Screening Taro (Colocasia esculenta) for Resistance to Taro Leaf Blight (TLB) Using a Detached-Leaf Disc Bioassay and Developing DNA Markers for Use In Selection

Taro (Colocasia esculenta) is a root crop of the Pacific Islands that is cultivated primarily for its starchy corm. Taro Leaf Blight (TLB) is a major disease that threatens the sustainability of taro caused by the oomycete pathogen Phytophthora colocasiae.  In Hawaii, it was estimated that 25%-50% of taro corms were lost due to this pathogen and other fungal diseases.Tolerance to TLB has been found within taro germplasm from Palau, Thailand, and Guam.  These tolerant varieties are crossed with Hawaiian taro in order to develop resistant Hawaiian lines.  Hybrids are tested for tolerance to TLB using a detached-leaf disc bioassay (Brooks, 2008).  Four discs are cut from the first fully developed leaf of each hybrid and inoculated with approximately 50 zoospores of a local isolation of P. colocasiae.  Mean lesion size is measured on day three and four for each hybrid.  Preliminary analysis shows approximately 35 hybrids that are highly tolerant to TLB.  The majority of the tolerant hybrids are a cross between Dirratengadik/Moi and (Red Moi/PH15)/Sawahn Kurasae. Microsatellite DNA and single nucleotide polymorphisms are being investigated for use in marker assisted selection. We have identified 4 microsatellite primer sets that give polymorphisms among some of the Hawaiian varieties.  These are insufficient to provide resolution among the Hawaiian varieties and the resulting hybrids, so we are in the process of evaluating more microsatellite primer sets. We are also sequencing several candidate genes in order to identify snp’s in taro.