*Article* **Role of** *Trichoderma aggressivum* **f.** *europaeum* **as Plant-Growth Promoter in Horticulture**

**Brenda Sánchez-Montesinos 1, Fernando Diánez 1,\* , Alejandro Moreno-Gavíra 1, Francisco J. Gea <sup>2</sup> and Mila Santos <sup>1</sup>**


Received: 4 June 2020; Accepted: 8 July 2020; Published: 13 July 2020

**Abstract:** The main objective of this study was to determine the capacity of *Trichoderma aggressivum* f. *europaeum* to promote pepper and tomato seedling growth compared to that of *T. saturnisporum*, a species recently characterised as a biostimulant. Consequently, in vitro seed germination and seedling growth tests were performed under commercial plant nursery conditions. Additionally, the effects of different doses and a mixture of both species on seedling growth under plant nursery and subsequently under greenhouse conditions were determined. Furthermore, mass production of spores was determined in different substrates, and their siderophore and indole acetic acid production and phosphate (P) solubilisation capacity were also determined. Direct application of *Trichoderma aggressivum* f. *europaeum* to seeds in vitro neither increases the percentage of pepper and tomato seed germination nor improves their vigour index. However, substrate irrigation using different doses under commercial plant nursery conditions increases the quality of tomato and pepper seedlings. Tomato roots increased by 66.66% at doses of 106 spores per plant. Applying *T. aggressivum* f. *europaeum* or *T. saturnisporum* under plant nursery conditions added value to seedlings because their growth-promoting effect is maintained under greenhouse conditions up to three months after transplantation. The combined application of the two species had no beneficial effect in relation to that of the control. The present study demonstrates the biostimulant capacity of *T. aggressivum* f. *europaeum* in pepper and tomato plants under commercial plant nursery and greenhouse conditions.

**Keywords:** *Trichoderma*; plant growth promotion; tomato; pepper; biostimulant
