NATIVE RHIZOBACTERIA IN ROSELLE ANTAGONISTS TO Phytophthora parasitica Dastur: ISOLATION AND CHARACTERIZATION

Abstract

Microbial communities in the rhizosphere are important in nutrition and plant health. In this research, culturable native bacterial populations in the roselle (Hibiscus sabdariffa L.) var. Tecoanapa rhizosphere were evaluated in the growth stages of initial growth, bud development and flowering at the locations: Las Ánimas, Saucitos, Pueblo Largo, Santa Rosa and Xalpatláhuac in the Tecoanapa county, Guerrero in southern México. Rhizobacteria antagonistic to Phytophthora parasitica was characterized in vitro phenotypically and genotypically. The total bacterial population density in the rhizosphere was log 3.50 and 6.56 CFU g^-1 root. The comparative study between sites showed that the average root CFU g^-1 in the early growth stage was statistically highest (P
> 0.05), and both magnesium (r = 0.92) and phosphorus content in the soil (r = 0.80) were significantly correlated with CFU values. According to the in vitro evaluation antagonism of 450 bacterial isolates to P. parasitica, we selected the 18 most efficient strains. The selected bacteria expressed lipolytic and proteolytic enzyme activity: 88.8 % produced siderophores, 44.4 % produced indole-3-acetic acid, and 72.2 % solubilized phosphates. Out of these 18 isolates, six strains expressed the five activities related with antagonism or growth promoters. Strains (n = 18) were genetically identified by polymerase chain reaction (PCR) by amplification and sequencing of the 16S rDNA region with primers 27F and 1492R. The genus identified in roselle rhizosphere with antagonist activity to P. parasitica and plant growth promotion were Serratia, Pseudomonas and Stenotrophomonas with a homology of 99 %. This is the first study that has been published on native culturable bacterial communities in the roselle rhizosphere.