Advanced Backcross QTL Analysis for the Whole Plant Growth Duration Salt Tolerance in Rice(Oryza sativa L.)

Salinity is a major factor limiting rice yield in coastal areas of Asia. To facilitate breeding salt tolerant rice varieties, the wholeplant growth duration salt tolerance（ST） was genetically dissected by phenotyping two sets of BC2F5 introgression lines（ILs） for four yield traits under severe natural salt stress and non-stress filed conditions using SSR markers and the methods of advanced backcross QTL（AB-QTL） analysis and selective introgression. Many QTLs affecting four yield traits under salt stress and nonstress conditions were identified, most（〉90%） of which were clustered in 13 genomic regions of the rice genome and involved in complex epistasis. Most QTLs affecting yield traits were differentially expressed under salt stress and non-stress conditions. Our results suggested that genetics complementarily provides an adequate explanation for the hidden genetic diversity for ST observed in both IL populations. Some promising Huanghuazhan（HHZ） ILs with favorable donor alleles at multiple QTLs and significantly improved yield traits under salt stress and non-stress conditions were identified, providing excellent materials and relevant genetic information for improving rice ST by marker-assisted selection（MAS） or genome selection.

Mining Applicable Elite Alleles of Growth Duration, Plant Height and Panicle Number per Plant by Conditional QTL Mapping in Japonica Rice

Unconditional and conditional QTL mapping were conducted for growth duration (GD), plant height (PH) and effective panicle number per plant (PN) using a recombinant inbred line (RIL) population derived from a cross between two japonica rice varieties Xiushui 79 and C Bao. The RIL population consisted of 254 lines was planted in two environments, Nanjing and Sihong, Jiangsu Province, China. Results showed that additive effects were major in all of QTLs for GD, PH and PN detected by the two methods, and the epistatic effects explained a small proportion of phenotypic variation. No interactions were detected between additive QTL and environment, and between epistatic QTL pairs and environment. After growth duration was adjusted to an identical level, RM80-160bp was detected as an applicable elite allele for PN, with an additive effect of 0.71. When effective panicle number per plant was adjusted to an identical level, RM448-240bp was detected as an applicable elite allele for GD, with an additive effect of 4.64. After plant height was adjusted to an identical level, RM80-160bp was detected as an applicable elite allele for PN, with an additive effect of 0.62, and RM448-240bp was detected as an applicable elite allele for GD, with an additive effect of 3.89. These applicable elite alleles could be used to improve target traits without influencing the other two traits.

Mining Elite Alleles of Growth Duration and Productive Panicle Number per Plant by Association Mapping with Conditional Phenotypic Value in Japonica Rice

To provide genetic information and materials for breeding hybrid japonica rice with wide adaptability and strong competitive advantage of yield, elite alleles and their carrier varieties of growth duration （GD） and productive panicle number per plant （PN） were detected. A natural population composed of 94 japonica varieties was phenotyped for the GD, PN and plant height （PH） in two environments. The conditional phenotypic data were transferred by the linear model method in software QGAStation 1.0, and association mapping based on the unconditional and conditional phenotype values of GD and PN was analyzed by using general linear model in software TASSEL. A total of 34 simple sequence repeat （SSR） marker loci associated with GD and PN were detected in the two environments. Among them, 15 were associated with GD, and 19 were associated with PN. Four elite alleles of RM8095-120bp, RM7102-176bp, RM72-170bp and RM72-178bp were associated with GD, and their carrier varieties were Hongmangshajing, Nipponbare, Hongmangshajing and Nannongjing 62401, respectively. These elite alleles from the carrier varieties can shorten GD by 2.03-9.93 d when they were introduced into improved materials. RM72-182bp associated with PN was an elite allele, and its carrier variety was Xiaoqingzhong. It can increase PN by three when introduced into improved materials. Moreover, these elite alleles can be used to improve target traits without influencing another two traits.

Grain yield and lodging-related traits of ultrashort-duration varieties for direct-seeded and double-season rice in Central China

Lodging is the most common constraint on grain yield of direct-seeded rice.There is limited information about lodging resistance and its related plant traits in direct-seeded and double-season rice(DDR)in Central China.This study aims to identify the plant traits that achieve high lodging resistance in ultrashort-duration varieties(about 95 days)of DDR.Field experiments were conducted in 2017 and 2018 in Wuxue County,Hubei Province,China,with four ultrashort-duration varieties grown under two nitrogen(N)rates.Lodging-related traits were measured on the 15 th day after heading,and yield and yield attributes were measured at maturity.The grain yield of the four varieties ranged from 4.59 to 7.61 t ha^(-1)across the two N rates,with a total growth duration of 85 to 97 days.Varietal differences in lodging index were mainly explained by the bending moment,which was closely related to plant height.Breaking resistance did not affect the lodging index significantly.Shortening plant height from 95.4 to 80.5 cm decreased the lodging index by 22.4%but did not reduce grain yield.Our results suggested that reducing plant height was effective in improving the lodging resistance of ultrashort-duration varieties of DDR.Lodging resistance should be enhanced by improving breaking resistance rather than reducing plant height to increase DDR grain yield further.

Variation in Gelatinization Characteristics of Storage Root Starch During Sweetpotato Growth and Development

The differential scanning calorimetry (DSC) and rapid visco-analyzer (RVA) were used to determine the starch gelatinizationcharacteristics during the growth of three sweetpotato cultivars. The results showed that the starch contents of threesweetpotato cultivars all decreased as growth progressed. Changes of the amylose contents differing in harvesting datesshould be discriminated according to the cultivars. At the early harvests amylose contents of Xushu18 and Zheda9201were relatively high, but those of Zhe3449 were low. As the growth duration of sweetpotatoes prolonged, the peaks ofDSC thermograms tended to occur at a low temperature and not to be so obstrusive with the increased width of the peak.Obvious decreases were observed, values of onset, peak and conclusion temperatures, as well as enthalpy of phasetransitions, as growth time lengthened. The peak viscosities, as determined through RVA, showed a rising tendency asgrowth progressed. In addition, statistical analysis revealed that there were correlations between the amylose content andgelatinization characteristics to some extent, which were affected by genotypes evidently.

Identification and Gene Mapping of Completely Dominant Earliness in Rice

The completely dominant earliness was identified in a genie male-sterile and early maturing indica line 6442S-7. F1 progenies from 6442S-7 crossed with thirteen various types of medium- or late-maturing varieties, shared the same heading date as 6442S-7. The segregation of heading date in the F2 and B1F1 populations showed that the earliness of 6442S-7 is mainly controlled by two dominant major genes. The local linkage map of one dominant earliness gene harbored in 6442S-7 was constructed with F2 population and four kinds of molecular marker techniques. The results showed that the gene was located between a RFLP marker C515 and a RAPD marker OPI 11.557 on the terminal region of short arm of rice chromosome 3, 10.9cM and 1.5cM from C515 and OPI11.557, respectively. The genetic distances from the target gene to two SSR markers, RM22 and RM231, and one AFLP marker, PT671, were 3.0, 6.7 and 12.4 cM, respectively. This gene, being identified and mapped first, is designated tentatively as Ef-cd(t). As a new genetic resource of completely dominant earliness, 6442S-7 has splendid future in rice improvement.

Isolation, Identification and Earliness Effect Analysis of Rice Dominant Earliness Gene Ef-cd

Ef-cd gene is a dominant earliness gene located on the short arm of rice chromosome 3. In this paper, through continuous backcross, self-pollination and molecular marker assisted selection, individual Ef-cd gene was isolated and its nearly isogenic lines were constructed by using early-maturing indica line 6442S-7 as the donor parent, and by using latematuring indica line Minghui 63 （MH63）, Shuhui 881 （SH881） and Shuhui 527 （SH527） as the recurrent parents （genetic background）, respectively. Further, it was found out that Ef-cd gene could generally advance rice to head 11-14 d earlier. So, it was considered that Ef-cd gene played an important role in rapid developing early-maturing and super high-yielding rice varieties.