Classificação de raças fisiológicas de Uromyces appendículatus e piramidação de genes de resistência ao patógeno em feijão do tipo carioca

Abstract

Visando contribuir com a padronização internacional da classificação de raças fisiológicas do fungo Uromyces appendiculatus, agente causal da ferrugem do feijoeiro comum, no presente trabalho foi realizada a caracterização de isolados do patógeno usando a nova série diferenciadora e o sistema binário de nomenclatura propostos no “3rd The Bean Rust Workshop”. Esses isolados, oriundos do estado de Minas Gerais, são utilizados nas avaliações dos genótipos resistentes a ferrugem desenvolvidos pelo programa de melhoramento do feijoeiro conduzido no BIOAGRO/UF V. O procedimento utilizado classificou 12 isolados em sete raças fisiológicas distintas: 21-3, 29-3, 53-3, 53-19, 61-3, 63-3 e 63-19. Espera-se que a adoção desse procedimento possa facilitar o intercâmbio de informações e o uso cooperativo dos resultados obtidos pelos diferentes grupos de pesquisa que, no mundo, estudam 0 U. appendiculatus. Com esta classificação, foram também identificadas fontes com amplo espectro de resistência: Mexico 309, Mexico 235 e PI 181996, as quais se mostraram incompatíveis com todos os isolados caracterizados. Em face à grande variabilidade apresentada por U. appendiculatus, e visando o controle genético eficiente e duradouro desse patógeno, outra meta do presente trabalho foi piramidar os genes de resistência Ur-5 (Mexico 309), Ur-I] (Belmidak RR-3, derivado de PI 181996) e Ur-ON (Ouro Negro) no background genético “carioca” do feijoeiro, utilizando o cultivar Rudá como genitor recorrente. Grãos do tipo carioca possuem maior aceitação pelo consumidor brasileiro. Para viabilizar a piramidação, a estratégia adotada foi o uso de marcadores moleculares, para estudos de fingerprinting e na seleção indireta dos genes.

Aiming to contribute to the international standardization of the classification of physiological races of the fungus Uromyces appendiculatus, the causal agent of common bean rust, this work characterized isolates of the pathogen using the new differential series and the binary nomenclature system recommended in the 3rd Bean Rust Workshop. These isolates were collected in the state of Minas Gerais, Brazil, and are used for the evaluation of bean rust resistant genotypes developed in the BIOAGRO/UF V breeding program. Twelve isolates were classified into seven physiological races: 21-3, 29-3, 53-3, 53-19, 61-3, 63-3 and 63-19. It is expected that the adoption of this classification procedure will facilitate the exchange of information among different research groups interested in common bean rust and its causal agent U. appendiculatus. The classification procedure also allowed the identification of resistance sources with ample resistance spectra: ‘Mexico 309’, ‘Mexico 235’ and ‘PI 181996’. These sources were incompatible with all the isolates analyzed. Considering the high variability of U. appendiculatus, and aiming the durable and efficient genetic control of this pathogen, in this work the following rust resistance genes were associated (pyramided) in the “carioca-type” genetic background Ruda: Ur- 5 (Mexico 309), Ur-I] (Belmidak RR-3, derived from PI 181996) and Ur-ON (Ouro Negro). Cultivars with “carioca-type” grains are preferred by the Brazilian consumer. Molecular markers were used for fingerprinting analyses and indirect selection during the pyramiding process in association with conventional breeding techniques, such as backcrossing and segregating generation advancement with genealogical control. SCAR markers 8119460 and SAE19890, and RAPD marker OPX11630, linked to Ur-5, Ur-I] and Ur-ON, respectively, were used to monitor the resistance alleles along the pyramiding process. The phenotypic selection of these three alleles was not possible because they present the same resistance spectra in relation to the isolates available in the BIOAGRO/UFV breeding program. F 3 seeds with pyramided Ur-5, Ur-I] and Ur-ON rust resistance alleles were obtained from F 2 plants harboring the three molecular markers, and also the “carioca-type” genetic background. Aiming to reach homozygosity for all three resistance loci, the F 3 population and subsequent generations will be conducted by a molecular-marker assisted genealogical breeding process. In addition to the activities already mentioned, the “carioca- type” cultivar BRSMG Talismã, which was recently recommended for commercial use in the Minas Gerais and Parana States, was evaluated as to its reaction to U. appendículatus isolates maintained in the fungal collection of BIOAGRO/UFV. It was also characterized with molecular markers 8119460, SAE19890 and OPXll630. The results demonstrate that ‘BRSMG Talismã” is susceptible to five of the 12 U. appendiculatus isolates tested. The three molecular markers analyzed were polymorphic between “BRSMG Talismã” and the resistance sources harboring the alleles Ur-5, Ur-I] and Ur-ON. That indicates the absence of these resistance alleles in cultivar BRSMG Talismã and that these markers can be used to monitor the possible simultaneous introgression of the resistance alleles in this cultivar.