been conducted in Pakistan regarding strawberry diseases, the present study was conducted to determine disease incidence and prevalence of important fungal diseases of the strawberry crop and the morpho-molecular characterization of associated fungal pathogens. For field-based disease assessment, a two year (2014-15 and 2015-16) disease survey of farmer fields was conducted in 12 important strawberry producing districts of Punjab (Rawalpindi, Sargodha, Gujranwala, Sialkot, Narowal, Sheikhupura, Lahore and Multan), Khyber Pakhtunkhwa (KPK) (Mardan, Charsadda and Swat) and important areas of Islamabad (ICT). On the basis of these surveys four major fungal diseases viz. Alternaira leaf spot (ALS), Fusarium fruit rot (FFR), Anthracnose (Colletotrichum) fruit rot (AFR) and Bortyis fruit rot (BFR) or gray mold were found to be prevalent, with no prevalence in district Swat during both years in case of FFR while maximum of 100 % were observed in case of all fungal diseases. Disease incidence of ALS was recorded from 17.25 % to 55 %, followed by no disease to 59 % in case of FFR while 14.13% to 44.71 % of AFR and 17.13 to 48.88 % as of BFR. Pathogens were identified on the basis of morpho-molecular characters. The morphological characterization was done on pathogenic isolates of 4 fungal pathogens viz. 82 isolates of Alternaria alternata, 77 isolates of Fusarium solani, 90 isolates of Colletotrichum spp. (68 isolates of C. acutatum and 21 isolates of C. xvi 3 gloeosporioides) and 92 isolates of Botrytis cinerea. These isolates were identified based on standard identification keys and results in identification of these pathogens. A total of fifty four (54) highly virulent and representative isolates from each district were subjected to molecular characterization. Of these, 12 isolates were each of A. alternata and B. cinerea while 19 isolates were Colletotrichum spp. (12 of C. acutatum and 7 of C. gloeosporioides) and 11 isolates were F. solani. These isolates were amplified with ITS gene primers (ITS1/ITS4), endopolygalacturonase (endoPG) gene primers (PG3/PG2b) for A. alternata, Beta (β)-tubulin (TUB2) primers (BT2a/BT2b) for Colletotrichum spp., translation elongation factor 1-alpha (TEF-1α) primer (ef1/ef2) for F. solani and Glyceraldehyde-3-phosphate dehydrogenase (G3PDH) primers (G3PDH_for/G3PDH_rev) was for B. cinerea. The nucleotide sequences further analyzed by phylogenetic software and resulted in genetic homology of current study isolates with previously reported isolates and hence confirmed the morphological identification. This research work provided the first comprehensive factual picture of fungal diseases of strawberry from Pakistan and proper morpho-molecular characterization of associated destructive pathogens and is expected to play a central function in future studies.