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A collection of Bacillus and Trichoderma isolates from Iran was investigated for the biological control of pear white root rot caused by Rosellinia necatrix. Among the isolates, B. amyloliquefaciens AP4, B. siamensis AP8 and T. harzianum T20a were selected based on their growth inhibition of R. necatrix in dual cultures, as well as by volatiles, diffusible extracts and culture filtrates. Four pear rootstocks (Pyrodwarf, OHF40, OHF60 and Williams) were assessed for white rot in the greenhouse following soil amendment with the three isolates. For OHF40 rootstock, none of the three isolates significantly reduced disease severity, whereas all three isolates significantly reduced disease severity for OHF69 rootstock. For Pyrodwarf rootstock, only T. harzianum T20a and B. amyloliquefaciens AP4 significantly reduced root rot, but all three isolates significantly reduced leaf fall. For Williams rootstock, all three isolates significantly reduced root rot, but only T. harzianum T20a significantly reduced leaf fall. Thus, the effectiveness of both the Bacillus and Trichoderma isolates was highly dependent upon the pear genotype. The lowest levels of white rot symptoms were observed in the Williams‐T. harzianum T20a interaction resulting in root rot severity of 46.6% and leaf fall of 4.7% at 70 dpi. While the effect of plant genotype on biocontrol activity has been reported frequently for Trichoderma, this is one of the first to report such an effect with a Bacillus biocontrol agent. Both Bacillus and Trichoderma can be effective biocontrol agents of pear white rot, but the plant genotype can have a major impact on their effectiveness. [ABSTRACT FROM AUTHOR]

White root rot is a serious soil-borne disease of several woods and crops. Recently, white root rot of tea shrubs and ornamental trees has increasingly been observed in Taiwan. Thirty-six isolates of white root rot pathogen, showing pear-shape swellings adjacent to the hyphal septa, had been isolated from samples of white root rot collected from Taiwan for about 4 years. The pathogen isolates produced Dematophora anamorph. Conidia of the pathogen were one-celled, hyaline, subglobal, with truncate base, 2.9–5.8 × 1.9–3.5 μm. Ascospore dimensions were in the range of 37.0–55.0 × 5.4–7.9 μm with a short, longitudinal and straight germ slit, which complied with Rosellinia necatrix. Based on molecular studies, the pathogen isolates collected from Taiwan except R701 were identified as R. nectarix. Isolate R701, which was relatively polymorphic in internal transcribed spacer DNA sequence than other isolates, was temporarily considered as R. necatrix-related pathogenic Rosellinia spp. All the tea cuttings ( Camellia sinensis) inoculated with isolates developed typical white root rot symptoms. Pathogenicity tests demonstrated the presence of variation in virulence among the Rosellina isolates. Most of the R. necatrix isolates originating from Acer morrisonense were less virulent than those that originated from other hosts. The pathogenic Rosellinia spp., isolate R701, was also highly virulent to both cultivars of tea cuttings. [ABSTRACT FROM AUTHOR]

Rosellinia necatrix, an ascomycete soil-inhabiting fungus, causes white root rot disease in a large number of plant species, especially fruit trees. The fungus, which occurs worldwide, is very aggressive and can kill infected trees. The biology and pathogenicity of the fungus are reviewed here, together with the current principal methods of disease control used in different pathosystems. [ABSTRACT FROM AUTHOR]

Summary: • The effect is reported here of cytochalasin E isolated from the fungus Rosellinia necatrix on photosynthesis in young leaves of Malus domestica (apple).• Cytochalasin E was administered via the petiole to excised leaves. The chlorophyll fluorescence emission spectrum and time resolved fluorescence decay were measured up to the point where visible leaf damage was observed.• Within 2 h, the ratio of fluorescence emission at 730 nm decreased with respect to the peak at 690 nm. Over 6 h a small blue shift in the 690 nm emission band to 685 nm was seen. The time resolved fluorescence decay showed changes over a similar timescale after administration of cytochalasin E. The control decay could be fitted by two components, τ1, 112 ps, τ2, 402 ps, but after 6 h treatment with cytochalasin E the decay required a further component τ3, 4.25 ns for a good fit.• Cytochalasin E has a direct effect on photosynthesis, possibly as a result of impairment of light harvesting. This might partially account for the pathogenicity of the root infecting R. necatrix. Fluorescence techniques may therefore provide an early detection system for the fungus, a necessary prerequisite for development of a control strategy. [ABSTRACT FROM AUTHOR]