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Trichoderma harzianum ITEM 3636 has been tested against different soil-borne peanut diseases, applied as a seed treatment. The strain protected mature peanut plants suggesting a long lasting protection, and was isolated from plant roots several months after the sowing in field assays. We hypothesized that T. harzianum ITEM 3636 colonizes peanut roots as an endophyte as was demonstrated with other few strains, and in this interaction, the fungi reside in plant roots and can protect the plant against a foliar disease. The spreadability of conidia on the surface of peanut seeds and the mycelial growth inside root tissues were studied through scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), respectively. Conidia from ITEM 3636 had an appropriate distribution on coated seed surfaces. Furthermore, the fungal mycelium colonized root surfaces forming appressorium-like structures and swollen cells. The overlay of green and red confocal images clearly showed fungal hyphae grew internally through epidermal and cortical cells. Once inside the root, T. harzianum ITEM 3636 increased the levels of jasmonic acid in roots but not of salicylic acid. Also, the effect of seed treatment in peanut plant defense against Nothopassalora personata was evaluated under greenhouse conditions. ITEM 3636 significantly decreased the number of affected leaflets, late leaf spot (LLS) incidence and severity, and induced higher levels of defense related enzymes in leaflets after challenge with the pathogen. No direct activation of JA or SA pathways was observed in the leaves of Trichoderma-induced peanuts plants. T. harzianum decreased the concentration of ABA, which may reflect that the strain might improve defense mechanisms of the plant, through ABA content. [ABSTRACT FROM AUTHOR]

Tomato is one of the most economically attractive vegetable crops due to its high yields. Diseases cause significant losses in tomato production worldwide. We carried out Polymerase Chain Reaction studies to detect the presence of genes encoding antifungal compounds in the DNA of Pseudomonas putida strain PCI2. We also used liquid chromatography-electrospray tandem mass spectrometry to detect and quantify the production of compounds that increase the resistance of plants to diseases from culture supernatants of PCI2. In addition, we investigated the presence of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase in PCI2. Finally, PCI2 was used for inoculation of tomato seeds to study its potential biocontrol activity against Fusarium oxysporum MR193. The obtained results showed that no fragments for the encoding genes of hydrogen cyanide, pyoluteorin, 2,4-diacetylphloroglucinol, pyrrolnitrin, or phenazine-1-carboxylic acid were amplified from the DNA of PCI2. On the other hand, PCI2 produced salicylic acid and jasmonic acid in Luria-Bertani medium and grew in a culture medium containing ACC as the sole nitrogen source. We observed a reduction in disease incidence from 53.33 % in the pathogen control to 30 % in tomato plants pre-inoculated with PCI2 as well as increases in shoot and root dry weights in inoculated plants, as compared to the pathogenicity control. This study suggests that inoculation of tomato seeds with P. putida PCI2 increases the resistance of plants to root rot caused by F. oxysporum and that PCI2 produces compounds that may be involved at different levels in increasing such resistance. Thus, PCI2 could represent a non-contaminating management strategy potentially applicable in vegetable crops such as tomato. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal (ECM) fungal associates of Alnus are relatively few in comparison with those associated with other tree hosts. The composition of ECM assemblages associated with Alnus seems to change very little across the Northern Hemisphere. However, Alnus-associated ECM assemblages from the Western United States, Mexico, and Argentina tend to differ from those in eastern North America and Europe, presumably due to their different biogeographic histories. Alnus glutinosa is a northern European species subjected to diverse environmental conditions. To address intrageneric host preference within two distantly related Alnus species ( Alnus acuminata and A. glutinosa), we tested the ECM colonization on seedlings of both species inoculated with natural soil from A. acuminata forests. Two tomentelloid ECM fungi from A. acuminata natural soils were determined from the anatomotyping and molecular analysis. Both species colonized A. glutinosa seedlings and presented similar relative abundances. Additional soil sequence data from A. acuminata sites suggest that a variety of tomentelloid taxa occur, including several unidentified Tomentella lineages. Maximum-likelihood and Bayesian inference analyses based on internal transcribed spacer (ITS) sequences from various locations do not reflect associations of taxa based on their biogeographic origin, and clades are in general constituted by sequences from diverse regions, including South America, Mexico, USA, and Europe. Results illustrate the probable role of specific tomentelloid fungi in the early colonization of seedlings in A. acuminata forests as well as their importance in the structure of the ECM propagule community at the sites. [ABSTRACT FROM AUTHOR]

The use of phosphate solubilizing plant growth-promoting microorganisms as inoculants assists in the hydrolysis of insoluble forms of phosphorus leading to increased plant growth. Pseudomonas putida PCI2 was evaluated for phosphatase activity and solubilization of AlPO and FePO. The effect of different incubation temperatures, concentrations of NaCl and different pH on growth of PCI2 and P solubilization was studied. PCI2 proved to be positive for phosphatase activity, solubilized AlPO and hydrolyzed Ca(PO) even in medium with 5 % NaCl. In addition, PCI2 produced 45 % units of siderophores. The production of IAA by PCI2 was stimulated in vitro by the addition of different concentrations of L-tryptophan to the culture medium. Assays with tomato seedlings showed that the length of the root was reduced as the concentration of IAA increased. On the other hand, inoculation with PCI2 caused a clear growth-promoting effect on shoot growth in the presence of L-tryptophan. P. putida PCI2 is adapted to different environmental conditions and has potential to be developed and used as an inoculant for increasing the growth of tomato plants. [ABSTRACT FROM AUTHOR]