Evaluation of the USDA Rice Core Collection for Sheath Blight Disease Using Micro-Chamber.

The USDA rice core collection, including 1,794 accessions from 114 countries, was developed using a stratified random sampling method to represent the entire NSGC collection including over 18,000 accessions. Sheath blight (Rhizoctonia solani) is one of the most important and widely distributed diseases worldwide and is capable of infesting numerous crops including rice. The objective of this study was to characterize the core collection for sheath blight resistance in comparison with common checks, resistant Jasmine 85 and susceptible Lemont. Each accession was evaluated in a micro-chamber made from 2-liter soft-drink bottle. The evaluation was conducted using randomized complete block design with three replicates and three plants individually inoculated with the pathogen and scored in each replicate. Data were analyzed using the GLIMMIX procedure in SAS version 9.1.3. Entry 1372 (PI 560285) from Colombia and 1475 (PI 614999) from China were most resistant, which resistances significant at 1% probability were 50.5% and 45.2%  stronger than Jasmine 85, respectively. Eighteen accessions (1%) were more resistant than Jasmine 85 at 5% probability. Furthermore, 301 accessions statistically had  similar resistance with Jasmine 85. The 321 accessions originated from 78 countries with the most from China (47 accessions), followed by India (17), Sri Lanka (14), Indonesia and Taiwan (13 each), Vietnam (11), Pakistan and Thailand  (9 each). A mini core developed from the entire core collection will be genotyped with about 150 SSR genome-wide markers covering every 10 cM for association mapping of the sheath blight resistance.