QTL Analysis Of Panicle Heterosis And Fine Mapping Of The Major QTL QLRL4 For The Longest Root Length In Rice

Rice is the most important food crop for more than half of the world’s population.Therefore,it is a target for breeders to improve rice yield.Hybrid rice,as a symbol for the 2^nd‘Green Revolution’,has contributed to food security in China.China is one of the first countries to study hybrid rice.However,the genetic mechanism underlying rice heterosis is still unclear.In order to investigate genetic mechanism for rice heterosis,132 recombinant inbred lines（RILs）derived from 9311 and PA64S,and a high-resolution genetic map generated by resequencing have been constructed.Then,a RILT1population was obtained by backcrossing the RIL population with 9311.Four traits of RIL and RILT1populations were phenotyped and analyzed,including panicle length（PL）,primary branches number（PBN）,secondary branches number（SBN）and spikelets number（SN）.The median parent values（MPV）of four traits of RILT1 population were found all positive,showing mid-parents heterosis.Significant correlations were also found among the four traits,especially between SN and SBN.A total of 11 QTLs were detected by QTL analysis with the RIL and RILT1 populations.Two QTL clusters,qPBNH-2,qSBNH-2 and qSNH-8,qSBNH-8,may have multiple effects.In order to improve rice yield,researchers focused on the aboveground part of rice.However,the underground part of rice,with many physiological and biochemical functions,such as absorbing water and fertilizer,fixing plants,synthesizing and transporting nutrients,are also closely related to rice yield.Because the root system is related to aboveground parts,therefore,the research on root development in rice seedling is also important to improve biomass and production.In order to investigate the root traits of rice seedling,148 RILs derived from 9311 and NPB,and a high-resolution genetic map by resequencing have been constructed.Seeds of 132 RILs harvested were cultivated in nutrient solution,and five traits of roots were measured,including the longest root length（LRL）,total root length（TRL）,root surface area（RSA）,root volume（RV）and root diameter（RD）.Significant correlations were observed among the traits.With a high-resolution genetic map of the RILs,26 QTLs were detected on all chromosomes.There were four QTL clusters on seven chromosomes,among which only the QTL related to LRL and RD detected on chromosome 4 was mapped at the same position in two replicates.With F₂ population of 9311 and NIL-qLRL4,a near isogenic line（NIL）harboring qLRL4 from NPB in9311 background,a major QTL for LRL,qLRL4 was fine mapped within 68.23 kb between In Del markers IND4-1 and IND4-3 on chromosome 4.