Screening Of High Yield, Drought And Salt Tolerant Plants From Backcross Introgression Lines And QTL Detectionfor Related Traits In Rice

Rice is one of the most important crops in the world. With unceasing increase of population underlimited land resources, it has been urgent to improve grain yield nowadays. However, with the influenceof unfavorable factors such as climate drought and salinity are becoming two detrimental abioticstresses which have caused serious deduction of rice production. Development of drought tolerance (DT)and salt tolerance (ST) rice variety is a most economic and effective way to minimize their damage andimprove grain yield.In the present study, backcross introgression lines (ILs), which were derived from Huanghuazhan(HHZ) as the recurrent parent, and four germplasm including OM1706, Gang46B, IR64and CR203asdonor parents, were used to develop high yiled (HY), DT and ST ILs through screening against GY, DTand ST and intercross identification, resulting in some ILs with two or multiple favorable target traits.Different selection strategies were then evaluated for their breeding efficiency. Meanwhile, QTLs forHY, DT and ST were detected using different trait-specific ILs, and some important favorable allelesstably expressed in different populations and environments were identified, providing some beneficialinformation for marker-assisted breeding for the three complex traits. The main results were describedas follows:1. Four ILs showing consistent HY across3growing seasons were obtained from HY selected ILs,4lines showing consistent DT across4growing seasons from DT selected ILs,111lines showingconsistent ST in three repeatedly experiments from ST selected ILs.2. By intercross screening,13lines showed HY and ST,5showed DT and ST. According toperformance of selected ILs under normal irrigated and drought stress conditions,19lines were selectedas HY and DT in Hainan condition, including11from ST selected ILs,1from HY selected ILs, and7from DT selected ILs. Similarly,18lines were selected as HY and DT in Beijing condition, including5from ST selected ILs,6from HY selected ILs, and7from DT selected ILs.3. Trait-specific selections are dependent on environment and donor. Relatively speaking,screening of HY and ST is more stable than that of DT. Using HHZ as a recipient, the donor CR203showed most contribution to HY in Hainan and Beijing environments; IR64showed most contributionto ST in green house and phototron conditions; OM1706showed most contribution to DT under Hainandrought stress condition whereas Gang46B showed most contribution to DT under Beijing droughtstress condition.4. Different screening ways showed various selection effectiveness of improving the target traits.First DT or ST then following HY screening would obtain more numbers of HY ILs than direct HYscreening does. Similarly, Direct DT screening or first ST then DT screening would get more numbersof DT ILs than screening DT from HY selected IL populations. The strategy of first ST then HY or DTscreening resulted in not only increased ST but also improved HY and DT.5. By selective IL mapping method total of15,13and16loci were detected and distributed all12chromosomes for HY, DT and ST, respectively. Through single marker analysis for corresponding random populations, some distorted loci associated with the target traits were repeatedly mapped andconfirmed and their additive effects were also estimated. Those loci detected by above two methods arerelatively durable, thus being probably more important QTLs underlying the target traits.6. Two genetic overlapping loci were detected for HY, DT and ST, two for HY and ST, three forHY and DT, and two for DT and ST. There were common2,1and3loci detected in differentpopulations for HY, DT and ST, respectively. There were six loci detected in the two populations for thesame trait, including two HY loci linked with RM219and RM57, one DT locus associated with RM335,and three ST loci associated with RM490, RM482and RM574/RM437. There were seven loci stablyexpressed in the same population across two years, including2DT loci (qDT2.2and qDT6.2) and fiveHY loci (qGY1.1, qGY6.1, qGY7.1, qGY5.3and qGY3).7. QTL mapping indicated that the donor alleles at15loci detected in the four populations undernormal and drought stress conditions in Hainan and Beijing were favorable to improve two or multipleyield component traits such as thousand grain weight (TGW), filled grains per panicle (FGP), spikeletnumber per panicle (SNP) and panicle number per plant (PNP). Among them, qFGP2.2，qFGP10.3，qSNP2.1and qSNP10.2were simultaneously detected in the two populations, and donor alleles atqSNP10.2increased SNP in both normal and drought stress conditions. Above loci are important stablyexpressed loci affecting yield or yield-related traits.8. The markers RM576, RM263, RM24, RM182, RM126and RM484were associated not only withHY, DT and ST, but also with QTLs underlying yield component traits, showing genetic overlapbetween abiotic stress tolerance and HY. More importantly, the QTLs associated with these markerswere all detected by two methods under two environments and/or two populations. The donor alleles atabove loci play an active role in improvement of HY, DT and ST, thus they have important value inmarker-assisted selection and pyramiding breeding in rice.