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The suppressive ability of several strains of cyclic lipopeptide-producing Bacillus rhizobacteria to grey leaf spot disease caused by Magnaporthe oryzae has been documented previously; however, the underlying mechanism(s) involved in the induced systemic resistance (ISR) activity in perennial ryegrass ( Lolium perenne L.) remains unknown. Root-drench application of solid-phase extraction ( SPE)-enriched surfactin and live cells of mutant Bacillus amyloliquefaciens strain FZB42-AK3 (produces surfactin, but not bacillomycin D and fengycin) significantly reduced disease incidence and severity on perennial ryegrass. The application of the treatments revealed a pronounced multilayered ISR defence response activation via timely and enhanced accumulation of hydrogen peroxide ( H2O2), elevated cell wall/apoplastic peroxidase activity, and deposition of callose and phenolic/polyphenolic compounds underneath the fungal appressoria in naïve leaves, which was significantly more intense in treated plants than in mock-treated controls. Moreover, a hypersensitive response ( HR)-type reaction and enhanced expression of LpPrx (Prx, peroxidase), LpOXO4 (OXO, oxalate oxidase), LpPAL (PAL, phenylalanine ammonia lyase), LpLOXa (LOX, lipoxygenase), LpTHb (putative defensin) and LpDEFa (DEFa, putative defensin) in perennial ryegrass were associated with SPE-enriched surfactin and live AK3 cell treatments, acting as a second layer of defence when pre-invasive defence responses failed. The results indicate that ISR activity following surfactin perception may sensitize H2O2-mediated defence responses, thereby providing perennial ryegrass with enhanced protection against M. oryzae. [ABSTRACT FROM AUTHOR]

Anthracnose disease of cool-season turfgrasses, caused by the fungus Colletotrichum cereale, has recently emerged as one of the most significant pathogens of Poa annua. Here we investigated the utility of four repetitive transposable elements as molecular markers for the analysis of C. cereale populations. Southern blot hybridization analysis revealed lineage-specific polymorphisms and distribution patterns for these transposons. Comparative phylogenetic analysis of three nonrepetitive protein coding DNA sequences against the transposon restriction fragment length polymorphisms indicated that the transposon sequences have similar evolutionary histories to those found in the sampled C. cereale population, despite the alteration of several transposon copies by repeat-induced point mutation. The variability and ubiquity of the Ccret2A15 transposon in C. cereale genomes suggest that this element could be used as a reliable DNA marker to discriminate between lineages of the fungus, identify hybrid genotypes, and analyze genetic diversity in populations of this turfgrass pathogen. [ABSTRACT FROM AUTHOR]

To date, managing salinity stress in agriculture relies heavily on development of salt tolerant plant varieties, a time-consuming process particularly challenging for many crops. Plant based biostimulants (PBs) that enhance plant defenses under stress can potentially address this drawback, as they are not crop specific and are easy to apply in the field. Unfortunately, limited knowledge about their modes of action makes it harder to utilize them on a broader scale. Understanding how PBs enhance plant defenses at cellular and molecular levels, is a prerequisite for the development of sustainable management practices utilizing biostimulants to improve crop health. In this study we elucidated the protective mechanism of copper chlorophyllin (Cu-chl), a PB, under salinity stress. Our results indicate that Cu-chl exerts protective effects primarily by decreasing oxidative stress through modulating cellular H2O2 levels. Cu-chl treated plants increased tolerance to oxidative stress imposed by an herbicide, methyl viologen dichloride hydrate as well, suggesting a protective role against various sources of reactive oxygen species (ROS). RNA-Seq analysis of Cu-chl treated Arabidopsis thaliana seedlings subjected to salt stress identified genes involved in ROS detoxification, and cellular growth. [ABSTRACT FROM AUTHOR]

Depletion of extractable silicon (Si) from surface soil depths has been observed in managed production systems. While not characterized as a plant essential nutrient, Si accrues in epidermal and vascular tissue of monocotyledonous plants. A field evaluation of granular Ca/Mg-rich liming agents was initiated on a creeping bentgrass (Agrostis stolonifera L. cv. Declaration) fairway in 2010. Excluding the control, treatments comprised 2440 kg (ha year)−1 topdressing of calcitic/dolomitic blended limestone or Ca/Mg-SiO3 in semi-annual or more frequent "split" applications. Each week of the 2011 and 2012 growing seasons, a dedicated wear simulator trafficked the fairway plots. Measures of canopy quality, clipping yield, tissue composition, soil pH, and plant-available soil Si levels were collected frequently. The described Ca/Mg-SiO3 annual topdressing rates correlated with acetic acid extractable Si levels >30 mg kg−1 in the 0- to 5-cm soil depth. Neither creeping bentgrass vigor, nutrition, nor leaf water content was influenced by significantly elevated levels of soil and tissue Si. Relative to non-trafficked plots, all split plots within trafficked main plots showed similarly reduced canopy quality regardless of topdressing treatment. If a critical threshold leaf Si concentration for creeping bentgrass wear tolerance enhancement exists, it is unlikely <11 g Si kg−1. [ABSTRACT FROM AUTHOR]

Proactive optimization of soil chemistry is a task commonly overlooked by agronomic practitioners. Agricultural field assessments have reported depletion of extractable soil silicon (Si) from shallow depths of intensively managed systems. While not recognized as a plant-essential nutrient, Si accumulates in epidermal and vascular tissue of grass leaves, sheaths, and shoots. A field study of Ca/Mg-silicate (SiO3) pelletized soil conditioner was initiated on a perennial ryegrass (Lolium perenne L. cvs. 1:1:1 Manhattan, Brightstar SLT, Mach 1) athletic field in 2010. Plots were trafficked by a wear simulator weekly, June through Sept. in 2011 and 2012. Canopy quality measures, clipping yield, tissue composition, soil pH, and plant-available soil Si levels were regularly collected over the two-year study. Under intense wear treatment (traffic), perennial ryegrass plots treated annually by granular application of 1220 or 2440 kg Ca/Mg-silicates per hectare showed significantly improved mean canopy density relative to plots receiving equal Ca and Mg as lime. These described Ca/Mg-SiO3 annual application rates coincided with acetic acid extractable soil Si levels > 70 mg kg−1 in the 0- to 8-cm soil depth. Experimental and temporal variability preclude reporting of a critical threshold concentration of leaf Si for improved perennial ryegrass wear tolerance. Future efforts towards this end should sample tissue of plots receiving wear treatment, rather than adjacent, non-worn proxies. [ABSTRACT FROM AUTHOR]