Abstract This study estimated the general and specific combining abilities and mean heterosis of tobacco lines of the varietal groups Flue-Cured Virginia (FCV) and Air-Cured Burley (BY). In addition, possible advantages and an improved strategy of using hybrids in tobacco breeding in the tropics were discussed. Ten BY and 13 FCV lines were crossed in a diallel mating design. The hybrids and parental lines were evaluated at two locations in Southern Brazil. The mean heterosis was 5.37% for FCV and zero for BY lines, although higher than 15% in some combinations. The occurrence of heterosis indicates dominance in the control of tobacco yield. Tobacco breeding programs must focus primarily on improving the performance of lines per se and then on the identification of the best hybrid by testing combinations.

RESUMO Várias características devem ser consideradas simultaneamente na seleção de cultivares de tabaco para atender às necessidades dos agricultores, fabricantes e consumidores. Nesse contexto os melhoristas devem conhecer as correlações entre as características de importância econômica, a fim de adotar a melhor estratégia de seleção para elas. A utilização de índices de seleção tem se mostrado uma das estratégias mais eficientes para selecionar caracteres correlacionados. No caso do tabaco, nenhum relato foi encontrado na literatura para a seleção de múltiplas características. Neste estudo, demonstramos a eficiência da Soma do Índice de Variáveis Padronizadas (SSV) para a seleção de múltiplas características em tabaco. O método foi avaliado usando uma coleção de treze linhagens parentais e seus híbridos oriundos de um esquema dialélico. Os híbridos, as linhagens parentais e as testemunhas foram avaliados em dois locais. As características avaliadas foram produtividade (YLD), índice geral de qualidade (IGQ), relação talo/lâmina, porcentagem total de alcalóides e porcentagem total de açúcares. Consideramos os pesos para o indíce de acordo com a importância econômica de cada característica: 0,4 para YLD, 0,3 para GQI e 0,1 para os demais caracteres. O índice SSV mostrou-se eficiente e fácil de interpretar, podendo ser utilizado para se ter ganho genético para quase todos os caracteres na direção desejada. A capacidade geral de combinação (CGC) explicou a maior parte da variação do índice na análise dialélica. A estimativa de heterose média foi de 2,02%. Algumas combinações de híbridos exibiram níveis de heterose maiores que 10%, indicando que uma maior atenção pode precisar ser dada à comercialização de híbridos F1.

ABSTRACT Several traits must be simultaneously considered in selection of tobacco cultivars for meeting the requirements of farmers, manufacturers and consumers. Breeders should have an understanding of associations between economically-important traits in order to devise the best strategy to have response to selection for all them. Utilization of selection indices has been shown to be one of the most efficient strategy for selecting for correlated characters. In tobacco, no reports can be found within the academic literature for multiple trait selection. In this study we demonstrate the efficiency of the Sum of the Standardized Variables Index (SSV) for multi-trait selection in tobacco. The method was evaluated using a collection of thirteen inbred lines and hybrids derived using a diallel scheme. The hybrids, parental lines, and checks were evaluated in two field locations. The traits assessed were yield (YLD), general quality index (GQI), leaf stem to lamina ratio, percent total alkaloids, and percent total sugars. We considered weights according to the economic importance of each trait: 0.4 for YLD, 0.3 for GQI and 0.1 for the remaining characters. The SSV index proved to be efficient and easy to interpret, and could be used to generate genetic gain for almost all characters in the desired direction. General combining ability (GCA) explained the larger part of the variation of the index in the diallel analysis. The mean heterosis estimate was 2.02%. Some hybrid combinations exhibited heterosis levels greater than 10%, indicating that increased attention might need to be given to commercialization of F1 hybrids.

Abstract In this study we aimed to investigate genetic control of the emergence speed index (ESI) and percentage of canopy coverage (PCC) in plants, and to evaluate whether these traits can be used to identify common bean plants that rapidly provide canopy coverage. Plants from a segregating population and progenies from a cross between a large leaf line and a small leaf line were evaluated. It was observed variability for ESI, however, the low magnitude of heritability indicates that the probability of success from selection is not high. The additive effect was predominant in genetic control of PCC. Nevertheless, this trait is highly affected by the genotype by environment interaction, which makes success from selection even more difficult. The association between ESI and PCC was also low. This information can guide decision making in programs that aim at fast canopy coverage in common bean.

Abstract The methodology available for evaluating the cooking quality of dry beans is impractical for assessing a large number of progenies. The aims of this study were to propose a new strategy for evaluating cooking quality of grains and to estimate genetic and phenotypic parameters using a selection index. A total of 256 progenies of the 13thcycle of a recurrent selection program were evaluated at three locations for yield, grain type, and cooked grains. Samples of grains from each progeny were placing in a cooker and the percentage of cooked grains was assessed. The new strategy for evaluating cooking quality was efficient because it allowed a nine-fold increase in the number of progenies evaluated per unit time in comparison to available methods. The absence of association between grain yield and percentage of cooked grains or grain type indicated that it is possible to select high yielding lines with excellent grain aspect and good cooking properties using a selection index.

Agribusiness is fundamental for the Brazilian economy. This has become possible due to the use of science and technology in agriculture in the last 35 years. Among the technologies, the use of improved cultivars stands out. This article presents the situation of the species grown in the country in recent years and the contribution of genetic plant breeding to the performance of these species. Challenges multiplied because of populational growth associated with the ever-growing concern of society with the environment. Breeders of the present and future must base plant selection in the field on new technologies so that it is possible to meet demand.

O objetivo deste trabalho foi analisar genótipos de cafeeiro (Coffea arabica) resistentes ao bicho-mineiro (Leucoptera coffeella), com uso de marcadores microssatélites. Foram avaliados 66 locos, dos quais 63 foram obtidos do banco de sequências expressas (EST) de café. Esses locos foram amplificados em "bulks" de progênies F5 de 'Siriema' (C. arabica x C. racemosa) resistentes e suscetíveis ao ataque da praga, em oito acessos de C. racemosa, e em uma população F6 de 'Siriema' com 91 indivíduos que segregam para resistência ao bicho-mineiro. Os polimorfismos foram verificados em dois locos de marcadores microssatélites (SSR), nos "bulks" das progênies suscetíveis. Os dois alelos polimórficos estiveram presentes em torno de 70% dos genótipos suscetíveis em F5 e em, aproximadamente, 90% dos indivíduos suscetíveis em F6. Entretanto, os marcadores EST-SSR polimórficos entre populações contrastantes para a resistência ao bicho-mineiro não foram correlacionados às características avaliadas. Os marcadores SSR apresentam polimorfismo inter e intraespecífico em C. arabica e C. racemosa.

The objective of this work was to analyze coffee (Coffea arabica) genotypes resistant to the coffee leaf miner (Leucoptera coffeella) using microsatellite markers. Sixty-six loci were evaluated, of which 63 were obtained from the Brazilian Coffee Expressed Sequence Tag (EST) database. These loci were amplified in bulks of individuals from F5 progenies of 'Siriema' (C. arabica x C. racemosa) resistant and susceptible to the insect, in eight samples of C. racemosa, and in a F6 population of 'Siriema' with 91 individuals segregating for resistance to the leaf miner. Polymorphisms were verified for two simple sequence repeat (SSR) loci in bulks of the susceptible progenies. The two polymorphic alleles were present in around 70% of the susceptible genotypes in F5 and in approximately 90% of the susceptible individuals in F6. However, the polymorphic EST-SSR markers among populations contrasting for resistance to leaf miner were not correlated to the evaluated characteristics. SSR markers show inter- and intraspecific polymorphism in C. arabica and C. racemosa.