Taro Disease Case Study

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BIOLOGYOF TARO LEAF BLIGHT (Phytophthora colocasiae Racib) - A REVIEW

ABSTRACT
Taro is a tropical tuber crop highly valued in developing countries. It is mostly susceptible to Phytophthora colocasiae, a leaf blight disease (TLB) causing a 25%-50% loss in yield. The pathogen results not only in reduction in vigor, quality and yield but also constitute a barrier to international exchange of germplasm. The warm, humid days, cool and wet nights of the tropics are ideal for reproduction and spread of the disease. The TLB pathogen has limited host range and the first symptoms are small, dark brown flecks or light brown spots on the upper leaf surface. These early spots often occur at the tips and edges of leaves where water accumulates. Resistance
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The genetic breeding can provide a practical method for controlling TLB and significantly alleviate the declining trend in taro production. Early cultural disease management has also been recommended in reducing the inoculums level and relative humidity in the field. More in depth studies are required to understand the pathogenicity and the mating types of different races if any of TLB pathogen.

Key words: Phytophthora colocasiae, Symptomatology, epidemiology, mating types, pathogenicity, resistance, and marker assisted selection.

INTRODUCTION
Taro (Colocasiae esculenta (L.) Schott) is one of the oldest cultivated crops grown for its edible corms and leaves. Taro corms and leaves are also accredited to have medicinal value and in reducing tuberculosis, ulcers, pulmonary congestion and fungal infection (Misra and Srivam, 2002). In spite of taro’s value as a food source, research aiming to the improvement of its cultivation has been limited. There are about 60 species in the genus Phytophthora all of which are plant pathogens. It is one of the most destructive genera of plant pathogens in temperate and tropical regions, causing annual
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The blight disease of taro is classified into Myceteae, Mastigomycota, Diplomastigomycota, Mycotina, Oomycetes, Peronosporales, Pythiaceae, Phytophthora. The scientific name being Phytophthora colocasiae Racib.The common name is taro leaf blight. Some of the internationally recognized Common Names include; In English; leaf blight of Colocasia spp., blight of dasheen and Phytophthora leaf blight (Jugurnauth et al., 2001).It is the major limiting factor in the cultivation of taro in many African regions and the most destructive fungal disease of taro. It is considered to have originated from South East Asia and was widely distributed throughout the tropical regions of the world (Seetohul et al., 2008). Phytophthora colocasiae is primarily a foliar pathogen but also affects petioles and corms. Taro leaf blight pathogen results not only in subsequent reduction in vigour, quality and yield of the crop, but also constitute a barrier to international exchange of germplasm (Ilondu, 2013). The pathogen is reported to survive inside the tubers during off season. Taro leaf blight epidemic occurs when night and day temperatures range between 20-220c and 25-280c respectively with relative humidity of 65% during the day and 100% at night accompanied by rainy weather.

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