Steps in Predicting the Relationship of Yield on Fungicide Dose

Abstract

A set of hypothetical steps has been defined, which links fungicide dose to marketable yield, whereby (i) increasing dose decreases symptom area, according to a dose-response curve, (ii) decreased symptom area increases crop green area index (GAI), (iii) increasing GAI increases fractional interception of photosynthetically active radiation, (iv) increased fractional interception increases crop dry matter accumulation, and (v) yield increases, depending on the partitioning of dry matter to the marketable fraction. One equation represented all five steps. By integrating this equation for light interception during the yield forming period and differentiating with respect to the ratio of fungicide cost over yield value, an analytical solution was obtained for the economic optimum dose. Taking published ranges of parameter values for the Septoria tritici wheat pathosystem as an example, yield-response curves and optimum doses were biologically plausible when compared with data from four field experiments. The analytical and empirical results imply that the dose required to optimize economic return will vary substantially between sites, seasons, and cultivars. Sensitivity analyses identified parameters describing specific facets of disease severity, fungicide efficacy, and assimilate partitioning as most influential in determining the dose optimum.

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

“…By contrast, under the relatively dull conditions of the United Kingdom, post-fl owering source and sink capacities of wheat seem to be in close balance (Beed et al, 2007). The effects of foliar disease on grain sink capacity are relatively small, whilst those on post-anthesis assimilation are large and thus for UK crops disease yieldloss relationships can be explained well in terms of post-anthesis assimilate availability (Paveley et al, 2001). The tolerance of these crops might therefore be improved by selection of traits that enhance post-anthesis radiation interception, RUE, or the utilisation of storage reserves in the presence of disease.…”

“…This can be summarised as follows: Y = Q * I * RUE * HI (7.1) Equation (7.1) has provided the conceptual framework for modelling the effects of pathogens and pests on crop growth and yield (Johnson, 1987;Waggoner, 1990;Rossing et al, 1992;Gaunt, 1995;Paveley et al, 2001;Bancal et al, 2007) and is a useful basis for identifying potential tolerance traits. Pathogen infection and subsequent disease can reduce yield through effects on radiation interception, RUE and dry mater partitioning to yield bearing structures, as illustrated in Figure 7.1.…”

“…Pathogen infection and subsequent disease can reduce yield through effects on radiation interception, RUE and dry mater partitioning to yield bearing structures, as illustrated in Figure 7.1. A more quantitative treatment of the relationships linking symptom area and yield is given by Gaunt (1995) and Paveley et al (2001). It follows, that tolerant genotypes will be those that possess traits that enable them to maintain high levels of PAR interception, RUE, and the formation of and partitioning of dry matter to yield bearing structures in spite of pathogen infection.…”

“…In other pathosystems, such as the wheat-Septoria tritci system, disease tends to develop late after canopy expansion has been completed and the stem carbohydrate reserves deposited. Its main effects are on the duration of the canopy post-fl owering and thus photosynthate supply for grain fi lling rather than the development of grain sink capacity (Paveley et al, 2001).…”

Changes in Gut Microbiota May Be Early Signs of Liver Toxicity Induced by Epoxiconazole in Rats

“…Epoxiconazole, a broad-spectrum azole fungicide, is widely used as antifungal in agriculture [12], where it is effective in preventing leaf blotch (Septoria tritici) [13] and rust (Puccinia triticina) in wheat [14], which ensues the possibility of human exposure due to the consumption of azole fungicide-contaminated food. Epoxiconazole may antagonize the androgen receptor and inhibit testosterone formation in vitro [15].…”