Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2016
Publication Date: 7/14/2016
Citation: Eizenga, G.C., Edwards, J., Yeater, K.M., McCouch, S.R., McClung, A.M. 2016. Transgressive variation for yield components measured throughout the growth cycle of Jefferson rice (Oryza sativa) x O. rufipogon introgression lines. Crop Science 56:1-12. DOI: 10.2135/cropsci2015.10.0603.
Interpretive Summary: Cultivated rice (Oryza sativa) is a major food crop for much of the world’s population, thus increasing yield is a major objective for rice breeding programs. One way to increase yield is to increase diversity in rice by introducing the genes (alleles) lost during the domestication process. An international study revealed the wild ancestral species, O. rufipogon, increased rice yields in selected progeny derived from hybridization with five diverse rice cultivars from around the world. To better understand these yield increases observed under field conditions, a set of breeding lines that were developed using O. rufipogon crossed with using the southern U.S. long grain cultivar Jefferson, were evaluated in an environmentally controlled greenhouse study to identify differences in plant development and traits associated with yield. Traits contributed from the O. rufipogon parent that increased yield were a longer growing cycle, longer panicles, increased number of seeds on the panicle and better seed set. These yield traits identified in this greenhouse study validated the previous field trial findings as well as identified new growth parameters that may have significant influence on yield. The fact that these yield-enhancing traits can be selected in the greenhouse will expedite the breeding process. Use of these lines in breeding programs to improve yield will increase the diversity of parents available for breeders to use in their efforts to develop higher yielding rice cultivars, especially in the USA.
Technical Abstract: Previous studies demonstrated alleles introduced into elite rice (Oryza sativa) cultivars from the wild ancestral species, O. rufipogon, enhanced yield and yield components as a result of transgressive variation. A study was conducted to unveil phenological and agronomic mechanisms that underlie increased yields in introgression lines (ILs) developed through backcrossing an O. rufipogon accession (IRGC105491) with the recurrent parent, Jefferson, a U.S. long grain variety. Phenological development, agronomic and yield component traits of Jefferson and eight ILs, each carrying a major introgression for one of six wild QTLs for yield (yld1.1, yld2.1, yld3.2, yld6.1, yld8.1 and yld9.1) were determined in five greenhouse studies over two years. A novel method to estimate above ground biomass nondestructively with digital images was also used. Overall, 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 for all ILs compared to Jefferson, with differences for five wild QTL (yld1.1, yld2.1, yld3.2, yld8.1, yld9.1) introgressions being significant. Three ILs with introgressions from yld6.1 and yld9.1 had significant increases in primary panicle branch number. Not unexpected, the ILs had more florets per panicle and introgressions for three of the six wild QTL (yld2.1, yld6.1, yld8.1) produced significantly more seed. These results support an additive model of transgressive variation where the agronomically inferior wild donor introgressions contribute variation in a suite of traits such as growth rate, flag leaf length, biomass and panicle size that result in increased yield in an elite recurrent parent genetic background.