Fusarium head blight (FHB), caused by Fusarium graminearum, is one of the most destructive wheat diseases worldwide. FHB infection can dramatically reduce grain yield and quality due to mycotoxins contamination. Wheat resistance to FHB is quantitatively inherited and many low-effect quantitative trait loci (QTL) have been mapped in the wheat genome. Synthetic hexaploid wheat (SHW) represents a novel source of FHB resistance derived from Aegilops tauschii and Triticum turgidum that can be transferred into common wheat (T. aestivum). In this study, a panel of 194 spring Synthetic Hexaploid Derived Wheat (SHDW) lines from the International Maize and Wheat Improvement Center (CIMMYT) was evaluated for FHB response under field conditions over three years (2017–2019). A significant phenotypic variation was found for disease incidence, severity, index, number of Fusarium Damaged Kernels (FDKs), and deoxynivalenol (DON) content. Further, 11 accessions displayed < 10 ppm DON in 2017 and 2019. Genotyping of the SHDW panel using a 90 K Single Nucleotide Polymorphism (SNP) chip array revealed 31 K polymorphic SNPs with a minor allele frequency (MAF) > 5%, which were used for a Genome-Wide Association Study (GWAS) of FHB resistance. A total of 52 significant marker-trait associations for FHB resistance were identified. These included 5 for DON content, 13 for the percentage of FDKs, 11 for the FHB index, 3 for disease incidence, and 20 for disease severity. A survey of genes associated with the markers identified 395 candidate genes that may be involved in FHB resistance. Collectively, our results strongly support the view that utilization of synthetic hexaploid wheat in wheat breeding would enhance diversity and introduce new sources of resistance against FHB into the common wheat gene pool. Further, validated SNP markers associated with FHB resistance may facilitate the screening of wheat populations for FHB resistance.
In September of 2008, a Septoria sp., the causal agent of Septoria leaf spot of pistachio (Pistacia vera L.) was isolated from leaf lesions in an orchard in southern New Mexico. Tree fruit and nut crops including pistachios are becoming an increasingly important part of New Mexico's agricultural industry with total cash receipts of $103 million in 2007 (3). This preliminary positive for Septoria prompted a survey of pistachio-growing counties in the state. The surveyed orchards accounted for approximately 30% of the pistachio acreage in New Mexico. Results indicated that all five pistachio-growing counties had orchards infected with a Septoria sp. Isolates of Septoria from leaf lesions were identified as Septoria pistaciarum Caracc. based on the following symptoms and morphological characteristics of the fungus: leaf lesions were usually circular, 0.5 to 3 mm in diameter, and contained many pycnidia per lesion; pycnidia were dark, ostiolate, and measured 101 to 255 × 69 to 133 μm; and conidia were hyaline, filiform, contained 3 to 9 septa, and measured 3 to 4 × 60 to 149 μm. Most orchards were only mildly affected. In severe cases, hundreds of leaf lesions were present on diseased leaves; large sections of the leaves turned tan and some trees defoliated prematurely. This widespread occurrence of Septoria leaf spot in New Mexico in 2008 suggests that the disease had already been present in the state for several years. A higher average rainfall in the summer of 2008 provided excellent conditions for disease development. Because of the high amounts of inoculum currently present in New Mexico orchards, Septoria leaf spot may emerge as a recurring disease problem for pistachio producers. This disease was first reported in the United States in Texas in 1971 and was also reported in Arizona in 1989 (1,2,4). To our knowledge, this is the first report of Septoria leaf spot of pistachio in New Mexico. References: (1) A. Chitzandis. Ann. Inst. Phytopathol. Benaki 10:29, 1956. (2) J. L. Maas et al. Plant Dis. Rep. 55:72, 1971. (3) New Mexico Agricultural Statistics, Department of Agriculture, 2007. (4) D. J. Young and T. Michailides. Plant Dis. 73:775, 1989.
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