Vanesa Analía Silvani

Mycorrhizal status of plant species in the Chaco Serrano Woodland from central Argentina

We examined the mycorrhizal type of 128 plant species in two patches of native vegetation of the Chaco Serrano Woodland, central Argentina, the largest dry forest area in South America. Of the 128 plant species investigated (belonging to 111 genera in 53 families), 114 were colonized by arbuscular mycorrhizal fungi (AM), orchid mycorrhizal associations were present in the five terrestrial orchid species analyzed, one ectomycorrhiza was only present in Salix humboldtiana Willd., and 96 harbored a dark septate endophyte (DSE) association. Co-occurrence of AM and DSE was observed in 88 plant species. We determine morphological types of arbuscular mycorrhizal fungi (Arum, Paris, and intermediate AM structures) and report the mycorrhizal status in 106 new species, 12 of which are endemic to central Argentina and two, Aa achalensis Schltr. and Buddleja cordobensis Griseb., are declared to be vulnerable species. Root colonization in the Chaco Serrano Woodland is widespread and should be considered in revegetation programs due to the deterioration of this particular ecosystem. Considering the predominance of AM and DSE associations and the various potential benefits that these associations may bring to plant establishment, they should receive special attention in conservation and reforestation of these woodlands.

Evaluation of Arbuscular Mycorrhizal Fungi Capacity to Alleviate Abiotic Stress of Olive (Olea europaea L.) Plants at Different Transplant Conditions

The capacity of roots to sense soil physicochemical parameters plays an essential role in maintaining plant nutritional and developmental functions under abiotic stress. These conditions generate reactive oxygen species (ROS) in plant tissues causing oxidation of proteins and lipids among others. Some plants have developed adaptive mechanisms to counteract such adverse conditions such as symbiotic association with arbuscular mycorrhizal fungi (AMF). AMF enhance plant growth and improve transplant survival by protecting host plants against environmental stresses. The aim of this study was to evaluate the alleviation of transplanting stress by two strains of Rhizophagus irregularis (GC2 and GA5) in olive. Our results show that olive plants have an additional energetic expense in growth due to an adaptative response to the growing stage and to the mycorrhizal colonization at the first transplant. However, at the second transplant the coinoculation improves olive plant growth and protects against oxidative stress followed by the GA5-inoculation. In conclusion, a combination of two AMF strains at the beginning of olive propagation produces vigorous plants successfully protected in field cultivation even with an additional cost at the beginning of growth.

Differential efficiency of two strains of the arbuscular mycorrhizal fungus Rhizophagus irregularis on olive ( Olea europaea ) plants under two water regimes

The water regime affects a wide variety of physiological and biochemical processes in plants including an increased production of reactive oxygen species (ROS) capable of causing oxidative damage to proteins, DNA and lipids. Arbuscular mycorrhizal fungi (AMF) colonize a wide range of plant species though the ability of different AMF species to promote host growth or contribute to plant water deficit resistance varies. The first phase of olive tree cultivation takes place in a nursery where plants usually suffer stress by drying. Currently, olive production systems do not use of AMF to counteract this problem. To study the colonization strategies of two AMF strains and their efficiency with respect to growth and their effect on enzymatic activities, we inoculated them individually and co-inoculated then on olive plants under nursery growing conditions. The results showed the benefits generated by these fungi in terms of growth and survival rate. Co-inoculation, particularly, improved growth and reduced the damage due to water stress, partly as a result of the activation of the antioxidant defenses in the olive plant host.

Combined effects of arbuscular mycorrhizal fungi and exogenous cytokinins on pomegranate (Punica granatum) under two contrasting water availability conditions

To our knowledge, there are no studies on the interactive effects of inoculation with arbuscular mycorrhizal fungi and cytokinin addition to plants under drought stress. We investigated the potential protective effect of arbuscular mycorrhizae on pomegranate plants, combined with exogenous cytokinin addition, under two contrasting soil water availability regimes. Our results showed that exogenous cytokinin addition enhances plant biomass, shoot to root ratio and water content, as well as increasing the anthocyanin content. However, a combination of AM fungal inoculation and cytokinin addition did not result in a synergistic protective effect against water stress. Plants were equally well protected against this stress by cytokinin spraying alone. The improvement of pomegranate growth was due mainly to exogenous cytokinin addition. Photosynthesis was promoted both by mycorrhizal inoculation alone and by exogenous cytokinin addition. The main protection against oxidative stress caused by drought was via enhanced accumulation of anthocyanins when the plants were sprayed with cytokinins. When cytokinins were used, the photosynthesis apparatus was also protected.

Arbuscular Mycorrhizal Fungal Association in Genetically Modified Drought-Tolerant Corn

The commercial use of genetically modified (GM) plants has significantly increased worldwide. The interactions between GM plants and arbuscular mycorrhizal (AM) fungi are of considerable importance given the agricultural and ecological role of AM and the lack of knowledge regarding potential effects of drought-tolerant GM corn ( L.) on AM fungal symbiosis. This work studied AM fungal colonization in five corn lines growing under two different irrigation regimes (30 and 100% of soil field capacity [SFC]). Four of the lines were GM corn, and two of these were drought tolerant. The experiment was conducted for 60 d in a growth chamber under constant irrigation, after which mycorrhization, corn biomass, and days to plant senescence (DTS) were evaluated. Arbuscular mycorrhizal fungal species of the order were predominant in the soil inocula. At the end of the experiment, all plants showed AM colonization. Mycorrhization was higher at 30% SFC than at 100% SFC. Within the same corn line, the AM fungi produced more vesicles in plant roots under drought stress. Among treatments, DTS varied significantly, and drought-tolerant GM corn lines survived longer than the wild-type corn when maintained at 100% SFC. Corn biomass did not vary among treatments, and no correlations were found between DTS or biomass and mycorrhization. We conclude that overexpression of the gene in corn plants under the experimental conditions of this study did not affect AM fungal infectivity and improved the tolerance of the corn to drought stress.

Arbuscular mycorrhizal fungal diversity in high-altitude hypersaline Andean wetlands studied by 454-sequencing and morphological approaches

The Laguna Brava Nature Reserve is a stressful habitat in the Andean Mountains (Argentina) dominated by extreme abiotic factors: high altitude and UV radiance, hypersalinity, alkalinity, and high concentrations of toxic elements in the soil. The sparse native vegetation that inhabits Laguna Brava and Mulas Muertas wetlands is frequently colonized by arbuscular mycorrhizal (AM) fungi. It is, however, unknown which AM species can survive in such a harsh environment and how those environmental conditions influence the AM communities. To answer these questions, 454-amplicon pyrosequencing and morphological (based on spore traits) approaches were used to assess fungal diversity. A total of 23 molecular operational taxonomic units and 14 distinct morphospecies of AM fungi were identified. The morphological characterization of AM fungal communities in Laguna Brava and Mulas Muertas, supported by the molecular data, revealed that Glomeraceae and Claroideoglomeraceae were the dominant families, confirming the predominance of generalist and ruderal AM fungal taxa but with stress-tolerant life history traits. Our results showed that the presence of AM fungi is strongly associated with local environmental variations in Laguna Brava (hypersalinity and high Na+, Sr, As and U contents in soils). The AM fungal communities in Laguna Brava and Mulas Muertas wetlands were similar according to the Simpson diversity index and the ecological distance estimated by Bray Curtis index. These results were also supported by the environmental parameters measured, as they did not vary between the studied sites. This study represents the first characterization of AM fungal community in a high-altitude Andean wetland in Argentina, improving our knowledge about these fungi from extreme environments.