Rot Test Research Articles

Decay resistance of treated wood with functionalised commercial silicones

Three commercial silicone emulsions with different functional groups i.e., quat-silicone micro-emulsion (<40 nm particle size), amino-silicone macro-emulsion (110 nm), and silicone macro-emulsion with alkyl-modified side groups (740 nm) were used to protect wood samples against fungal decay. The addition of the emulsions to an agar growth medium revealed that all three silicone formulations inhibited the growth of Coniophora puteana and Trametes versicolor compared to the controls without silicone. Wood mini-blocks of pine sapwood and beech wood were treated with 2%, 5%, 10%, and 15% concentration of silicone emulsions and tested for their resistance against basidiomycete decay. Quat-silicone and amino-silicone emulsions at higher concentrations imparted resistance of wood to both types of basidiomycetes, while the alkyl-modified silicone formulation did not enhance the resistance. In a soft rot test according to ENV 807, wood treated with an amino-sililcone emulsion showed the lowest weight loss and loss of dynamic MOE. Quat-silicone micro-emulsion had a lower effect, while the alkyl-modified silicone emulsion did not cause reduction in weight and strength loss compared to the untreated controls. The increased resistance against soft rot might be attributed to a lag in fungal colonization rather than to a sustained effect of protection.

Reação de genótipos de Phaseolus vulgaris à podridão do colo e ao oídio

A podridão do colo (Sclerotium rolfsii) e o oídio (Erysiphe polygoni) são de constante ocorrência na cultura do feijoeiro (Phaseolus vulgaris) no estado de Santa Catarina. O uso de genótipos com resistência genética é uma das alternativas de manejo destas doenças. Avaliou-se a reação a podridão e ao oídio em 80 e 75 genótipos de feijão respectivamente. Os testes foram conduzidos em casa de vegetação em um delineamento em blocos ao acaso. Para os testes com a podridão do colo, cada semente dos genótipos foi inoculada com dois esclerócios de S. rolfsii. A infecção por oídio ocorreu naturalmente. Usou-se a cv. Rio Tibagi como padrão de média resistência à podridão ou de média susceptibilidade ao oídio. Os genótipos menos afetados pela podridão do colo e que diferiram da 'Rio Tibagi' foram: grupo preto - LA 95105428, FT 646 e Acesso 57; grupo colorido - BAF 50. A maioria dos genótipos não diferiu da 'Rio Tibagi', porém o mais afetado pela podridão do colo foi o BAF 10. Os genótipos mais susceptíveis ao oídio foram o Acesso 57 (Preto) e o FGP CF 101 (Preto). Os genótipos menos afetados pelo oídio foram: grupo preto - Acessos 60 e 36, FGP CF 058, TB 95-03, LM95103904 e LP 96-58; grupo colorido - Akitã, LP 94-1 e LP 96-162.

The Significance of Accelerated Laboratory Testing Methods Determining the Natural Durability of Wood

Summary Under laboratory conditions basidiomycete and soft rot tests were carried out on more than 20 hardwood species and 3 softwood species together with reference species to evaluate their natural durability according to the European standard EN 350 part 1. The basidiomycetes tests were carried out using Gloeophyllum trabeum, Coniophora puteana, Poria placenta and Coriolus versicolor, all fungal strains in malt agar tests and in agreement with the EN 113. Such tests did not provide a solid basis to classify all wood species according to known durability classes (EN 350, part 2). There was only a distinct differentiation noted between those species belonging to the group with a durability classified 1 to 3 and those classified 4 to 5. Conclusively, only limited additional information on durability of tropical hardwoods was gained from brown rot tests. Despite both types of laboratory tests on soft rot, prescribed in ENV 807 (vermiculite and soil) which show the essential differences to the basidiomycete test results, it has not been possible to classify the durability subdivisions in a more substantial way. Adding to these tests the durability classification, based upon a field stake test (EN 252) and a greenhouse accelerated stake test, was also carried out. Using this last method, results can be gathered more rapidly and consequently confirm the efficiency of lab tests. Generally it is perceived that lab tests and accelerated tests are important tools in the prediction of the natural durability of wood. To further improve the predictability value, durability testing would be enhanced when using a hazard class orientation. Therefore the function of the conclusive end product can be identified in a more obvious way.

First Report of Basil Leaf Spot Caused by Pseudomonas cichorii in Louisiana and Cultivar Screening Results.

A leaf spot of basil, Ocimum basilicum L., was observed on container-grown and field plantings of cultivars Aussie Sweet and Sweet Basil. The disease was of minor importance under field conditions, but was of potential economic importance in seedling production. Gray to black, watersoaked, necrotic spots commonly developed at leaf margins. Large numbers of bacteria were released from cut lesions when viewed by light microscopy. Single colony bacterial isolates were established on nutrient dextrose agar (NDA) and yeast extract-dextrose-calcium carbonate agar (YDC). Pathogencity tests were performed by misting a water suspension containing 104 bacterial cells per ml on healthy basil plants. Plants were held for 24 h in a dew chamber at 26°C and then moved to a greenhouse for observation. Typical leaf spots developed on inoculated plants in 2 days, but not on healthy control plants, and the bacterium was reisolated. The bacterium was characterized as a gram-negative, motile rod, negative for potato rot test, positive in tobacco hypersensitivity test, and oxidase positive. Isolates were identified as Pseudomonas cichorii according to the Biolog Microplate system (similarities ranged from 0.937 to 0.995). Screening tests were conducted by inoculating 15 basil cultivars, six replicates each, and rating them for disease severity based on a scale of 1 to 5 in which 1 = no disease and 5 = dead plants. Cultivars most resistant to bacterial leaf spot (ratings in parentheses are averages of two tests and those followed by the same letter are not significantly different according to Tukey's Studentized Range Test, P = 0.05) were Green Bouquet (2.0 a), Piccolo (2.2 a), Mrs. Burn's Lemon (2.2 a), Genovese (2.4 a), and Dark Opal (2.5 ab). Moderately susceptible cultivars were Bush Green (2.8 abc), Sweet Basil (2.8 abc), Large Green (2.9 abcd), Lemon (3.1 abcd), and Mexican Spice (3.6 bcd). The most susceptible cultivars were Lettuce Leaved (3.8 cd), Thai (3.8 cd), Napoletano (4.0 de), Green Ruffles (5.0 e), and Purple Ruffles (5.0 e). Bacterial leaf spot of basil caused by P. cichorii was first reported in the U.S. from Florida (1). Other bacterial diseases reported on basil include leaf blight from Egypt caused by P. syringae (2) and leaf necrosis from California caused by P. viridiflava (3). This is the first report on the occurrence of basil bacterial leaf spot in Louisiana and the first reported information on cultivar susceptibility.

Analysis of conductance responses during depolymerization of pectate by soft rot Erwinia spp. and other pectolytic bacteria isolated from potato tubers.

Different bacteria isolated from potato tubers were screened for their pectolytic properties by examining pitting in polypectate agar, recording conductance responses in polypectate medium and performing potato tuber soft rot tests. For bacteria found positive in conductimetry, the role of polygalacturonase (PG) and pectate lyase (PL) in the generation of conductance changes in a polygalacturonic acid (PGA) medium was further analysed using enzyme activity staining after gel electrophoresis and high-performance anion exchange chromatography. The extent of the conductance changes during depolymerization of PGA was dependent on the amounts of galacturonate monomers and oligomers accumulated in the medium. In comparison with an unidentified saprophyte and a Klebsiella strain, both mainly having PL activity, soft rot Erwinia spp. rapidly produced larger conductance responses, due to a combined action of multiple forms of PG and PL. The responses of Erwinia spp. were initially associated with the accumulation of large amounts of monomers and saturated dimers to heptamers, due to PG activity. Subsequently, as well as monomers and saturated dimers, large amounts of unsaturated dimers were also detected, due to PL activity. The role of PG as an important conductimetric factor was also demonstrated for a pectinase preparation derived from Aspergillus niger. Besides detection, automated conductimetric assays in pectate media may also be useful for monitoring of pectolytic activity in pectinase preparations and for screening of pectolytic activity of microorganisms under different media and growth conditions.

Assessing six Austrian potato cultivars for resistance toErwinia carotovora subsp.atroseptica

The susceptibility of six new Austrian cultivars to soft rot, stem rot and blackleg caused byErwinia carotovora subsp.atroseptica was assessed over 2 years in two locations. Soft rot susceptibility was assessed by whole tuber and half tuber tests, stem rot by stem inoculation and blackleg by planting inoculated tubers in the glasshouse. The susceptibility of the cultivars tested with the tuber and blackleg test methods were in general agreement. The half tuber test was more precise in differentiating intermediate levels of susceptibility than the whole tuber test. The reaction of the cultivars to soft rot could be classified as susceptible (Gina and Romina), moderately susceptible (Ditta, Sonja and Bintje), or slightly susceptible (Treff, Komet and Desiree). Results from the stem rot test did not agree with this classification and also depended upon the physiological state of plants as influenced by growing season and glasshouse conditions.

Infection of flowers and fruits of red raspberry by Botrytis cinerea

The frequency and site of symptomless infection of flower buds, flowers, and fruits of red raspberry by Botrytis cinerea was studied using surface‐disinfestation and culture techniques. Flower buds were rarely infected but open flowers were rapidly colonized and necrotic stamens and styles were an important source of infection for the developing fruit. The receptacle tissue within the drupelet cluster cavity was mostly sterile. Dichlofluanid sprays reduced symptomless infection of fruits and were more effective when applied early. Post‐harvest rot tests indicated that incidence of grey mould was not related to symptomless infection unless fruits were surface‐disinfested before subjecting to the rotting test.

The effect of inoculating flowers and developing fruits with Botrytis cinerea on post‐harvest grey mould of red raspberry

SUMMARYRaspberry flowers were inoculated in the glasshouse and field with dry conidia of Botrytis cinerea and the fruits derived from them subjected to post‐harvest rot tests at c. 20°C and high humidity. Apparently healthy fully‐ripe picked fruits derived from inoculated flowers developed grey mould faster than those from non‐inoculated flowers in all tests.In the glasshouse experiments, fruits from inoculated tightly closed flower buds rotted more slowly than those from inoculated open flowers or those at later developmental stages. Fruits from inoculated whole flowers rotted more rapidly than those from emasculated flowers; the addition of pollen to emasculated flowers had little effect on post‐harvest grey mould.In the dry summer of 1984 no fruits in the field from inoculated whole flowers rotted before ripening, but in the wet season of 1985 pre‐harvest grey mould was common and the surviving healthy fruits rotted in c. 1 day after picking.Only minor differences were detected in host susceptibility to post‐harvest grey mould in both glasshouse and field tests, the ranking of genotypes varied depending on whether or not flowers had been inoculated. The susceptibility of pistils of 40 Rubus genotypes to infection was examined 7 and 28 days after inoculation of stigmas with dry conidia. Conidia germinated on the stigmas and produced hyphae which grew through transmitting tissues of the styles to infect carpels symptomlessly in 17 red raspberries, one blackberry, two Rubus spp. and one hybrid. No germination occurred on stigmas of cv. Carnival and New York Selection 817.