Abstract
The current research elucidated the agronomical, physiological, qualitative characteristics and mineral composition of lettuce (Lactuca sativa L. var. longifolia) after treatments with a beneficial fungus Trichoderma virens (TG41) alone or in combination with a vegetal biopolymer-based biostimulant (VBP; ‘Quik-link’). The experiment consisted of lettuce plants grown in three N conditions: sub-optimal (0N kg ha−1), optimal (70N kg ha−1), and supra-optimal (140N kg ha−1) N levels. Lettuce grown under 0N fertilization showed a significant increase in fresh yield when inoculated with TG41 alone (45%) and a greater increase with TG41 + VBP biostimulant (67%). At 48 days after transplanting, both the TG41 alone or TG41+VBP biostimulant induced higher values of CO2 assimilation in comparison to the control. The mineral concentrations in leaf tissues were greater by 10% for K and 12% for Mg with the TG41+VBP treatments compared to the untreated lettuce. The lettuce plants receiving either TG41 alone or TG41+VBP biostimulants had a significantly lower nitrate content than any of the untreated controls. In non-fertilized conditions, plants treated with TG41+VBP biostimulants produced lettuce of higher premium quality as indicated by the higher antioxidant activity, total ascorbic acid (+61%–91%), total phenols (+14%) and lower nitrate content when compared to the untreated lettuce.
Highlights
Rapid growth in the world population will determine an increase in global food demand that is expected to double by 2050 [1]
The total number of fungal colonies recovered from soil rhizosphere in the nine treatments ranged between 2.0 × 105 and 6.5 × 105 colony forming units (CFU) g−1 of soil and was significantly (p < 0.05) influenced by the interaction of the two tested factors: N fertilization level (N) and vegetal biopolymer-based biostimulant (VBP) biostimulant application
The in vitro tests performed with the beneficial microbe (TG41) and non-microbial VBP biostimulant at the dose applied in the greenhouse experiment did not demonstrate any inhibition of the germination and growth of the fungi concentration
Summary
Rapid growth in the world population will determine an increase in global food demand that is expected to double by 2050 [1]. The intensification in agricultural production appears to be the only useful strategy to meet the rapidly growing food demand in the future, this imposes stress to the agroecosystem [1], presents serious problems to the ecosystem and health [2,3,4], since it requires high-input resource cropping systems (such as greenhouse horticulture), that are not ecologically sustainable [5]. To date, the efforts to reduce N fertilizer use while at the same time attempting to increase NUE have been proven ineffective. This can be attributed to the inability of crop plants to adapt to low N availability conditions, which limit the activation of the physiological processes necessary for increasing crop production [7,15]
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