Protective effects of a wheat cultivar mixture against splash‐dispersed septoria tritici blotch epidemics

Abstract

The use of cultivar mixtures to control foliar fungal diseases is well documented for windborne diseases, but remains controversial for splash-dispersed diseases. To try to improve this strategy, a cultivar mixture was designed consisting of two wheat cultivars with contrasted resistance to Mycosphaerella graminicola, responsible for the rainborne disease septoria tritici blotch (STB), in a 1:3 susceptible:resistant ratio rather than the 1:1 ratio commonly used in previous studies. The impact of natural STB epidemics in this cultivar mixture was studied in field experiments over 4 years. Weekly assessments of the number of sporulating lesions, pycnidial leaf area and green leaf area were carried out on the susceptible cultivar. In years with sufficient STB pressure, disease impacts on the susceptible cultivar in the mixture were always significantly lower than in the pure stand (e.g. 42% reduction of pycnidial leaf area for the three upper leaves in 2008 and 41% in 2009). In years with low STB pressure (2010 and 2011), a reduction of disease impacts was also shown but was not always significant. After major rainfall events, the number of sporulating lesions observed on the susceptible cultivar after one latent period was reduced on average by 45% in the mixture compared to the pure stand. All the measurements showed that a susceptible cultivar was consistently protected, at least moderately, in a mixture under low to moderate STB pressure. Therefore, the results prove that the design of an efficient cultivar mixture can include the control of STB, among other foliar diseases.

Edge effect: Liquid sheet and droplets formed by drop impact close to an edge

“…Current mitigation techniques of foliar diseases, such as the intensive use of chemicals or genetically modified organisms, can be complemented by polyculture [13,75,76] or integrated culture [77]. Our work has shown how both impact speed and distance from an edge shape the statistics of ejected droplets upon raindrop impact.…”

“…Rain was found to be correlated with the dispersal of foliar diseases such as Septoria leaf blotch and Fusarium head blight, affecting wheat and rice, respectively [8][9][10]. Prior studies mainly focused on dispersal statistics collected at the level of crop fields or parcels [9,[11][12][13]. Investigations at the level of leaf and plant remain scarce [11,[14][15][16].…”

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

“…In most cases, STB severity in cultivar mixtures is moderately reduced compared to the expectation based on the severity in the pure stands, although Cowger & Mundt (2002) did not observe a consistent pattern. In particular, Gigot et al (2013) found that a susceptible cultivar was consistently protected in a mixture under low to moderate STB levels. Subsequent greenhouse experimentation (Vidal et al, 2017) and a modelling study (Vidal et al, 2018) have demonstrated the importance of canopy structure for the efficacy of a mixture.…”

“…Cultivar mixtures suppress the development of disease epidemics when the mixture components have contrasting levels of resistance to the targeted disease (Wolfe, 1985;Finckh & Wolfe, 2006;Gigot et al, 2013). Consequently, most studies investigated mixtures of disease-susceptible and diseaseresistant cultivars (cf.…”

“…However, this situation may improve with the recent studies on Ethiopian durum wheat landraces (Kidane et al, 2017), Tunisian landraces (Aouini, 2018), and the publication of the fully assembled durum wheat genome (Maccaferri et al, 2019). Karisto, Fakhfakh, Cultivar mixtures for STB control Kouki, Mikaberidze, Yahyaoui Similarly, cultivar mixtures for controlling STB have been studied in bread wheat but not in durum wheat (Mundt et al, 1995;Mille & Jouan, 1997;Cowger & Mundt, 2002;Mille et al, 2006;Gigot et al, 2013;Vidal et al, 2017). In most cases, STB severity in cultivar mixtures is moderately reduced compared to the expectation based on the severity in the pure stands, although Cowger & Mundt (2002) did not observe a consistent pattern.…”