Genetic Analysis Of Low Amylose Content And Mapping Of Quantitative Trait Loci (QTL) For Thermotolerance Of Qualities In Rice

Amylose content is a key determinant of eating quality of rice. Low amylose rice, which stands for the medium type between non-glutinous and glutinous rice, is not only favour of consumers relishing soft and flexible texture rice, but also particularly suited for processing convenience and mixed rice or other kinds of ready-to-eat food. So, the elucidation of genetic bases controlling low amylose and the exploitation of new genes and alleles are badly needed for rice quality breeding. In addition, the temperature during grain filling is one of the most important environmental factors affecting rice quality. High temperature largely degraded the rice appearance, milling and cooking and eating quality and had been one of the most disadvantage factors for high quality rice producing in the southern of our country.In the present study, seven cultivars, i.e. Haopil, Haopi2, Haomuxi, Haoanmen, R6547, Mirukikuin and W3668 and a backcross inbred lines of Nipponbare / Kasalath // Nipponbare were used to analysis the heredity and temperature susceptibility of low amylose and map the QTLs conferring thermotolerance of rice qualities. The main results were as follows.1. F₁ seeds were skewed toward the high amylose parent in all the crosses between low amylose mutant Haopil, Haopi2, Haomuxi, Haoanmen, R6547, Mirukikuin and W3668 and the ordinary high amylose or waxy rice cultivars. The segregation of amylose content agreed with the expected 3 high:l low ratio in F2 seeds and lhigh:1low in BC1F1 seeds, showing that the genes conferring low amylose in all the studied cultivars were single recessive and allelic to wx. A F2 population from the cross between Haopil and high amylose japonica cultivar Erpingtou was constructed to map the gene in Haopi conferring low amylose content. As a result, it was located on chromosome 6,3.9 cM and 5.4 cM from the SSR markers RM190 and RM588 respectively, in the same genomic region as Wx. The result also suggested that the low amylose gene in Haopil might be allelic to wx. SDS-PAGE analysis showed the contents of granule-bound starch synthase (GBSS) were much lower in Haopil, Haopi2, Haomuxi, Haoanmen and R6547 compared with the ordinary rice, while in Mirukikuin and W3668 were almost the same as that in the wild type parents, implying that the mutation mechanisms were different between these two types rice. The study on temperature susceptibility showed thatHaopil, Haopi2, Haomuxi, Haoanmen and R6547 were much sensitive to temperature, for the amylose content of which increased significantly in low temperature. Comparatively, Mirukikuin and W3668 were less sensitive to temperature.2. A total of 23 QTLs for thermotolerance of grain milling quality were identified in Nanchang and Nanjing. Among them, 6, 9 and 8 QTLs were for thermotolerance of brown rice recovery (BR), milled rice recovery (MR) and head rice recovery (HR) respectively. 7 QTLs were identified in both the two locations, 3 of which showed significant QTL by environment interactions (QE). 21 digenic interactions were detected, and none of which was simultaneously detected in both the two locations. QTLs for heat tolerance of BR, MR and HR were simultaneously detected in the region of R617-R3375-R2672 on chromosome 12 and R830-R3166-R1838 on chromosome 5, and for BR and MR in the region of C1226-R1440 on chromosome 7. A QTL for heat tolerance of HR was detected in the region of C1488-C39 which was tightly linked to C1226-R1440. These regions should be important for heat tolerance of milling quality and should be studied further.3. A total of 26 QTLs for thermotolerance of chalkiness traits were detected. Among them, 7, 9 and 10 QTLs were for thermotolerance of percentage of grains with chalkiness (PGC), square of chalky endosperm (SCE) and degree of endosperm chalkiness (DEC) respectively. 6 QTLs in all the three traits were simultaneously detected in both the two locations, 5 of which showed significant QTL by environment interactions (QE). 33 digenic interactions were detected, and none was simultaneously detected in both the two loca...