[Two pleiotropic intervals of rice were assessed using NILs constructed by two methods].

Spikeletes per panicle (SPP) is one of the important yield components in rice (Oryza sativa L.). Appropriate heading date (HD) and plant height (PH) are prerequisites for desired yield. In this study, the near isogenic lines (NILs) of chromosome 7, which harbored QTLs controlling HD, PH and SPP were constructed based on the primary QTLs results of the recombinant inbred lines (RILs) derived from Zhenshan 97 and HR5. The near isogenic lines (RILs) of chromosome 8, which harbored QTLs of HD, PH, and SPP, were constructed using heterogeneous inbred family based on RILs. The genetic effects of two pleiotropic intervals were assessed accurately in these two NILs. The QTLs identified by the two near isogenic lines indicated that the three traits were controlled by the same QTL or tightly linked QTL. The QTLs controlling the three traits had the same direction on additive effects and dominant effects. And these traits showed bimodal or discontinuous distributions in respective NILs. These results imply that the same gene might control the three traits simultaneously (i.e., the gene pleiotropism). Along with this, the relationships between HD and PH and yield, the application of significantly positive correlation for the three traits in breeding program, and the advantage and disadvantage of the two constructing NILs methods were also discussed in this study.

[Biological characters of rice on P-deficient soils with different pH value].

With pot culture, this paper studied the biological characters of four low-P tolerant rice genotypes 99011, 580, 508 and 99112 and two low-P sensitive rice genotypes 99012 and 99056 on three P-deficient soils with different pH. The results indicated that on test soils, 580, 508 and 99112 had similar low-P tolerant ability. 99011 had poor low-P tolerant ability on alkaline soil, with its relative grain yield being 11.9% and 10.4% less than that on acid and neutral soil, respectively. 99012 showed a relatively stronger low-P tolerant ability on alkaline soil, and its relative grain yield was 19.6% higher than that on acid soil and 22.2% higher than that on neutral soil. 99056 showed a stronger low-P tolerant ability on acid soil, and its relative grain yield was 25.0% and 19.6% higher than that on alkaline and neutral soil, respectively. The effects of soil P level and soil type on rice grain yield mainly manifestied on the number of available spike. The P concentration and its relative value in flag leaves of 99011, 580, 508 and 99112 were significantly higher than those of 99012 and 99056, which might be another factor resulting in the stronger low-P tolerant ability of 99011, 580, 508 and 99112 than 99012 and 99056.

Genetic analysis of agricultural traits in rice related to phosphorus efficiency.

Relative tillering ability, available spike, biomass, and grain yield of P1, P2, F1, and F(2,3) were used to study the genetic development of rice related to phosphorus efficiency with a quantitative genetic model. The results indicated that under a low-P condition, the relative tillering ability and the relative available spike were apt to the additivity-dominance-epistasis model with two couples of major genes, between which additive, dominant and epistatic effects existed, and with multi-gene modifications. Their maximum major gene effect mostly indicated additivity, but sub-maximum major gene effect mostly indicated dominance. Relative biomass and grain yield were apt to the additivity-dominance-epistasis and multi-genes model. The heritabilities of the major genes were 60.08% and 37.70%, and those of the multi-genes were 32.15% and 58.9%, respectively. This meant that the heritabilities of the relative tillering ability, the relative available spike, and the relative biomass were high, so they were ideal indexes for rice breeding tolerating to low-P stress; whereas, the heritability of the relative grain yield was low, which meant that the grain yield was easily affected by the environment.

Characterization of the genetic basis for yield and its component traits of rice revealed by doubled haploid population.

Main-effect QTL, epistatic effects and their interactions with environment are important genetic components of quantitative traits. In this study, we analyzed the QTLs, epistatic effects and QTL by environment interactions (QE) underlying nine traits of yield and yield-component, using a doubled-haploid (DH) population consisted of 190 lines from the cross between an indica parent Zhenshan 97 and a japonica parent WYJ 2, and tested in two-year replicated field trials. A genetic linkage map with 179 SSR (simple sequence repeat) marker loci was constructed. A mixed linear model approach was applied to detect QTLs, digenic interactions and QEs for the nine traits. In total, 57 QTLs of main effects, 41 digenic interactions, eight QEs and seven interactions of epistasis by environment were detected. Each of the main-effect QTLs individually explained 1.3 % to 25.8% of the phenotypic variations. And they collectively explained 11.5% to 66.8% of the phenotypic variations for these traits. Most of the traits (except seed setting) had the QTLs simultaneously detected in two years. Many of the traits shared same QTLs with each other, which is consistent with their significant phenotypic correlations. The pleiotropism or tight linkage of QTLs for different traits might be the important genetic base for trait correlations. The environmental influences on the stability of the trait performance were also discussed.

Genetic analysis of the panicle traits related to yield sink size of rice.

In the study, ten panicle traits associated with yield sink size were measured in a recombinant inbred population derived from Zhenshan 97 x Minghui 63. Generally, spikelets per panicle were more closely correlated with number of secondary branch per panicle, spikelets on secondary branch per secondary branch, and spikelet density. A total of 53 QTL were detected for ten traits in two years. Approximately 43.4% QTLs were detected in both two years, suggesting environmental effects on traits. Five chromosomal regions (G359-RG532 and C567-C86-RG236 on chromosome 1, R712-RM29 on chromosome 2, P-RG424 on chromosome 6, C148-RM258 on chromosome 10) were detected to have effects on multiple panicle traits. QTLs for traits, which were correlated, were generally localized in similar chromosomal regions, suggesting that pleiotropy and (or) linkage are the molecular basis of relationship between them. A large number of digenic interactions were detected, 18.2% of which were detected simultaneously in both two years. The proportion of common interactions was trait-depended, ranging 8.7% for spikelets on secondary branch per secondary branch to 32.6% for panicle length. Approximately 26.7% of common two-locus combinations had pleiotropic effects by simultaneously influencing two or more traits. Overall, the results indicate that each panicle trait is controlled by several QTLs, genotype x environment interaction, and a large number of epistatic interactions.