Search

Camellia huana is an endangered species with a narrow distribution in limestone hills of northern Guangxi and southern Guizhou provinces, China. We used one chloroplast DNA (cpDNA) fragment and 12 pairs of microsatellite (simple sequence repeat; SSR) markers to assess the genetic diversity and structure of 12 C. huana populations. A total of 99 alleles were detected for 12 polymorphic loci, and eight haplotypes and nine polymorphic sites were detected within 5200 bp of cpDNA. C. huana populations showed a low level of genetic diversity (n = 8, Hd = 0.759, Pi = 0.00042 for cpDNA, NA = 3.931, HE = 0.466 for SSRs), but high genetic differentiation between populations (FST = 0.2159 for SSRs, FST = 0.9318 for cpDNA). This can be attributed to the narrow distribution and limestone habitat of C. huana. STRUCTURE analysis divided natural C. huana populations into two groups, consistent with their geographical distribution. Thus, we suggest that five natural C. huana populations should be split into two units to be managed effectively.

The paste viscosity attributes of starch, measured by rapid visco analyzer (RVA), are important factors for the evaluation of the cooking and eating qualities of rice in breeding programs. To determine the genetic roots of the paste viscosity attributes of rice grains, quantitative trait loci (QTLs) associated with the paste viscosity attributes were mapped, using a double haploid (DH) population derived from Zhongjiazao 17 (YK17), a super rice variety, crossed with D50, a tropic japonica variety. Fifty-four QTLs, for seven parameters of the RVA profiles, were identified in three planting seasons. The 54 QTLs were located on all of the 12 chromosomes, with a single QTL explaining 5.99 to 47.11% of phenotypic variation. From the QTLs identified, four were repeatedly detected under three environmental conditions and the other four QTLs were repeated under two environments. Most of the QTLs detected for peak viscosity (PKV), trough viscosity (TV), cool paste viscosity (CPV), breakdown viscosity (BDV), setback viscosity (SBV), and peak time (PeT) were located in the interval of RM6775–RM3805 under all three environmental conditions, with the exception of pasting temperature (PaT). For digenic interactions, eight QTLs with six traits were identified for additive×environment interactions in all three planting environments. The epistatic interactions were estimated only for PKV, SBV and PaT. The present study will facilitate further understanding of the genetic architecture of eating and cooking quality (ECQ) in the rice quality improvement program.

Cadmium (Cd) contamination in rice has been a hot topic of research because of its potential risk to human health. In this study, a double haploid (DH) population derived from Zhongjiazao 17 (YK17) (an early-season indica cultivar)×D50 (a tropical japonica cultivar) was used to identify quantitative trait loci (QTLs) associated with Cd concentration in brown rice (CCBR) and Cd concentration in milled rice (CCMR). Continuous and wide variation for CCBR and CCMR were observed among the DH population. Correlation analysis revealed a positive and highly significant correlation between the two traits. A total of 18 QTLs for CCBR and 14 QTLs for CCMR were identified in five different pot and field trials. Two pairs of QTLs for CCBR (qCCBR2-1 and qCCBR2-2, qCCBR9-1 and qCCBR9-2) and one pair of QTLs for CCMR (qCCMR5-1 and qCCMR5-2) were detected in multiple trials. The alleles increasing CCBR at the qCCBR2-1/qCCBR2-2 and qCCBR9-1/qCCBR9-2 QTLs were contributed by YK17 and D50, respectively, whereas the D50 allele at the qCCMR5-1/qCCMR5-2 QTLs increased CCMR. Eight pairs of QTLs for CCBR and CCMR, qCCBR2-2 and qCCMR2-2, qCCBR3 and qCCMR3, qCCBR4-2 and qCCMR4-1, qCCBR4-3 and qCCMR4-2, qCCBR4-4 and qCCMR4-3, qCCBR5 and qCCMR5-2, qCCBR7 and qCCMR7, and qCCBR11-1 and qCCMR11-2, co-localized on chromosomes 2, 3, 4, 5, 7, and 11, respectively. For all of these QTL pairs, except qCCBR5/qCCMR5-2, the additive effects came from YK17. In addition, four CCMR QTLs showing significant additive×environment interaction and two pairs of CCMR QTLs with bi-allelic epistatic interactions were identified. The results of this study could facilitate marker-assisted selection of breeding rice varieties with low Cd accumulation in grain.

In rice, the contents of protein and amino acids are the major parameters of nutritional quality. Co-localization of quantitative trait loci (QTLs) for heading date and protein content were reported, but pleiotropism of heading-date genes on protein contents has not been investigated. Here, we reported that rice florigen gene RFT1 plays an important role in controlling amino acid contents of rice grain. Firstly, 73 QTLs for the contents of 17 amino acids in unmilled rice were detected using recombinant inbred lines (RILs) of the indica rice cross Zhenshan 97 (ZS97)/Milyang 46 (MY46). Then, the effect of the largest cluster consisting of 14 QTLs, located in proximity to the rice florigen genes RFT1 and Hd3a, was validated using three populations consisting of near isogenic lines (NILs) that only segregated a region covering the target QTL. The first and second NIL populations were derived from a residual heterozygote identified from the ZS97/MY46 RIL population, consisting of homozygous lines that were only segregated in a 29.9-kb region covering the two florigen genes and a 1.7-kb region for RFT1, respectively. The third NIL population was segregated for the RFT1ZS97 transgene in the background of japonica rice cultivar Zhonghua 11. In all the three NIL populations, RFT1 was shown to have a strong effect on the contents of most amino acids, with the ZS97 allele always having the reducing effects. By comparing QTLs for amino acid contents detected in the ZS97/MY46 RIL population and genes/QTLs previously identified for heading date difference between ZS97 and MY46, possible pleiotropism on amino acid contents was also shown for other key heading-date genes including Hd1, Ghd7, and OsGI.

Background Thousand grain weight is a key component of grain yield in rice, and a trait closely related to grain length (GL) and grain width (GW) that are important traits for grain quality. Causal genes for 16 quantitative trait loci (QTL) affecting these traits have been cloned, but more QTL remain to be characterized for establishing a genetic regulating network. A QTL controlling grain size in rice, qGS10, was previously mapped in the interval RM6100–RM228 on chromosome 10. This study aimed to delimitate this QTL to a more precise location. Method A total of 12 populations were used. The ZC9 population comprised 203 S1:2 families derived from a residual heterozygous (RH) plant in the F9 generation of the indica rice cross Teqing (TQ)/IRBB52, segregating the upper region of RM6100–RM228 and three more regions on chromosomes 1, 9, and 11. The Ti52-1 population comprised 171 S1 plants derived from one RH plant in F7 of TQ/IRBB52, segregating a single interval that was in the lower portion of RM6100–RM228. The other ten populations were all derived from Ti52-1, including five S1 populations with sequential segregating regions covering the target region and five near isogenic line (NIL) populations maintaining the same segregating pattern. QTL analysis for 1,000-grain weight, GL, and GW was performed using QTL IciMapping and SAS procedure GLM. Result Three QTL were separated in the original qGS10 region. The qGL10.1 was located in the upper region RM6704–RM3773, shown to affect GL only. The qGS10.1 was located within a 207.1-kb interval flanked by InDel markers Te20811 and Te21018, having a stable and relatively high effect on all the three traits analyzed. The qGS10.2 was located within a 1.2-Mb interval flanked by simple sequence repeat markers RM3123 and RM6673. This QTL also affected all the three traits but the effect was inconsistent across different experiments. QTL for grain size were also detected in all the other three segregating regions. Conclusion Three QTL for grain size that were tightly linked on the long arm of chromosome 10 of rice were separated using NIL populations with sequential segregating regions. One of them, qGS10.1, had a stable and relatively high effect on grain weight, GL, and GW, providing a good candidate for gene cloning. Another QTL, qGS10.2, had a significant effect on all the three traits but the effect was inconsistent across different experiments, providing an example of genotype-by-environmental interaction.

Camellia wumingensis, a neglected species known only from limestone areas of Guangxi, China, is formally described and illustrated here. It is morphologically similar to C. flavida var. patens in having current-year branchlets purplish red, petiole adaxially grooved, flowers axillary or terminal, ovary glabrous, capsule oblate, and seeds brown, but is readily distinguished by the leaf texture and size, number of secondary veins, flower size, flower bud shape and size, number of petals, degree of fusion of the outer filaments, and pericarp thickness. Other related species C. flavida and C. pinguoensis var. terminalis are also compared with C. wumingensis in the paper, and the differences between them are obvious. In addition to a diagnosis and detailed description, information on the geographical distribution, images of morphological characters and pollen grains, and a provisional conservation status assessment are provided for this species. [ABSTRACT FROM AUTHOR]

Camellia flavida is an endangered species of yellow camellia growing in limestone mountains in southwest China. The current classification of C. flavida into two varieties, var. flavida and var. patens, is controversial. We conducted a genetic analysis of C. flavida to determine its taxonomic structure. A total of 188 individual plants from 20 populations across the entire distribution range in southwest China were analyzed using two DNA fragments: a chloroplast DNA fragment from the small single copy region and a single-copy nuclear gene called phenylalanine ammonia-lyase (PAL). Sequences from both chloroplast and nuclear DNA were highly diverse; with high levels of genetic differentiation and restricted gene flow. This result can be attributed to the high habitat heterogeneity in limestone karst, which isolates C. flavida populations from each other. Our nuclear DNA results demonstrate that there are three differentiated groups within C. flavida: var. flavida 1, var. flavida 2, and var. patens. These genetic groupings are consistent with the morphological characteristics of the plants. We suggest that the samples included in this study constitute three taxa and the var. flavida 2 group is the genuine C. flavida. The three groups should be recognized as three management units for conservation concerns.