Abstract
Microbial inoculants such as Trichoderma-based products are receiving great interest among researchers and agricultural producers for their potential to improve crop productivity, nutritional quality as well as resistance to plant pathogens/pests and numerous environmental stresses. Two greenhouse experiments were conducted to assess the effects of Trichoderma-based biostimulants under suboptimal, optimal and supraoptimal levels of nitrogen (N) fertilization in two leafy vegetables: Iceberg lettuce (Lactuca sativa L.) and rocket (Eruca sativa Mill.). The yield, nutritional characteristics, N uptake and mineral composition were analyzed for each vegetable crop after inoculation with Trichoderma strains T. virens (GV41) or T. harzianum (T22), and results were compared to non-inoculated plants. In addition, the effect of the Trichoderma-based biostimulants on microbes associated with the rhizosphere in terms of prokaryotic and eukaryotic composition and concentration using DGGE was also evaluated. Trichoderma-based biostimulants, in particular GV41, positively increased lettuce and rocket yield in the unfertilized plots. The highest marketable lettuce fresh yield was recorded with either of the biostimulant inoculations when plants were supplied with optimal levels of N. The inoculation of rocket with GV41, and to a lesser degree with T22, elicited an increase in total ascorbic acid under both optimal and high N conditions. T. virens GV41 increased N-use efficiency of lettuce, and favored the uptake of native N present in the soil of both lettuce and rocket. The positive effect of biostimulants on nutrient uptake and crop growth was species-dependent, being more marked with lettuce. The best biostimulation effects from the Trichoderma treatments were observed in both crops when grown under low N availability. The Trichoderma inoculation strongly influenced the composition of eukaryotic populations in the rhizosphere, in particularly exerting different effects with low N levels in comparison to the N fertilized plots. Overall, inoculations with Trichoderma may be considered as a viable strategy to manage the nutrient content of leafy horticulture crops cultivated in low fertility soils, and assist vegetable growers in reducing the use of synthetic fertilizers, developing sustainable management practices to optimize N use efficiency.
Highlights
Is the European leader for leafy vegetable production with about 15,000 ha and 150 kilo-tons per annum in protected greenhouses1 that are mainly produced in Campania region and in northern regions of Lombardia and Veneto
In the unfertilized conditions, the highest number of fungal colonies in lettuce was observed in the treatments with GV41 (1.7 × 107 colony forming units (CFU) g−1 of soil), followed by not different from the untreated control (NoT) (1.0 × 107 CFU g−1 of soil) and with plants inoculated with T22 (3.6 × 106 CFU g−1 of soil)
Under optimal N conditions, the fungal concentration did not differ between NoT and T22 treatments (1.3 × 107 CFU g−1 of soil), which were significantly higher than that of GV41 (1.8 × 106 CFU g−1 of soil)
Summary
Is the European leader for leafy vegetable production with about 15,000 ha and 150 kilo-tons per annum in protected greenhouses that are mainly produced in Campania region (southern Italy) and in northern regions of Lombardia and Veneto. Leafy vegetable crop production relies heavily on nitrate (NO3−) availability which constitutes the most important source of nitrogen (N) (Colla et al, 2010, 2011). Half of the N fertilizer applied is utilized by the vegetable crops, the remainder is lost by leaching to the soil, which can contribute to surface and groundwater contamination (Tilman et al, 2002). The search for strategies to improve agricultural practices, aimed at increasing uptake efficiency without affecting crop productivity, represents a strong stimulus for researchers, extension specialists as well as vegetable growers (Colla et al, 2018). Over the past three decades many efforts have been employed to enhance crop nitrogen use efficiency (NUE), through plant breeding programs and biotechnological approaches, with limited success and economic benefits due to the complexity of the genetic traits involved (Xu et al, 2012)
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