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Previous issue date: 2005-03-31 / A ramulose é uma das principais doenças do algodoeiro no cerrado brasileiro, maior região produtora. Conduziram-se dois ensaios em campo visando selecionar plantas com resistência à ramulose em linhagens e em acessos sem características comerciais. As mesmas linhagens também foram avaliadas para resistência à mancha de ramulária, mancha angular, mosaico das nervuras e ao complexo Fusarium e nematóide. Foi possível distinguir entre resistência e suscetibilidade à ramulose em ambos os ensaios de campo (P< 0,0001 e P=0,002, ensaio de linhagens e acessos do banco de germoplasma, respectivamente). Para avaliar possível série diferenciadora de raças de Colletotrichum gossypii var. cephalosporioides (Cgc), seis isolados do patógeno foram inoculados em 30 acessos de algodoeiro. Destes acessos, dois desenvolveram ou não sintomas dependendo do isolado usado. Esses acessos, em conjunto a outros dois resistentes e dois suscetíveis aos isolados empregados, foram selecionados para compor uma série diferenciadora para distinguir raças de Cgc. Com base em 133 isolados estudou-se a estrutura genética de populações de Cgc em três regiões com diferentes idades de cultivo. Foram analisados 23 locos AFLP e detectou-se baixa diversidade genética total (H t =0,139) e baixa diversidade genética dentro de subpopulações (H s =0,133). O número médio de migrantes foi estimado em 11,9 indivíduos a cada geração entre as três subpopulações. Não foi observada formação de estrutura sexuada (peritécio) in vitro após pareamento de 17 isolados em todas as combinações possíveis. Apenas um grupo de compatibilidade vegetativa foi identificado com base em testes de complementação usando 76 mutantes auxotróficos na rota de metabolismo do nitrato. Inferiu-se que a população brasileira de Cgc tem estrutura clonal, com ausência de grupos de compatibilidade vegetativa e sem aparente reprodução sexuada. Ocorre grande fluxo gênico e sementes infectadas desempenham importante papel nessa dispersão, principalmente para áreas novas. Isolados de Cgc foram também caracterizados quanto à sensibilidade aos fungicidas carbendazim, tebuconazole e azoxystrobin. Não houve evidências de resistência de Cgc aos fungicidas avaliados. Os valores de ED 50 para os fungicidas carbendazim, tebuconazole e azoxystrobin variaram, respectivamente, de 0,037 a 1,474, de 0,020 a 0,191 e de 0,019 a 0,068 μg i.a./mL. O controle químico em condições de campo reduziu o progresso da doença, todavia não evitou perdas significativas em produtividade. / “Ramulose” or “Witches’ broom” is caused by Colletotrichum gossypii var. cephalosporioides (Cgc) and is one of the main cotton diseases in the savannah region of Brazil, the major producing area. Two field assays were conducted with breeding lines and active germplasm bank (AGB) accessions to select cotton resistant genotypes. The breeding lines were also evaluated to ramularia leaf spot, bacterial blight, mosaic vein virus, and nematode - fusarium complex resistance at field conditions. Resistant and susceptible genotypes were differentiated in both assays (P< 0.0001 and P=0.002 for breeding lines and AGB accessions assays, respectively). In order to establish a set of cotton differential series to detect Cgc pathotypes, six Cgc isolates were inoculated in 30 cotton genotypes. Reaction of two cotton accessions varied according to Cgc isolate. These two in addition to two resistant and two susceptible accessions were selected to form a cotton differential set to determine Cgc pathotypes.Pathogen population structure was investigated by analyzing 133 isolates collected from three major cotton producing areas. A total of 23 AFLP loci were analyzed. The total and within subpopulation genetic diversity were low, H t = 0.139 and 0.133, respectively. The estimated average number of migrants among the subpopulations, per generation, was 11.9. No sexual structure (perithecium) was formed in crosses established in vitro for 17 isolates in all possible combinations. A single vegetative compatibility group (VCG) was identified based on complementation tests using 76 auxotrophic mutants in nitrate metabolic pathway. One mutant did not form heterokarion and was self-incompatible. Genotypic diversity varied among subpopulations and one haplotype was found in high frequency in all subpopulations. There was no correlation between genetic and geographic distances. There is strong evidence that the population of Cgc has a clonal structure, with no VCG, and sexual reproduction does not seem to play an important role. Gene flow among subpopulations was high and infected seeds are important to pathogen introduction/dispersal into new areas. Sensitivity of Cgc isolates to carbendazim, tebuconazole, and azoxystrobin was assessed. Baseline population sensitivity was established with isolates collected where no fungicide was used. For in vitro assays, the ED 50 values of carbendazim (n=88 isolates) ranged from 0.037 to 1.474 μg a.i./mL, a 40-fold sensitivity factor. No resistance to carbendazim (ED 50 > 10 μg a.i./mL) was detected. Similarly, ED 50 values for tebuconazole (n=91) and azoxystrobin (n=82) were low and ranged from 0.020 to 0.191 and from 0.019 to 0.068 μg a.i./mL, respectively. In a field assay, disease progress was followed on the susceptible cultivar BRS Ipê. Plots artificially inoculated were treated twice with fungicides in several combinations. Fungicides were not effective in controlling ramulose, although differences (P=0.007) regarding area under the disease progress curve among treatments were detected. Lack of disease control was attributed to heavy rain during the season as well as a delay in the first fungicide application. / Tese importada do Alexandria
| Identifer | oai:union.ndltd.org:IBICT/oai:localhost:123456789/10234 |
| Date | 31 March 2005 |
| Creators | Suassuna, Nelson Dias |
| Contributors | Maffia, Luiz Antônio, Brommonschenkel, Sérgio Hermínio, Mizubuti, Eduardo Seiti Gomide |
| Publisher | Universidade Federal de Viçosa |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | Portuguese |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Source | reponame:Repositório Institucional da UFV, instname:Universidade Federal de Viçosa, instacron:UFV |
| Rights | info:eu-repo/semantics/openAccess |
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