An in vitro antagonistic activity evaluation of rhizobacteria against Fusarium oxysporum f. sp. radicis-lycopersici (Forl) isolated from the Algerian west.

Abstract

The use of biological antagonists is a promising technique for the protection of plants without having a fatal effect on the environment. The in vitro confrontation tests is an obligatory step for the selection of successful antagonistic agents, what has ends in our study to the selection of two rhizobacteria: **Bacillus subtilis and* Pseudomonas fluorescens,** isolated from the rhizosphere of tomato healthy plants and which were tested for their in vitro inhibitive power against five isolates of Fusarium oxysporum f. sp. radicis-lycopersici (Forl). The results of the direct confrontation on different culture media demonstrated that rhizobacteria have an inhibitive effect on the pathogenic, while noticing a performance of P. fluorescens with an inhibition which varies between 73,77 and 80 %, comparing with 56,36 and 60,46 % for B. subtilis. The inhibition by volatile substances of P. fluorescens varies between 25 and 39,53 %, compared with 18,86 and 32,55 % by volatile substances of B. subtilis. Rhizobacterial cell-free supernatant showed an inhibition from the first until the seventh incubation day against the five fungal isolates, when mycelia growth reaches 5±0,2 cm in presence of P. fluorescens cell free supernatant, and it reaches 5,9±0,3 cm in presence of B. subtilis* cell free supernatant compared with 8,5 cm on control plates without rhizobacteria cell free supernatant.

Introduction

The tomato plant can be infected by different phytopathogenic fungi which affect the agriculture yield. Among these phytopathogenic fungi, we find Fusarium oxysporum which is the most frequent and the most important species of the fungal microflora of cultivated soils (Messiaen and Cassini, 1968). Fusarium crown and root rot is an important soilborne disease, with the potential to limit productivity in glasshouse and field tomato crops. Fusarium oxysporum f. sp. radicis-lycopercisi is the forma specialis which parasites a single host who is the tomato, causing crown root which is one of the most frequent diseases and the gravest in the Algerian North (Hamini, 2010).

Various ways are used to control the tomato root rot, as the chemical, genetic, cultural, physical and biological control; the latter remains the most important intervention way (Karimi et al., 2012). Among the antagonists who reign in saturated soil by microflora equilibrated for the environment and the biotope, we meet the presence of Pseudomonas and Bacillus species that inhibit the growth of phytopathogenic fungi by direct or indirect methods (Abdulkareem et al., 2014).

Previous study was realised on the combination between Plant growth-promoting rhizobacteria (PGPR) and conventional pesticides to increase their efficacy and broaden the disease control spectrum (Myresiotis et al., 2012).

But other researchers suggest that the use of PGPR without conventional pesticides stay the friendliest method to inhibit the growth of different spices of Fusarium in their natural environment without harming the environment (Nandhini et al., 2012; Karimi et al., 2012; Prashar et al., 2013; Abdulkareem et al., 2014).

After these results we realised a prospecting and we noticed an agricultural fields of healthy tomatoes and a good quality yield in the region of Messerghine, Oran (Algeria), which led us to set as aims the in vitro selection of antagonistic rhizobacteria with a successful inhibiting effect on the Fusarium oxysporum f. sp. radicis-lycopersici growth in a first part, to be used in a next study in vivo.

Source : An in vitro antagonistic activity evaluation of rhizobacteria against Fusarium oxysporum f. sp. radicis-lycopersici (Forl) isolated from the Algerian west.