Abstract
BackgroundDue to the diversity of rice varieties and cropping systems in China, the limitation of seeding density and seedling quality makes it hard to improve machine-transplanted efficiency. Previous studies have shown that indica and japonica varieties varied in machine transplanting efficiency and optimal seeding density. In this study, a RIL population derived from ‘9311’ and ‘Nipponbare’ were performed to explore the seedling traits variations and the genetic mechanism under three seeding densities.ResultsThe parents and RIL population exhibited similar trends as the seeding density increased, including seedling height and first leaf sheath length increases, shoot dry weight and root dry weight decreases. Among the 37 QTLs for six traits detected under the three seeding densities, 12 QTLs were detected in both three seeding densities. Five QTL hotspots identified clustered within genomic regions on chromosomes 1, 2, 4, 6 and 11. Specific QTLs such as qRDW1.1 and qFLSL5.1 were detected under low and high seeding densities, respectively. Detailed analysis the QTL regions identified under specific seeding densities revealed several candidate genes involved in phytohormones signals and abiotic stress responses. Whole-genome additive effects showed that ‘9311’ contributed more loci enhancing trait performances than ‘Nipponbare’, indicating ‘9311’ was more sensitive to the seeding density than ‘Nipponbare’. The prevalence of negative epistasis effects indicated that the complementary two-locus homozygotes may not have marginal advantages over the means of the two parental genotypes.ConclusionsOur results revealed the differences between indica rice and japonica rice seedling traits in response to seeding density. Several QTL hotspots involved in different traits and specific QTLs (such as qRDW1.1 and qFLSL5.1) in diverse seeding densities had been detected. Genome-wide additive and two-locus epistasis suggested a dynamic of the genetic control underlying different seeding densities. It was concluded that novel QTLs, additive and epistasis effects under specific seeding density would provide adequate information for rice seedling improvement during machine transplanting.
Highlights
Due to the diversity of rice varieties and cropping systems in China, the limitation of seeding density and seedling quality makes it hard to improve machine-transplanted efficiency
The degree of difference decreased when Second leaf length (SLL) and Root dry weight (RDW) were measured as the increasing of seeding density, while the degree of difference between the parents for Seedling height (SH), First leaf sheath length (FLSL), First leaf length (FLL) and Shoot dry weight (SDW) increased with increasing density
These results indicated that seedling quality of the parents and recombinant inbred lines (RILs) population on plastics nursery tray generally declined with the increase of seeding density, and the influences of seeding density on indica and japonica varied on traits
Summary
Due to the diversity of rice varieties and cropping systems in China, the limitation of seeding density and seedling quality makes it hard to improve machine-transplanted efficiency. Due to the tight growing season, the limitation of seeding density and seedling quality makes it more difficult to improve the efficiency for mechanized transplanting [10,11,12,13]. It has been used in hybrid rice, which accounts for about 60% of the rice producing area, the traditional rice mechanical transplanting technology cannot fully exploit the high yield advantage of hybrid rice, mainly due to the poor seedling cultivation, such as high seeding density, poor quality of seedlings, high rate of seedlings injury and large amount of seedlings per hill [14,15,16,17]. Due to the diversity of growth characteristics of different types of cultivars, it is necessary to make the seedlings with uniform size, consistent growth, and seedling characteristics suitable for appropriate ecological zones, planting systems and planting methods under machine transplanting
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