Microevolutionary trend in Pratylenchus coffeae sensu stricto (Nematoda: Pratylenchidae): The diversity in PCR-RFLP phenotype, compatibility on host plants and reproductive segregation

PCR-RFLP analyses, reproduction tests on sweet potato and taro, as well as inter-RFLP-phenotypic hybridization were performed using 20 isolates of Pratylenchus coffeae and two isolates of P. penetrans to identify relationships between these nematodes. F194 and F195 primers yielded rDNA ITS region amplification products of ca. 1,080 bp (Japanese and Indonesian isolates), and ca.1,020 bp (Guatemalan isolate) that were digested using Hinf I, Alu I, Dde I, and Hha I restriction endonucleases. There were four distinct DNA fragment patterns for isolates of P. coffeae that were designated to be RFLP phenotypes A, B, C and D. All the Japanese isolates corresponded to RFLP-phenotypes A, B or C. The Indonesian isolate was phenotype A and the Guatemalan isolate was phenotype D. The Pf/Pi ratios 55 days or 90 days after inoculation to sweet potato in a greenhouse experiment differed between phenotypes. Phenotype A isolates had the greatest Pf/Pi of 1.1 - 17.3. Phenotype B and C had values of 0.05 - 0.40 and 0.12 - 0.36 respectively. Reproduction on taro in a greenhouse experiment differed among phenotypes. Phenotypes A and B had greater reproduction (Pf/Pi>1) than did phenotypes C (Pf/Pi=0). Laboratory hybridization tests between phenotypes A * B, A * C, and B * C generated abundant F sub1 hybrids, though reciprocal breedings of A * D and A * P. penetrans failed to reproduce. Inbreedings of F sub1s obtained from A * C were rarely successful, those from A * B generated a few F sub2s in 1/3 of replications, and those from B * C generated F sub2s in 2/3 of replications, suggesting incomplete reproductive isolation among the three rDNA RFLP phenotypes of P. coffeae. The allopatric distribution accompanied by distinct host adaptation, thermal adaptation and incomplete reproductive isolation exemplify microevolution in the P. coffeae species complex. Jpn. J. Nematol. 33 (2), 57-76 (2003).