Multiple Loci and Epistases Control Genetic Variation for Seed Dormancy in Weedy Rice (Oryza sativa)

Abstract

Weedy rice has much stronger seed dormancy than cultivated rice. A wild-like weedy strain SS18-2 was selected to investigate the genetic architecture underlying seed dormancy, a critical adaptive trait in plants. A framework genetic map covering the rice genome was constructed on the basis of 156 BC 1 [EM93-1 (nondormant breeding line)/ /EM93-1/SS18-2] individuals. The mapping population was replicated using a split-tiller technique to control and better estimate the environmental variation. Dormancy was determined by germination of seeds after 1, 11, and 21 days of after-ripening (DAR). Six dormancy QTL, designated as qSD S -4, -6, -7-1, -7-2, -8, and -12, were identified. The locus qSD S -7-1 was tightly linked to the red pericarp color gene Rc. A QTL ϫ DAR interaction was detected for qSD S -12, the locus with the largest main effect at 1, 11, and 21 DAR (R 2 ϭ 0.14, 0.24, and 0.20, respectively). Two, three, and four orders of epistases were detected with four, six, and six QTL, respectively. The higher-order epistases strongly suggest the presence of genetically complex networks in the regulation of variation for seed dormancy in natural populations and make it critical to select for a favorable combination of alleles at multiple loci in positional cloning of a target dormancy gene. S EED dormancy, the temporary failure of a viableThere are basically two categories of seed dormancy. Coat-imposed dormancy is enforced by seed covering seed to germinate under favorable conditions, is an adaptive trait that promotes the survival of many plants.tissues such as the glume and palea (or hull), the pericarp and testa, and in some cases the endosperm. EmRapid and uniform seed germination has been selected in crops, but a moderate degree of dormancy is desirable bryo dormancy is imposed by the factors within the embryo itself (Bewley and Black 1994). Embryo dorfor cereals to resist preharvest sprouting (PHS). Preharvest sprouting is germination of seeds on the plant after mancy has been reported for wild oat and wheat (Naylor and Simpson 1961; Flintham 2000) and was maturation, but before harvest of the crop, when moist conditions prevail or untimely rains occur. It can cause suggested in rice (Takahashi 1963); however, most genetic research has focused on coat-imposed dormancy. a substantial loss of yield and reduce grain quality (Ringlund 1993). Dormancy is a genetically complex trait Coat-imposed dormancy in rice is controlled by the maternal genotype on the basis of research using genetic controlled by polygenes with effects modified by the and somatic approaches (Seshu and Sorrells 1986; genetic background and environmental factors ( JohnGu et al. 2003( JohnGu et al. ). son 1935Anderson et al. 1993). A major approach to Primary dormancy develops during seed developdetermine the genetic architecture for seed dormancy ment and maturation. Environmental factors, such as is to dissect it into quantitative trait loci (QTL), such the temperature, humidity, and light, strongly affect the as in Arabidopsis (...

Isolation of three dormancy QTLs as Mendelian factors in rice

“…Some dormancy QTLs in cultivated rice lost their effect upon drying (Lin et al, 1998). Dormancy QTLs identified from weedy rice could be grouped into relatively early, constant, and late expression categories during afterripening (Gu et al, 2004), which was similar to that from Arabidopsis (Alonso-Blanco et al, 2003). Thus, time of afterripening is an important environmental factor affecting expression of dormancy genes.…”

“…Many dormancy QTLs have been identified from model plants and major cereal crops. For example, dormancy QTLs are distributed over all five chromosomes (chr) in Arabidopsis (Arabidopsis thaliana) ( Van der Schaar et al, 1997;Alonso-Blanco et al, 2003;Clerkx et al, 2004) and 11 of the 12 chr in cultivated (Oryza sativa) (Wan et al, 1997;Lin et al, 1998;Dong et al, 2002;Miura et al, 2002), wild (O. rufipogon) (Cai and Morishima, 2000;Thomson et al, 2003), and weedy (O. sativa) (Gu et al, 2004) rice. Dormancy QTLs in barley (Oberthur et al, 1995;Li et al, 2003;Prada et al, 2004), sorghum (Lijavetzky et al, 2000), and wheat (Anderson et al, 1993;Kato et al, 2001;Mares and Mrva, 2001;Groos et al, 2002;Osa et al, 2003;Kulwal et al, 2004) have been identified to seek gene resources to impart resistance to preharvest sprouting (PHS) and to manipulate germination programs in the malting process.…”

Identification of QTLs for Seed Germination Capability after Various Storage Periods Using Two RIL Populations in Rice

“…The same formula applied to all storage periods. Seed germination capability was transformed by sin -1 (x) -0.5 for statistical analysis (Gu et al, 2004).…”

SEED DORMANCY BREAKING TREATMENTS FORAFRICAN PURSLANE (Zaleya pentandra)

“…Weed control is a crucial part of an efficient crop production system, which can be facilitated by new methods to break seed dormancy (Gu et al, 2004). It is important to predict the weed seed dormancy in terms of timing and degree of weed emergence under field conditions to develop appropriate weed management approaches.…”