GENOME ORGANIZATION OF PHYTOPHTHORA-MEGASPERMA F-SP GLYCINEA

The genome organization of the soybean pathogenPhytophthora megasperma f.sp.glycinea (Pmg) was characterized. The GC content ofPmg nuclear DNA was estimated to be 48% by melting temperature analysis. DNA reassociation kinetics using S1 nuclease digestion were used to estimate the genome size. Assuming three sequence complexity classes, the haploid genome ofPmg was estimated to be 6.2 × 107 bp in size. The single-copy component was estimated to be 47% of the genome, with two repetitive classes composing 35 and 15%, and the foldback 3% of the genome. Genomic reconstruction hybridization was performed to confirm the genome size estimate. Two random single-copy sequences were cloned and mixed with the total genomic DNA at ratios corresponding to a range of possible genome sizes. The hybridization signals from the genomic DNA and cloned DNA were then compared. The results confirmed the estimate from reassociation analysis. © 1991 Academic Press, Inc.