Molecular Characterization of Fusarium spp. Associated with Sugarcane Pokkah Boeng from the Philippines Using Partial Translation Elongation Factor-1α (TEF-1α) Gene Sequences

The increasing incidence of pokkah boeng has been observed throughout the sugarcane-producing areas in the Philippines. Sugarcane plants exhibiting characteristic symptoms of the disease were collected from different areas in the three major geographical regions: Luzon, Visayas and Mindanao. Symptoms surveyed in Visayas and Mindanao fields were more severe and diverse than those observed in Luzon. A total of 306 Fusarium spp. were isolated from these diseased plant samples on potato dextrose medium and water agar medium, and molecular identification using the genus-specific primer pair (ITS-Fu-f/r) and translation elongation factor (TEF)-1 alpha gene sequencing were performed. Chlorosis after 30 days of inoculation and leaf necrosis after 45 days of inoculation in sugarcane seedlings (VMC 86-550) was observed, wherein 37% (112 out of 306) isolates were proven pathogenic. Traditional taxonomic characterization of the 112 pathogenic isolates identified them as F. sacchari, F. proliferatum, F. verticillioides, F. subglutinans, F. graminareum and F. incarnatum. This was further supported by molecular identification of the representative 56 isolates based on TEF-1 alpha sequences as F. sacchari (66%), F. proliferatum (16%), F. incarnatum (7%), F. verticillioides (5%) and F. subglutinans (5%). Furthermore, these fungal pathogens were established as closely related species regardless of geographical origin based on the established clustering pattern in the constructed phylogenetic tree. These findings are important information on the etiology of pokkah boeng in the Philippines, and in formulating studies for control measures of the pathogen to prevent the disease from becoming an epidemic which may cause extensive loss to the sugarcane industry in the future. This is the first report on characterizing the pathogenic Fusarium spp. on sugarcane pokkah boeng in the Philippines.