A survey for the self-fertile phenotype of Phytophthora infestans was
conducted during the 1999·2001 growing seasons. Blighted potato were sampled
from fields in different localities (EI-Rahmania, Housh Eissa, Kafr EI·Dawar, and Kafr
EI-Zayat) in EI·Behera Governorate and the surrounding area where isolates of . P.infestans were recovered. Out of 23 P.infestans isolates made in the first year
(1999), only one isolate was self·fertile (SF). In the second year (2000), one more SF
isolate was detected among 50 P.infestans isolates, while in the third year (2001 )
three isolates out of 172 were SF. That constituted 4.3%,2%, and 1.7% for the three
years of the study, respectively. Propagations made from single sporangia and single
hyphal tips of the recovered SF isolates segregated A 1, A2, and few SF colonies. This supported the view that self-fertility in P.infestans was a mixture of A 1 and
A2 mating types hyphae that interacted to form SF colonies and later segregated
where new strains of P.infestans could be evolved. The low frequency of the SF
isolates (2%) revealed in the present study with its high percentage of oospore
abortion (15.3%), low viability (2.4%), and germination (1.8%) may indicate that the
threat posed by the interaction between A 1 and A2 mating type isolates is real. The
potential for the time being could be undetectable. However, creation of new more
vigorous strains via this mechanism can not be excluded.