Effects of pre‐ and post‐inoculation photoperiod on the severity of Melampsora medusae leaf rust of Populus species

Abstract

Disease severity, based on six parameters (time from inoculation to flecking and eruption of uredinia, uredinial density and the amo'unts of urediniospoies produced), was assessed on leaf discs cut from four cultivars of Populus spp. raised with either a long (15 h) or a short {10^ h) photoperiod. The discs were inoculated with race 4 of Melampsora medusae and subsequently incubated with either a long (15 h) or a short (10 h) photoperiod. While disease severity, based OB most parameters, was lower in discs from the continuing long photoperiod (15 h pre-and 15 h post-inoculation) than from the continuing short photoperiod (10 h pre-and 10 li postinoculation), maximum severity was developed by discs given a combination of a short pre-and a long post-inoculation photoperiod. The relative contribution of the cultivar, the pre-and the post-inoculation photoperiod and their second-and third-order interactions to variation in disease severity depended on the parameter employed to assess severity. The parameters used are elements of disease monocycles and their possible significance in modelling epidemics is discussed.

Influence of clonal susceptibility, leaf age and inoculum density on infections by Melampsora larici‐populina races E1 and E3

“…The suspension of spores was sprayed uniformly on the leaf discs using an electric micronizer; after each inoculation the micronizer was washed with 95% ethanol and air dried. All the leaf discs were then incubated in a growth cabinet and received first a 64h dark period at 16 + 1°C followed by a photothermo period of 8h darkness at 16 + 1°C and 16 h light with intensity of 10000 lx, corresponding to 15 W/m^ (=60//E/mVs) with light tending to blue A = 475 (nm) at 23 ± 1°C (SINGH and HEATHER 1983;PINON and PEULON, 1988).…”