Dynamics and characterization of the endophytic community of Melia azedarach trees infected with phytoplasmas

LOPEZ GASTÓN, M; CARDOZO, M; Y NAMTZ; E GALDEANO; M M COLLAVINO

Simposio; Micrope. Microbe-assisted crop production ? opportunities, challenges & needs; 2017

We studied Melia azedarach endophytic community considering the effect of phytoplasma infection, plant organ and sampling season on a two year-survey, and analyzed in vitro plant growth promoting activities.403 isolates were characterized by Rep-PCR and 16S rDNA. Community diversity was affected by organ source, but not by season or infection status. Diversity was higher in root samples, being the most represented orders Bacillales (31%), Burkholderiales (30%), Rhizobiales (17%) and Pseudomonadales (13%). Enterobacteriales were present only in leaf samples, and Burkholderiales only in root ones. Within root isolates, the proportion of Burkholderiales and Rhizobiales was higher during the autumn season while Bacillales and Enterobacteriales increased during the spring. Leaf community was affected by phytoplasma infection since Bacillales and Enterobacteriales were found in higher proportion in infected leaves.N fixation, P solubilization, indol acetic acid (IAA) production, ACC deaminase activity, siderophore and antibiotic production were assayed. Bacillus and Burkholderia isolates had the highest functional diversity. Isolates from Bacillus, Pseudomonas, Enterobacter, Burkholderia and Paenibacillus grew on Nfb medium and were positive for nifH gene PCR amplification. 97% of the isolates had P solubilizing activity, being Pseudomonas and Kosakonia highly efficient. 50 isolates showed IAA production, 3 from Enterobacter, Pseudomonas and Bacillus produced twice the reference strain Azospirillum brasiliensis. 38 isolates produced siderophores and 16 had acc deaminase activity. In both activities, most of the positive isolates corresponded to order Burkholderiales and showed considerably higher production than the control strain (Pseudomonas putida). 15 of the 23 Pseudomonas isolates were PCR positive for genes (phl, prn, phz, and plt) related to antibiosis activity while only one Bacillus isolate showed amplification of zma gene (zwitermycin).In conclusion, M. azedarach root and leaf endophytic communities are different in structure, diversity and composition as well as in their response to phytoplasma infection and seasonal conditions. Besides, they have high PGPB potential as reflected by their diverse and efficient functional activities. Selected isolates of Burkholderia, Bacillus and Pseudomonas are being tested now for their growth promoting activities after plantlet inoculation.