*3.2. Siderophore Production, IAA and P Solubilisation*

TA and TS siderophore production was observed in the formation of an orange-coloured zone around the fungal colonies at 24 and 48 h, and the production of TA was higher, in both cases. No increase in the diameter of the halo (mm) was detected at 72 h in any isolate (Table 2).


**Table 2.** Siderophores and IAA production by *Trichoderma* isolates.

Values are average of five replications; values after ± represent standard deviation. IAA: indole-3-acetic acid; +Trp: with L-tryptophan; −Trp: without L-tryptophan.

Although both *Trichoderma* strains exhibited an in vitro ability to produce IAA in medium supplemented with and without 100 mg L−<sup>1</sup> tryptophan during a 7-day period, the production of *T. saturnisporum* was higher under both conditions tested (Table 2). In both TA and TS, IAA production increased in the medium supplemented with tryptophan.

The effects of TA and TS on the soluble phosphate concentration are shown in Figure 2. The initial concentration of P in the medium was used to quantify the concentration of P solubilised by both isolates. As shown in Figure 2, P solubilisation was significant from the fifth day of incubation, with no significant differences between the two isolates. Furthermore, no change in the pH of the medium was detected, which remained at approximately 6.5–7.

**Figure 2.** Effects of *Trichoderma aggressivum* f. *europaeum* (TA) and *Trichoderma saturnisporum* (TS) on phosphate solubilisation in National Botanical Research Institute's phosphate (NBRIP) broth containing tribasic calcium phosphate (10 g). T0: NBRIP broth without *Trichoderma* isolates. The results are shown as the average of the three replicates, in g L<sup>−</sup>1. Mean standard deviation is expressed in the error bar (*n* = 3). For each isolate, columns marked with different letters indicate a significant difference at *p* < 0.05.
