Brown root rot (BRR), caused by the white rot fungus Phellinus noxius, is an epidemic disease of diverse broadleaved and coniferous tree species in many tropical and subtropical regions. Flooding and trenching control measures are difficult to implement, and chemical controls can have an adverse impact on ecosystems. Previous studies have provided in vitro evidence for the potential use of Trichoderma spp. for biocontrol of BRR. Here, we analyzed the in vitro antagonistic and mycoparasitic abilities of four Trichoderma spp. isolates against four P. noxius isolates in dual culture and Ficus microcarpa wood blocks. A convenient inoculation system based on root inoculation of a highly susceptible loquat (Eriobotrya japonica) with P. noxius-colonized wheat-oat grains was developed to examine the effect of Trichoderma treatment in planta. Preventive application of Trichoderma asperellum TA, the isolate showing high antagonistic activity in vitro, was effective in preventing and delaying the wilting of P. noxius-inoculated loquat cuttings in greenhouse trials. To understand the specific niche in which T. asperellum TA interacts with P. noxius, KOH-aniline blue fluorescence microscopy was used to investigate the colonization of loquat roots by P. noxius and/or T. asperellum TA. Dilution plating assays were also conducted to quantify Trichoderma populations in the rhizosphere and potting mix. T. asperellum TA was able to robustly establish in the rhizosphere and potting mix but with scarce root penetration limited to the superficial layer. We discuss the timing and strategy for applying antagonistic Trichodema sp. on living trees or in BRR-infested areas for BRR management.

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Citrus bacterial canker caused by Xanthomonas axonopodis pv. citri is a devastating disease resulting in significant crop losses in various citrus cultivars worldwide. A biocontrol agent has not been recommended for this disease. To explore the potential of bacilli native to Taiwan to control this disease, Bacillus species with a broad spectrum of antagonistic activity against various phytopathogens were isolated from plant potting mixes, organic compost and the rhizosphere soil. Seven strains TKS1-1, OF3-16, SP4-17, HSP1, WG6-14, TLB7-7, and WP8-12 showing superior antagonistic activity were chosen for biopesticide development. The genetic identity based on 16S rDNA sequences indicated that all seven native strains were close relatives of the B. subtilis group and appeared to be discrete from the B. cereus group. DNA polymorphisms in strains WG6-14, SP4-17, TKS1-1, and WP8-12, as revealed by repetitive sequence-based PCR with the BOXA1R primers were similar to each other, but different from those of the respective Bacillus type strains. However, molecular typing of the strains using either tDNA-intergenic spacer regions or 16S–23S intergenic transcribed spacer regions was unable to differentiate the strains at the species level. Strains TKS1-1 and WG6-14 attenuated symptom development of citrus bacterial canker, which was found to be correlated with a reduction in colonization and biofilm formation by X. axonopodis pv. citri on leaf surfaces. The application of a Bacillus strain TKS1-1 endospore formulation to the leaf surfaces of citrus reduced the incidence of citrus bacterial canker and could prevent development of the disease.

1984. Ethylene production and toxigenicity of methionine and its derivatives with riboflavin in cultures of VerticUUum, Fusarium and Colletotrichum species exposed to light. Ethylene was produced by VerticUUum dahliae Kleb. grown in liquid Czapek's medium. The rate of ethylene production was enhanced by light but was not affected by shaking or the growth rate of the cuitures. L-, D-and OL-methionine, DL-ethionine and a-keto-y-methylthiobutyric acid (KMBA) were good substrates for ethyiene production. KMBA may be an intermediate in ethylene production and it appears to be degraded to ethylene either enzymatically by peroxidase or photochemically in the presence of riboflavin. Addition of riboflavin or briefly heating the cuitures to 10()°C enhanced ethylene production greatly, whiie the addition of sodium azide, potassium cyanide and cataiase were very inhibitory. The SS4 (non-defoiiating) pathotype of V. dahliae produced significantly more ethylene (up to 108.4 nl ethylene h' from 20 ml-10-day-old cultures) than did the T9 (dei'oliating) pathotype with all substrates tested. The results suggest that the in vitro rate of ethylene production is not related to the relative virulence of pathotypes of V. dahliae on cotton. A number of VerticUUum species, Fusarium oxysporum f. sp. vasinfectum and Colletotrichum dematium var. truncatum were able to produce ethylene in liquid Czapek"s medium containing 1 mM I,-methionine under continuous light. Riboflavin, although highly stimuiatory to ethylene production, caused a fungicidal reaction to all the fungi tested in Czapek's medium containing L-methionine under continuous light. The fungicidal effect of the riboflavin-methionine-light combination occurred at concentrations of riboflavin and methionine less than 1.33 \xM and 0.5 mM, respectively. No fungicidal activity was detected when the cultures were grown in total darkness or when either methionine or riboflavin was omitted from the culture medium.Additional key words -KMBA, Photodynamic effect.

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