Estratégias de seleção e análise de gerações em progênies de cafeeiro

Abstract

Coffee production is considered one of the main agricultural activities in Brazil and several factors can influence the crop production and yield which will directly impact fruit quality. Among these factors, diseases are responsible for significant losses and the search for new cultivars that are more adapted, productive and resistant is a fundamental tool for a more sustainable production. Therefore, genetic improvement programs are of paramount importance for maintaining the continuous enhancement of favorable alleles in the population in order to obtain genetic progress. Given this, the present work aims to 1) evaluate different selection strategies of Arabica coffee progenies, with high productive potential and resistance to brown eye spot, based on the phenotypic value and individual heritability of agronomic traits, 2) as well as to analyze genetic traits in different cycles of selection. The experiment was implemented in 2018, adopting a 3.6 x 0.70 meters spacing. The experimental design used was in randomized blocks with three replications and 30 treatments, being 28 progenies in F4:5 generation obtained by the genetic improvement program of EPAMIG, resulting from the crossings Icatu Amarelo IAC 2944 x Catuaí Amarelo IAC 62 and Icatu Amarelo IAC 2944 x IAC 5002 (backcross performed by IAC between Catuaí Amarelo IAC H2077-2-12-70 and Mundo Novo IAC 515-20) and the cultivars MGS Aranãs and Catuaí Vermelho IAC 144 adopted as controls. The variables sampled at the time of harvest were vegetative, stem diameter (cm) and the number of plagiotropic branches in the main rush, percentage of empty fruits, yield (bags ha-1), beverage yield (liters of freshly harvested coffee), sieve percentage 17 and above, sieve percentage of 16 and above of flat grains for 2019/2020 and 2020/2021 harvests and the severity of brown eye spot evaluated between January and May 2021. Data were analyzed using mixed models to predict the breeding values following the REML/BLUP procedure with using SELEGEN – REML/BLUP software. The variations were evaluated through the likelihood ratio test after verifying the normality of the residuals and detecting the homogeneity of the variance. Then, the selection strategies were applied: direct way, correlated response, the sum of Mulamba and Mock ranks with pre-fixed economic weights and economic weight based on the coefficient of genetic variation, FAI-BLUP index, index of the sum of standardized variables and graphical analysis based on individual progeny heritability. We used the percentage of coincidence and Spearman’s correlation to compare strategies and gains obtained with the simultaneous selection of multiple characters. For the intergenerational analysis, the heritability between families was estimated and the magnitude of variation and genetic progress between superior progenies was calculated. It was concluded that the gain with the correlated response to selection was not significant for the variables considered. The selection of multiple characters was maximized with the adoption of the Mulamba and Mock Index associating pre-fixed weights (MM(PE)), with the selection of potential progenies 1 (2 CV-2 BL II ), 3 (2 CV 8 BL I), 16 (15 CV 6 BL IV ), 19 (28 CV 1 BL II ), 20 (28 CV 10 BL I ) and 21 (28 CV 6 BL II ). The graphical analysis is promising for selection for the resistance to brown cercosporiose and productivity, being interesting to explore these two variables. The studied progenies presented genetic variability for breeding and their performance is superior to the previous generation with genetic gains of 7.46% and -1.633,69% for harm from cercosporiose, as a function of the ideotype. Therefore, the employed strategies are efficient for the enhancement of favorable allele with increments in the phenotypic means.