Genetics and linkage analysis of grain dormancy and tyrosinase in wheat

Abstract

Pre-harvest sprouting due to low levels of seed dormancy, and high levels of the enzyme tyrosinase adversely affect the quality of wheat flour. The present knowledge of the genetics of tyrosinase and dormancy is inconsistent and inconclusive. Knowledge of the genetics of resistance to dormancy and tyrosinase will aid selection in breeding programs and will also facilitate linkage analysis with molecular markers. The main objectives of this research were to determine the number of genes involved in seed dormancy and tyrosinase activity in wheat and to develop molecular markers for these genes. Seeds from recombinant inbred lines matured under controlled environmental conditions (16$\sp\circ$C day/night) were evaluated for dormancy in germination tests performed at 15$\sp\circ$C and 20$\sp\circ$C. Two dormancy genes were identified in the population (BiggarBSR/RL4555) and lines carrying either or both genes could be identified using the germination tests at both temperatures. A RAPD marker (primer UBC303) wasidentified as linked to one dormancy gene by 25.74 cM ($\pm$ 5.2 cM) however the chromosome location of the dormancy gene was not determined. A quantitative calorimetric microtiter plate assay was developed to measure levels of tyrosinase activity in individual wheat kernels. All currently registered Canadian common wheat cultivars had high levels of tyrosinase activity while all Canadian durum wheat cultivars had no tyrosinase activity. A synthetic hexaploid wheat (RL5710) with no tyrosinase activity was identified and used as a parent in crosses to produce segregating populations. A strong gene and a weaker gene which interact epistatically were identified in the segregating F$\sb2$ and F$\sb3$ populations. The genes were located on chromosomes 2DS and 2A as determined by the analysis of alien addition and substitution lines. The knowledge of the chromosome location allowed the development of molecular markers linked to the tyrosinase loci from RFLP markers previously mapped to chromosome group 2. RFLP markers (B15C and ABGO19) flanking the gene on 2DS were identified. Each marker was shown to be linked by approximately 15 cM on either side of the tyrosinase gene. This would result in a selection error rate of 8% when both markers were used together.