Endophytic bacterial community composition of Melia azedarach and its relation with phytoplasma infection

CARDOZO MARINA; LOPEZ GASTON MAURA; GALDEANO, E.; COLLAVINO M.M

La Falda

Workshop; 2do Taller Latinoamericano sobre Rizobacterias Promotoras del Desarrollo Vegetal.; 2014

PGPR Latinoamérica

Phytoplasmas have been reported infecting hundreds of plant species in the 5 continents with an increasing incidence and causing important yield losses. Control of such diseases is very difficult because of the phytoplasmas habitat restricted to phloem cells. Understanding the interactions of phytoplasmas with other plant host associated microorganisms might be useful to develop alternative techniques based on biological control. Endophytic bacteria in particular are considered more efficient due to their close contact with the host plant and the pathogen. The aim of this work was to analyze the endophytic community composition of China-tree (Melia azedarach) and analyze its relation with phytoplasma infection, using culture dependent and independent methods. Samples were taken from China-tree roots, leaves and stems infected or not with phytoplasmas. Symptomatic and asymptomatic samples (leaves and stems) were taken from infected plants. Phytoplasma presence was assayed by PCR. Samples were collected during January and February. Plant tissue was disinfected and bacteria-cells enriched. The suspensions were used for bacteria isolation and DNA extraction. A 16S rDNA library was generated using 799F-1492R primers. The cultivable endophytic bacteria were isolated in TSA medium, grouped by their Rep-PCR profiles and identified by 16S rDNA sequencing. 16S rDNA sequence analysis of total DNA showed that 100% of the clones assayed (100 clones) corresponded to phytoplasmas. We also analyzed the endophytic community by culture-dependent methods. Out of 250 isolates, we found 81 Rep-PCR profiles. Most of them were proteobacteria of the orders Pseudomonadales (45%), Enterobacteriales (16%) and Burkholderiales (7%) or firmicutes of order Bacillales (29%). Mostly Bacillales (68%) and Burkholderiales (24%), and in less proportion Pseudomonadales (5%), were isolated from root samples while in leaf samples predominated orders Pseudomonadales (61%), Enterobacteriales (22%) and Bacillales (15%). In infected tissues, order Enerobacteriales was higher represented (23%) than in healthy ones (4%). Pseudomonadales did not show differences between infected (43%) or non-infected (48%) plants while orders Bacillales and Burkholderiales presented higher percentage in healthy (35% and 9 %, respectively) than the infected ones (25% and 5 %, respectively). This preliminary results show that China-tree endophytic community is affected mainly by the tissue type. The phytoplasma infection seems to differentially affect the representation of particular groups.