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Taro Leaf Blight (Phytophthora colocasiae) is a highly infectious fungal plant disease that is characterized by the formation of large brown lesions on the leaves of infected taro plants.〔Nelson, S., Brooks, F., and Teves, G. July 2011. Taro leaf blight in Hawaii. College of tropical agricultural and human resources.〕 Lesions are the result of oomycetes leaching nutrients out of the leaves via haustoria to create white powdery rings of sporangia.〔Singh, D., Jackson, G., Hunter, D., Fullerton, R., Lebot, V., Taylor, M., Iosefa, T., Okpul, T., and Tyson, J. July 2012. Taro leaf blight - a threat to food security. Agriculture. 2, 182 - 203.〕 This pathogen grows best in high humidity and high rainfall environments offering the pathogen means of dispersal via rain splash as well as a warm humid environment that favors hyphal growth across the infected plant.〔“Phytophthora colocasiae.” 2013. == Hosts and Symptoms == First described in Java by Marian Raciborski in 1900, taro leaf blight is caused by the oomycete Phytophthora colocasia (P. colocasiae) which infect primarily Colocasia spp. and Alocasia marcorhiza.〔 P. colocasiae primarily infects leaves, but can also infect petioles and corms.〔 Symptoms on leaves initially occur where water droplets accumulate and eventually form small, brown spots surrounded by halos on the upper surface of leaves.〔 These spots expand very quickly and form large brown lesions.〔Hunter, D., Pouono, K., and Semisi, S. 1998. The impact of taro leaf blight in the pacific islands with special reference to Samoa. Journal of South Pacific Agriculture.〕 The entire leaf can be destroyed within a few days of the initial appearance of symptoms under wet conditions.〔Misra, R.S, Sharma, K., and Mishra, A.J. September 2008. Phytophthora leaf blight of taro (Colocasia esculenta) - a review. The Asian and Australian Journal of Plant Science and Biotechnology. 2 (2), 55-63.〕 The undersides of leaves have spots that look water-soaked or gray, and as they expand, blight forms and the leaf is destroyed within a few days.〔 Symptoms occur in a day/night pattern where water soaked areas expand during the night and then dry out during the day. As a result, additional water marks form leading to increasingly larger lesions. As the lesions expand, sporangia develop most actively at the margin of the lesion and progress to attack healthy tissue.〔 One characteristic feature found on leaves is the formation of bright orange droplets oozing out from above and below water soaked leaf surfaces.〔 As a result, the droplets dry out during the day and become crusty.〔 Another sign of P. colocasiae infection are masses of sporangia that form a white, powdery ring around the lesion. Symptoms on petioles includes gray to brownish black lesions that can occur anywhere on the petioles. Petioles become soft and may break as the pathogen destroys the host.〔 Symptoms on corms are often rubber-like and soft as well as having a light tan color. These symptoms occur rapidly and can arise anywhere on the corm and are often subtle in early stages. Decayed corm tissue appears brown and turns purplish in advanced stages of infection.〔 Lesions can also be formed by sporangia that are splashed by rain. The dead central area breaks and falls out as the lesion gets larger.〔 The rate of spread for this disease is very high which results in a high percentage of yield loss.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Taro leaf blight」の詳細全文を読む スポンサード リンク
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