MOLECULAR AND MORPHOLOGICAL EVALUATION OF DOUBLED HAPLOID LINES IN MAIZE .1. HOMOGENEITY WITHIN DH LINES

The homogeneity of anther culture-derived lines of maize has been eval uated by means of field observations and molecular markers. The homoge neity of the doubled haploid (DH) lines was shown by the absence of se gregation for morphological oligogenic traits. The intravariance for p olygenic traits for 42 DH and two conventionally derived lines was sim ilar, which confirmed the homozygosity of the DH lines. More than 100 RFLP markers were tested on 189 DH lines derived from two crosses, DH5 x DH7 and A188 x DH7, and 60 single-seed descent (SSD, F6) lines deri ved from A188 x DH7. The overall rate of heterozygosity for all of the DH lines was approximatively 1% and pertained to 6 lines out of 189, while it was 8.5% for the SSD lines after four selfings. A precise des cription of the material used suggested that the events which led to t his unexpected heterozygozity in DH lines were more likely to have occ urred after rather than during the androgenetic process. Nine duplicat ed pairs of genotypes were found within the DH lines, indicating that a single microspore-derived structure can fragment to give two identic al plantlets. Despite the extensive screening with more than 100 marke rs, only 2 lines showed unexpected banding profiles, and these were pr obably gametoclonal variants. The use of a direct regeneration system that avoids any callus phase might explain this low frequency of gamet oclonal variation.