EFFECT OF POLLEN SELECTION FOR ALACHLOR TOLERANCE IN MAIZE

Pollen selection can lead to correlated responses in the subsequent sp orophytes because many genes are expressed in both haploid and diploid phases. This study was conducted to evaluate the effects of pollen se lection for tolerance to the herbicide alachlor [2-chloro-N-(2,6-dieth ylphenyl)-N-(methoxymethyl) acetamide] in maize (Zen mays L.). Tassels of the single cross hybrid K55 (tolerant) x Ky226 (susceptible) were grown in absence (control) and in presence (selected) of alachlor (1 g L(-1)). Mature pollen from this process was used to make backcrosses to Ky226 (susceptibility being recessive). The selected population out performed the control population (88 vs. 81%; P less than or equal to 0.01) for percentage of normal seedlings (i.e., not injured by alachlo r) when compared in a held trial treated with the herbicide (5 kg a.i. ha(-1)). Pollen of plants grown without alachlor was analyzed in vitr o; in presence of the herbicide in the medium (50 mg L(-1)) the select ed population exceeded the control population for pollen tube length ( 334 vs. 308 mu m; P less than or equal to 0.01). Two cycles of pollen selection were also conducted in the single cross hybrid K55 x H99 (su sceptible) following the backcross procedure to the susceptible parent . Seeds of control and selected populations were exposed to alachlor ( 1 g L(-1)), and seedlings were grown in the greenhouse. For percentage of normal seedlings, we obtained a gain (16%) in the first cycle and an additional gain (10%) in the second cycle. The results indicate tha t genes controlling alachlor tolerance in maize are expressed in both haploid and diploid phases and that pollen selection can be effectivel y applied to improve the trait.