A study involving variation in strains of the potato scab organism as isolated from a soil in British Columbia is reported. Associated with this is a study of soils from scab-free and scab-infested areas. Exchange capacity and related studies of a number of soil samples indicate a trend toward higher average exchange capacity, higher average exchange calcium and higher average calcium-potassium ratios in the samples from scab-infested areas. There is also a trend toward higher organic matter content and lighter soil textures in the scab-producing soils. In spite of these trends no definite correlations can be established under the method of soil sampling adopted. Thirty-four strains of Streptomyces scabies isolated from diseased White Rose tubers grown on the ranch vary markedly in cultural characteristics and in pathogenicity. The effect of hydrogen ion concentration on four of these strains shows a positive correlation between pH, amount of growth and hydrogen ion concentration up to the optimum pH of 7 to 8 and beyond this range a negative correlation exists. The inhibiting acid pH is 3.4 for two strains and between 4.0 and 5.5 for the other strains. The limiting alkaline pH appears to be beyond pH 11.6. Microphotographs of the Streptomyces scabies show typical open spirals and chains of conidia 0.5 to 1.0 microns in diameter. Scab control measures conducted in pots in the greenhouse and using a severely scab-infested soil sample from the ranch indicate no control by mercuric chloride applications. Applications of sulphuric acid, sulphur and calcium hydroxide indicate that a pH of 8.0 or greater is an effective but not complete control. An acid pH of 5.0 gives less control than pH 8.0 and more acidic reactions give even less control. The applications of these necessary to effect control are too high to be of practical value. The fungicidal effect of compound P-162 as determined under laboratory procedures is no indication of its efficacy in the field or greenhouse. Laboratory technique indicates that most strains are completely inhibited at 100 to 230 parts per million of compound P-162 while in the greenhouse tests 40 parts per million proved effective in giving partial control. The practical value of P-162 in the field is as yet to be determined since its commercial value and its usefulness as a control measure in the field is unknown. / Land and Food Systems, Faculty of / Graduate

Thesis (M. Sc.(Plant Pathology))--University of Pretoria, 2006. / Includes bibliographical references. Available on the Internet via the World Wide Web.

No description available.

The root system is a vital and dynamic part of a plant throughout its lifetime. Its spatial distribution is the consequence of multiple interactions with the surrounding soil medium. In particular, the presence of pathogens in soil may influence the development of the plant, especially the below-ground part, in both its physiology and its structure. Studies of diseased plant roots may take different approaches and investigate disease effects at different levels. In this study, two groups of four potato (Solanum tuberosum L.) plants were grown in middle-sized plastic pots in a greenhouse, and their root systems, together with the soil medium (i.e., sieved and autoclaved homogeneous sand), were submitted to computed tomography (CT) scanning every two weeks until 10 weeks after planting. For the "diseased" group, sand was inoculated with Streptomyces scabies EF-35, the causal agent of potato common scab, at the time of planting. Disease effects on tissue density of roots and below-ground organs, space occupancy and complexity were assessed by analyzing the CT scanning data in the spatio-temporal approach. Fluctuations of tissue density over time were different, on average, between the two groups. They were characterized by an increase of density in Week 2 for the diseased group, reflecting a hardening of tissue, and a delayed decrease relative to the "healthy" group, suggesting a slower transfer of energy from the seed potato to growing roots. Space occupancy, which was studied via volumetric growth rates evaluated from CT scan data, and complexity, which was quantified by the fractal dimension estimated from skeletonized 3-D images constructed from CT scan data, also showed differences in the first part of the experiment. Original analytical procedures based on data transformation and curve fitting in histogram analysis of CT numbers were developed to obtain those results. In conclusion, the new approach presented here, which is based on the advanced processing of CT scanning data collected over time on developing plant root systems and below-ground organs, can be recommended for future phytopathological applications.

Ensyeh Sarikhani Soil microbial communities in agroecosystems and natural habitats contributing to resistance and resilience of the soil environment. Summary The control of common scab of potatoes (CS) includes resistant varieties (cultivars), precise fertilization, increase of soil moisture, and chemical treatments. Yet, these management practices do not have common or reproducible results at differing sites. A monitoring study was done in 32 sites to evaluate the relation between CS and biological/chemical soil parameters. Correlations were observed between scab severity and content of nutrients such as Fe, N, and Ca in soil and periderm, and between disease severity and abundance of actinobacteria and total bacteria, together with the pathogenicity determinant, txtB gene (biosynthetic gene of thaxtomin) in both soil and periderm of potatoes. The findings led to novel conclusions, which can help to understand relationships applicable in scab control. Peat and DTPA chelated iron were supplemented to pots filled with soil conducive for CS in order to determine the effects of soil organic matter, iron and pH on CS development. The results were compared with data obtained for a suppressive soil from a nearby field with naturally low CS severity. Both peat and iron supplements decreased CS and the combination...

Orientador: Suzete Aparecida Lanza Destéfano / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-17T18:58:40Z (GMT). No. of bitstreams: 1 Correa_DanieleBussioliAlves_M.pdf: 2704976 bytes, checksum: 40df9160618a30b2959f8df5ff93e585 (MD5) Previous issue date: 2011 / Resumo: A batata ocupa o quarto lugar em volume de produção mundial de alimentos após o arroz, trigo e milho. O Brasil é o maior produtor dentre os países da América Latina, porém ainda apresenta baixa produtividade devida às doenças que afetam a cultura. Dentre as doenças bacterianas, a sarna da batata é uma das mais importantes economicamente e sua ocorrência é generalizada no mundo. Diferentes espécies do gênero Streptomyces estão associadas à essa doença e os principais sintomas se caracterizam por lesões irregulares que podem tomar toda a superfície do tubérculo, acarretando diminuição do seu valor comercial ou, até mesmo, impedindo a sua comercialização. Atualmente, a incidência da sarna está aumentando consideravelmente, tornando-se um fator limitante do cultivo de batata no Brasil. O presente trabalho teve por objetivo a identificação de linhagens de Streptomyces sp. associadas à sarna da batata, provenientes de diferentes regiões produtoras do Brasil, por meio de taxonomia polifásica. Cento e noventa linhagens de Streptomyces foram analisadas, sendo 165 nacionais obtidas dos estados da Bahia, Goiás, Minas Gerais, Paraná, São Paulo, Rio Grande do Sul e Santa Catarina; 13 de material vegetal importado do Chile, França e Holanda; e 12 linhagens Tipo de Streptomyces representantes de espécies associadas à sarna. Na caracterização morfológica as linhagens apresentaram heterogeneidade com relação à micromorfologia de hifas e coloração dos esporos. A patogenicidade das linhagens foi avaliada pela presença dos genes nec1, tomA (tomatinase) e txtAB (taxtomina A) e os resultados indicaram que 94 linhagens (52,8%) apresentaram amplificação dos três genes de patogenicidade avaliados, 14 (7,9%) não apresentaram nenhum dos genes e 70 (39,3%) mostraram sinal positivo de amplificação para um ou mais genes. Para algumas linhagens a confirmação da patogenicidade foi efetuada por meio de testes em minitubérculos de batata. Nos testes moleculares, incluindo amplificação com primers específicos para S. scabiei e S. turgidiscabies, PCR-RFLP do gene atpD e análises das seqüências dos genes atpD, gyrB, recA, rpoB e trpB, foi possível a separação das linhagens analisadas em diferentes perfis genéticos. As análises das características morfológicas, patogênicas e moleculares permitiram a identificação de 57 linhagens pertencentes à S. scabiei, 28 à espécie S. ipomoeae, 13 à S. caviscabies/S. setonii, 12 à S. europaeiscabiei e duas à S. sampsonii. As 66 linhagens restantes apresentaram características distintas das espécies Tipo testadas, podendo representar possíveis novas espécies de Streptomyces associadas à sarna no Brasil / Abstract: Potato is the world's fourth most important food crop after rice, wheat and maize. Brazil is the biggest producer among the countries of Latin America, but it still has low productivity due to diseases that affect the crop. Among the bacterial diseases, the potato scab is one of the most economically important, and its occurrence is widespread in the world. Different species of the genus Streptomyces are associated with this disease and the main symptoms are characterized by irregular lesions that can affect all the tuber surface causing decrease of its commercial value or preventing its commercialization. Currently, the incidence of potato scab is increasing considerably, becoming a limiting factor in potato production in Brazil. This study aimed to identify Streptomyces strains associated with potato scab, from different potato growing areas in Brazil, through polyphasic taxonomy. One hundred and ninety strains of Streptomyces were analyzed, including 165 Brazilian strains obtained from potatoes coming from the states of Bahia, Goias, Minas Gerais, Parana, Sao Paulo, Rio Grande do Sul and Santa Catarina; 13 of plant material from Chile, France and Netherlands; and 12 type strains of Streptomyces species associated with potato scab. In the morphological characterization, the strains showed heterogeneity in the hyphal micromorphology and color of spores. The pathogenicity of strains was investigated by presence of the nec1 and tomA genes, and txtAB operon (thaxtomin A). The results indicated that 94 strains (52.8%) showed amplification of the three pathogenicity genes, 14 (7.9%) showed no amplification of the genes and 70 (39.3%) showed positive signal for only one or more genes. The pathogenicity of some strains was confirmed with artificial inoculation onto potato minitubers. In the molecular tests, including PCR amplification with specific primers for S.scabiei and S. turgidiscabies, analysis of PCR-RFLP of atpD gene and sequences analysis of the atpD, gyrB, recA, rpoB and trpB genes, the strains could be separated into different genetic profiles. The morphological, pathogenic and molecular data allowed identifying of 57 strains belonging to S. scabiei, 28 to S. ipomoeae, 13 to S. caviscabies/S. setonii, 12 to S. europaeiscabiei and two to S. sampsonii. The 66 remaining strains showed different genetic profiles in comparison with the type strains of Streptomyces, and may represent new species of Streptomyces associated with potato scab in Brazil / Mestrado / Genetica de Microorganismos / Mestre em Genética e Biologia Molecular