The Combination of Trichoderma harzianum and Chemical Fertilization Leads to the Deregulation of Phytohormone Networking, Preventing the Adaptive Responses of Tomato Plants to Salt Stress.

Plants have evolved effective mechanisms to avoid or reduce the potential damage caused by abiotic stresses. In addition to biocontrol abilities, Trichoderma genus fungi promote growth and alleviate the adverse effects caused by saline stress in plants. Morphological, physiological, and molecular changes were analyzed in salt-stressed tomato plants grown under greenhouse conditions in order to investigate the effects of chemical and biological fertilizations. The application of Trichoderma harzianum T34 to tomato seeds had very positive effects on plant growth, independently of chemical fertilization. The application of salt stress significantly changed the parameters related to growth and gas-exchange rates in tomato plants subject to chemical fertilization. However, the gas-exchange parameters were not affected in unfertilized plants under the same moderate saline stress. The combined application of T34 and salt significantly reduced the fresh and dry weights of NPK-fertilized plants, while the opposite effects were detected when no chemical fertilization was applied. Decaying symptoms were observed in salt-stressed and chemically fertilized plants previously treated with T34. This damaged phenotype was linked to significantly higher intercellular CO2 and slight increases in stomatal conductance and transpiration, and to the deregulation of phytohormone networking in terms of significantly lower expression levels of the salt overlay sensitivity 1 (SOS1) gene, and the genes involved in signaling abscisic acid-, ethylene-, and salicylic acid-dependent pathways and ROS production, in comparison with those observed in salt-challenged NPK-fertilized plants.

Biodiversity of Trichoderma strains in Tunisia.

Trichoderma strains were sampled in 4 different bioclimatic zones of Tunisia, a Mediterranean North African country with strong climatic and edaphic variability from north to south, to assess the genetic diversity of endemic species of Trichoderma and their relationship to the bioclimatic zones. In all, 53 strains were isolated and identified at the species level by analysis of their internal transcribed spacers regions 1 and 2 (ITS1 and ITS2) of the rDNA cluster and (or) a fragment of the translation elongation factor 1 (tef1) gene, using an online interactive key for species identification in Trichoderma and ex-type strains and taxonomically established isolates of Trichoderma as references. At least 2 different species were observed in each ecosystem. Trichoderma harzianum clade VI and Trichoderma longibrachiatum were present in forest soils in north Tunisia; Trichoderma atroviride and Trichoderma hamatum were found in cultivated fields in northeast Tunisia; T. harzianum clade VI, a Trichoderma sp. close to the T. harzianum complex, and Trichoderma saturnisporum were isolated from forest soils in central Tunisia; and T. harzianum clade II and T. hamatum were present in oasis soils in south Tunisia.

Specific PCR assays for the detection and quantification of DNA from the biocontrol strain Trichoderma harzianum 2413 in soil.

Strain identification in situ is an important factor in the monitoring of microorganisms used in the field. In this study, we demonstrated the use of sequence-characterized amplified region (SCAR) markers to detect genomic DNA from Trichoderma harzianum 2413 from soil. Two primers (SCAR A1/SCAR A1c) were tested against DNA of 27 isolates of Trichoderma spp. and amplified a 990-bp fragment from T. atroviride 11 and a 1.5-kb fragment from T. harzianum 2413, using an annealing temperature of 68 degrees C. These fragments showed no significant homology to any sequence deposited in the databases. The primer pair, BR1 and BR2, was designed to the 1.5-kb fragment amplified from T. harzianum 2413, generating a SCAR marker. To test the specificity of these primers, experiments were conducted using the DNA from 27 Trichoderma spp. strains and 22 field soil samples obtained from four different countries. PCR results showed that BR1 and BR2 amplified an 837-bp fragment unique to T. harzianum 2413. Assays in which total DNA was extracted from sterile and nonsterile soil samples, inoculated with spore or mycelium combinations of Trichoderma spp. strains, indicated that the BR1 and BR2 primers could specifically detect T. harzianum 2413 in a pool of mixed DNA. No other soil-microorganisms containing these sequences were amplified using these primers. To test whether the 837-bp SCAR marker of T. harzianum 2413 could be used in real-time PCR experiments, new primers (Q2413f and Q2413r) conjugated with a TaqMan fluorogenic probe were designed. Real-time PCR assays were applied using DNA from sterile and nonsterile soil samples inoculated with a known quantity of spores of Trichoderma spp. strains.