EVIDENCE FOR REDUCED SEXUAL REPRODUCTION OF ZYMOSEPTORIA TRITICI FOLLOWING TREATMENT WITH FLUXAPYROXAD AND IMPLICATIONS FOR INITIAL INFECTION OF WHEAT CROPS.

Zymoseptoria tritici (previously Mycosphaerella graminicola) is the causal agent of septoria tritici leaf blotch (STB), a globally important fungal disease of bread, feed and durum wheat. Airborne ascospores originating from over-winter crop residues are considered to be the primary source of initial infection. The active ingredient fluxapyroxad (BASF) belongs to the chemical group of carboxamides and is a succinate dehydrogenase inhibitor (SDHI) fungicide. Fluxapyroxad has strong efficacy against the key foliar diseases of winter wheat: STB, yellow rust and brown rust. The objective of the study was to test the effects of foliar applications of fluxapyroxad on the life cycle components of Z. tritici. We report here the effects of foliar applications of fluxapyroxad on initial inoculum and subsequent effects on disease level in the following crop. A large-plot field experiment was carried out in Herefordshire, UK, during 2010-2011. Fluxapyroxad was applied at conventional timings (Zadoks scale at z.32 and z.39, decimal growth stages GS32 and GS39) as a solo product and in co-formulation with epoxiconazole, and was evaluated by comparison with epoxiconazole and an untreated control for its effects on late season STB. Autumn ascospore release was measured in field plots using volumetric spore traps. A second wheat crop was established in the following year (2011-2012) using minimum tillage cultivation techniques, so that crop residues from the previous crop remained exposed. The second wheat crop was not treated with fungicide. The original plot boundaries from the preceding year were located and each plot was monitored for STB. A significant positive relationship was found between late season septoria leaf blotch severity and the mean number of ascospores released from over-winter crop residues. Foliar applications of fluxapyroxad reduced the number of ascospores released and this reduction correlated positively with pre-stem extension (z.31) STB severity in the following crop. A second field experiment was conducted in 2012 in which similar treatments were applied. After harvest crop residues (stems and leaves) were collected from the plots and stored over winter under ambient conditions. Ascospores were harvested onto agar plates following induced spore release in the laboratory. Reductions in ascospore release following foliar application of fluxapyroxad were confirmed. Furthermore, ascospores produced from crop residues from treated plots showed a reduction in length and rate of germination when compared with ascospores from untreated plots, which could indicate a potential fitness cost. This evidence indicates that applications of fluxapyroxad could reduce the risk of STB in following wheat crops in the same field. Applications to fields at a regional scale may reduce primary infections of newly emerging wheat crops over a wide area.

Quantifying the non-fungicidal effects of foliar applications of fluxapyroxad (Xemium) on stomatal conductance, water use efficiency and yield in winter wheat.

The active ingredient fluxapyroxad belongs to the chemical group of carboxamides and is a new generation succinate dehydrogenase inhibitor (SDHI) in complex II of the mitochondrial respiratory chain. It has strong efficacy against the key foliar diseases of winter wheat in the UK: Septoria leaf blotch, yellow stripe rust and brown rust. Fluxapyroxad is marketed under the brand name of Xemium, was launched in 2012 and is available in the UK as a solo product (Imtrex) for co-application with triazoles, in co-formulation with epoxiconazole (Adexar), or in a three way formulation with epoxiconazole and pyraclostrobin (Ceriax). The objective of the study was to quantify the direct effects of Xemium on stomatal conductance and yield, mediated through stimulation of host physiology. Three field experiments and two controlled environment (CE) experiments were conducted across three cropping seasons (2010-2012) in Herefordshire and Cambridge, in the UK. Xemium was evaluated against boscalid, pyraclostrobin (F500), epoxiconazole and an untreated control. Across site-seasons, disease severity was significantly reduced when Xemium was applied as a foliar spray. Healthy canopy size and duration was increased by Xemium and canopy greening effects were seen shortly after application. Stomatal conductance was found to be consistently lower in Xemium treated plants but reduced stomatal opening was not found to be detrimental to yield in these experiments. Large, beneficial effects of Xemium on water use efficiency were found at the canopy level and this finding was supported by measurements of instantaneous water use efficiency at the leaf level. Effects on season long water use efficiency were largely driven by improvements in yield for a given amount of water uptake. Foliar applications of Xemium reduced the water required to produce 1.0 t grain per hectare by 82,330 L(82 t) when compared with an untreated crop. Yield was significantly higher in Xemium treatments and this was achieved primarily through increases in grains ear. Evidence is presented hereto show that in addition to controlling visible disease symptoms, Xemium is able to exert positive physiological effects on the host. The yield increase from plots treated with Xemium applied at standard commercial timings was shown to exceed that which can be explained solely through good disease control and the associated loss of healthy canopy area. Approximately 1.0 t ha(-1) (12%) yield was produced by Xemium treatments which could not be accounted for through the control of visible disease symptoms.