Agroecological consequences of silicon supplementation for a legume cultivation: Two-year-long field observations

Supplementing plants with silicon (Si) often improves plant productivity and resilience to biotic and abiotic stresses, but this is mostly reported in highly controlled experimental environments. The ecological consequences of Si supplementation, including environmental benefits and potential risks, are therefore poorly understood and require field-scale evaluation of how Si supplementation affects the wider ecosystem, such as invertebrate communities and soil physicochemical properties. We conducted the first field assessment of how a legume (lucerne; Medicago sativa) agroecosystem and its associated invertebrate communities responded to two levels of Si supplementation (calcium silicate slag), over two years. We quantified seasonal changes in the abundance and diversity of aboveground arthropod communities, crop yield, elemental and nutritional chemistry, and soil pH as well as soil chemistry. The highest rate of Si supplementation increased bioavailable Si in the soil by 181% and soil pH from 5.2 to 6.3, relative to untreated plots, with a significant positive correlation between increased soil bioavailable Si and pH. Si supplementation led to an increase in crop yield by up to 52%; however, the magnitude varied with season. Foliar concentrations of Si tended to increase with Si supplementation, but this increase was marginally significant, potentially due to a dilution effect of higher shoot biomass. Si supplementation did not affect concentrations of most soil elements we quantified or forage quality of lucerne. We recorded over 13,600 arthropods; Si supplementation led to a shift in community structure and overall increased diversity of arthropod functional groups. Notably, the saprophytic fly family, Lauxaniidae was more abundant on Si-supplemented plots compared to untreated plots, potentially due to increased plant turnover. These results indicate that silicon supplementation of a legume agroecosystem, using a by-product of steel production, provides productivity benefits that outweigh some possible detrimental impacts on the ecosystem (i.e. decreased arthropod abundances, toxic metal contamination or reduced forage quality), which we did not detect in our current field study. This management intervention enhances crop yield, so could reduce the need for conventional fertilisers as well as changing soil pH to be more beneficial to crops and some arthropod groups

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

Mycorrhizal fungi compromise production of endophytic alkaloids, increasing plant susceptibility to an aphid herbivore

1. Symbiosis plays a critical role in plant biology. Temperate grasses often associate with several symbiotic fungi simultaneously, including Epichloë endophytes and arbuscular mycorrhizal (AM) fungi, in shoots and roots, respectively. These symbionts often modulate plant–herbivore interactions by influencing nutritional traits (i.e. AM fungi-mediated nutrient uptake) and/or the secondary chemistry (i.e. endophytic alkaloids) of their host plant. Moreover, such grasses also accumulate large amounts of silicon (Si) from the soil, which can be deposited in tissues to act as a physical anti-herbivore defence. 2. Recent evidence suggests that both endophytes and AM fungi independently facilitate Si uptake. However, the consequences of their interactions with piercing-sucking insects (i.e. aphids), or whether Si supply, endophytes, and AM fungi interact in this regard, are currently unknown. While Si deposition may be less effective against aphids than other herbivores (i.e. chewing caterpillars), Si supply can also alter plant secondary metabolite defences, which could affect sucking insects. 3. In a factorial greenhouse experiment, we evaluated whether these components, acting alone or in combination, altered (1) foliar primary chemistry, (2) Si and symbiont-chemical (endophytic alkaloids) defences, as well as (3) performance of the bird cherry-oat aphid (Rhopalosiphum padi) feeding on tall fescue (Festuca arundinacea). 4. Endophytes decreased all aphid performance parameters, including population growth and reproduction by 40%, but their impact was reversed by the presence of AM fungi, leading to a 52% increase in aphid performance compared with plants solely hosting endophytes. This improvement in performance was associated with reduced loline alkaloid levels and higher shoot nitrogen in AM-endophytic plants. Endophytes and AM fungi exhibited antagonism, with endophytes reducing AM colonization by 34% and AM presence decreasing endophyte loline alkaloids by 44%. While both fungi jointly increased Si accumulation by 39% under Si-supplied conditions, Si had no noticeable effects on aphids. Moreover, although Si supply had no identifiable effects on AM colonization, it reduced endophyte peramine alkaloids by 24%. 5. Synthesis. Our findings indicate that symbiotic fungal partnerships and silicon provision may benefit plants but could weaken anti-herbivore defences when combined. Revealing the complex interactions among diverse fungal symbionts and showcasing their effects on different anti-herbivore defences (chemical and physical) and herbivore performance for the first time

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

First record of Phytomyza rufipes Meigen, 1830 (Diptera, Agromyzidae) affecting Canola in Uruguay.

ABSTRACT.- The leafminer Phytomyza rufipes Meigen, 1830 (Diptera, Agromyzidae) is an oligophagous pest of plants of the family Cruciferae. These include Canola, Brassica napus L. We report the record of P. rufipes in Uruguay, which is confirmed through molecular characterization using DNA barcoding. Characteristic damage symptoms and immature stages of the pest were first confirmed on a Canola crop in Flores, Uruguay. © The authors