O. J. Alabi, Department of Plant Pathology, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350;
J. M. Crosslin, USDA-ARS Vegetable and Forage Crops Research Unit, Prosser, WA 99350;
N. Saidov, International Center for Agricultural Research in the Dry Areas (ICARDA), IPM CRSP project, 700000, P. O. Box 4564, 6 Osiya Str., Tashkent, Uzbekistan; and
R. A. Naidu, Department of Plant Pathology, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350
Potato (Solanum tuberosum L.) is widely grown as a staple food and cash crop in Tajikistan and is an important food security crop in the country. In June 2011, we conducted a survey of potatoes in farmers' fields in the Buston and Dushanbe regions (about 200 miles apart) of Tajikistan. Potato plants with stunted growth and leaves showing chlorotic spots, curling, and necrotic spots and rings were observed with the disease incidence monitored in 10 fields each in Buston and Dushanbe areas varying between 10 and 60%. Representative samples from symptomatic plants tested positive for Potato virus Y (PVY) using virus-specific immunostrips (Agdia Inc., Elkhart, IN). Leaf samples from symptomatic plants were collected from Buston and Dushanbe areas, imprinted on FTA Classic Cards (Whatman International Ltd., Maidstone, UK), air dried, and shipped to the lab at Washington State University for confirmatory diagnostic tests. Total nucleic acids were eluted from FTA cards (1) and subjected to reverse transcription (RT)-PCR with primers (PVY/Y4A and PVY/Y3S) specific to the coat protein of PVY (3). Samples infected with PVY ordinary strain (PVYO), tuber necrosis strain (PVYNTN), tobacco veinal necrosis strains (PVYEU-N and PVYNA-N), and a recombinant strain (PVYN:O) were included as references to validate RT-PCR results. A single DNA product of approximately 480 bp was amplified from potato samples that tested positive with PVY-specific immunostrips. The amplified fragments from two samples from Dushanbe and six from Buston areas were cloned separately into pCR2.1 (Invitrogen Corp., Carlsbad, CA) and two independent clones per amplicon were sequenced from both orientations. Pairwise comparison of these sequences showed 90 to 100% identity among the cloned amplicons (GenBank Accession Nos. JQ743609 to JQ743616) and 90 to 100% with corresponding nucleotide sequence of reference PVY strains (GenBank Accession Nos. JQ743617 to JQ743621). A global phylogenetic analysis of sequences revealed the presence of PVYO in both samples from Dushanbe and one sample from Buston regions and presence of PVYNTN in the remaining five samples from the Buston region. Because of the possible occurrence of mixed infections of PVY strains (2), further studies are needed to determine the presence of mixed infections of two or more strains of PVY and their specificity to potato cultivars. To our knowledge, this study represents the first confirmed report of two distinct strains of PVY in potato in Tajikistan. The occurrence of PVYNTN, a quarantine pathogen in many countries (2), warrants additional investigations to improve sanitary status of potato fields and to facilitate the availability of virus-free seed in clean plant programs for significant yield increases in Tajikistan.
References: (1) O. J. Alabi et al. J. Virol. Methods 154:111, 2008. (2) S. Gray et al. Plant Dis. 94:1384, 2010. (3) R. P. Singh et al. J. Virol. Methods 59:189, 1996.