In Vitro and in Vivo Potential of Plant Growth-Promoting Rhizobacteria as Biological Control Agents against Alternaria terricola

In this study, the antagonistic effects of 14 Plant Growth-Promoting Rhizobacteria strains (PGPRs) against the phyto-pathogenic species Alternaria terricola Woudenb. & Crous were investigated, both in vitro and in vivo. The obtained results revealed significant inhibition effects of the 14 PGPR strains against A. terricola in both direct contact and indirect bioassays with significant variation. The dual in vitro culture tests revealed substantial inhibition rates in the growth of A. terricola strain, ranging from 25±5.41% (Pseudomonas koreensis O3RR25) to 71.87±3.12% (Bacillus megaterium FR1.11). Moreover, the indirect antagonism test showed that the volatile organic compounds produced by the 14 tested PGPR strains significantly inhibited the growth of A. terricola mycelium, with variations ranging from 36.61±0.94% (P. brassicacearum O3RR24) to 67.75±0.94% (B. megaterium FR1.11). Microscopic examination of A. terricola following exposure to the volatile compounds revealed significant structural damage, including inhibition of conidial germination, deformations, thin or fissured structures, irregular lengths, and the formation of empty segments. The in vivo application of B. megaterium FR1.11 resulted in the reduction of fungal development on detached leaves and tomato seedlings. This treatment engendered a significant increase in the levels of chlorophyll a, b and total, carotenoids, polyphenols, and proline in infected tomato seedlings compared to the control. Applying this PGPR strain to infected tomato plants allowed maintaining comparable level of malondialdehyde as the control. B. megaterium FR1.11 showed considerable in vitro and in vivo antifungal activity and could serve as a promising candidate for biological control strategies targeting phytopathogenic species of the genus Alternaria.

In Vitro and in Vivo Potential of Plant Growth-Promoting Rhizobacteria as Biological Control Agents against Alternaria terricola Keywords:

Antifungal activity , Bio-fungicides , PGPRs , Plant protection.