Genótipos de Coffea arabica L. do banco ativo de germoplasma resistentes a doenças

Abstract

Coffee diseases cause direct and indirect losses to the producer, respectively, consisting of decreased productivity and increased production cost due to the control employed. Thus, the development of resistant cultivars is preponderant for the productive system in the constant search for the coffee producer‟s efficiency and consequent profitability. Currently, numerous resistant cultivars are available, especially against coffee rust (Hemileia vastatrix). However, only one cultivar has been found to resist the aureolate spot (Pseudomonas syringae pv. garcae) and none that resist cercosporiosis (Cercospora coffeicola). Therefore, new sources of resistance must be identified to insert alleles and enhance genetic resistance. In this context, the study of coffee accessions from the Active Germplasm Bank of Minas Gerais (BAG in Portuguese) is essential since it contains genetic and phenotypic variability, which can be intensively worked on justifying its importance for genetic improvement. Given the above, the study‟s objectives were to verify the existence of genetic variability among 28 accessions and select parents to be used in crosses in the generation of variability, focusing on rust, cercosporiosis, and coffee bacteriosis resistance. Additionally, we verified if the enzymatic constitution and bioactive compounds present in coffee trees are correlated with resistance to these diseases. The 28 accessions of BAG were evaluated in screening experiments for resistance to coffee rust (cultivar Catuaí Vermelho IAC 99 was used as a susceptibility standard and Catiguá MG 2 as a resistance standard) and to the aureolated coffee spot. The screening results allowed the selection of the 15 most promising approaches regarding the resistance to both diseases. The accessions selected in the screening were used in three experiments for resistance to coffee rust, aureolous spot, and cercosporiosis, using „Catuaí Vermelho IAC 99‟ as a susceptibility standard and „Catiguá MG 2‟ as a resistance standard in the rust experiment. We selected eight accessions with complete resistance to rust and five with moderate resistance to aureolate spot. It was impossible to select any accessions for cercosporiosis because there was no genetic variability for resistance. The constitutive activity of the enzymes peroxidase (POX), polyphenol oxidase (PPO), and phenylalanine ammonia lyase (PAL) and the contents of the bioactive compounds chlorogenic acid, caffeine, trigonelline, total phenols, and lignin were analyzed and compared to the resistance to the diseases. There was no correlation between the constitutive composition and resistance to rust, aureolus spot, and cercosporiosis. We identified two accessions with simultaneous resistance to rust and aureolate spot. Therefore, the results are promising for use in breeding programs focusing on the development of resistant cultivars.