No abstract

1. Natural grassland ecosystems are increasingly threatened by excessive loadings of nutrients and by the presence of species bred for high productivity. By manipulating grazing regimes and nutrient availability, agricultural practices facilitate the establishment and spread of certain forage plant species outside managed landscapes, challenging local biodiversity. The ecological success of some species in the invaded range sometimes seems to be associated with the symbiosis with foliar fungal endophytes. Symbiotic fungi may increase the competitiveness of host species, but also the resistance to herbivory through the production of toxic secondary compounds such as alkaloids. While progress has been made in understanding how soil nutrients modulate other benefits offered by fungal endophytes to plants (e.g. stress tolerance, competitive ability, etc), the consequences for a higher trophic level (i.e. herbivores) and the potential feedbacks on plant invasion have not been explored yet. 2. We explored the relative and interactive importance of soil nitrogen (N) and phosphorus (P) in modulating the interaction of the invasive grass tall fescueassociated with fungal endophytes-and native herbivores in a natural grassland. We hypothesized that N and P nutrients modulate differentially leaf quality traits, namely nutritional value and fungal alkaloid contents, determining the level of damage by native insect herbivores on the exotic tall fescue. 3. We found that only the addition of P significantly increased native caterpillar density in the field, which corresponded to a concomitant increase in leaf damage. In contrast to expectations, the concentration of the alkaloid ergovaline in leaves was not strongly related to N. It was the level of soil P which dictated the concentration of the element (P) in the leaves and reduced the level of defence against herbivores in this endophyte-symbiotic species. Then, herbivore performance increased, and plants were more prone to be attacked. 4. Synthesis. Our study indicates a strong control of soil P fertility on the triple interaction among plants, fungal endophytes and native herbivores. This highlights the potential role of increased soil nutrients on the invasion spread of endophytesymbiotic forage plants in natural grasslands.

The plant piquillín (Condalia microphylla) grows in arid regions of Argentina and is the cause of mal del piquillín in cattle. The salient histologic features of this leukomyelopathy are vacuolation of white matter and axonal degeneration in the spinal cord. The histologic lesions can be experimentally reproduced in cattle and pigs by feeding milled bark of the plant, but naturally occurring piquillín toxicosis has not been reported previously in pigs. The authors report an outbreak of progressive ataxia on an Argentine hog farm, where partially consumed piquillín plants were found in the pens of affected pigs. Histologic lesions included vacuolation of white matter, edema, and mild axonal degeneration in lumbosacral segments of the cord. The diagnosis of mal del piquillín was based on the history, clinical signs, histologic changes, and elimination of other potential causes of leukomyelopathy. No new outbreaks developed after elimination of piquillín from the hog lots. Results of this investigation indicate that C microphylla toxicosis can affect pigs under natural conditions and should be included in the differential diagnosis for porcine ataxia and leukomyelopathy in regions where the plant grows.

Aspergillus flavus is a filamentous, saprophytic fungus, whose colonization occurs mainly in cereal grains and oilseeds once harvested. Under certain conditions, it could produce mycotoxins called aflatoxins, known as powerful human liver carcinogens. The aim of the present study was to describe the antifungal activity of extracts of Peltophorum dubium, a species from northern Argentina (Oriental Chaco), against A. flavus. The antifungal activities of different collection sites are reported. The extracts exhibited a minimum inhibitory concentration of 125 µg/mL, and the differences between the treatments and the inoculum control were 11 mm of P. dubium A and 10 mm of P. dubium F in colony growth. Moreover, hyphae treated with the extracts stained blue with Evans blue showed alterations in the membrane and/or cell wall, allowing the dye income. Bio-guided fractionation, High Performance Liquid Chromatography diode array ultraviolet/visible (HPLC UV/VIS DAD), and Ultra-High Performance Liquid Chromatography Electrospray Ionization Mass Spectrometry (UPLC ESI-MS) analyses were conducted to characterize the extracts and their active fractions. The HPLC UV/VIS DAD analysis allowed the determination of the presence of flavonoids (flavonols and flavones), coumarins, terpenes, and steroids. UPLC ESI/MS analysis of active fractions revealed the presence of Kaempferol, Apigenin, Naringenin, Chrysin and Daidzein.