Antagonistic Activities of Trichoderma spp. on Phytophthora Root Rot of Sugar Beet

Trichoderma species are among important antagonists of plant pathogenic fungi. The main purpose of this study was to evaluate the biocontrol potential of native Trichoderma spp. isolates from sugar beet fields against Phytophthora drechsleri and P. cryptogea, the causal agents of Phytophthora root rot of sugar beet. During 2007–08, 85 isolates of Trichoderma spp. from sugar beet fields in eight parts of Fars province, Iran were isolated. Based on morphological and physiological characteristics, eight species could be distinguished: T. asperellum, T. atroviride, T. brevicompactum, T. harzianum, T. longibrachiatum, T. spirale, T. tomentosum and T. virens. Their antagonistic activities  including competition, colonization and antibiosis against Phytophthora isolates both in vitro and in planta were investigated. Different species and even different isolates of one species differed in their antagonistic capacities. High competitive abilities were shown by T. asperellum, T. atroviride, T. harzianum and T. virens in pre colonized plates, and by the former three species in dual cultures. T. harzianum and T. atroviride efficiently colonized both species of Phytophthora. T. asperellum Ksh2, T. virens DB6r, T. virens DB2 and T. virens DB3 and T. harzianum MS3 gave the highest growth inhibition. In in planta experiments, T. harzianum MS3 and FG4 and T. virens DB6r were the most efficient in suppressing root rot of sugar beet seedlings. Our results suggest that T. harzianum MS3 is the best native candidate for the biocontrol of this disease.