Doctor of Philosophy (PhD)


Plant, Environmental and Soil Sciences

Document Type



Rice will continue to be a staple food for the foreseeable future, and plant breeding can foment the resilience of this crop. Applied breeding programs with clear objectives can effectively develop varieties that satisfy stakeholder needs. The majority of U.S.-produced rice is destined to export markets, and Latin America is the largest importer of U.S. rice, receiving 59% of total exports in 2021. Since 2010, Latin American importers voiced concerns about the quality of U.S. rice, mainly the high chalk content of milled rice and the stickiness of cooked rice. To address these issues, the objectives of this project were: characterize U.S. and Latin American rice quality parameters for use in breeding programs and explore the variation within the major gelatinization temperature (GT) classes defined by the Alk alleles using a subjective and a quantitative method.

A panel of 88 southern U.S. varieties was characterized for components of visual and cooking quality and compared to 21 popular samples from Latin America. Amylose content was the primary component differentiating U.S. and Latin American rice and explained the primary differences in cooking characteristics. This research defined the target product profiles in U.S. germplasm for the Latin American market. Molecular markers can facilitate the selection of the Low-GT and Wxa alleles for Alk and Waxy genes, which confer desirable cooking quality.

A panel of 39 lines was genotyped at the functional mutation of the Alk gene and phenotyped for GT using the alkali spreading value (ASV) rating method and the quantitative Rapid Visco Analyzer (RVA) method. Correlation between ASV ratings and RVA values was highest at 1.7% KOH (R=-0.98), followed by 1.9% KOH (R=-0.94) and 1.5% KOH (R=-0.91). An extra-low GT subclass was observed with the RVA and validated with 1.5% KOH. To investigate the underlying differences between the subclasses, we evaluated a bi-parental breeding population (n=164 lines) derived from a cross between a high-AC/low-GT Latin American variety and a low-AC/low-GT U.S. medium grain variety. A single-marker ANOVA identified a single significant locus that corresponds to the Waxy amylose gene region on chromosome 6, corresponding to a mutation on exon 10 that confers the Wxa high amylose allele.



Committee Chair

Famoso, Adam

Available for download on Saturday, June 08, 2024