QTL Mapping For Plant Type, Ear Traits And Genetic Analysis Of A Male Sterile Line In Maize (Zea Mays L.)

The development of yield is the main objectives in maize breeding. Many studies have shown that the increased plant density, optimization of plant type and ear traits are the major contributor to maize yield improvement in China and elsewhere in the world. Therefore, the genetic dissection of plant type and ear traits is especially important in maize breeding. In the study, a set of introgression lines (ILs) were produced using the inbred line NongXi928 as recipient parents by means of marker-assisted backcrossing. Both ILs and DH lines were utilized to QTL analysis for plant type and ear traits. Furthermore, the genetic basis of plant type and ear traits were investigate under two different densities treatment. Meanwhile, a new cytoplasmic male sterile line discovered in the backcrossing population was indentified for type of male sterile, stage of microspore abortion and genetic mechanism. The major results are as follows:1. A series of 161 introgression lines were developed with NongXi928 as the recurrent parents and 4 elite inbred lines as donor, respectively through 4 cycles advanced backcross, 2-3 cycles self-cross and SSR-based marker-assisted selection. Genetic evaluation showed that 986 segments from the donor line were introgressed into NongXi928. The number of introgressed segment ranged from 2 to 13 with an average of 6.12 per lines. The average length of introgressive segment was 65.04 cM, varying from 4.24 to 269.20 cM. The length and the number of introgressed segment varied along with the different donor and different chromosomes. Recovery of the Nongxi928gnome ranged from 84.25% to 97.59% with an average of 92.64% in this ILs poplation. These ILs could be used into fine mapping of QTL and functional genomics researches in maize.2. Based on the phenotype of plant type and ear traits that were investigated in two years, 30 QTL for plant type related traits and 18 QTL for ear traits were detected in ILs population. Those QTL were mapped on 10 chromosomes and explained 7.07%–28.75% of the phenotypic variance. Some QTL for diverse traits were located in the same or adjacent chromosome region. Three QTL-rich regions were formed on chromosome 3 in the interval umc1399-umc1307, chromosome 6 in the interval bnlg1538-umc159 and umc1614-bnlg1154.3. Differences between density of 60,000 and 90,000 plants per hectare were significant for plant height (PH), ear height (EH), internode number (IN), average internode length (AIL), stalk diameter (SD) and ear height coefficient (EHC) in the DH population. Both PH and EH were positively significantly correlated with EHC, but EH had more influence on EHC than PH. Twenty-seven additive QTL and four pairs of QTL with epistatic effect were detected for the investigated traits, of which seven QTLs with significant environment interactions were indentified. Only seven QTL were detected simultaneously under both densities. Six important regions distributed on chromosome 1, 8, 9 and 10 were found to exist constitutive QTL (detected in more than two environments, with contribution rate more than 10%) for plant type related traits.4. The ear length, ear diameter, kernel number per row, length of bare tip and kernel width had significant differences, but kernel row number per ear, kernel length, kernel thickness and 100 Grain weigh had no differences under the two densities treatment in DH population. Fourteen additive QTL and one pair of QTL with epistatic effect were detected for ear traits, of which three QTL with significant environment interactions were indentified. Only three QTL were detected simultaneously under both densities. Two important regions distributed on chromosome 4 and 5 were found to exist constitutive QTLs for ear traits.5. A male sterility line ( NongXi928cms-Q1261) was discovered in the BC3F1 population obtained using Q1261 as the donor genotype and NongXi928 as the recipient genotype. The male sterility characteristic of NongXi928cms-Q1261 was stable, no anthers exposed on tassel and pollen aborted completely. The cytoplasmic male sterile gene, which was classified into S type of CMS, originated from Q1261, and its nuclear sterile gene originated from NongXi928, which was controlled by a pair of recessive genes. The microspores started degrading at the late stage of microspore and degenerated completely at the mature pollen stage. Such male Sterility of NongXi928cms-Q1261 can be maintained by Zheng58 and PH6WC.