Transgressive Variation for Yield Components Measured throughout the Growth Cycle of Jefferson Rice (Oryza sativa) x O-rufipogon Introgression Lines

Previous studies demonstrated that alleles introduced into elite rice (Oryza sativa L.) cultivars from the wild, ancestral species Oryza rufipogon Griff. enhanced yield as a result of transgressive variation. A study was conducted to unveil the phenological and agronomic mechanisms that underlie increased yields in introgression lines (ILs) developed through backcrossing an O. rufipogon accession [International Rice Germplasm Collection (IRGC) 105491] with the recurrent parent, 'Jefferson', a U.S. long-grain variety. Phenological development and agronomic and yield component traits of Jefferson and eight ILs, each carrying a major introgression for one of six quantitative trait loci (QTLs) for yield (yld 1.2, yld 2.1, yld 3.2, yld 6.1, yld 8.1, and yld 9.1) were determined in greenhouse studies over 2 yr. A novel method to estimate aboveground biomass nondestructively with digital images was used. The higher yielding ILs had slower phenological development and produced more biomass than Jefferson. Comparison of the yield component traits at maturity revealed longer flag leaves and panicles in all ILs than in Jefferson, with differences for five wild QTLs (yld 1.2, yld 2.1, yld 3.2, yld 8.1, and yld 9.1) introgressions being significant. Three ILs with introgressions from yld 6.1 and yld 9.1 had significant increases in primary panicle branch number. Six of the ILs had more florets per panicle and introgressions for three of the wild QTLs (yld 2.1, yld 6.1, and yld 8.1) produced significantly more seed. These results support an additive model of transgressive variation, where the inferior wild donor introgressions contribute variation in traits (e.g. growth rate, flag leaf length, and panicle size) that increase yield in an elite genetic background.