HAPLO-DIPLOID GENE-EXPRESSION AND POLLEN SELECTION FOR TOLERANCE TO ACETOCHLOR IN MAIZE

The objectives of this research were to determine if genes controlling the reaction to the herbicide acetochlor in maize (Zea mays L.) are a ctive during both the haploid and the diploid phases of the life cycle and if pollen selection can be utilized for improving sporophytic res istance. Pollen of eight inbred lines, previously characterized throug h sporophytic analysis for the level of tolerance to acetochlor, showe d a differential reaction to the herbicide for in vitro tube length; m oreover, such pollen reactions proved to be significantly correlated ( r=0.786, df=6) with those of the sporophytes producing the pollen. Po llen analysis of two inbred lines (i.e. Mo17, tolerant, and B79, susce ptible) and their single cross showed that the in vitro pollen-tube le ngth reaction of the hybrid was intermediate between those of two pare nts. An experiment on pollen selection was then performed by growing t assels of Mo17xB79 in the presence of the herbicide. Pollen obtained f rom treated tassels showed a greater tolerance to acetochlor, assessed as in vitro tube length reaction, than pollen obtained from control t assels. Moreover, the backcross [B79 (Mo17xB79)] sporophytic populatio n obtained using pollen from the treated tassels was more tolerant (as indicated by the fresh weight of plants grown in the presence of the herbicide) than was the control backcross population. The two populati ons did not differ when grown without the herbicide. These findings in dicate that genes controlling the reaction to acetochlor in maize have haplodiploid expression; consequently, pollen selection can be applie d for improving plant tolerance.