No abstract

In breeding of sweet sorghum hybrids, non-additive genetic effects are important in phenotypic expression of the traits of interest. The aim of this study was to evaluate the general combining ability (GCA) of sweet sorghum lines and the specific combining ability (SCA) of the hybrids for agronomic and technological traits. Five fertility restorer lines, four male-sterile lines, and their hybrids from partial diallel crosses were evaluated in experiments laid out in a 5 x 6 triple rectangular lattice design in the municipalities of Lavras, MG and Sete Lagoas, MG, Brazil. Diallel analysis was performed using the Griffing model adapted to partial diallel crosses. There was a significant effect of GCA and SCA for most of the traits evaluated, indicating the participation of additive or dominant genes in inheritance. The restorer lines CMSX508, BRS 511, CMSXS643, and CMSXS646 show potential for use as parents in sorghum breeding programs.

The objective of this work was to evaluate the potential per se of male-sterile and fertility-restorer lines of sweet sorghum (Sorghum bicolor), as well as to detail the heterosis manifested for some traits directly or indirectly related to ethanol production, accumulation rate, and predictability. Evaluations were performed for 20 genotypes, of which 4 are fertility-restorer lines (R), 3 are male-sterile lines (A), and 12 are experimental hybrids (H) resulting from the partial diallel cross between lines A and R, besides a commercial hybrid CV198 used as a check, in four harvest seasons. The experiments were carried out in the municipalities of Lavras and Sete Lagoas, in the state of Minas Gerais, Brazil. The measured traits were plant height, green mass production, juice extraction, total soluble solids content, and megagrams of Brix per hectare. The male-sterile A1 and the fertility-restorer R1 and R3 lines show the best potential per se, considering all traits and their accumulation rate and predictability over harvest times. Heterosis is significant for all traits. The H11, H13, H14, H21, H22, and H33 hybrids are promising because of their better performance per se and higher heterosis.

Grasses with desirable traits for agriculture and livestock production are continually being sought. The genus Urochloa comprises many species of good forage potential, although studies have mostly focused on commercial cultivars. Karyotype data can be used to characterize species and generate information for taxonomy and evolutionary studies and contribute to breeding programs. The mode of reproduction is also an essential piece of information to determine breeding strategies. This study aimed to characterize the karyotypes of Urochloa arrecta (Hack. ex T. Dur. & Schniz) O. Morrone & F. Zuloaga and a pentaploid cytotype of U. brizantha (Hochst. ex A. Rich.) R. Webster, including the mapping of ribosomal DNA (rDNA) sites and nuclear DNA content and indicating the mode of reproduction. Slides were prepared using the flame drying technique and were subjected to fluorescent in situ hybridization with 35S and 5S rDNA probes. DNA content was estimated by flow cytometry. The classification of the reproduction mode was based on the amplification of the primers N14 and p779/p780. Urochloa arrecta presented 2C = 2.66 pg of DNA, karyotype formula 2n = 4x = 34 m + 2sm, four chromosomes with 35S rDNA sites, and four other chromosomes with 5S rDNA sites. The absence of amplification products with the primers N14 and p779/p780 provided evidence of sexual reproduction. Urochloa brizantha presented 2C = 4.52 pg of DNA and karyotype formula 2n = 5x = 45 m. Five chromosomes presented 35S rDNA, and eight other chromosomes displayed 5S rDNA sites. Polymerase chain reaction results indicated that this cytotype has an apomictic mode of reproduction. The organization of karyotypes suggests an allopolyploid origin for both genotypes. Possible applications of the information found are discussed.