Development of Melampsora ciliata rust on nursery-grown poplars in north-western Himalayas

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 October. The lowest disease index (5.5%) was recorded in P. yunnanensis whereas 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. trichocarpa (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 curve 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 production was highest in P. nigra x P. trichocarpa and lowest in P. maximowiczii x P. berolinensis 'Oxford'.