Optimization of Inplanta Factors Influencing the Development of Doubled Haploid Wheat Production via Maize Cross Technique

Abstract

Production of agronomically important wheat (Triticum aestivum L.) varieties in a very short time can be achieved by the doubled haploid production techniques. These techniques ensure homozygosity in wheat that results in enhanced characteristics such as yield and disease resistance. One method of developing doubled haploid wheat lines is by the intergeneric cross of wheat with maize (Zea mays L.) or the wide hybridization. In this method, maize acts as a donor. Maize pollen grains are used to pollinate wheat florets, as the result of fertilization a haploid wheat embryo is developed, the genetic material of maize is eliminated and the embryo contains only n number of wheat chromosomes. Further, the embryo is rescued and cultured in vitro. The embryo develops into a haploid plantlet which is then treated with chromosome doubling agents like colchicine. Chromosome doubling results in a homozygous sporophyte generation. Wheat and maize are ‘Rabi’ and ‘Kharif’ crops, respectively. Their growth conditions are different and the growth stages are majorly dependent on environmental factors. In the current study, to ensure the availability of both crops at the same time, the off-seasonal crop was grown in a glass house in controlled temperature and the heading duration of wheat plants was synchronized with the tasseling duration of maize by sowing maize seeds 15-20 days prior to the wheat. In a maize x wheat cross, the development of a haploid embryo depends on the genotypes of both crops and environmental conditions affecting the growth stages of the plants. The main focus of this study was to optimize the in planta factors such as the viability of pollen grains, caryopsis induction after pollination and embryo development. Genotypes of both crops were tested individually to find out the optimal maize x wheat cross; several concentrations of 2,4-D were used after pollination to find the best outcome. In this study, 6 wheat varieties and 6 maize varieties were crossed in a line x tester fashion (Line = wheat, tester= maize) to improve the efficiency of the maize x wheat system for haploid embryo production. Two parameters were considered, the caryopsis/seed formation number and embryo formation number in pollinated florets (number of caryopsis formed per 100 florets pollinated and number of embryos formed per caryopsis developed) vii to find out the frequency of haploid embryo formation across the genotypes. Both maize and wheat genotypes had an effect on embryo formation frequency, as described by the earlier studies, the overall effect of maize pollinators was higher but the variation across the wheat varieties showed that the embryo formation is also highly dependent on the wheat genotypes. The Pakistan-2013 variety showed the highest embryo formation frequency (10.93% - 38.54%) regardless of the pollinator. While the Anaj-2017 displayed the least embryo count per caryopsis (0% - 15.06%).