Is the onset of septoria tritici blotch epidemics related to the local pool of ascospores?

Abstract

To elucidate the early epidemic stages of septoria tritici blotch, especially the relationship between the onset of epidemics, the local availability of primary inoculum, and the presence of wheat debris, the early disease dynamics and airborne concentration in Zymoseptoria tritici ascospores were concomitantly assessed at a small spatiotemporal scale and over two years, using spore traps coupled with a qPCR assay. One plot, with the crop debris left, provided a local source of primary inoculum, while the other plot, without debris, lacked any. According to the assay's limits of detection, daily spore trap samples were classified as not detectable or not quantifiable, detectable, and quantifiable. The proportions of samples assigned to the different classes and numbers of spores in samples classified as quantifiable were significantly different between years, time periods (from November to March) and spore trap location (field with or without debris). The effect of year on the airborne ascospore concentration was high: 22 daily peaks with more than 230 ascospores m−3 day−1 were identified in the autumn of 2012/13, but none in the autumn of 2011/12. The local presence of wheat debris had no obvious effect on the amount of airborne ascospores or on the earliness of the two epidemics, especially in the year with high inoculum pressure (2012/13). These results suggest that the amount of primary airborne inoculum available in a wheat crop is not a limiting factor for the onset of an epidemic.

Seasonal Changes Drive Short-Term Selection for Fitness Traits in the Wheat Pathogen Zymoseptoria tritici

“…Fifteen isolates representative of the initial population (Pi) was sampled by destructive harvesting (five plants randomly collected in five 1-m 2 quadrats per plot, located 20 m away from each other) at the beginning of the epidemic, in late autumn (from 24 November to 8 December 2009), from the first 15 lesions detected on the first leaves of seedlings. The first contaminations probably occurred in late October as soon as the first wheat leaves emerged and originated exclusively from wind-dispersed ascospores of distant origin, because no wheat residues were present in the field (23,24). Fifteen isolates representative of the final population (Pf) was sampled at the end of the epidemic, in early summer (12 July 2010), from the first 15 lesions found on either the antepenultimate (F3) or penultimate (F2) leaf of the main tiller.…”

Assessment of molecular detection of Fusarium circinatum in insects and passive spore traps in Pinus radiata plantations

“…It was decided to assess the trapping frequencies, because it is an appropriate measurement for the analysis of the spatial distribution of spore depositions within stands (Garbelotto et al, 2007). Moreover, previous experience using paper filter spore traps has shown that qPCR Ct values can be below the detection limit of the assays (Aguayo et al, 2018;Fourie et al, 2014), which means that the pathogen is present in the samples, but not at quantifiable concentrations (Grosdidier et al, 2017;Morais, Sache, Suffert, & Laval, 2016). In these cases, it is better to class these samples into a "detectable but not quantifiable class," as suggested by Morais et al (2016).…”

“…Moreover, previous experience using paper filter spore traps has shown that qPCR Ct values can be below the detection limit of the assays (Aguayo et al, 2018;Fourie et al, 2014), which means that the pathogen is present in the samples, but not at quantifiable concentrations (Grosdidier et al, 2017;Morais, Sache, Suffert, & Laval, 2016). In these cases, it is better to class these samples into a "detectable but not quantifiable class," as suggested by Morais et al (2016). In our study, if one of the spore traps or one batch of insects was positive, the trap by location was considered positive.…”

Improved control of Septoria tritici blotch in durum wheat using cultivar mixtures

“…Within necrotic lesions, the fungus begins to reproduce asexually and later sexually (Eyal et al 1987;Eyal 1999;Ponomarenko et al, 2011). Airborne ascospores typically constitute the primary inoculum released from wheat debris (Suffert & Sache, 2011;Morais et al, 2016). Pycnidiospores are splash-dispersed and are transmitted more locally infecting nearby plants.…”