Two recombinant inbred line(RIL)populations,one derived from a cross between Zhongyouzao 8(indica)and Toyonishiki(japonica)and the other from a cross between Qishanzhan(indica)and Akihikari(japonica),were grown in Liaoning and Sichuan Provinces,China,to study the panicle type index(PTI,the ratio of a number of node position on panicle axis where the secondary branch with the most numerous secondary branch grains is located to the number of primary branches)and its relationships with subspecies characteristics and yield traits.With continuous distribution of PTI and numerous of lines with different PTIs in the progenies,indica-japonica hybridization could be a method for breeding cultivars with ideal panicle type.PTI was significantly influenced by environments,with a significant decrease from Liaoning to Sichuan.A significantly negative correlation was found between PTI and most of subspecies characteristics.PTI varied remarkably with different subspecies types.As a whole,it showed a trend of indica(H)>indicalinous(H')>japonicalinous(K')>japonica(K).However,it is not appropriate to regard PTI as a parameter for subspecies classification in rice because it was recombined in the filial generations of cross between indica and japonica rice.The negative correlations were found between PTI and most of panicle characteristics,as well as yield-related traits.Based on PTI,most of lines from the two populations were middle dominant panicle type(the number of grains on the secondary branch is numerous in middle position of the panicle)and lower dominant panicle type(the number of grains on the secondary branch is numerous in lower position of the panicle and becomes less towards the top of panicle)with significant yield advantages.
To select highly informative microsatellite markers (SSRs) and establish a useful genetic SSR framework for rice genotyping, 15 rice (Oryza sativa L.) cultivars including six indica varieties and nine japonica varieties were used to analyze the polymorphism information content (PIC) value of 489 SSR markers. A total of 1 296 alleles were detected by 405 polymorphic markers with an average of 3.2 per locus. The PIC value of each chromosome was ranged from 0.4039 (chromosome 2) to 0.5840 (chromosome 11). Among the two rice subspecies, indica (0.3685-0.4952) gave a higher PIC value than japonica (0.1326-0.3164) and displayed a higher genetic diversity. Genetic diversity of indica was high on chromosome 12 (0.4952) and low on chromosome 8 (0.3685), while that for japonica was high on chromosome 11 (0.3164) and low on chromosome 2 (0.1326). A SSR framework including 141 highly informative markers for genotyping was selected from 199 SSR markers (PIC > 0.50). Ninety-three SSR markers distributed on 12 chromosomes were found to be related to indica-japonica differentiation. Of these 93 pairs of SSR primers, 17 pairs were considered as core primers (all the japonica varieties have the same specific alleles, while the indica varieties have another specific alleles), 48 pairs as the second classic primers (all the japonica or indica varieties have the same specific alleles, while the indica or japanica varieties have two or more other specific alleles ) and 28 pairs as the third classic primers (all the japonica and indica varieties have two or more alleles, but the specific alleles are different between japonica and indica). Thirty-two SSR markers were selected to be highly informative and useful for genetic diversity analysis of japonica varieties. This work provides a lot of useful information of SSR markers for rice breeding programs, especially for genotyping, diversity analysis and genetic mapping.
