Quantitative relationships between inoculum of Melampsora larici‐epitea and corresponding disease on Salix

Abstract

Six Salix clones were inoculated with urediniospores of four isolates of Melampsora larici-epitea at five inoculum levels using a leaf-disc method. Disease reactions were recorded using a digital camera; the number and size of uredinia were examined using image analysis software; and spore yield per leaf disc was measured. In three Salix / Melampsora combinations, S. × mollissima 'Q83'/Q1 (LET4); S. viminalis '78183'/ V1 (LET1); and S. × stipularis / V1, pustule numbers increased as inoculum density became higher. In the remainder, S. viminalis 'Mullatin'/ V1; S. × calodendron /DB (LET3); and S. burjatica 'Korso'/ K (LR1), pustule numbers initially increased, then decreased as inoculum densities exceeded 140 -360 spores per disc. Calculated infection efficiency ranged from 0·11 to 0·20 on the three willows inoculated with V1: 0·16 -0·68 for S. × calodendron / DB; 0·20 -0·55 for 'Q83'/Q1; and 0·07 -0·48 for Korso / K. In single-spore inoculations, up to 10% of spores produced single uredinia. Infection efficiency increased sharply between inoculum densities of 1-40 spores per leaf disc. Spore yield was more closely correlated to pustule area (accounting for 61·2% variance for the combined data) than to the number of pustules (42·7% variance). For spore yields in relation to pustule numbers, clone-specific individual lines having different intercepts and slopes fitted significantly better than either a single line for all the tested willows, or parallel lines fitted to each clone ( P < 0·001). For spore yields in relation to pustule area, clonespecific individual parallel lines were significantly better than a single line ( P < 0·001).

Arabidopsis thaliana as a model for the study of plant–virus co-evolution

“…Analyses of a variety of wild host species, including A. thaliana, and a variety of pathogens, including fungi, oomycetes and bacteria, have been reported (e.g. Kaltz et al 1999;Kaltz & Shykoff 2002;Pei et al 2002;Thrall et al 2002;Laine 2005;Salvaudon et al 2005;Goss & Bergelson 2006;Sicard et al 2007), but we are not aware of similar studies with plant viruses. Genetic variation for resistance to viruses is well known to occur among genotypes of wild relatives of crops, which are important resources for breeding resistance to viruses into crop cultivars.…”

Rust resistance in Salix to Melampsora larici‐epitea

“…Recent study suggested that the number of spores applied can greatly influence the number of pustules produced in M. larici‐epitea (Pei et al ., 2002). In this study, disease was scored based on pustule area and inoculum density data according to the method described by Pei & Hunter (in press) using the following steps: (i) for each clone/isolate combination, a slope factor was calculated by dividing average square root pustule area per leaf disc by the square root of the inoculum density per leaf disc for the isolate; (ii) for each isolate, the clone which produced the largest pustule area (the most susceptible reaction) was chosen and the maximum slope factor was calculated by dividing its average square root of the pustule area by the square root of inoculum density (an average maximum slope factor, AMSF) was calculated by averaging the maximum slope factors for all the isolates); (iii) disease was scored for each clone/isolate combination using 0–4 scales.…”

Resistência de genótipos de videira à ferrugem

“…A densidade do inóculo pode interferir na severidade das ferrugens (Melching, 1981;Pei et al, 2002;Gilles & Kennedy, 2003); assim, o entendimento da relação entre densidade de inóculo e a intensidade da doença é importante em estudos de caracterização de resistência às ferrugens. Pelos mesmos motivos, deve ser conhecida a infl uência da idade da folha na severidade.…”