YIELD LOSSES DUE TO INBREEDING AND THE USE OF MOLECULAR MARKERS (RAPD) FOR ASSESSMENT OF GENETIC PURITY IN HYBRID CORN (Zea Mays L.)

Resumo

The production of hybrid corn (Zea mays L.) requires the complete removal of pollen of the female parent prior to pollination. The objectives of this study were to evaluate the percentage of female selfed plants that results in losses due to inbreeding and to assess the usefulness of RAPD approach in monitoring genetic purity of three kinds of commercial hybrid maize. Contamination levels of 0%, 1%, 2%, 3%, 4%, 5%, 6%, 8% and 10% in the female parent HS for seed production of hybrids BRS 201 and BRS 205 were used. In another trial, contamination levels of 0%, 1%, 3%, 5%, 8% and 10% were used in the BRS 3123 hybrid seeds. Contamination level was monitored leaving female plants without detasseling in the hybrid production field. Determination of cob appearance, kernel colour, grain and ear yield of these hybrids were carried out in the field, at maturity. DNA from F1-hybrids and their parents was employed to RAPD screening with 80 primers. The product was 456 bands, being 8 bands polymorphic. Field comparisons at maturity were generally more accurate at low levels of contamination. Yield losses increased with admixture levels; and it was up 27% for BRS 201, 8% for BRS 205 and 25% for BRS 3123. The primers, OPN-04 and OPR-19, were able to discriminate the contaminants among the pure seed hybrids and their parents. The RAPD procedure was able to detect polymorphism and contaminants in the seed lots, up to 3%. The results of this work indicate the practical usefulness of RAPD markers in monitoring purity tests and inbreed lines identification of commercial maize hybrids. Other advantages of the DNA approach included speed and the ability to determine the percentage of female self prior to harvest.