OCCURRENCE OF A2 MATING TYPE AND MICROMORPHOLOGY OF OOSPORES OF PHYTOPHTHORA INFESTANS IN GOLESTAN PROVINCE OF IRAN

Abstract

The aim of this study was to determine the mating types, origin and micromorphology of oospores of Ph. infestans isolated from the potato fields in Golestan province of Iran during 2014-16. In total, 197 isolates were assessed for mating type. The average frequencies of mating types A₁ and A₂ were 85.8 and 14.2% respectively. A₂ mating type was found only from two regions. A total of 9 self-fertile isolates (5.3%), which only belonged to the A₁ mating type were detected. The average value for oospore production index (OPI) within the interaction zone between the two isolates was estimated one (very low) in A₁×A₁ and four (very high) in A₁×A₂ crosses. Oospores of hybrid origin were observed in A₁ ×A₂ and self-fertile oospores only in A₁ ×A₁ paired cultures. Parthenogenetic oospores (without antheridia) were not observed in A₁ ×A₁ or A₂ ×A₂ paired cultures. The results of oospores micromorphology indicated that the antheridia in hybrid oospores were amphigynous and from half spheric to nearly spheric, almost hyaline, from 18.5-23.5 × 10.5-15.5 µm in size. Oogonia were nearly spheric from nacarat to brown in colour. The colour of the hybrid oospores varied from brown to dark-brown, spheric, varied from 25-35 µm in diameter with two thick walls with thickness of 2.5-5.5 µm. The self-fertile oospores were with a thin wall with thickness of 1.5 µm, spherical and varied from 40-60 µm in diameter. The monitoring of A₁ and A₂ mating type ratios of oospores are important to aid in the prediction of the extent of sexual recombination and thus the risk of long-lived oospores serving as primary inoculum sources in the main potato production regions.