Co-inoculation with dark septate endophytes improves root architecture, nutrient uptake, and growth in tomato (<i>Solanum lycopersicum</i> L.)

Dark septate endophytes (DSEs) form a morpho-functional group of root-inhabiting fungi with great potential as plant growth promoters. In this study, we isolated a DSE from tomato roots identified as <i>Alternaria alternata</i> (Fr.) Keissl. (C23). To test its capacity as a growth promoter in tomato plants, this strain was compared and co-inoculated with the DSE strain <i>Exserohilum rostratum</i> (Drechsler) K.J. Leonard &amp; Suggs (GR1A), previously isolated from Rhodes grass roots. The DSE isolated showed a differential ability to synthesize cellulolytic enzymes and siderophores, as well as indole acetic acid-type compounds. The strain GR1A revealed higher levels of other phytohormones, including salicylic acid, gibberellic acid, kinetin, 6-benzylaminopurine, and abscisic acid. However, the co-inoculation in tomato plants revealed a higher effect than after inoculation with each strain individually. Co-inoculated plants showed increases in height (8%), leaf area (18%), dry weight of stem (9.7%), and carotenoid content (147%). In addition, in leaves and stems, the phosphorus and potassium content increased by 15% and 19%, respectively, compared to the uninoculated control. Moreover, the root architecture was notably modified by co-inoculation, with increases in root area (16%), total root length (29%), and lateral root production (55%), while root diameter was smaller (24%) in comparison to the uninoculated control. The results suggest that both DSE isolates, either individually or in co-inoculation, could be promising candidates in the design of sustainable biofertilization strategies for the cultivation of tomatoes.