Streptomyces alni as a biocontrol agent to root-rot of grapevine and increasing their efficiency by biofertilisers inocula

Root-rotted samples of grapevine cv. superior were collected from Nobaria province, Beheira Governorate, Egypt. Fusarium oxysporum Schlech. was the most fungal causing root-rot syndrome of grapevine and directly affected the yield productivity. Seven isolates of Streptomyces were isolated from grapevine rhizospheric soil and screened for antagonistic activities against F. oxysporum on dual culture plate. All isolates showed antifungal activity, but isolate No. 1 exhibited the highest activity. It was identified as Streptomyces alni according to morphological, cultural, physiological and biochemical studies. The properties of the antagonism were revealed by scanning electron microscopy (SEM) examination of F. oxysporum and S. alni on PDA medium. The forms of antagonism found in this study according to the interaction between the S. alni and the pathogen indicated a hyperparasite, including inhibition of fungal growth and colonisation of S. alni over F. oxysporum hyphae. Also, malformation and lysis of F. oxysporum hyphae and conidiophores were observed. Conidia and normal branches of fungal hyphae were absent. Greenhouse and field studies were performed to evaluate the ability of S. alni and some commercial biofertilisers incorporated into the soil for root-rot control. Pot trails indicated that antagonistic S. alni isolate and biofertilisers i.e. blue green algae, phosphoren and rhizobacterin reduced the root-rot incidence of grapevine plants Cv. superior. Soil treatment before sowing with 50 ml of S. alni suspension (1 × 10⁸ spore/ml) + 50 g of rhizobacterin for each pot was the best and significant treatment reduced root-rot of grapevine plants. Also, the total count of F. oxysporum in rhizosphere soil of grapevine treated plants was reduced compared with control. Under field conditions, drenching soil of diseased grape trees with a spore suspension of S. alni (1 × 10⁸ spore/ml) 200 ml/tree + 250 g/tree of rhizobacterien caused a significant reduction in root rot of treated grapevine trees as well as high fruit yield/tree when compared with other treatments. The obtained results suggest that S. alni could be used successfully in combination with biofertilisers, as environmentally safe, for controlling root-rot of grapevine and other soil-borne plant pathogens especially with organic farming systems.