Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 22, 1998
Publication Date: N/A
Interpretive Summary: The yield potential of a plant is affected by two types of physiological factors - source and sink components of yield. Source components of yield are those that define the plant's ability to capture light energy, e.g. leaf size and concentration of chloroplast in the leaf. Sink components include such factors as number of seed heads produced and number and size of the florets (potential grains)per seed head. Sink components are largel affected by the health of the plant during critical stages of development. A healthy plant will produce the maximum number of stems, seed heads, and potential grains genetically possible. A plant experiencing stress will decrease its sink size to compensate. If stress is experienced during seed head production, fewer and/or smaller seed heads will be produced. Stress during grain fill will cause the plant to produce grain in only a portion of the flowers it has already produced. Excessive production and maintenance of source components (e.g. high tiller number or overly long leaf length) can even contribute to nutrient/energy deficiencies that decrease sink components later in the plant's growth cycle. This study identified the chromosomal location of genetic factors associated with various source and sink components and identified three types of yield component genes - those that affect leaf shape but not size, those that increase seed head size and potential grain number without increasing actual grain weight per seed head and so do not increase final yield, and those that increase both leaf size (source) and grain weight per seed head(sink). Using molecular markers to select for this third type of yield gene can improve rice yields more effectively than can phenotypic selection of yield components which would be compounded by all three types genes.
The genetic basis underlying the relationship between the source leaves (the top two leaves) and the sink capacity in rice was investigated using RFLP/QTL analysis. F4 progeny from a cross between Lemont (japonica) and Teqing (indica) were evaluated for yield components including source components such as leaf length, width, and area; and sink components such as panicle length, floret number per panicle, and grain weight per panicle QTLs for these characters were located through their linkage with 115 well distributed RFLP markers. Path analysis indicated that 50% of the phenotypic variation in the primary sink capacity (grain weight per panicle)was attributable to variation of the flag leaf area. Thirteen QTLs and 30 pairs of epistatic loci were identified as influencing the length, width and area of the source leaves and the size of the sink as measured by panicle length, floret density and floret number per panicle. Two QTLs (QLl3b and QLw4) and 7 pairs of epistatic loci are largely responsible for the observed correlation between increased source- and increased sink- capacity. Other QTLs only influenced source- or sink-component measures, but were not associated with the primary yield component (grain weight per panicle). QTLs associated with panicle morphology but not with grain weight per panicle at least partially explain yield component compensation whereby an increase in one yield component is associated with a decrease in a second component such that yield is not increased. The identification of molecular markers linked with QTLs that positively impact both source and sink capacities will allow these important yield QTLs to be manipulated through marker-assisted selection more effectively than they could be manipulated through phenotypic selection alone.