Influence of crop growth and structure on the risk of epidemics by Mycosphaerella graminicola (Septoria tritici) in winter wheat

Abstract

Generally, it is recognized that inocula of Septoria tritici present on the basal leaves of winter wheat crops are spread towards the top of the canopy by splashy rainfall. This mechanism of inoculum dispersal is commonly accepted to be a key limit on disease progression. Therefore, attempts to forecast epidemics of S. tritici often quantify rainfall by some means, but largely ignore measurement of pathogen and host variables. In the present study, we show that new wheat leaves emerge initially at a height below established leaves that can contain sporulating lesions of S. tritici. This presents the possibility of horizontal inoculum transfer, even without splashy rainfall. The extent and duration of overlap between emergent and established leaves was found to differ considerably with cultivar and sowing date. Nitrogen application had little effect on overlap, because differences in crop phenology, e.g. leaf area and nodal length, were relative. However, estimates of raindrop penetration to the base of crop canopies suggested that vertical movement of inoculum is affected by nitrogen application. Crops receiving more nitrogen are denser, and therefore less rainfall reaches the base of the canopy. The interactions between crop and pathogen development are discussed with reference to the implications for predicting disease risk. In particular, cultivar traits that promote disease escape are quantified.

Weather Conditions Associated with the Release and Dispersal of Zymoseptoria tritici Spores in the Argentine Pampas Region

“…The magnitude of these observations enhances the coincidence of our results with those obtained by other authors [4,8,18,19,23,26,27,29,30].…”

“…The results of our work also highlight the importance of solar radiation and the intensity of the rain, besides the temperature and the relative humidity, cited by other authors [4,18,19], in the release and dispersal of pycnidiospores.…”

“…If all the parts of the trap are ready, in 8 hours per day, it is possible to assemble 10 samplers. This system of monitoring guaranteed to obtain comparable observations with those obtained by other authors [4,8,18,19,23,26,27,29,30] affirming its use at experimental level. In this work, we studied the weather variables associated with release and dispersal of the conidia and ascospores of the pathogen, both in the air and in the rainwater, under Buenos Aires province conditions.…”

“…The movement of this type of spores was characterized by a vertical direction from the basal leaves to the highest leaves in the canopy that occurred during periods of splash rain and a horizontal movement between leaves close to each other, occurring without highenergy rainfall. Both mechanisms are most probably critical to disease progression [4].…”

Recent Advances on Integrated Foliar Disease Management with Special Emphasis in Argentina Wheat Production

“…Considering the main foliar diseases in wheat during the last decade, 18 major genes conferring resistance to the pathogen have been identified for resistance to Septoria tritici. They were: Stb1 located on the chromosome 5BL [27], Stb2 on the chromosome 3BS [28], Stb3 on the chromosome 6DS [29], Stb4 on the chromosome 7DS [30]; Stb5 on the chromosome 7DS [31]; Stb6 on the chromosome 3AS [32]; Stb7 on the chromosome 4AL [33]; Stb8 on the chromosome 7BL [34]; Stb 9 on the chromosome 2B [35], Stb10 on the chromosome 1D [36]. Stb 11 on the chromosome 1BS [37], Stb12, on the chromosome 4AL [36], Stb13 on the chromosome 7BL [38], Stb14 on the chromosome 3BS [38], Stb15 on the chromosome 6AS [39], Stb16 on the chromosome 3D [40], Stb17 on the chromosome 5A [41] and Stb 18 on the chromosome 6DS [42].…”