Chen Li-yun

Comparative Analysis of Genetic Diversity and Structure in Rice Using ILP and SSR Markers

Genetic diversity of 36 rice entries from the United States Department of Agriculture (USDA) rice collection was assessed using 103 ILP (intron length polymorphism) and 54 SSR (simple sequence repeats) markers. A total of 236 and 332 alleles were detected by the ILP and SSR markers, respectively. On average, the SSR markers produced higher polymorphism information content value and number of alleles than the ILP markers. Whereas the Neis genetic distance measured using the SSR markers was much higher than that measured using the ILP markers. Mantels test indicated that there was a statistically significant correlation (r=0.827, P<0.001) between the two marker systems. UPGMA clustering based on the ILP and SSR markers resulted in consensus dendrograms. The cophenetic correlation coefficient (r=0.918, 0.878 and 0.924, P<0.001 for the ILP, SSR and combined markers, respectively) showed a highly accurate dendrogram represented the genetic distance among these entries. The 36 entries were divided into four groups. Four African Oryza glaberrima accessions were clustered within a distinct group (I), and the remaining entries were separated into three groups (II, III and IV). All the entries could be also clustered into two main groups: One was composed of III and IV, considered as indica group, and the other was composed of I (O. glaberrima) and II (japonica-like). Model-based cluster analysis revealed that the japonica-like group maintained very pure ancestry while the indica group shared mixed ancestry, especially for group III, which had seven admixtures sharing from 19.5% to 30.0% of ancestry with group IV (based on SSR markers). It is suggested that ILP and SSR markers could be very useful for the genetic study and breeding in rice.

Thoughts and Practice on Some Problems about Research and Application of Two-Line Hybrid Rice

The main problems about research and application of two-line hybrid rice were reviewed, including the confusing nomenclature and male sterile lines classification, the unclear characteristics of photoperiod and temperature responses and the unsuitable site selection for male sterile line and hybrid rice seed production. In order to efficiently and accurately use dual-purpose genic male sterile lines, four types, including PTGMS (photo-thermo-sensitive genic male sterile rice), TGMS (thermo-sensitive genic male sterile rice), reverse PTGMS and reverse TGMS, were proposed. A new idea for explaining the mechanism of sterility in dual-purpose hybrid rice was proposed. The transition from sterile to fertile was involved in the cooperative regulation of major-effect sterile genes and photoperiod and/or temperature sensitive ones. The minor-effect genes with accumulative effect on sterility were important factors that affected the critical temperature of sterility transfer. In order to make better use of dual-purpose lines, the characterization of responses to photoperiod and temperature of PTGMS should be made and the identification method for the characterization of photoperiod and temperature responses of PTGMS should also be put forward. The optimal ecological site for seed production could be determined according to the historical climate data and the requirements for the meteorological conditions during the different periods of seed production.

Physiological and biochemical characteristics in flag leaves of the C Liangyou series of hybrid rice combinations at late growth stages.

The contents of chlorophyll, soluble sugars, soluble proteins and thiobarbituric acid reaction substance (TBARS), chlorophyll fluorescence parameters, net photosynthetic rate as well as the activities of superoxide dismutase (SOD) and peroxidase (POD) of flag leaves at the late growth stages were studied by using C Liangyou series of hybrid rice combinitions as material and Shanyou 63 as control. The C Liangyou series of hybrid rice combinations used in the experiment included C Liangyou 396, C Liangyou 87, C Liangyou 755 and C Liangyou 34, which all used C815S as male sterile line. The contents of chlorophyll, soluble sugars and soluble proteins in flag leaves of the C Liangyou series combinations at the late growth stages were higher than those of the control, whereas the TBARS content was lower than that of the control. The activities of SOD and POD were significantly higher than those of the control on the 7th day after heading, and then decreased slowly. ΦPSII value and qP value of flag leaves decreased at the late growth stages, and these two parameters in flag leaves of the C Liangyou series combinations were higher than those of the control, while the qN value increased at the late growth stages and was lower than that of the control. The net photosynthetic rate of flag leaves at the late growth stage was higher compared with the control. These results suggest that slow senescence and strong photosynthetic capability in flag leaves at the late growth stages are the physiological basis of the C Liangyou series combinations.