Abstract
Eighty-three isolates of Phytophthora infestans from The Netherlands have been selected for analysis of nuclear Feulgen-DNA (F-DNA) content, mating type and metalaxyl sensitivity. Twenty-eight were isolated prior to 1987, and the remaining 55 isolated during 1987. Seven of the 12 pre-1987 A2 mating type isolates were diploid, with the remaining five being either tetraploid or diploid-polyploid heterokaryons. Conversely of the sixteen pre-1987 A1 isolates, only five have been identified as being diploid. Two of the remaining eleven appeared to be triploid, eight tetraploid and one a diploid-polyploid heterokaryon. All sixteen of the A1 isolates selected for analysis were metalaxyl resistant, whereas only two of the A2 isolates were metalaxyl resistant. Of all pre-1987 A1 isolates, 101 were metalaxyl sensitive and 20 metalaxyl resistant, whereas only 2 of the thirteen A2 isolates were metalaxyl resistant. Sixteen of the 129 isolates analyzed from the 1987 population were mating type A2, 110 mating type A1, and 3 self fertile. Forty-five of the A1 mating type isolates and 10 of the A2 isolates were selected for DNA analysis. On the basis of DNA content it was determined that 38 of the A1 isolates were tetraploid, 5 triploid and 2 diploid. The distribution of ploidy values within the 1987 A2 population was 7 tetraploid, 1 triploid, and 2 diploid. Eighty-seven of the 1987 A1 isolates were metalaxyl sensitive and 23 resistant, whereas 13 of the A2 isolates were sensitive and 3 resistant.
Published Version
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