Occurrence of new populations and mating types of Phytophthora infestans (Mont) de Bary in Serbia

Late blight disease caused by Phytophthora infestans is an important disease of potato and tomato in Serbia. The prevalence of late blight has increased in recent years similar to the situation in the rest of the world. During the 2001 and 2002 growing season late blight infected potato leaf samples were collected from the region of Guca, Serbia. P. infestans was isolated as pure cultures from diseased plant material by using several growing methods. Purified cultures were grown on rye A agar for further characterisation studies and storage in order to determine the structure of the Serbian P. infestans populations and to compare them with other European isolates. Mating types were determined from 48 isolates collected at 13 different potato fields in 2001. Four isolates were used as a control obtained from potato fields in 2002. Each isolate was paired on rye A agar with the known A1 (US-1) and A2 (US-8) test cultures. A PCR-RFLP method applying the two primer pairs PIMTP2R / PIMTP2F (P2) and PIMTP4R / PIMTP4F (P4) was used to identify mitochondrial DNA (mtDNA) haplotypes. Enzymatic digestion was performed using the restriction enzyme MspI for the P2 amplification product and EcoRI for the P4 product. From the restricted fragments the haplotypes can be differentiated. Our results showed that among the surveyed P. infestans isolates both mating types are present in Serbia. However, A1 mating type isolates were distributed at 11 locations whereas the A2 mating type was limited to two locations. All the isolates tested belong to the la haplotype, whereas haplotypes Ib, IIa and IIb, being rare in Europe, could not be detected in our survey. The data obtained in this study support the hypothesis that "new populations" of P. infestans do already exist in some Serbian areas