Biocontrol of Pythium Damping-Off on Pepper (Capsicum Annuum) with Selected Fungal and Rhizobacterial Agents

Pythium ultimum is a common soilborne pathogen causing serious losses of pepper seedlings in nurseries and few weeks post-planting. Two pepper associated-P. ultimum isolates (P1 and P2) were shown pathogenic to pepper cv. Altar causing post-emergence damping-off with P2 isolate being the most aggressive. Fungal and bacterial antagonists have been evaluated in vitro and in vivo for their ability to suppress P. ultimum. In dual culture assay, Trichoderma harzianum, T. viride and Gliocladium virens inhibited pathogen radial growth by 18.54, 17.52 and 15.24%, respectively, relative to control, while none of the tested bacteria was shown able to significantly inhibit pathogen growth. However, drastic changes in pathogen hyphae expressed as strong lysis, the formation of mycelial cords and mycoparasitism have been observed. Pepper seeds treated with fungal antagonists’ conidial suspensions showed 60, 50 and 60% less pre-emergence damping-off infections, respectively, compared to the positive control. When tested as root dipping, only G. virens resulted in 40% reduced post-emergence damping-off. An improved seedlings fresh weight, by 79.31 and 76%, was respectively induced by G. virens-, and T. viride-based treatments while an increment of 27.58, 25.33 and 22.22 % was recorded following treatments with G. virens, T. viride and T. harzianum, relative to the positive control. The majority of tested bacterial isolates, applied as a seed treatment, had significantly improved the emergence percentage of inoculated seedlings as compared to control with Burkholderia glathei isolate 35 being the most efficient. When applied as root dipping, reduction of post-emergence damping-off ranged between 40 and 100% with Pseudomonas aureofaciens isolate 314 being the most effective agent. Seedlings treated with P. aureofaciens (314) and Bacillus pumilus (420) showed 35.38 and 28.51% higher heights, respectively. Plant weight was enhanced by 73.06, 61.18, 77.39, 61.8 and 67.93% over control following treatments with P. aureofaciens isolates 314 and 31, Bacillus pumilus 420, P. fluorescens and P. putida 227.