The interaction of fertiliser treatment with tolerance to powdery mildew in spring barley

Crop Tolerance of Foliar Pathogens: Possible Mechanisms and Potential for Exploitation

“…More commonly, tolerance has been defi ned in terms of the ability to maintain an acceptable seed yield, or some other measure of plant fi tness or productivity, under a given severity of pathogen infection, thus distinguishing it from resistance (Caldwell et al, 1958;Schafer, 1971). A further distinction has been made between tolerance of the pathogen and tolerance of disease (Gaunt, 1981;Clarke, 1984;Newton et al, 1998;Inglese & Paul, 2006). According to Inglese & Paul (2006) tolerance of infection is the relationship between the presence of the pathogen and disruption of normal host physiology, whereas tolerance of disease is the relationship between host growth or fi tness and the physiological disruption resulting from infection.…”

“…The most common measurement of infection severity is the area under disease progress curve (AUDPC) which provides a measure of lesion area integrated over time (Kramer et al, 1980;Inglese & Paul, 2006). Newton et al (1998) used a variation of this approach to determine the relative tolerance of powdery mildew amongst spring barley genotypes. The yield loss of a genotype in response to disease was plotted against its AUDPC and a common relationship for all genotypes fi tted by linear regression (Figure 7.2).…”

“…Thus, the relative tolerance of spring barley cultivars to leaf rust measured in a two-year study differed between years (Kramer et al, 1980). Similarly, spring barley genotypes designated as tolerant of powdery mildew infection varied between years and fertilizer N treatments (Newton et al, 1998(Newton et al, , 2000. Part of the variation may arise from the practice of estimating AUDPC in terms of the percentage leaf area occupied by visible disease symptoms scored on a whole plant basis, rather than absolute area, as it provides no indication of the reduction in potential radiation interception resulting from infection.…”

“…In principle, tolerance can be quantifi ed from the relationship between fungal biomass (or a surrogate measure such as the quantity of DNA) and yield (Newton et al, 1998). However, tolerant genotypes identifi ed from estimates of fungal biomass do not necessarily correspond to those identifi ed from measurements of visible symptom area (Newton et al, 1998), which may refl ect genotypic variation in the relationship between the amount of fungal biomass in the tissue, the extent of symptom development and the disruption caused to host physiology.…”

“…However, tolerant genotypes identifi ed from estimates of fungal biomass do not necessarily correspond to those identifi ed from measurements of visible symptom area (Newton et al, 1998), which may refl ect genotypic variation in the relationship between the amount of fungal biomass in the tissue, the extent of symptom development and the disruption caused to host physiology. Consequently, when selecting a technique for quantifying tolerance it is important to be aware of what is actually being measured and the mechanisms through which the measured variable might impact on yield.…”