Identification And Analysis Of A QTL For Leaf Size In Rice

Carbohydrates produced by photosynthesis is the primary source of grain yield in rice (Oryza sativa L.), of which 80% is from the top three leaves. The founctional leaf size is an impotant factor determining the amount of carbohydrates generated by photosynthesis. Thus it is important to genetically analyze the morphological characteristics, such as the leaf size of functional leaves, especially flag leaf in rice improvement. Recently, few genes related to leaf size of rice was reported, and no QTL was fine mapped, though many QTLs were identified by segregant populations. In this study, a F₂ segregating population and two nearly isogenetic line (NIL) populations, heterozygous family (F₃) and homozygous progeny (F₄) developed from some F₂ individuals, were constructed and used to confirm and validate a QTL for flag leaf size on chromosome 1, which was previously detected in a backcross recombinant inbred population derived from a cross between two indica (O. sativa L. ssp. indica) cultivar (ZS97B and 9311). The objectives of this study were to analyse the genetic bases of leaf size and its relationship with yield components, and to provide useful information for plant-type breeding and yield breeding in rice. The main results are as follows:1. Using a F₂ segregating population, the QTLs for flag leaf length, flag leaf width and flag leaf area; second top leaf width and second top leaf area; panicle weight and number of second branch were detected in the interval of RM283-RM8083 (about 20cM) on chromosome 1, which implied the existing of pleiotropic effect.2. Mean value of each F3 family was used to rectify the phenotype of corresponding F₂ plant for substitution mapping and QTL mapping. The result indicated that in the region of RM151-RM10481 existed a pleiotropic QTL, which could control flag leaf length, width and area; second top leaf length and area; panicle weight, spikelet number, number of second branch and panicle length simutanously. Except for leaf width and panicle length, the variance explaining percentage of the QTL for these traits were all above 15%, and for flag leaf length, panicle weight and second branch number, they were 32.49%,33.57% and 23.04% respectively. Meanwhile in the neighboring region of RM10481-RM5346, a QTL was found for second top leaf width.3. Basing on the genotype analysis of F3 family, homozygous plants were chosen out to construct substitution line- F4 progeny and used for fine mapping. The pleiotropic QTL in the region of RM3746-RM10481 (about 7.1cM) was confirmed and validated controlling length, width and area of flag leaf, length, width and area of second top leaf, heading date, spikelet number, grain weight and panicle length simutanously. While the major QTL for panicle weight and second branch number was located in the interval of RM10315-RM10346, which contained Gn1a ,a cloned gene related yield.4. In F₄ progeny, correlation analysis between the invested traits suggested that flag leaf length was significantly correlated with flag leaf width, flag leaf area, second top leaf length, second top leaf area, heading date, spikelet number, panicle weight, number of second branch. Pleiotropic or tighly linkage of multi-gene may be its genetic basis.