Taro was the fifth most-produced root crop in the world during 2010, with global production of 9.0 billion kilograms (Food and Agriculture Organization of the United Nations, 2010). It is one of the most important staple crops in the Pacific Islands, and is grown widely in Africa, Asia, the Caribbean, and South America (Plucknett et al., 1970). It is a non-graminaceous monocot consumed primarily for its starchy corm (Plucknett et al., 1970). In addition, taro leaves serve as a vegetable, providing good sources of dietary fiber and vitamin C (Ferguson et al., 1992).
Taro probably originated in the Indo-Malayan area, where the genetic diversity of the species is highest (Cho et al., 2007; Ivancic and Lebot, 2000). It was probably domesticated in several geographic areas, including Papua New Guinea, from where it was carried by the Austronesians as they migrated to Polynesia, Micronesia, and finally to Hawai‘i in 900–1000 CE (Cho et al., 2007). As a result of this distribution, it is not surprising that taro cultivars of Oceania derive from a common, but narrow, genetic base (Lebot and Aradhya, 1991).
Taro leaf blight, caused by the oomycete pathogen Phytophthora colocasiae, is a major disease that threatens the sustainability of taro production globally (Miyasaka et al., 2012; Nelson et al., 2011; Ooka, 1994). In Hawai‘i, taro yields have declined over the past 30 years with particularly steep decreases during recent years due, in part, to pests and diseases (Miyasaka et al., 2012). According to the U.S. Department of Agriculture (USDA, 2006), taro production in 2005 was only 4 million pounds, the lowest amount since record keeping began in 1946. Several factors contributing to this low production were rainy weather, TLB, and taro pocket rot (another disease caused by a Phytophthora species) (USDA, 2006).
Phytophthora colocasiae was introduced to Hawai‘i during the 1920s and probably contributed to the extinction of dozens of traditional Hawaiian cultivars (University of Hawai‘i, 2009). Due to the ease of global transport and trade between countries, TLB has spread to new geographic areas across the Pacific, the Caribbean, and Africa. In 1993, this disease was introduced to American and Western Samoa, where it devastated the traditional Samoan taro cultivars (e.g., Niue) that were highly susceptible to this disease. This epidemic resulted in zero taro production in Samoa from 1994 to 1998 until the introduction of TLB-resistant taro cultivars (Trujillo and Menezes, 1995). When TLB reached the Dominican Republic in 2004, it caused dramatic losses in the production of the TLB-susceptible, commercial taro cultivar (R.P. Duverge, personal communication). Recently, TLB reached Ghana and Nigeria (Bandyopadhyay et al., 2011; Omane et al., 2012).
In Hawai‘i, there was a need to evaluate the existing taro germplasm for resistance to TLB. Recent breeding programs have crossed TLB-resistant cultivars from other areas of the world with commercial cultivars in Hawai‘i (Cho et al., 2007; Trujillo et al., 2002). However, there is a lack of knowledge about TLB resistance of Hawaiian cultivars and other cultivars maintained in the taro collection at the University of Hawai‘i’s Kauai Research Station.
The objective of this 12-year study was to evaluate the taro germplasm in Hawai‘i for yield, resistance to TLB and corm rot, and corm quality. The Hamakua Coast of Hawai‘i Island was well suited for this study due to its high annual rainfall and environmental conditions that are conducive to epidemics of TLB.
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