Induction of defense-related genes in tomato plants after treatments with the biocontrol agents Pseudomonas chlororaphis ToZa7 and Clonostachys rosea IK726.

Abstract

Pseudomonas chlororaphis ToZa7 is a promising biocontrol agent possessing valuable characteristics and reducing disease severity caused by Fusarium oxysporum f. sp. radicis-lycopersici (Forl) in tomato. In this study, the strain's ability to induce three pathogenesis-related (PR) genes (PR-1a, GLUA, and CHI3) in tomato, was studied using quantitative reverse transcription PCR. The genes PR-1a and GLUA were up-regulated after 120h exposure to P. chororaphis ToZa7 (15.22- and 13.11-fold, respectively), as compared to the untreated control, without challenge inoculation by the pathogen. To study the effects of individual or combined application of P. chororaphis ToZa7 and the compatible biocontrol fungus Clonostachys rosea IK726, challenged with the pathogen, the expression patterns of the above three PR genes were monitored, in tomato roots. Expression of PR1-a was noteworthy, especially 48h after challenge inoculation, when C. rosea IK726 alone or in combination with P. chororaphis, ToZa7 was pre-inoculated on tomato roots (38.53-fold and 53.74-fold, respectively). Expression of PR1-a, 72h after challenge inoculation, was the highest in P. chororaphis ToZa7, among biocontrol treatments. Expression of CHI3 was much lower, while up-regulation of GLUA was overall not observed. Confocal laser scanning microscopy of intact tomato roots and bacterial counts of superficially disinfected roots revealed, for the first time, that P. chororaphis ToZa7 colonizes the exterior as well as the internal tissues.