QTL Mapping Of Plant Height And Ear Height In Maize

The plant height and ear position of maize are two key important agronomically traits associated with planting density, lodging resistance and mechanized harvesting. To increase grain yield, the increasing of planting density of maize is an effective way used in the major areas of maize production through-out the world, but is also involves the risk of root lodging, which can cause lower production. To avoid lodging, one of the major methods is to moderately decrease plant height and ear position. Therefore, it has important practical significance to elucidate the genetic basis of plant height. In this study, we constructed an F2 segregation population with 465 individuals as mapping population, which was derived from two recombinant inbred lines, W1 and W2, found in the process of improvement that have obvious difference in plant height and leaf type. QTL mapping were carried out to analysis the genetic basis of plant height and ear height based on the genotype of F2 population and phenotypic data in three environments. The main findings in this experiment are as follows.1. W1 and W2 are derived from two recombinant inbred lines that developed by crossing a recipient line(Mc) with a donor line(HB522) through two cycles of backcrosses and four cycles of self-cross. The W1 shows a higher plant height and flat leaf phenotype, while W2 is shorter and has a rolled-leaf phenotype. Through comparison of plant height, internode number and internode length between W1 and W2, the results show that W1 and W2 have the same number of internodes, while the length of internodes has significant difference(p<0.05), indicating that the observed difference of plant height between the two lines was caused by difference in the length of the internodes. Cytological observation showed the internodes cells in W1 were significantly longer than that in W2(p<0.01), thus indicating that the higher plant height of W1 relative to W2 was due to the increased cell lengths of internode.2. The parent W1 has a flat leaf, while the leaf of W2 became curled from the seventh leaf and the new leaves show a greater degree of curling than those of mature leaves which only curled at the top. Cross-section observation of the eighth leaf and ear leaf showed that both the number and the morphology of motor cell changed in W2 relative to W1, thus resulting in the curled leaves in W2. And exogenous GA treatment for W2 showed that the PH of treated W2 were significantly taller than that of untreated W2, indicating that the response pathway to GA in W2 was normal.3. A total of 1052 genome-wide SSR markers were used to analyze the polymorphism between the parents W1 and W2, and 86 polymorphic markers were found, mainly distributed on chromosome 3, 4, 5 and 9. The percentage of polymorphic markers on relevent chromosome accounts for 25.58%、20.93%、18.60%、16.28%, respectively, indicating that the donor chromosome causing height difference between W1 and W2 mainly focused on the four chromosomes.4. Using CIM, 5 QTL for plant height and 3 QTL for ear height were found by single-environment analysis in F2 population and F2:3 families. The QTL for plant height accounted for 3.30%-22.22% of phenotypic variation and displayed additive and partial dominance effect, one of the plant height QTL q PH3-2 was detected in three environment and accounted for 8.47%-22.22% of phenotypic variation, the QTL q PH9-1 was detected in two environment and accounted for 6.53% and 14.57% of phenotypic variation,respectively; the QTL for ear height accounted for 3.97%-9.63% of phenotypic variation and all displayed partial dominance effect, one of the QTL q EH3-1 was detected in two environment and explained 6.80% and 9.63% of phenotypic variation. This study also found 2 QTL using about 200 BC1 population, q PH3-4 and q PH3-5. The QTL q PH3-4 accounted for 17.76% of phenotypic variation, which was mapped in a adjacent chromosomal location with q PH3-2 found in F2 population and F2:3 families; the QTL q PH3-5 accounted for 7.77% of phenotypic variation, which was also detected in F2 population and F2:3 families.