Genotype-Independent Regeneration Of Hybrid Maize Cultivated At The Coastal Region Of Kenya

ABSTRACT

Maize (Zea mays L.) is the most important cereal food crop in many tropical and subtropical regions. Though the demand is steadily increasing, the productivity of maize has been declining due to several production factors over the past years. Statistics have shown that the world population is expected to double by 2050. With this population growth, food insecurity in the tropics is expected to increase. Therefore, reliable technologies that ensure enhanced production of food crops, such as maize, should be adopted to meet the increasing demand. Despite conventional breeding having contributed significantly toward maize production it is faced by many limitations such as time resources, low accuracy and limited genetic biodiversity. Biotechnology, that entails transformation of maize, demands an efficient and reproducible regeneration system from totipotent explants, in which immature zygotic embryos have mostly been used. However, one striking feature in all previous research is that callus induction and somatic embryogenesis is genotype dependent. The objective of this study was to develop an efficient and reproducible regeneration protocol for PH4 and DK 8031 maize genotypes cultivated at the coastal region of Kenya as a prerequisite for its improvement through genetic engineering technology using Agrobacterium tumefaciens mediated transformation. Immature embryos harvested at the age of 8 to 18 days after pollination were tested for their response to callus induction and regeneration efficiency using 2,4-D and dicamba as growth regulators. Through this research, a reproducible protocol for embryonic callus induction and regeneration of maize genotypes cultivated at the coastal region of Kenya was established. Enhanced capacity in tissue culture and genotypes of maize adapted to coastal conditions with excellent regeneration potentials has been released for incorporation in breeding programs. Minitab was used to calculate one way and two-way ANOVA to determine the influence of the age of immature embryo, growth regulator concentrations and genotypes on embryonic callus induction and regeneration frequency. To achieve genotype independent embryogenic callus induction, immature embryos of PH4 and DK 8031 should be harvested at 12 days after pollination. The optimum concentrations of growth regulators for callus induction is 3mg/l dicamba and 2mg/l 2,4-D. Immature embryos older than 12DAP can induce the same number of embryogenic calli obtained at 12DAP by increasing the concentrations of the growth regulator. Research findings in this study, revealed genotype independent embryogenesis on MS medium supplemented with 2, 4-D and dicamba. The younger the embryos (10-12 days after pollination) the less the hormone required for embryogenesis. Older embryos of PH4 (16-18DAP) require higher hormoneconcentration for embryogenesis. In this study, it is recommended that further research should be carried out on regeneration potential of other hybrid maize genotypes adapted to coastal regions of Kenya using other auxins such as picloram