| The bottleneck of mechanized rice production is machine transplanting,and the key of machine transplanting is seedling raising.The quality of rice seedling is related to the transplanting efficiency,growth,and yield.The efficiency of machine transplanting is mainly limited by two aspects.One is the seeding density;the other is the root injury.Our study aimed at the genetic basis of seedlings traits in response to seeding density and the effect of root injury on the yield and yield-related traits using an indica-japonica RIL population.The main contents were:1.The relationship between seedling quality and seeding density was analyzed.Compared with flat tray,seedlings in bowl-shaped blanket-like tray had heavy and uniform roots,which were in line with machine transplanting.The difference of seedling traits among three seeding densities were significant.With the increase of seeding density,compared with flat tray,seedlings in bowl-shaped blanket-like tray were less affected in SDW and RDW.The interaction between seeding tray type and seeding quantity were not significant.On the other hand,the average trait values of broadcast seedling were higher than that of drill seedling,but the uniformity of drill seedling was higher than that of broadcast seedling.Compared with broadcast seedling,the variation range of drill seedling was smaller as increasing of seeding density,indicating less sensitive to seeding density.The interaction between seeding method and seeding density had significant effects on root length and root number.2.A RIL population derived from 9311 and NIP were performed to explore the seedling traits variations and the genetic mechanism in three seeding densities.The parents and RIL population exhibited similar trends as the seeding density increased,including SH and FLSL increases,SDW and RDW decreases.Among the 37 QTLs detected under the three seeding densities,12 QTLs were detected in both three seeding densities,and 5 QTL hotspots were identified.Two QTLs,qRDW1.1 and qFLSL5.1 were specifically detected under low and high seeding densities,respectively.Detailed analysis the QTL regions revealed several candidate genes involved in phytohormones signals and abiotic stress responses.The results of genome-wide additive effect and epistatic effect also showed the dynamic changes of genetic control of seedling traits under different seeding densities.3.We conducted transcriptome analysis of shoot and root of NIP and 9311 under LD and HD.The results showed that the number of DEGs between shoot and root was the highest,followed by the varieties,and the seeding density was the lowest.The number of DEGs in 9311 responded to seeding density was less than that of NIP.The number of DEGs in root response to seeding density were more than those of shoot.There were only 4 genes in response to seeding density jointly detected by shoot and root,suggesting the difference of tissues in response to seeding density.The stimulus response and stress response were enriched between LD and HD.The pathways of various metabolism,plant hormone signal transduction and plant-pathogen interaction were changed between NIP and 9311.4.The variation of yield and yield-related traits,the difference of QTLs,genome-wide additive effect and epistatic effect were analyzed by artificial root cutting.The results showed that the effect of yield in root cutting was through tiller per plant.The effect of root cutting in NIP was less than 9311.A total of 16 QTLs were detected,except qGPP2.1 and qYD2.1 were detected only in control,the remaining QTLs were both detected in control and root cutting.The number of bins with positive effects between 9311 and NIP were consistent with the trait performance,and more bins with positive effects were detected in high-value parents.Except for heading date and tiller per plant,the number of negative epistasis effects was the majority. |
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