BACKCROSSING AND INTERMATING IN AN EXOTIC X ADAPTED CROSS OF MAIZE

Incorporation of exotic germplasm into the U,S. maize (Zea mays L,) ge rmplasm pool has often been proposed. Backcrossing and intermating wer e studied as techniques for incorporation of exotic germplasm using th e populations AS-A and MN-ETO. Three levels of backcrossing (0, 1, and 2 backcrosses) and cycles of intermating (1, 3, and 5 cycles) were ex amined in all combinations by extracting 100 random S-1 lines from eac h treatment for field evaluation. All lines were evaluated for eight t raits in six environments. Data for grain yield, grain harvest moistur e, lodging, plant height, ear height, number of days to 50% silk emerg ence, number of days to 50% pollen shed, and a selection index (SI) [S I = grain yield (kg ha(-1)) - 18.8 x harvest moisture (g kg(-1))] were analyzed. Analyses on trait means, genetic variances, correlated resp onses, selection differentials, and frequency distributions indicated that backcrossing generally shifted means and resulted in smaller gene tic variances. Phenotypic correlations were both increased and decreas ed depending on the comparison examined. Changes of selection differen tials of secondary traits were consistent with phenotypic correlations , The effect of backcrossing on the means of selected and unselected l ines was very similar, Many changes were maturity related. Intermating levels used had no detectable effect on the populations, Significant differences were found, but these were isolated and did not form trend s across intermating levels or backcross treatments, The results of th is study suggest that backcrossing is useful in the incorporation of e xotic germplasm, but results do not support the use of repeated interm ating.