Cytology, Mode of Reproduction, and Forage Quality of Selected Species of Brachiaria Griseb. (Chromosome Numbers, Fiber Structure, Pachytene Analysis, Apomixis)
Do Valle, Cacilda B.
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https://hdl.handle.net/2142/71623
Description
Title
Cytology, Mode of Reproduction, and Forage Quality of Selected Species of Brachiaria Griseb. (Chromosome Numbers, Fiber Structure, Pachytene Analysis, Apomixis)
Author(s)
Do Valle, Cacilda B.
Issue Date
1986
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Abstract
The genus Brachiaria includes several species of economic importance as pastures throughout the tropics. Most of the species investigated are polyploids of the basic chromosome number x = 9. Apomixis is the predominant mode of reproduction within the genus. To define chromosome behavior during meiosis and mode of reproduction, a small but diverse Brachiaria collection was assembled. Species studied included: B. brizantha, B. decumbens, B. ruziziensis, B. humidicola, B. dictyoneura, B. plantaginea, B. deflexa, and B. jubata. Chromosome number of 2n = 2x = 36 was recorded in all accessions of B. brizantha and B. decumbens. B. plantaginea, B. deflexa, and B. jubata were found to have 2n = 4x = 36. Chromosome numbers for B. humidicola and B. dictyoneura were determined to be 2n = 6x = 54. B. ruziziensis is a diploid species, 2n = 2x = 18. Meiosis was irregular for most species, except for B. ruziziensis and B. deflexa. Uni-, tri- and quadrivalents at diakinesis and metaphase were often observed. Complete sexuality was observed in B. ruziziensis, B. deflexa, and B. plantaginea, B. brizantha, B. decumbens, B. humidicola, B. dictyoneura, and B. jubata were found to be highly apomictic. However, in every accession of each species, sexual embryo-sacs were found. A study of chromosome morphology at pachytene in B. ruziziensis was also undertaken. All nine members of the complement were identified based on centromere position, arm ratio, and size distribution of chromomeres. An idiogram was prepared for this species for the first time. Five species of Brachiaria were evaluated for cell-wall composition and digestibility: B. brizantha, B. decumbens, B. ruziziensis, B. humidicola, and B. dictyoneura. Significant differences were detected among species for cell-wall constituents and digestibilities. Brachiaria ruziziensis had the lowest neutral detergent fiber, acid detergent fiber, cellulose, and hemicellulose concentrations and the highest digestibility values of all species studied for both leaf and stem fractions. The effect of induced polyploidy on cell-wall components, digestibility, and monosaccharide composition of the neutral detergent fiber hydrolysate of two diploid populations of B. ruziziensis were compared to their induced tetraploid counterparts. In contrast to what has generally been reported, the tetraploid populations had significantly higher concentrations of structural carbohydrates, particularly cellulose and lignin, than the diploid lines. However, digestibility of these carbohydrates was not significantly affected. The two diploid lines responded similarly to induced polyploidy.
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