Size, shape and intensity of aggregation of take‐all disease during natural epidemics in second wheat crops

Abstract

Point pattern analysis (fitting of the beta‐binomial distribution and binary form of power law) was used to describe the spatial pattern of natural take‐all epidemics (caused by Gaeumannomyces graminis var. tritici) on a second consecutive crop of winter wheat in plots under different cropping practices that could have an impact on the quantity and spatial distribution of primary inoculum, and on the spread of the disease. The spatial pattern of take‐all was aggregated in 48% of the datasets when disease incidence was assessed at the plant level and in 83% when it was assessed at the root level. Clusters of diseased roots were in general less than 1 m in diameter for crown roots and 1–1·5 m for seminal roots; when present, clusters of diseased plants were 2–2·5 m in diameter. Anisotropy of the spatial pattern was detected and could be linked to soil cultivation. Clusters did not increase in size over the cropping season, but increased spatial heterogeneity of the disease level was observed, corresponding to local disease amplification within clusters. The relative influences of autonomous spread and inoculum dispersal on the size and shape of clusters are discussed.

Effect of host and inoculum patterns on take-all disease of wheat incidence, severity and disease gradient

“…The fact that the abscissa of the inflection point of the disease gradient was constant and the slope became steeper and steeper indicates that the epidemic spreads more by local intensification than extensification. This result seems in accordance with the almost constant size of disease foci observed in the field over one growing season (Gosme et al 2007). Contrary to what might have been expected, no effect of the sowing pattern on the disease gradient could be detected.…”

“…Such methods include soil cultivation (ploughing can bury the infected residues (Colbach 1994)). But tillage also influences the disease spatial structure (Gosme et al 2007), which might have an effect on the speed of the epidemics.…”

The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms

“…In general, soilborne pathogens tend to be more aggregated or clustered, compared to foliar pathogens. An aggregated distribution has been demonstrated with pathogens such as Phytophthora, Verticillium, Gaeumannomcyes, and Macrophomina (Ristaino et al 1993;Johnson et al 2006;Gosme et al 2007;Mihail and Alcorn 1987). These patterns are also more likely to be preserved from year to year.…”

Spatial distribution of Aphanomyces euteiches inoculum in a naturally infested pea field

“…For example, similar distributions have been observed for the wheat/ Gaeumannomyces graminis var. tritici (Gosme et al 2006) and pepper/Phytophthora capsici (Larkin et al 1995) pathosystems. The field studied here had not been sown with peas for at least 10 years.…”