*4.1. Actinobacterial Strains and Growth Conditions*

A total of 60 actinobacterial strains isolated from different substrates or geographical areas of west-central Cuba were included in this study. They were recovered from rhizosphere (21), stem (15) or root (9) samples from a wide diversity of hosts, among other sources (Table 6), and stored in the laboratory at 4 ◦C for no more than 72 h until processing. For isolation of actinobacteria from rhizosphere samples, 1 g of each sample was suspended in 9 mL of sterile distilled water (SDW) by vortexing and incubated in water bath at 55 ◦C for 6 min. Subsequently, serial dilutions (up to 10–5) were performed. The same procedure was carried out with stem or root samples, but they were previously macerated in a mortar with sterile sand. In all cases, 100 μL aliquots of each dilution were

spread in 9.0 cm diameter Petri dishes containing casein-starch agar (CSA) supplemented with filtered cycloheximide (100 μg/mL) and nalidixic acid (30 μg/mL) [34]. The inoculated Petri dishes were incubated at 28 ◦C for 28 days in darkness. Based on macroscopic characters i.e., texture, appearance, surface with or without aerial mycelium, colonies of actinobacteria were selected, transferred to CSA, and incubated as described before. Subsequently, spore suspensions were obtained from the pure cultures of each selected strain, and they were kept in 2 mL translucent screw-capped microtubes (Zhejiang Runlab Technology Co., Taizhou, China) at −20 ◦C in 20% glycerol for further studies [35]. The collection belongs to the Microbiology Laboratory of the CBQ of the Universidad Central "Marta Abreu" de Las Villas (Cuba).


**Table 6.** Origen of actinobacterial strains used in this study.


**Table 6.** *Cont.*

<sup>a</sup> Strains selected for biochemical characterization. <sup>b</sup> Strains selected for qualitative determination of their chitinolytic, cellulolytic and proteolytic activity. <sup>c</sup> Strains selected for *in planta* bioassays. \* All actinobacterial strains used in this study were collected in Cuba by Dr. C. R. Medina-Marrero (CBQ: 'Centro de Bioactivos Químicos').
