Integrated control of cotton root rot disease by mixing fungal biocontrol agents and resistance inducers

The aim of this study was to evaluate mixtures of bioagents and resistance inducers for protection of cotton roots against root infecting fungal pathogens. Three biological control agents (BCAs); Trichoderma hamatum (TM), Trichoderma harzianum (TZ) and Paecilomyces lilacinus (PL) and two resistance inducers (RIs); Bion (benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester) (BTH), salicylic acid (SA) were applied individually or in combination to test their efficacy in controlling cotton root rot disease caused by Fusarium oxysporum (FO) and Pythium debaryanum (PD) under greenhouse and field conditions. In greenhouse experiments, all applied treatments protected cotton seedlings against FO root rot. Disease index percentage (DI%) was significantly reduced up to 78.8%, while germination percentage increased significantly up to 199.60% compared with the infected control. All treatments significantly reduced PD DI% compared to infected controls. In field experiments, the maximum protection of cotton roots against FO and PD resulted from application of TM + PL + SA + BTH, where DI% was reduced to 72.3% and 69.3% relative to infected controls, respectively. Increase in cell wall fractions (cellulose, hemicelluloses and lignin) resulted from application of both BCAs and RIs in case of PD. Lignin content significantly increased 1.68–1.93 (FO) and 1.07–1.39 (PD) fold over the infected controls. A significant increase in free phenolics content was positively proportional to the degree of plant resistance against the two pathogens. The main conclusion of this study is that by combining BCAs with RIs there was increased consistency of suppression of root rot of cotton seedlings caused by either F. oxysporum or P. debaryanum.