Development of leaf rust (Melampsora ciliata) in different species, hybrids
and cultivars of poplar (Populus spp.) was studied in nursery-grown plants
. Five different criteria were used to assess the disease development. The
mean disease index on 10 August was 9.4% which increased to 70.0% on 10 Oct
ober. The lowest disease index (5.5%) was recorded in P. yunnanensis wherea
s the maximum was recorded in P. x euramericana 'Rubra-Poiret' (59.5%). The
apparent infection rate per unit per day was highest in P. nigra x P. tric
hocarpa (9.7 x 10(-2)) whereas the minimum occurred in P. maximowiczii x P.
berolinsis 'Oxford' (3.3 x 10(-2)). The area under the disease progress cu
rve was a maximum in P. x euramericana 'Rubra-Poiret' (26.7) and a minimum
in P. yunnanensis (1.6). Complete defoliation by the first half of October
occurred in P. nigra x P. trichocarpa, which also had the maximum apparent
infection rate and area under the disease progress curve. Inoculum producti
on was highest in P. nigra x P. trichocarpa and lowest in P. maximowiczii x
P. berolinensis 'Oxford'.