ABSTRACT: Sorghum breeding programs are based predominantly on developing homozygous lines to produce single cross hybrids, frequently with relatively narrow genetic bases. The adoption of complementary strategies, such as genetic diversity study, enables a broader vision of the genetic structure of the breeding germplasm. The purpose of this study was to evaluate the genetic diversity of sorghum breeding lines using structure analysis, principal components (PC) and clustering analyses. A total of 160 sorghum lines were genotyped with 29,649 SNP markers generated by genotyping-by-sequencing (GBS). The PC and clustering analyses consistently divided the R (restorer) and B (maintainer) lines based on their pedigree, generating four groups. Thirty-two B and 21 R lines were used to generate 121 single-cross hybrids, whose performances were compared based on the diversity clustering of each parental line. The genetic divergence of B and R lines indicated a potential for increasing heterotic response in the development of hybrids. The genetic distance was correlated to heterosis, allowing for the use of markers to create heterotic groups in sorghum.

RESUMO. Os solos do cerrado são caracterizados por apresentarem elevada acidez e alumínio solúvel em níveis tóxicos para as plantas, o que assume um papel de fator limitante ao aumento da produtividade destas culturas. A toxidez causada pelo alumínio afeta o desenvolvimento das plantas e em particular, inibe o crescimento das raízes e a absorção de água e nutrientes pela planta. Com o presente trabalho objetivou-se fenotipar híbridos de sorgo granífero quanto à tolerância ou susceptibilidade ao alumínio tóxico. O estudo foi realizado em câmara de crescimento na Embrapa Milho e Sorgo, entre os dias 04/04 a 30/05/2014. Foi realizado um experimento em solução nutritiva testando-se dois níveis de Al (0 e 27 µM), em 18 híbridos de sorgo, utilizando delineamento de blocos ao acaso, com duas repetições. Como testemunhas foram utilizadas as linhagens ATF 13B (suscetível) e ATF 14B (Tolerante). Com base nos caracteres avaliados: crescimento líquido de raiz após 120 horas, crescimento líquido de raiz após 168 horas e o crescimento relativo de raiz seminal após 168 horas foi possível distinguir os híbridos tolerantes dos suscetíveis. Os híbridos BRS 310 e BRS 373 apresentaram tolerância significativa, com redução no crescimento abaixo de 30% quando submetidos ao estresse de alumínio. O híbrido BRS 330 foi classificado em grupo intermediário com redução de tamanho de raiz em torno de 50%. Todos os outros híbridos foram suscetíveis com reduções de crescimento de raiz muito afetado pelo alumínio.

ABSTRACT. Sorghum (Sorghum bicolor L. Moench) is one of the most important cereal crops in the world. In Brazil, the acreage of grain sorghum during off-season is quite expansive. Most of this area is the Cerrado, a Brazilian biome that is similar to a Savannah and is characterized by high acidity and soluble aluminum at toxic levels for plants. The aluminum acts as a limiting factor in achieving high yields. The purpose of this work was to phenotype sorghum hybrids for aluminum tolerance. Eighteen hybrids were evaluated in a nutrient solution containing {0} or {27} µM Al3+. The work was carried out in a growth chamber at the Embrapa Maize and Sorghum, from April 4 to May 30, 2014. The lines ATF 13B (susceptible) and ATF 14B (tolerant) were used as check cultivars. Based on the Net Root Growth after 120 hours (NRG120), Net Root Growth (NRG168) after 168 hours and Relative Net Root Growth after 168 hours (RNRG168), it was possible to distinguish tolerant hybrids from susceptible ones. The high aluminum saturation reduced root growth by 70%. The hybrids BRS 310 and BRS 373 were tolerant to aluminum stress under nutrient solution. The hybrid BRS 330 was clustered in an intermediate group, with an approximately 50% root growth reduction. The other hybrids were susceptible with significant root reduction.

O objetivo deste trabalho foi estimar a capacidade combinatória de 58 linhagens parentais de sorgo previamente selecionadas para tolerância ao Alumínio (Al). Cento e sessenta e cinco híbridos obtidos a partir do cruzamento destas linhagens foram avaliados em três níveis de saturação de Al. A saturação de Al reduziu a altura das plantas de sorgo, mas não alterou a data de florescimento dos híbridos. A Capacidade Geral de Combinação (CGC) das linhagens fêmeas foi significativa para todas as características. A CGC dos machos foi significativa somente para altura de plantas. A Capacidade Específica de Combinação (CEC) foi significativa somente para dias para florescimento. As linhagens com maior CGC para produção de grãos foram F7, F14, F17, F20, F21, F24, F29, F31, F41, F42, F48, F51, F54, e F55, sendo que F29, F48 e F51 também contribuíram para reduzir a data de florescimento dos híbridos. M2 foi a melhor linhagem-macho.

The purpose of this study was to estimate combining ability of 58 sorghum lines previously selected for Aluminum (Al) tolerance. One hundred sixty-five hybrids were evaluated at three levels of Al saturation (0%, 20% and 50%) at the same season. General Combining Ability (GCA) effects were significant for female lines for all three traits. GCA effects for male lines were significant only for plant height. Specific Combining Ability (SCA) effects were significant only for flowering time. The ratio GCA to SCA was greater than the unity, indicating the prevalence of additive effects for the control of Al tolerance. F7, F14, F17, F20, F21, F24, F29, F31, F41, F42, F48, F51, F54 and F55 lines contributed to increase yield, while F29, F48 and F51 also contributed to reduce flowering time. M2 was the best male line since it contributed to increase yield and plant height, and to reduce flowering time.