Here, multiple functions of jasmonic acid (JA) in maize (Zea mays) are revealed by comprehensive analyses of JA-deficient mutants of the two oxo-phytodienoate reductase genes, OPR7 and OPR8. Single mutants produce wild-type levels of JA in most tissues, but the double mutant opr7 opr8 has dramatically reduced JA in all organs tested. opr7 opr8 displayed strong developmental defects, including formation of a feminized tassel, initiation of female reproductive buds at each node, and extreme elongation of ear shanks; these defects were rescued by exogenous JA. These data provide evidence that JA is required for male sex determination and suppression of female reproductive organ biogenesis. Moreover, opr7 opr8 exhibited delayed leaf senescence accompanied by reduced ethylene and abscisic acid levels and lack of anthocyanin pigmentation of brace roots. Remarkably, opr7 opr8 is nonviable in nonsterile soil and under field conditions due to extreme susceptibility to a root-rotting oomycete (Pythium spp), demonstrating that these genes are necessary for maize survival in nature. Supporting the importance of JA in insect defense, opr7 opr8 is susceptible to beet armyworm. Overall, this study provides strong genetic evidence for the global roles of JA in maize development and immunity to pathogens and insects.

Annual decreases in soybean (Glycine max L. Merrill) yield caused by diseases were estimated by surveying university-affiliated plant pathologists in 28 soybean-producing states in the United States and in Ontario, Canada, from 2010 through 2014. Estimated yield losses from each disease varied greatly by state or province and year. Over the duration of this survey, soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) was estimated to have caused more than twice as much yield loss than any other disease. Seedling diseases (caused by various pathogens), charcoal rot (caused by Macrophomina phaseolina (Tassi) Goid), and sudden death syndrome (SDS) (caused by Fusarium virguliforme O’Donnell & T. Aoki) caused the next greatest estimated yield losses, in descending order. The estimated mean economic loss due to all soybean diseases, averaged across U.S. states and Ontario from 2010 to 2014, was $60.66 USD per acre. Results from this survey will provide scientists, breeders, governments, and educators with soybean yield-loss estimates to help inform and prioritize research, policy, and educational efforts in soybean pathology and disease management.

Transcription activator-like (TAL) effectors from Xanthomonas citri subsp. malvacearum (Xcm) are essential for bacterial blight of cotton (BBC). Here, by combining transcriptome profiling with TAL effector-binding element (EBE) prediction, we show that GhSWEET10, encoding a functional sucrose transporter, is induced by Avrb6, a TAL effector determining Xcm pathogenicity. Activation of GhSWEET10 by designer TAL effectors (dTALEs) restores virulence of Xcm avrb6 deletion strains, whereas silencing of GhSWEET10 compromises cotton susceptibility to infections. A BBC-resistant line carrying an unknown recessive b6 gene bears the same EBE as the susceptible line, but Avrb6-mediated induction of GhSWEET10 is reduced, suggesting a unique mechanism underlying b6-mediated resistance. We show via an extensive survey of GhSWEET transcriptional responsiveness to different Xcm field isolates that additional GhSWEETs may also be involved in BBC. These findings advance our understanding of the disease and resistance in cotton and may facilitate the development cotton with improved resistance to BBC.

Annual decreases in corn yield caused by diseases were estimated by surveying members of the Corn Disease Working Group in 22 corn-producing states in the United States and in Ontario, Canada, from 2012 through 2015. Estimated loss from each disease varied greatly by state and year. In general, foliar diseases such as northern corn leaf blight, gray leaf spot, and Goss's wilt commonly caused the largest estimated yield loss in the northern United States and Ontario during non-drought years. Fusarium stalk rot and plant-parasitic nematodes caused the most estimated loss in the southern-most United States. The estimated mean economic loss due to yield loss by corn diseases in the United States and Ontario from 2012 to 2015 was $76.51 USD per acre. The cost of disease-mitigating strategies is another potential source of profit loss. Results from this survey will provide scientists, breeders, government, and educators with data to help inform and prioritize research, policy, and educational efforts in corn pathology and disease management. Accepted for publication 26 August 2016.

Plant and fungal lipoxygenases catalyze the oxidation of polyunsaturated fatty acids, creating fatty acid hydroperoxides (oxylipins). Fungal oxylipins are required for normal fungal development and secondary metabolism, and plant host-derived oxylipins interfere with these processes in fungi, presumably by signal mimicry. The maize lipoxygenase gene ZmLOX3 has been implicated previously in seed-Aspergillus interactions, so we tested the interactions of a mutant maize line (lox3–4, in which ZmLOX3 is disrupted) with the mycotoxigenic seed-infecting fungi Aspergillus flavus and Aspergillus nidulans. The lox3–4 mutant was more susceptible than wild type maize to both Aspergillus species. All strains of A. flavus and A. nidulans produced more conidia and aflatoxin (or the precursor sterigmatocystin) on lox3–4 kernels than on wild type kernels, in vitro and under field conditions. Although oxylipins did not differ detectably between A. flavus-infected kernels of the lox3–4 and WT maize, oxylipin precursors (free fatty acids) and a downstream metabolite (jasmonic acid) accumulated to greater levels in lox3–4 than in WT kernels. The increased resistance of the lox3–4 mutant to other fungal pathogens (Fusarium, Colletotrichum, Cochliobolus, and Exserohilum) is in sharp contrast with results described herein for Aspergillus, suggesting that outcomes of lipoxygenase-governed host-pathogen interactions are pathogen-specific.