Genotypic and phenotypic variation among 16 isolates of Ramularia areola of Gossypium hirsutum collected from five different geographical regions of Brazil was studied through virulence spectrum on three cultivars in the glasshouse and through ERIC-and REP-PCR and ITS1-5.8S-ITS2 rDNA analysis. Difference in virulence spectrum and molecular analysis of some isolates was observed. ERIC-and REP-PCR showed similar results and revealed a high level of diversity among the isolates. A unique profile for both ERIC and REP was obtained for most isolates. On the other hand, the ITS rDNA analysis did not show different PCR-RFLP patterns. While some isolates differed among each other considering genotypic and phenotypic reactions, no clear cut evidence was found about the existence of genetic lineages of R. areola in Brazil. Identification of genetic variability among the R. areola isolates originated from different geographic regions would permit screening of Brazilian germplasm and achieve sources with a wide spectrum of resistance. This is the first report of the genotypic and phenotypic variability among the R. areola isolates originated from five cotton growing regions of Brazil.

Areolate mildew, caused by Ramularia areola is an important disease affecting cotton in Brazil. A few years ago this disease was of secondary importance since it used to occur almost at the end of the crop cycle. However, in recent years the disease has gained considerable importance in the main cotton growing areas of Brazil. Amongst control alternatives is the use of fungicides and resistant cultivars the latter being preferred. In order to study the inheritance of cotton resistance to R. areola, plant populations derived from the crossing between the resistant line FMT02102996 and the susceptible cultivar Novaes, T.G.; Almeida, W.P.; Schuster, I.; Aguiar, P.; Mehta, Y.R.. Inheritance of cotton resistance to Ramularia areola. Summa Phytopathologica, v.37, n.2, p.150-152, 2011.Keywords: Gossypium hirsutum, genetics, inheritance of resistance.Palavras-chave adicionais: Mancha-de-ramularia, Gossypium hirsutum, genética. RESUMOA mancha-de-ramularia, doença causada pelo fungo Ramularia areola, é uma das doenças de destaque na cotonicultura brasileira. Há alguns anos atrás, esta doença era considerada de final de ciclo da cultura, mas em anos recentes tornou-se a doença de maior importância econômica nas principais regiões produtoras de algodão do Brasil. Dentre as alternativas de controle, estão o uso de fungicidas e o uso de cultivares resistentes, sendo que o último é o preferido. Visando estudar a herança da resistência do algodoeiro a R. areola, foram avaliadas populações derivadas do cruzamento entre a linhagem FMT02102996, como resistente e a cultivar FMT 701, como suscetível. As plantas Novaes, T.G.; Almeida, W.P.; Schuster, I.; Aguiar, P.; Mehta, Y.R.. Herança de resistência do algodoeiro a Ramularia areola. Summa Phytopathologica, v.37, n.2, p.150-152, 2011.FMT 701, were evaluated. These plants were classified as resistant or susceptible by means of artificial inoculation in greenhouse. The segregation test was done through ÷2 test. Results indicated that cotton resistance to areolate mildew is controlled by a dominant gene. This finding can assist in planning cotton breeding programs aimed at incorporating resistance to R. areola in nem cultivars, constituting basic information for the beginning of the genetic mapping of this resistance gene in agronomically desirable cotton cultivars.foram classificadas como resistentes ou suscetíveis por meio de inoculação artificial em casa de vegetação. Realizou-se teste de segregação por meio de teste qui-quadrado. Os resultados obtidos indicam que a resistência do algodoeiro à mancha-de-ramularia é condicionada por um gene dominante. Este resultado pode auxiliar o planejamento dos programas de melhoramento do algodoeiro na incorporação da resistência a R. areola em novas cultivares, também consti tuin do informaç ão bási ca p ara o i níci o de trabalhos de mapeamento genético deste gene de resistência agronomicamente desejável.A mancha-de-ramularia, doença causada pelo fungo Ramularia areola, é uma das doenças de destaque na cotonicultura brasileira. Também ...

There is a lack of information about the level of resistance of cotton genotypes to a wider range of Ramularia areola isolates occurring across the cotton growing areas of Brazil. For this purpose, firstly it is necessary to know the existence or not of genotypic and phenotypic variability among the R. areola isolates from different geographical origins. The objective of the present investigation was to verify the existence of phenotypic variability among 23 R. areola isolates collected from six cotton growing states of Brazil. Two resistant genotypes, FMT 02102996 and CNPA BA 2003-2059, and the susceptible genotype FMT 701 were individually inoculated with 23 R. areola isolates under glasshouse conditions and the severity of infection was evaluated 30 days after inoculation. Genotypes CNPA BA 2003-2059 and FMT 02102996 were susceptible to three isolates and resistant to the rest of the isolates. Genotype FMT 701 was susceptible to all the isolates except the isolates 22.3 and 42.7. Results indicate the existence of variability among R. areola isolates and that the three genotypes are useful in distinguishing phenotypic variability within isolates of this pathogen.

Earlier studies showed that the resistance of cotton genotype FMT 02102996 to Ramularia areola is governed by one dominant gene. More recently, the resistance of another genotype CNPA BA 2003-2059 to R. areola was detected under field and glasshouse conditions. Present investigation was conducted to verify the mechanism of resistance of the genotype CNPA BA 2003-2059 and to find out if the resistance of these two genotypes is governed by the same or by different genes. Segregating plant populations derived from the cross between the resistant genotype CNPA BA 2003-2059 and the susceptible genotype FMT 701, the back cross populations, as well as those derived from the cross between the two resistant genotypes were evaluated for disease severity by artificial inoculations under glasshouse conditions. The ratio of plants segregating for resistance and susceptibility was studied by χ2 test. The results indicated that the resistance to R. areola in genotype CNPA BA 2003-2059 is governed by one dominant gene and that the resistance in each one of the resistant genotypes is governed by a different dominant gene. These results may assist the local breeding programs aimed at pyramiding resistance genes to this pathogen and may form the basis for genetic mapping of resistance genes. Key words: Gossypium hirsutum, genetics, inheritance of resistance. RESUMO Mecanismo de resistência e presença de genes diferentes de resistência a Ramularia areola em dois genótipos de algodoeiroA mancha-de-ramulária, causada por Ramularia areola, é uma das doenças de importância econômica para o Brasil. Estudos anteriores demonstraram que a herança da resistência do genótipo FMT 02102996 a R. areola é governada por um gene dominante. Recentemente, a resistência do genótipo CNPA BA 2003-2059 a este patógeno foi verificada em casa de vegetação e no campo. O presente estudo foi realizado para verificar o mecanismo de resistência deste genótipo e verificar se os genes de resistência dos dois genótipos resistentes são os mesmos. Foram avaliadas populações segregantes derivadas do cruzamento entre o genótipo resistente CNPA BA 2003-2059 e o genótipo suscetível FMT 701, dos retrocruzamentos, e também do cruzamento entre os dois genótipos resistentes. As plantas foram classificadas como resistentes ou suscetíveis por meio de inoculação artificial. Com base nos resultados, constatou-se que a resistência do genótipo CNPA BA 2003-2059 é condicionada por um gene dominante e que os dois genótipos possuem um gene diferente de resistência. Estes resultados podem auxiliar o planejamento dos programas de melhoramento do algodoeiro visando piramidar genes de resistência a R. areola em novas cultivares, ao mesmo tempo constituindo informação básica para o início de trabalhos de mapeamento genético deste gene de resistência. Palavras-chave: Gossypium hirsutum, genética, herança de resistência.

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