Reciprocal effects of silicon supply and endophytes on silicon accumulation and Epichloë colonization in grasses

Cool season grasses associate asymptomatically with foliar Epichloë endophytic fungi in a symbiosis where Epichloë spp. protects the plant from a number of biotic and abiotic stresses. Furthermore, many grass species can accumulate large quantities of silicon (Si), which also alleviates a similar range of stresses. While Epichloë endophytes may improve uptake of minerals and nutrients, their impact on Si is largely unknown. Likewise, the effect of Si availability on Epichloë colonization remains untested. To assess the bidirectional relationship, we grew tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne) hydroponically with or without Si. Grasses were associated with five different Epichloë endophyte strains [tall fescue: AR584 or wild type (WT); perennial ryegrass: AR37, AR1, or WT] or as Epichloë-free controls. Reciprocally beneficial effects were observed for tall fescue associations. Specifically, Epichloë presence increased Si concentration in the foliage of tall fescue by at least 31%, regardless of endophyte strain. In perennial ryegrass, an increase in foliar Si was observed only for plants associated with the AR37. Epichloë promotion of Si was (i) independent of responses in plant growth, and (ii) positively correlated with endophyte colonization, which lends support to an endophyte effect independent of their impacts on root growth. Moreover, Epichloë colonization in tall fescue increased by more than 60% in the presence of silicon; however, this was not observed in perennial ryegrass. The reciprocal benefits of Epichloë-endophytes and foliar Si accumulation reported here, especially for tall fescue, might further increase grass tolerance to stress

Silicon and Epichloë-endophyte defences in a model temperate grass diminish feeding efficiency and immunity of an insect folivore

Plants deploy diverse anti-herbivore defences which reduce feeding and performance of herbivores. Temperate grasses use silicon (Si) accumulation and Epichloë-endophytes for physical and chemical (i.e. endophytic-alkaloids) defence against insect herbivores. Recent studies suggest that Epichloë-endophytes increase Si accumulation in their host grass. It is unknown, however, how this affects Si-deposition on the leaf surface, their impacts on insect herbivore feeding efficiency and their immunity to potential infection/parasitism. To address this knowledge gap, we grew tall fescue (Festuca arundinacea) hydroponically with and without Si, in the absence or presence of the novel AR584 Epichloë-strain. We exposed plants to Helicoverpa armigera (Lepidoptera: Noctuidae) in both in situ (intact leaves) and ex situ (excised leaves) feeding trials and determined the effects of Si and endophyte defences on herbivore feeding efficiency, growth rates and immunity against potential infection/parasitism. Endophytic plants supplied with Si showed 110% and 143% increases in leaf silica density and leaf Si concentrations, respectively, when exposed to herbivory, compared to non-endophytic plants that were herbivore-free. Despite the endophyte-mediated increases in Si concentrations, H. armigera was only affected by Si supply; growth rates decreased by 87% and most feeding efficiency indices decreased by at least 30%. Si supply also increased mandibular wear by 16%, which was negatively correlated with H. armigera growth rates. Cellular and humoral immunity of H. armigera were negatively affected by both Si and endophytes. Endophytic-loline alkaloid concentrations were unaffected by Si supply or herbivory, whereas herbivory increased peramine concentrations by 290%. To our knowledge, this is the first report of Si defences and Epichloë-endophyte derived alkaloids compromising insect immunity via reduced melanisation response. Using tall fescue and H. armigera, our study suggests that deploying both physical (i.e. Si accumulation) and chemical (i.e. endophytic-alkaloids) defences acting against multiple insect herbivore traits, including feeding efficiency, growth and immunity, may be a successful defence strategy in temperate grasses. This multi-faceted defence may be particularly difficult for insect herbivores to overcome. Read the free Plain Language Summary for this article on the Journal blog

ISOCAS: la importancia de conocer su biología para optimizar su manejo.

El conocimiento de la biología de las isocas es una herramienta de gran valor para evitar o atender a tiempo los problemas causados por estos insectos en pasturas y cultivos. El presente artículo aborda en forma ilustrativa los principales aspectos de su biología, daños y manejos agronómicos recomendados

Protección de pasturas durante la implantación.

Una buena implantación es el cimiento para pasturas de alta productividad. Este artículo trata sobre cómoproteger a las pasturas, durante su fase inicial, de enfermedades,plagas y malezas.Los tres primeros meses pos-siembra son críticos para el establecimiento de pasturas productivas. Todas lasprácticas de manejo que contribuyan a una rápida germinación y un vigoroso establecimiento de plántulascontribuyen ,también, a minimizar la incidencia de enfermedades,plagas y malezas. Un buen barbecho dela chacra, alta calidad de semilla, siembra en fechas óptimas y a densidades correctas, fertilización apropiaday regulación de la sembradora en función de la cama de siembra, juegan un rol fundamental para potenciar elresultado de cualquier medida de protección vegetal

Aspectos biológicos y daño de la pulguilla de la alfalfa (Sminthurus viridis) en Uruguay.

- La pulguilla de la alfalfa provoca daño en otoño y primavera,principalmente en leguminosas forrajeras.- Se identifica por su forma globosa (1,5-2 mm) y por saltar al ser perturbada- El daño es fácil de reconocer ya que las hojas quedan transparentes (rae la epidermis).- El manejo se basa inicialmente en pastorear o cortar la pastura dañada, y revisar luego de 7 días. - Los insecticidas solo se utilizan en casos de daño severo y persistente.CONSIDERACIONES FINALESAntes de recurrir al control químico se debe realizar la correcta identificación del daño y del agente causaldel mismo, pues no todos los insectos que habitan nuestras pasturas causan daños. La pasturadebe ser monitoreada periódicamente.El objetivo de un programa de manejo integrado (MIP) es reducir el daño causado por una plaga a nivelestolerables, para sostener el equilibrio del ecosistema se debe permitir ciertos niveles de daño.Se recomienda consultar a su técnico de campo antes de considerar un manejo químico y considerarestrategias de control cultural. El uso indiscriminado de insecticidas tiene consecuencias directas en elsistema ecológico del pastizal

Biología y manejo del 'bicho bolita' (bicho de la humedad).

- En condiciones de siembra directa, los isópodos son potencialmente un problema- Presentan hábitos nocturnos - - Debido a su habilidad de enrollarse son fácilmente identificables - Pueden consumir el 10 % de residuos- Viven aproximadamente 3-4 años- Tienen preferencia por leguminosas, consumiendo cotiledones, inclusive semillas- Período crítico: implantación- Período crítico en soja, desde el día 2 hasta el día 12 después de la siembra- Se recomienda el monitoreo de la chacra previo a la siembra, para ello es necesario la inspección del rastrojo en distintas zonas de la chacr

Short-term exposure to silicon rapidly enhances plant resistance to herbivory.

Abstract: Silicon (Si) can adversely affect insect herbivores, particularly in plants that evolved the ability to accumulate large quantities of Si. Very rapid herbivore-induced accumulation of Si has recently been demonstrated, but the level of protection against herbivory this affords plants remains unknown. Brachypodium distachyon, a model Si hyperaccumulating grass, was exposed to the chewing herbivore, Helicoverpa armigera, and grown under threeconditions: supplied Si over 34 d (+Si), not supplied Si (-Si), or supplied Si once herbivory began (-Si +Si). We evaluated the effectiveness of each Si treatment at reducing herbivore performance and measured Si-based defenses and phenolics (another form of defense often reduced by Si). Although Si concentrations remained lower, within 72 h of exposure to Si, -Si +Si plants were as resistant to herbivory as +Si plants. Both +Si and -Si ? +Si treatments reduced herbivore damage and growth, and increased mandible wear compared to Si. After 6 h, herbivory increased filled Si cell density in -Si ? +Si plants, and within 24 h, -Si ? +Si plants reached similar filled Si cell densities to +Si plants, although decreased phenolics only occurred in +Si plants. We demonstrate that plants with short-term Si exposure can rapidly accumulate Si-based antiherbivore defenses as effectively as plants with long-term exposure

Reciprocal effects of silicon supply and endophytes on silicon accumulation and Epichloë colonization in grasses.

Abstract: Cool season grasses associate asymptomatically with foliar Epichloë endophytic fungi in a symbiosis where Epichloë spp. protects the plant from a number of biotic and abiotic stresses. Furthermore, many grass species can accumulate large quantities of silicon (Si), which also alleviates a similar range of stresses. While Epichloë endophytes may improve uptake of minerals and nutrients, their impact on Si is largely unknown. Likewise, the effect of Si availability on Epichloë colonization remains untested. To assess the bidirectional relationship, we grew tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne) hydroponically with or without Si. Grasses were associated with five different Epichloë endophyte strains [tall fescue: AR584 or wild type (WT); perennial ryegrass: AR37, AR1, or WT] or as Epichloë-free controls. Reciprocally beneficial effects were observed for tall fescue associations. Specifically, Epichloë presence increased Si concentration in the foliage of tall fescue by at least 31%, regardless of endophyte strain. In perennial ryegrass, an increase in foliar Si was observed only for plants associated with the AR37. Epichloë promotion of Si was (i) independent of responses in plant growth, and (ii) positively correlated with endophyte colonization, which lends support to an endophyte effect independent of their impacts on root growth. Moreover, Epichloë colonization in tall fescue increased by more than 60% in the presence of silicon; however, this was not observed in perennial ryegrass. The reciprocal benefits of Epichloë-endophytes and foliar Si accumulation reported here, especially for tall fescue, might further increase grass tolerance to stress