Mating types of Phytophthora colocasiae on the island of Upolu, Samoa
Taro leaf blight (TLB) caused by Phytophthora colocasiae is a damaging disease that destroyed Samoaâ€™s taro industry following its introduction in 1993. The aim of this study was to determine the occurrence of the A1 and A2 mating types of P. colocasiae for a more comprehensive understanding of the risk the pathogen poses for the future of the taro industry in Samoa. In September 2015, 54 isolates of P. colocasiae were collected from taro leaf blight lesions from 13 farms around the island of Upolu, Samoa. The mating types of each isolate was determined by observation of oospore formation when paired with tester isolates of Phytophthora nicotianae of known mating types (A1 or A2). Fifty isolates were found to be A2 mating type and four did not form oospores with either mating type. No A1 or self-fertile isolates were found. These results suggest that the A1 mating type has not been introduced to the island of Upolu, preventing the formation of oospores between compatible mating types of P. colocasiae and lessening the risk of new and potentially more threatening genotypes of the pathogen from emerging through genetic recombination.
Keywords taro leaf blight, Colocasia esculenta, taro, sexual reproduction
Hine R, Aragaki M 1963. Pathogenicity, vitamin nutrition and cultural characteristics of isolates of Phytophthora parasitica from carnation and other hosts in Hawaii. Phytopathology 53: 1194â€“1197.
Jeffers SN, Martin SB 1986. Comparison of two media selective for Phytophthora and Pythium species. Plant Disease 90: 1038â€“1043.
Lin M, Chen J, Uchida JY, Kadooka CY 2014. Mating type distribution, fungicide sensitivity, and phylogenetic relationships of Phytophthora colocasiae. Plant Protection Bulletin 56(1): 25-42.
Ko WH 1979. Mating-type distribution of Phytophthora colocasiae on the island of Hawaii. Mycologia 71(2): 434â€“437.
Shrestha S, Hu J, Fryxell RT, Mudge J, Lamour K 2014. SNP markers identify widely distributed clonal lineages of Phytophthora colocasiae in Vietnam, Hawaii and Hainan Island, China. Mycologia 106(4): 676â€“685.
Singh D, Jackson G, Hunter D, Fullerton RA, Lebot V, Taylor M, Iosefa T, Okpul T, Tyson JL 2012. Taro leaf blight - a threat to food security. Agriculture 2(3): 182â€“203.
Tyson JL, Fullerton RA 2007. Mating types of Phytophthora colocasiae from the Pacific region, India and South-east Asia. Australasian Plant Disease Notes 2(1): 111â€“112.
Tyson JL, Taylor RK, Curtis CL, Manning MA 2014. A pre-harvest rot of persimmon fruit caused by Phytophthora cactorum in New Zealand. Australasian Plant Disease Notes 9(1): 122.
Zhang KM, Zheng FC, Li YD, Ann PJ, Ko WH 1994. Isolates of Phytophthora colocasiae from Hainan Island in China: evidence suggesting an Asian origin of this species. Mycologia 86(1): 108â€“112.