Germplasm Accessions Resistant to Straighthead in the USDA Rice Core Collection1

The USDA rice core collection, containing 1,801 accessions from 115 countries or sources and representing about 10% of the whole collection, was established by a stratified random-sampling method. A total of 990 accessions in the core collection that headed in 110 days or less and were 150 cm or less in height were evaluated for straighthead resistance on a 1 to 9 scale with 1 being very resistant and 9 being very susceptible. Twenty-six accessions showed resistance with straighthead ratings ranging from 1.3 to 3.0. The resistant accessions originated from 10 countries, and varied in heading from 62 to 101 days, and plant height from 68 to 124 cm. Ten accessions were straighthead tolerant with ratings from 3.3 to 4.0. The tolerant accessions were from 7 countries, and varied from 56 to 100 days in heading and 66 to 124 cm in plant height. A preponderance of the straighthead-resistant accessions are believed to be indicas, while most of the tolerant ones are believed to be japonicas. Thus, among the 990 accessions in the test, 36 accessions or 3.6% were either resistant (26) or tolerant (10). Twenty-four accessions or 2.4% had straighthead ratings from 4.1 to 5.0, 58 accessions or 5.9% from 5.1 to 6.0, 263 accessions or 26.6% from 6.1 to 7.0, 386 accessions or 39.0% from 7.1 to 8.0, and 223 accessions or 22.5% from 8.1 to 9.0. These resistant germplasms, diversified in origin, maturity, and plant height, can be used to improve straighthead resistance in rice breeding in the southern U.S. 1 This is a completed study. AAES Research Series 517