11Fusarium head blight (FHB) or scab mainly caused by Fusarium asiaticum is a 12 devastating fungal disease in wheat. In China, carbendazim (MBC) and its mixture 13 with other fungicides are the main fungicides for controlling the disease. But resistant 14 populations have been developed seriously in the field. The fungicides for controlling 15 the disease are limited. So screening novel fungicides for controlling FHB is urgent. 16 The fungicide pydiflumetofen (development code number: 17 SYN545974),3-(Difluoromethyl)-N-methyl-N-[1-methyl-2-(2,4,6-trichlorophenyl)eth 18 yl]-1H-pyrazole-4-carboxami.d.e, is a novel succinate dehydrogenase inhibitor (SDHI) 19 that was developed by Syngenta. In the research, the baseline sensitivities for different 20 isolates of F.asiaticum from various regions of China to pydiflumetofen were 21 established. The 50% effective concentration (EC 50 ) value of pydiflumetofen on 22 suppressing mycelial growth against 116 isolates of F.asiaticum was 0.019 to 0.2084 23 μg/ml and their average value was 0.0745 ± 0.0367 μg/ml. The EC 50 value of 24 pydiflumetofen on suppressing conidium germination against 116 isolates of 25 F.asiaticum was 0.0583 to 0.4237 μg/ml and their average value was 0.1813 ± 0.0861 26 μg/ml. The results indicated that the fungicide had strong inhibition effect on mycelial 27 growth and conidium germination against F.asiaticum in vitro. The EC 50 values 28 distribution of 116 isolates measured by mycelial growth assay or by conidium 29 germination assay was a unimodal curve and could be used for detecting any 30 sensitivity changes of F. asiaticum populations to pydiflumetofen in the future. The 31results of cross-resistance analysis indicated that there was no positive or negative 32 cross-resistance between pydiflumetofen and carbendazim / phenamacril. In field 33 trials, though FHB incidence of control was very severe, pydiflumetofen at 125, 150 34 and 200 g ai ha -1 all provided more than 80% control efficacy which was significantly 35 higher than that of phenamacril at 375 g ai ha -1 or MBC at 600 g ai ha -1 in 2015 and 36 2016. In conclusion, pydiflumetofen had very high activity against F. asiaticum in 37 vitro and excellent efficacy for controlling FHB could also manage 38 carbendazim-resistant F.asiaticum populations in the field. 39
A screening of common wheat cultivars revealed that Triticum aestivum 'Thatcher' was resistant to Triticum isolates of Magnaporthe oryzae, whereas T. aestivum 'Chinese Spring' was susceptible. When F2 seedlings from a cross between 'Thatcher' and 'Chinese Spring' were inoculated with the Triticum isolates, resistant and susceptible seedlings segregated in a 15:1 ratio, suggesting that the resistance of 'Thatcher' was conditioned by two major genes. An inoculation test of 'Chinese Spring' substitution lines carrying individual chromosomes from 'Thatcher' indicated that these genes, designated Rmg2 and Rmg3, were located on chromosomes 7A and 6B.
The pathogenicity to wheat (Pwt1) locus conditions host species specificity of Magnaporthe oryzae on wheat. GFSI1-7-2 (Setaria isolate) carries the avirulence allele (PWT1) at this locus while Br48 (Triticum isolate) carries the virulence allele (pwt1). An F(1) culture derived from a cross between GFSI1-7-2 and Br48 was backcrossed with Br48 to produce a tester population in which PWT1 alone segregated. When hexaploid wheat lines were inoculated with the BC(1)F(1) testers, they were all resistant to all PWT1 carriers and susceptible to all pwt1 carriers, suggesting that they recognize PWT1. When barley cultivars were inoculated with the testers, they showed the same pattern of reactions as the hexaploid lines, suggesting that the barley cultivars also recognize PWT1. These results suggest that PWT1 is a fundamental gene that universally conditions the avirulence of Setaria isolates on two staple crops, hexaploid wheat and barley. Interestingly, tetraploid wheat lines did not recognize PWT1. Molecular mapping using the F(1) and BC(1)F(1) populations revealed that the Pwt1 locus is located on chromosome 2 and tightly linked to the ribosomal DNA locus and a telomere.
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