Genetic analyses of amylose content in maize (Zea mays L.)

The project was designed to analyze amylose content inheritance and to find how many modifier genes are involved in amylose starch synthesis and where they are on maize chromosomes. The objectives were (1) to conduct genetic analyses of amylose content using a triploid endosperm model; (2) to search for modifier genes and loci on the chromosomes for the trait and determine genetic effects of them via QTL mapping; (3) to measure amylose content by near infrared transmittance spectroscopy (NITS), a quick, non-destructive way to screen a large amount of materials from germplasm; (4) to analyze thermal properties of amylose starch through differential scanning calorimetry (DSC) providing information for selecting high amylose materials.;A maize inbred line, GEMS-0067 (Reg. no GP-550, PI 643420) possesses high amylose modifier gene(s) that, together with the recessive amylose extender1 (ae1) gene, raises the starch amylose percentage to at least 70%. GEMS-0067 represents the only public source of the high amylose modifying genes to date in the USA. It is important to reveal the genetic effects and gene interactions leading to the development of high amylose inbred lines and hybrids. In the maize kernel the endosperm is under triploid genetic control. Based on the triploid model, nine generations were derived from a cross between H99ae and GEMS-0067. Additive, dominance and epistatic effects were studied using data from two locations in Missouri (MO) and South Dakota (SD) over two years (2005 and 2006). The triploid models for MO and SD were separately established based on the corresponding data in 2006. The additive and type 1 dominance effects in MO, and the additive, type 1 dominance, type 2 dominance, additive x additive, additive x dominance and dominance x dominance effects in SD were significantly different from zero meaning that those effects played important role in amylose synthesis. Both broad-sense and narrow-sense heritabilities were high indicating that high amylose content could be effectively selected for in a segregating generation.;The second study was designed to determine the genetic effects and to identify the location of modifier gene(s) via quantitative trait loci (QTL). The F2 and F3 derived from a cross of (H99aexGEMS-0067) were planted in South Dakota in 2005 and 2007, respectively. Amylose content was measured by amylose-iodine colorimetry while the genotypes of F2 and F3 individuals were scored for polymorphisms of simple sequence repeat (SSR). The results showed that amylose content followed semi-dominance inheritance because the average of value of amylose content in the F2 was roughly mid-parent. The frequency distributions in F2 and F 3 were close to Normal distribution. A major QTL was detected on the short arm of chromosome 5 between umc1784 and umc2400 , 2.0cM away from umc2400. It explained 43% of the total variance. It had a high additive effect, and low dominance effect. A candidate gene, SbeI, is located in this interval near the peak of the QTL. The allele of starch branching enzyme 1 (SbeI) in GEMS-0067 might play the main role in the increase of amylose content with the ae1 background.;The aims of the third and fourth study were to determine amylose content in different generations at two locations in Missouri (MO) and South Dakota (SD) using colorimetry and NITS and to investigate the thermal properties of amylose starch by DSC. Calibration and validation regression models for predicting amylose content were built using spectrum data at two locations generated by NITS. The 62.6% and 57.1% of the total variance was explained by two models, respectively. NITS regression model could be used to predict amylose content in an unknown sample. The regression models based on the data of the thermal properties produced by DSC were established. There was no common trend found in onset, endset temperature and enthalpy during amylose starch gelatinization at two locations. The peak gelatinization temperature could be taken as a key indicator for screening the lines with high amylose content.;The conclusions for the whole project were as follows: (1) amylose content followed semi-dominance inheritance. It has highly inheritability. Model adequacy was depended on locations. (2) The QTL was found on chromosome 5 explaining 41% of the total variance. A SSR marker, umc2400, was 2 cM away from the QTL. Sbe1 could be a strong candidate for one of modifier genes. (3) NITS regression model could be used to predict amylose content in an unknown sample. It became a fast, non-sample preparing way to determine amylose content and is suitable for screening a large amount of materials from the germplasm in amylose breeding practice. (4) Peak gelatinization temperature can be a unique indicator for selecting high amylose maize in terms of DSC.