Tropical Red Algae-Derived Biostimulant Improves Tomato Yield through Structural and Reproductive Trait Responses under Semi-Arid Field Conditions

Abstract

Improving tomato productivity without pushing unnecessary vegetative growth is important in semi-arid production systems. In this single-season field study, we evaluated RK20, a biostimulant derived from tropical red algae, for its effects on vegetative growth, reproductive behaviour, fruit structural traits, and yield of tomato (Solanum lycopersicum L.) under western Indian field conditions. The experiment was laid out in a randomised block design with seven treatments and three replications, including four RK20 doses (50–300 g acre⁻¹), two commercial biostimulants, and an untreated control. RK20 did not significantly alter plant height, chlorophyll content, or NDVI. That part stayed fairly stable. The response came elsewhere. Stem girth, flowering, fruit width, pericarp thickness, and yield per plant improved significantly under RK20 application. The 100–200 g acre⁻¹ range gave the most consistent response, with stem girth increasing by about 16–17%, flower production by nearly 40%, and yield per plant by about 26–28% over the control. Correlation, regression, and principal component analyses further suggested that yield variation tracked reproductive and fruit-structural traits more closely than canopy-related indicators. Within the limits of a single-season dataset, RK20 appears to have improved tomato productivity mainly through a better reproductive and fruit-building response rather than through increased vegetative biomass. These results justify further multi-season testing of tropical red algae-derived biostimulants under semi-arid tomato systems.