Developmental Genetics On Grain Weight In Rice

Two sets of tested materials were derived from partial diallel cross among nine different typesof selected rice varieties (lines).Based on experimental data at different developmental stages in early and late seasons, Estimations of genetic effects for rice grain weight at some developmental stages (0-t) or some special developmental periods (t-1-t) were conducted by using additive-dominant genetic model and developmental genetic model for quantitative traits.Analysis on unconditional genetic variance revealed that in early season the developmental dynamics of grain weight of rice was mainly controlled by dominant effects, and additive genes nearly expressed in the early period and expressed with little effects in the late period. In late season the entire courses of grain weight filling were affected by dominant and additive effects in turn, additive effects functioning principally in the early period, then dominant effects in the middle period and additive effects in the late period again. Analysis on conditional genetic variance indicated conditional dominant-effect genes expressed strikingly with large variation range during the entire courses of grain filling in early season. Additive- and dominant-effect genes governed grain filling commonly and the fonner acted mainly with less variation range of total genetic effects in late season,compared to that in early season.The results by heritabilities analysis found that narrow sense heritabilites during the entire courses of grain filling varied greatly between early and late season. The estimated narrow sense heritabilities remained little or zero in early season so that the selection for grain weight became unliable to be effective. The estimated narrow sense heritabilities all remained high level in late season, making the selection conducted in middle-late period liable to gain good result.Kinetic analysis on heterosis for grain weight at different developmental stages indicated that unconditional heterosis over mid-parent value based on population mean did not appear significant at 5% level in the early period(3d~12d) and turned positively significant as the developmental process proceeded inearly season. Unconditional heterosis over mid-parent value based on )x>pulation mean appeared positively significant in the middle period (9d~18d) of grain filling and became unsignificant in the late period(21d~30d) in late season. The result of analysis on unconditional heterosis could be interpreted rationally by conditional heterosis.The unconditional genetic relation between grain weight at different stages and final grain weight pointed out that additive relation coefficients did not reach significant level and dominant relation coefficient tended to increase as developmental process proceeded in early season. Additive relation coefficient all . reached significant or the most significant level during the entire courses of grain filling and dominant relation coefficient attained the most significant level only in the late period (21d~30d) in late season. Analysis on conditional genetic relation showed that there existed difference in the relation between grain weight at different stages and final grain weight between early and late seasons. During the latter half courses of grain filling, the relation was mainly controlled by dominant-eifect genes in early season and by additive-effect genes in late season.Analysis on unconditional genetic relation among grain weights at different developmental stages indicated that the relation was governed mainly by dominant-effect genes in early season and the relation in late season was controlled by additive-effect genes with a trend to become closer as the developmental process proceeded. The results by analysis on conditional genetic relation among grain weight at different stages found that dominant relation did not appear close in the early period of grain filling and turned more significant as late stages approached in early season. Additive relation between two adjoining stages became closer as the d...