Apple Rot Research Articles

Differentiation of Isolates of Glomerella cingulata and Colletotrichum spp. Associated with Glomerella Leaf Spot and Bitter Rot of Apples Using Growth Rate, Response to Temperature, and Benomyl Sensitivity

Cultural characteristics were investigated as a way to distinguish isolates of Glomerella cingulata and Colletotrichum spp. associated with Glomerella leaf spot and bitter rot of apples from those that cause only bitter rot. The growth rate, response to temperature, and benomyl sensitivity of 27 isolates of Glomerella cingulata, 12 isolates of Colletotrichum gloeosporioides, and 7 isolates of C. acutatum, collected from apple orchards located in the U.S. and Brazil and previously characterized based on morphology, vegetative compatibility, and mitochondrial DNA (mtDNA) haplotypes, were determined. These isolates represent the genetic and molecular diversity within isolates of C. gloeosporioides, C. acutatum, and G. cingulata from apples found in a previous study. Slower growth, lower optimum growth temperature, and less sensitivity to benomyl distinguished isolates of C. acutatum from isolates of G. cingulata and C. gloeosporioides. However, growth rate and benomyl sensitivity were not useful for distinguishing between G. cingulata and C. gloeosporioides or differentiating isolates of G. cingulata that cause leaf spot and bitter rot from those that only cause bitter rot. Accepted for publication 17 May 2005. Published 19 July 2005.

Population Diversity within Isolates of Colletotrichum spp. Causing Glomerella Leaf Spot and Bitter Rot of Apples in Three Orchards in North Carolina.

The population diversity within isolates of Glomerella cingulata and Colletotrichum spp. associated with Glomerella leaf spot and bitter rot of apples was studied in an orchard of cv. Granny Smith located in Wilkes County, NC, and one orchard each of cultivars Granny Smith and Gala located in Lincoln County, NC. Morphological characters and vegetative compatibility groups (VCGs) were used to determine diversity within the species. The relative frequencies of the morphological types found within each species in each orchard were also determined. G. cingulata was the predominant species associated with bitter rot in the three orchards and Glomerella leaf spot in the Gala orchard. In the three orchards, different morphological types were observed within isolates of G. cingulata and Colletotrichum acutatum, but not within isolates of Colletotrichum gloeosporioides. Isolates of C. gloeosporioides were not found in the orchard of cv. Granny Smith in Lincoln County. In the other two orchards, C. gloeosporioides represented the lowest proportion of the population. Three VCGs were found among isolates of G. cingulata (VCG-1, 2, and 6), two among isolates of C. gloeosporioides (VCG-9 and 10), and two among isolates of C. acutatum (VCG-15 and 16). VCGs 2, 6, 9, 10, 15, and 16 were found in the Granny Smith orchard in Wilkes County, VCGs 1, 2, and 6 in the Gala orchard in Lincoln County, and VCGs 2 and 6 in the Granny Smith orchard in Lincoln County. Differences in frequencies among the different morphological types found within the three orchards remained relatively similar throughout the season and from year to year, suggesting that the relative frequencies of G. cingulata, C. gloeosporioides, and C. acutatum remain stable in an orchard once the fungi are established.

Effects of culture media and environmental factors on mycelial growth and pycnidial production of Potebniamyces pyri

Potebniamyces pyri (anamorph Phacidiopycnis piri) is the causal agent of Phacidiopycnis rot of apples and pears. The disease has recently been recognized in pears in the USA. Little information on the basic biology of the fungus is available. In this paper, we report the effects of culture media, temperature, water potential and pH on mycelial growth, and the effects of media and light on pycnidia production. Prune juice agar was the best for rapid mycelial growth. Pear juice agar, apple juice agar, potato dextrose agar, and oatmeal agar (OMA) also favoured mycelial growth. Czapek-Dox agar was not suitable for mycelial growth. The fungus was able to grow at temperatures from -3 to 25 degrees C. Optimal mycelial growth occurred between 15 and 20 degrees. The average radial growth rate on OMA was 3.9 mm d(-1) at 15 degrees and 4.4 mm d(-1) at 20 degrees. Mycelial growth was not observed after 10 d at 30 degrees, but growth resumed at 20 degrees. The fungus failed to resume growth at 20 degrees after being incubated for 10 d at 35 degrees. The fungus was able to grow at water potentials as low as -4 MPa but no growth took place at -7.3 MPa. Active mycelial growth was observed on OMA at pH between 3.2 and 6.1. Optimal growth was observed at pH around 4 and no growth was observed at pH 7.1. No pycnidia or very few formed on the nine media at 20 degrees in the dark. Fluorescent light significantly stimulated formation of pycnidia. OMA was the best medium for production of pycnidia and macroconidia. Pycnidia that formed on 8-wk-old OMA cultures incubated at 20 degrees under 12 h dark/12 h light produced abundant macroconidia and the technique is recommended for inoculum production of conidia for research.

Fosfitos para o controle de podridões pós-colheita em maçãs ‘Fuji’ durante o armazenamento refrigerado

Foi conduzido um experimento com o objetivo de avaliar o efeito da aplicação de adubos foliares contendo fosfitos de potássio e fosfitos de cálcio mais boro sobre o controle de podridões em maçãs ‘Fuji’ durante a frigoconservação. O delineamento experimental utilizado foi o inteiramente casualizado com quatro repetições de 25 frutos. Foram realizadas quatro lesões distribuídas de forma eqüidistante na região equatorial dos frutos, com 3mm de diâmetro e 5mm de profundidade. Os frutos foram submersos em uma solução com suspensão de esporos, onde permaneceram por 20 segundos. Após, foram aplicados os tratamentos: 1 - Testemunha (água); 2 - Iprodione (75g 100L-1); 3 - cloreto de cálcio( CaCl2) a 2%; 4 - fosfito de potássio (250mL 100L-1) + CaCl2 (2%); 5 - fosfito de potássio (250mL 100L-1); 6 - fosfito de cálcio mais boro (300mL 100L-1); e 7 - fosfito de potássio (250mL 100L-1) na suspensão de esporos por uma hora. Os frutos foram armazenados em ambiente refrigerado à temperatura de 0°C durante 14 dias. As avaliações foram realizadas na saída da câmara e aos 2, 4, 6 e 8 dias a 20°C. Verificou-se que os frutos tratados com fosfito de potássio (250mL 100L-1) + CaCl2 (2%) apresentaram a menor incidência de podridões e o menor diâmetro de lesão. Esses resultados foram semelhantes aos obtidos com a aplicação do fungicida padrão Iprodione e superiores à aplicação de fosfito de potássio isoladamente. O uso de fosfito de cálcio mais boro não foi eficiente.

Effects of Treatment with a Composite Preparation (2-Chloroethylphosphonic Acid and Methacide) or Butylated Hydroxyanisole on Ethylene Release in Apples

We studied the effect of a Russian composite preparation (2-chloroethylphosphonic acid and methacide) and butylated hydroxyanisole on ethylene release in whole fruit and peel disks of two apple cultivars, Antonovka obyknovennaya (Antonovka) and Simirenko's rennet (Simirenko). Treatment with the composite preparation was followed by an increase in ethylene release from whole apples and peel disks. The development of microbial infection (fruit rot) in whole apples became less pronounced after the treatment. Treatment of whole apples with the antioxidant butylated hydroxyanisole (BHA) increased the intensity of ethylene release during the first subsequent days; thereafter, ethylene release decreased and was 10-15% lower than in the control on days 10-12. In model experiments, BHA decreased ethylene release from apple peel disks below control levels as early as on day 1 after the treatment. Antonovka apples gave quick responses to the treatment. In the late-ripening Simirenko apples, the response persisted for a longer period. Our results suggest that treatment with physiologically active preparations affects ethylene release, ripening, and preservation of apples in storage.

INTEGRATION OF CHEMICALS AND BIOCONTROL AGENTS FOR MANAGING WHITE ROOT ROT OF APPLE

ISHS XXVI International Horticultural Congress: Managing Soil-Borne Pathogens: A Sound Rhizosphere to Improve Productivity in Intensive Horticultural Systems INTEGRATION OF CHEMICALS AND BIOCONTROL AGENTS FOR MANAGING WHITE ROOT ROT OF APPLE

BIOCONTROL ACTIVITY OF ANTAGONISTIC YEASTS AGAINST PENICILLIUM EXPANSUM ON APPLE

Penicillium expansum causes severe rots on apple fruit during storage and shelf life. Aiming at the development of new antagonistic yeast active in controlling postharvest pathogens of fruit, several isolates were obtained from fig (Ficus carica) and cactus pear (Opuntia ficus-indica) grown in untreated orchards in Northern Sardinia (Italy). Two yeast strains of Candida guillermondii were selected for their remarkable antagonistic properties against P. expansum on apple. A film-forming strain of Saccharomyces cerevisiae isolated from wine was also included in the experiments. In trials carried out on the cv. Golden Delicious and Fuji, the yeasts applied alone or in the presence of various additives reduced apple rot with up to 100% efficacy. Killed yeast cells and culture filtrates had no biocontrol activity. Addition of different sugars in the apple wound had no detrimental effect on the biocontrol potential of the tested yeasts. Conversely, several nitrates significantly inhibited the antagonistic capability of C. guillermondii, thus suggesting that competition for nitrogen should play a major role in the biocontrol activity of the antagonistic yeast.

Effect of Preharvest Application of Cyprodinil on Postharvest Decay of Apples Caused by Botrytis cinerea.

Dry-eye rot and gray mold of apple are important diseases caused by Botrytis cinerea. Fungicides available for their control are lacking, and this study was conducted to determine if cyprodinil (Vangard) could be used for this purpose. The mean EC50 value of cyprodinil for 32 Botrytis spp. isolates (27 from apple) was 0.02 μg ml-l, indicating that apple isolates are generally very sensitive. Some of the isolates (19%) were less sensitive and had EC50 values greater than 0.03 μg ml-l, and one isolate from 'Gala' apple was considerably less sensitive at 0.095 μg ml-l. Bloom sprays of cyprodinil alone in 1998 and 1999 or in combination with myclobutanil or metiram in 1998 reduced Botrytis spp. infection on developing fruit. Postharvest application of cyprodinil in 1998 indicated that cyprodinil protected apples from gray mold for 3 months. Cyprodinil applied 2 to 3 weeks before harvest in 1999 reduced lesion diameters 68 and 62% on 'Jonagold' and 'Gala' apples, respectively, that had been wounded and inoculated with B. cinerea after storage at 1°C for 6 months. In similar trials on 'Gala' apples in 2000 and 2001, preharvest applications of cyprodinil consistently reduced gray mold incidence and lesion diameter on inoculated apples stored for 6 months. New preharvest use patterns for cyprodinil are discussed for control of postharvest diseases caused by B. cinerea.

Control of bitter rot and blue mold of apples by integrating heat and antagonist treatments on 1-MCP treated fruit stored under controlled atmosphere conditions

To maximize control of fruit decay by alternatives to synthetic fungicides after harvest, various control strategies can be integrated. Treatment of fruit with antagonists is one of the most promising alternatives. This treatment, however, has little or no eradicative activity, which limits its use. Fruit treatment with hot air (at 38 °C) for 4 d has eradicative but no residual activity against blue mold (caused by Penicillium expansum ) on apple, and 1-methylcyclopropene (1-MCP) is an ethylene receptor inhibitor which slows apple maturation and, presumably, extends action of natural defense mechanisms. An antagonist, Metchnikowia pulcherrima T5-A2, was used in combination with heat and 1-MCP treatments to control bitter rot (caused by Colletotrichum acutatum ) and blue mold (caused by P. expansum ) on ‘Golden Delicious’ apples under controlled atmosphere (CA) conditions. 1-MCP treatment increased bitter rot and blue mold decays, but both of these decays were effectively controlled on 1-MCP treated apples by a combination of the antagonist and heat treatments. C. acutatum is a weaker pathogen than P. expansum , and bitter rot, even on the control treatments, developed only after 4 months in CA storage followed by 2 weeks incubation at 24 °C. In contrast, non-treated fruit inoculated with P. expansum were completely decayed after 2 months in CA. The antagonist controlled bitter rot more effectively than blue mold, while blue mold was more effectively controlled by heat treatment. The use of 1-MCP on harvested fruit to inhibit maturation can predispose fruit to decay, but the alternatives to synthetic fungicides are capable of preventing this increase in decay.

Apple Quality, Storage, and Washing Treatments Affect Patulin Levels in Apple Cider

Patulin is a mycotoxin produced primarily by Penicillium expansum, a mold responsible for rot in apples and other fruits. The growth of this fungus and the production of patulin are common in fruit that has been damaged. However, patulin can be detected in visibly sound fruit. The purpose of this project was to determine how apple quality, storage, and washing treatments affect patulin levels in apple cider. Patulin was not detected in cider pressed from fresh tree-picked apples (seven cultivars) but was found at levels of 40.2 to 374 μg/liter in cider pressed from four cultivars of fresh ground-harvested (dropped) apples. Patulin was not detected in cider pressed from culled tree-picked apples stored for 4 to 6 weeks at 0 to 2°C but was found at levels of 0.97 to 64.0 μg/liter in cider pressed from unculled fruit stored under the same conditions. Cider from controlled-atmosphere-stored apples that were culled before pressing contained 0 to 15.1 μg of patulin per liter, while cider made from unculled fruit contained 59.9 to 120.5 μg of patulin per liter. The washing of ground-harvested apples before pressing reduced patulin levels in cider by 10 to 100%, depending on the initial patulin levels and the type of wash solution used. These results indicate that patulin is a good indicator of the quality of the apples used to manufacture cider. The avoidance of ground-harvested apples and the careful culling of apples before pressing are good methods for reducing patulin levels in cider.

Cultural Management of Microbial Community Structure to Enhance Growth of Apple in Replant Soils

ABSTRACT Apple replant disease typically is managed through pre-plant application of broad-spectrum soil fumigants including methyl bromide. The impending loss or restricted use of soil fumigants and the needs of an expanding organic tree fruit industry necessitate the development of alternative control measures. The microbial community resident in a wheat field soil was shown to suppress components of the microbial complex that incites apple replant disease. Pseudomonas putida was the primary fluorescent pseudomonad recovered from suppressive soil, whereas Pseudomonas fluorescens bv. III was dominant in a conducive soil; the latter developed within 3 years of orchard establishment at the same site. In greenhouse studies, cultivation of wheat in replant orchard soils prior to planting apple suppressed disease development. Disease suppression was induced in a wheat cultivar-specific manner. Wheat cultivars that enhanced apple seedling growth altered the dominant fluorescent pseudo-monad from Pseudomonas fluorescens bv. III to Pseudomonas putida. The microbial community resident in replant orchard soils after growing wheat also was suppressive to an introduced isolate of Rhizoctonia solani anastomosis group 5, which causes root rot of apple. Incorporation of high glucosinolate containing rapeseed ('Dwarf Essex') meal also enhanced growth of apple in replant soils through suppression of Rhizoc-tonia spp., Cylindrocarpon spp., and Pratylenchus penetrans. Integration of these methods will require knowledge of the impact of the biofumigant component on the wheat-induced disease-suppressive microbial community. Implementation of these control strategies for management of apple replant disease awaits confirmation from ongoing field validation trials.

Wheat Genotype-Specific Induction of Soil Microbial Communities Suppressive to Disease Incited by Rhizoctonia solani Anastomosis Group (AG)-5 and AG-8

ABSTRACT The induction of disease-suppressive soils in response to specific cropping sequences has been demonstrated for numerous plant-pathogen systems. The role of host genotype in elicitation of the essential transformations in soil microbial community structure that lead to disease suppression has not been fully recognized. Apple orchard soils were planted with three successive 28-day cycles of specific wheat cultivars in the greenhouse prior to infestation with Rhizoctonia solani anastomosis group (AG)-5 or AG-8. Suppressiveness to Rhizoctonia root rot of apple caused by the introduced isolate of R. solani AG-5 was induced in a wheat cultivar-specific manner. Pasteurization of soils after wheat cultivation and prior to pathogen introduction eliminated the disease suppressive potential of the soil. Wheat cultivars that induced disease suppression enhanced populations of specific fluorescent pseudomonad genotypes with antagonistic activity toward R. solani AG-5 and AG-8, but cultivars that did not elicit a disease suppressive soil did not modify the antagonistic capacity of this bacterial community. When soils were infested prior to the initial wheat planting, all cultivars were uniformly susceptible to R. solani AG-8. However, when pathogen inoculum was added after three growth-cycles, wheat root infection during the fourth growth-cycle varied in a cultivar specific manner. The same wheat cultivar-specific response in terms of transformation of the fluorescent pseudomonad community and subsequent suppression of Rhizoctonia root rot of apple was observed in three different orchard soils. These results demonstrate the importance of host genotype in modification of indigenous saprophytic microbial communities and suggest an important role for host genotype in the success of biological control.

Phylogenetic analysis of Alternaria spp. associated with apple core rot and citrus black rot in South Africa

Dry core rot of apple (DCR) and Alternaria black rot of citrus (ABR) have in the past respectively been ascribed to Alternaria alternata and A. citri. In recent years, however, it has been speculated that several other species of Alternaria could also be associated with these diseases. In an attempt to elucidate the identity of these taxa, 25 isolates associated with DCR, and 26 isolates associated with ABR were selected for molecular characterisation. Nucleotide sequences of 1116 sites including the histone gene section and the internal transcribed spacers (ITS 1 and 2) of the rRNA gene were determined for these isolates. The gene trees generated from the individual and combined data sets using maximum parsimony, maximum likelihood and neighbour-joining analysis methods distinguished five clades with strong bootstrap support, namely Alternaria sp., A. arborescens, A. infectoria, A. tenuissima, and a clade containing isolates variable in morphology, referred to as the Alternaria group. In the alignment of the combined ITS and histone data set, unique transition/transversion substitutions, as well as positional insertions and deletions were observed for each of the above clades. In addition, key sequences in the form of serial composing nucleotides in both the ITS and histone sections of the alignment were also discovered for the molecular identification of A. arborescens, A. infectoria and A. tenuissima. The final phylogeny also indicated that no host specificity existed among the species associated with these two post-harvest disease complexes. Contrary to the host specificity observed on leaf diseases of these hosts in the field, it appears that the post-harvest diseases are the result of adverse storage conditions and opportunism of different small-spored Alternaria spp.

The Canadian Phytopathological Society Annual Meeting, Waterton Lakes National Park, Alberta, 2002

The Canadian Phytopathological Society Annual Meeting, Waterton Lakes National Park, Alberta, 2002

First Report of Phytophthora syringae Causing Rot on Apples in Cold Storage in the United States.

A decay of 'Granny Smith' apples (Malus domestica Borkh.) was observed in 1988, 1990, and 1991 on fruit grown in the lower Hood River Valley of Oregon and stored at 0°C. Harvested fruit were drenched with thiabendazole and stored in October in all years. In mid-November, fruit were sized, drenched with sodium hypochlorite, and returned to cold storage. Decay was observed in January when fruit were removed from cold storage, sorted, and packed. Decayed areas were light brown and firm with a slightly indefinite margin. Losses were less than 1% of fruit packed. Diseased fruit were surface-disinfested with 95% ethanol, and tissue pieces were transferred aseptically to potato dextrose agar acidified with lactic acid and incubated at approximately 22°C. The fungus consistently isolated was identified as Phytophthora syringae (Kleb.) Kleb. based on morphological characters (3). Sporangia were persistent and averaged 60 μm long (range 59 to 69) × 40 μm wide (range 37 to 43). Antheridia were paragynous, and oospores averaged 37 μm (range 31 to 46). 'Golden Delicious', 'Granny Smith', and 'Gala' apples were inoculated with mycelial plugs from a 7-day-old culture of P. syringae and incubated 12 days at 5°C and 7 to 12 days at 22°C. Twenty fruit of each cultivar were used-ten were inoculated, and ten uninoculated fruit served as controls. Lesions developed on all inoculated fruit but not on uninoculated controls. Lesions were spherical, chocolate brown, and firm with no evidence of external mycelia. Lesion morphology was similar on all cultivars. P. syringae was reisolated from lesion margins of all infected fruit. This postharvest decay of apples has not been observed in the Hood River Valley since 1991. Fruit rot of apples caused by P. syringae is known in Canada (1) and is common in the United Kingdom (2), but has not been reported previously in the United States. To our knowledge, this is the first report of postharvest decay of apples by P. syringae in the United States.

Characterisation of Alternaria species-groups associated with core rot of apples in South Africa

Alternaria core rot of red apple cultivars is a serious post-harvest disease in South Africa. Thirty isolates of Alternaria spp. previously isolated from apple, together with reference isolates of A. alternata and A. infectoria, were characterised and grouped according to their sporulation patterns and conidial morphology. Isolates were identified as belonging to A. arborescens, A. infectoria and A. tenuissima species-groups. The isolates were also analysed for production of mycotoxins and other secondary metabolites and their cultural characteristics on DRYES medium were recorded. Apple fruit were artificially inoculated with the thirty-two Alternaria isolates and the resulting lesion types were recorded. A data matrix was constructed using all these characters and subjected to cluster analysis to show the similarity between different isolates. Isolates classified as A. infectoria species-group based on sporulation patterns, cultural and biochemical data could be easily differentiated from isolates classified as A. arborescens and A. tenuissima species-groups, which clustered close together. Isolates were further subjected to DNA sequence analysis of the internal transcribed spacers (ITS) 1 and 2 of the nuclear rRNA gene. A phylogeny estimated from the ITS data set delineated two clades, one being typified by the A. infectoria species-group, and the other representing both A. tenuissima and A. arborescens species-groups. The ITS data set clearly separated isolates of A. infectoria species-group from the other species-groups, as all isolates had a distinction of 35 base pair insertions and 6 base pair deletions in the ITS regions. The results obtained in the present study showed that the major pathogens associated with core rot disease of Top Red apples in South Africa belong to the A. tenuissima species-group.

British Columbia Regional Meeting, 2001, The Canadian Phytopathological Society / Réunion régionale de la Colombie-Britannique, 2001, La Société Canadienne de Phytopathologie

British Columbia Regional Meeting, 2001, The Canadian Phytopathological Society / Réunion régionale de la Colombie-Britannique, 2001, La Société Canadienne de Phytopathologie

Mechanisms of natural soil suppressiveness to soilborne diseases.

Suppressive soils are characterized by a very low level of disease development even though a virulent pathogen and susceptible host are present. Biotic and abiotic elements of the soil environment contribute to suppressiveness, however most defined systems have identified biological elements as primary factors in disease suppression. Many soils possess similarities with regard to microorganisms involved in disease suppression, while other attributes are unique to specific pathogen-suppressive soil systems. The organisms operative in pathogen suppression do so via diverse mechanisms including competition for nutrients, antibiosis and induction of host resistance. Non-pathogenic Fusarium spp. and fluorescent Pseudomonas spp. play a critical role in naturally occurring soils that are suppressive to Fusarium wilt. Suppression of take-all of wheat, caused by Gaeumannomyces graminis var. tritici, is induced in soil after continuous wheat monoculture and is attributed, in part, to selection of fluorescent pseudomonads with capacity to produce the antibiotic 2,4-diacetylphloroglucinol. Cultivation of orchard soils with specific wheat varieties induces suppressiveness to Rhizoctonia root rot of apple caused by Rhizoctonia solani AG 5. Wheat cultivars that stimulate disease suppression enhance populations of specific fluorescent pseudomonad genotypes with antagonistic activity toward this pathogen. Methods that transform resident microbial communities in a manner which induces natural soil suppressiveness have potential as components of environmentally sustainable systems for management of soilborne plant pathogens.

Glasshouse screening for biological control agents of Phytophthora cactorum on apple (Malus domestica)

In glasshouse trials, 504 fungi and 120 bacteria and actinomycetes were evaluated for their ability to control root rot of apple (Malus domestica Borkh.) seedlings caused by Phytophthora cactorum (Lebert & Cohn) Schroeter. Ten fungi consistently reduced apple seedling mortality in two screens. In a further seedling screen, disease caused by P. cactorum was significantly (P < 0.05) lower in pots treated with Microsphaeropsis sp. F15, Oidiodendron sp. F762, Paecilomyces sp. F46, Penicillium sp. F120, T. koningii F176, F929, and F950, and T. harzianum TW. 178 (1–30% incidence) compared with the pathogen control (71% incidence). Five isolates provided control statistically equivalent (P < 0.05) to that obtained by the fungicide treatment (metalaxyl + mancozeb). In a separate bacterial screen, Flavobacterium sp. B219 significantly reduced seedling mortality (15%) compared with the pathogen control (77%). This bacterium provided 65% disease control of P. cactorum on MM 106 apple rootstocks over a 14‐week period (statistically equivalent to the fungicide) and significantly increased rootstock height, total fresh weight, and rootstock dry weights. Although 10 fungal treatments also provided a level of disease control (25–73%) on rootstocks after 14 weeks, only Penicillium sp. F120 (73%) gave significant control. Across all trials, Flavobacterium sp. B219, Oidiodendron sp. F762, and T. harzianum TW.178 consistently provided control that was statistically equivalent to the fungicide treatment.

Impact of carbon starvation on stress resistance, survival in soil habitats and biocontrol ability of Pseudomonas putida strain 2C8

Exposure to carbon-limited growth conditions has been shown to induce resistance to a variety of environmental stresses in bacteria. Adaptation to nutrient-limited conditions by repeated culture on soil agar media was found to induce resistance to osmotic tension, oxidative stress and carbon limited culture conditions in Pseudomonas putida strain 2C8. Rifampicin resistant derivatives of strain 2C8 adapted to nutrient-limited conditions (strains 2C8-26A rif and 2C8-28C rif) did not exhibit enhanced survival in bulk soil relative to the parental strain. However, colonization of the apple rhizosphere by 2C8-26A rif and 2C8-28C rif was superior to that of the parental strain, 2C8 rif. Improved colonization of the apple rhizosphere was not the result of an elevated ability to utilize apple root exudates as a sole carbon source. Enhanced colonization of the rhizosphere by carbon starved derivatives of 2C8 rif was associated with improved biological control of Rhizoctonia root rot of apple caused by an introduced strain of Rhizoctonia solani AG 5. These findings demonstrate that inoculum production conditions can significantly alter the survival and efficacy of strain 2C8, and should be carefully considered in optimizing the use of this biocontrol rhizobacterium.