Kdr. Wadia et Dr. Butler, INFECTION EFFICIENCY OF PHAEOISARIOPSIS-PERSONATA AND THE INFLUENCE OF DIFFERENT WETNESS PATTERNS ON GERM-TUBE GROWTH OF THE PATHOGEN, Plant Pathology, 43(5), 1994, pp. 802-812
Controlled environment studies with Phaeoisariopsis personata, the cau
sal agent of late leaf spot disease of groundnut (Avachis hypogaea), h
ave shown that infection is enhanced if leaves are exposed to alternat
e wet and dry periods (intermittent wetness) compared with continuous
wetness. Detailed investigations to elucidate this phenomenon revealed
more germ tubes per conidium and more branching of germ tubes with in
termittent wetness than with continuous wetness. With intermittent wet
ness there was clear evidence of tropic growth of germ tubes and branc
hes towards stomata and subsequent penetration. With continuous wetnes
s, germ tube growth did not appear to be directional and germ tubes co
mmonly passed over the stomatal guard cells, therefore leading to rela
tively few stomatal penetrations, For both wetness regimes, stomatal p
enetrations continued to increase with increased leaf wetness for at l
east 6 days after inoculation and there was a linear relationship betw
een the number of stomatal penetrations and the number of resultant le
sions. Infection efficiency was markedly increased when the spore load
was reduced to 0.1 conidia per cm(2) (about one spore per leaflet).