| Late blight caused by the oomycete Phytophthora infestans (Mont.) de Bary is a disastrous disease on potato worldwide. The occurrence and epidemics of this disease are mainly dominated by the structure and variation of P. infestans population. Since the reports about occurrence and epidemics of potato late blight rapidly increased from 1980s, the concerning researches on late blight has been focusing on the population structure of the pathogen again in recent years. The present paper systematically revealed the genetic diversity of P. infestans in Fujian province, China, by analyzing the phenotypic and genotypic structure of 108 strains collected from 2001-2006 in Fujian province. The relative results derived from the work are of significance to the breeding for resistance to late blight, and the management of the disease.Main results were summarized as follows:1. The results from the metalaxyl-sensitivity test showed that, among 108 strains collected from Fujian province, the number of strains with resistance, intermediate resistance, and sensitive to metalaxyl were 103, 4, and 1, the frequency of strains with resistance, intermediate resistance, and sensitive to metalaxyl were 95.4%, 3.7%, and 0.9%, respectively. The results showed that strains collected from the different year in Fujian province were significant difference in their responses to metalaxyl.2. The results from the mating types test showed that, among 108 strains collected from Fujian province, the number of strains with Al mating type, A2 mating type, and not-known mating type were 101, 1, and 6, the frequency of strains with Al mating type, A2 mating type, and not-known mating type were 93.5%, 0.9% , and 5.6% , respectively. No self-fertility isolate was found. The results showed that there is sexual reproduction occurred in Fujian province, and the distribution of strains of mating types collected from the different areas were significant difference in Fujian province. 3. The results from the allozyme genotype for Gpi, Pep showed that, among 108 strains collected from Fujian province, four different Gpi, Pep genotypes could be distinguished in Fujian province. The frequency of four different Gpi, Pep genotypes with Gpi 100/100/111 Pep 100/100, Gpi 100/100 Pep 100/100, Gpi 100/111 Pep 100/100, Gpi 90/90 Pep 92/92 were 81.5%, 16.7%, 0.9% and 0.9%. The results showed strains with Gpi 100/100/111 Pep 100/100 have replaced the other allozyme genotypes, some new characteristics of allozyme genotype have emerged in the population.4. The results from mitochondria DNA (mtDNA) haplotype showed that, among 108 strains collected from Fujian province, there is three mtDNA haplotype Ib, IIa, IIb in Fujian province, not including mtDNA haplotype Ia. The number of strains with mtDNA haplotype Ib, IIa, IIb was 1, 4, 103, the frequency of strains mtDNA haplotype Ib, IIa, IIb were 0.9%, 3.7%, 95.4%. The results showed strains with mtDNA haplotype IIb have replaced the other mtDNA haplotypes, some new characteristics of mtDNA haplotype have emerged in the population.5. Genomic fingerprints of 63 strains of the pathogen Phytophthora infestans from different hosts were analyzed by using 12 RAPD primers selected from 150 random primers with abundant polymorphisms. Genomic DNA from different strains were amplified with the 12 selected primers and 92 marked bands were produced, of which 95 bands were polymorphic, accounting for 92.4% of the total bands produced. Based on the genetic distance, a dendrogram was constructed with the software NTSYSpc Version 2.1, and the 63 tested strains were divided into eleven genetic groups. Analysis showed that the genetic variation was very rich among the tested strains, some strains from one area were closely related to some strains from another area, but some isolae from a area were not closely related to some strains from same area, migration of the late blight fungus along with potato and potato might be a cause of this situation.The evidences from above results not only reflected that the phenotypic and genotypic structure of P. infestans population in Fujian province shared complex diversity, but also showed some typic characteristics including that A1 mating type and highly metalaxyl resistance are the dominated components of phenotypic structure, and mtDNA haplotype IIb and Gpi, Pep genotypes with Gpi 100/100/111 Pep 100/100 are new popular characters of genotypic structure, the genetic variation was very rich among the tested.
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