Biostimulants are gaining popularity as a tool for enhancing plant growth, mitigating abiotic stress, and improving crop yield and quality. Defined as substances or microorganisms that stimulate natural plant processes. Although skepticism about their efficacy initially limited their use, a growing body of research evidence demonstrates their positive effects on crop systems under both controlled environments and field conditions. However, the continuous development of new biostimulant formulations reinforces the need for further validation under commercial agricultural conditions. This study evaluates the effects of eight commercial biostimulant protocols, each with different composition and modes of action on tomato (Solanum lycopersicum) growth, fruit quality, and yield. The objectives are to: 1) quantify the effects on plant growth with parameters such as plant height, stem diameter and leaf chlorophyll content) 2) assess the impact on yield and fruit quality at harvest. The experiment followed a randomized complete block design with three replicates, each comprising eight treatments. Each plot contained 25 tomato plants, and data were collected from 10 selected plants per plot. Biostimulants were applied weekly or biweekly, via drench or foliar spray, according to the manufacturer’s instructions. Growth parameters were measured throughout the experiment, while yield and quality assessments were at harvest and during postharvest storage. According to the analysis of variance, plant height was significantly affected by protocol. Protocol 5 was statistically superior to the control in two of the three replicates followed by protocol 8 with one statistical significance in the three replicates compared to the control. There was not any statistical difference in diameter of treated plants compared to the control, however plants treated with protocol 8 had the greatest diameter in two of the three replicates. For the chlorophyll content, treatment 1 was the only one that showed a significant increase compared to the control. In terms of color, protocol 2 and 5 significantly increased fruit brightness while protocol 5 and 7 enhanced color saturation and protocol 1 altered hue compared to the control. The firmness of fruits at harvest was 2.08 to 2.85 kg without any significant differences within the protocol. In yield, protocol 5 was statistical significance in marketable weight, number 8 was statistical significance in count and weight in unmarketable category. According to the above, there is a significant benefit of specific biostimulants as treatments 5 and 8 in promoting tomato plant growth and improving certain fruit quality parameters. Key words: Biostimulants, protocol, plant growth.
