Carine Simioni

Variabilidade genética de caracteres forrageiros em Paspalum

The objective of this work was to determine the genetic variability and the expression of traits of interest for forage production in species of Paspalum. The experiments were carried out in different locations and crop years in randomized block design with three replicates. Five accessions of P. nicorae and two of P. guenoarum were evaluated, besides the cultivar Pensacola (P. notatum), used as a control. The following traits were determined: leaf/stalk ratio; harvest index; and total, leaf, and stalk dray matter. Both main effects (genotype, years, and locations) and the interactions among factors had significant influence on the evaluated traits. The evaluated accessions showed genetic variability in traits of interest for forage production, and their performance varied according to the location and year of cultivation. Total and leaf dry matter production are the traits that most contribute to the detection of the observed genetic variability, regardless of the year of evaluation.

Meiotic analysis in induced tetraploids of Brachiaria decumbens Stapf

The meiotic behavior of three tetraploid plants (2n=4x=36) originated from somatic chromosome duplication of sexually reproducing diploid plants of Brachiaria decumbens was evaluated. All the analyzed plants presented abnormalities related to polyploidy, such as irregular chromosome segregation, leading to precocious chromosome migration to the poles and micronuclei during both meiotic divisions. However, the abnormalities observed did not compromise the meiotic products which were characterized by regular tetrads and satisfactory pollen fertility varying from 61.36 to 64.86%. Chromosomes paired mostly as bivalents in diakinesis but univalents to tetravalents were also observed. These studies contributed to the choice of compatible fertile sexual genitors to be crossed to natural tetraploid apomicts in the B. decumbens by identifying abnormalities and verifying pollen fertility. Intraespecific crosses should reduce sterility in the hybrids produced in the breeding program of Brachiaria, a problem observed with the interspecific hybrids produced so far.

Sexual polyploidization in red clover

Because sexual polyploidization broadens genetic basis and supply plant breeders with more variability for the selection process, it can be useful in red clover breeding. This paper reports results of three crossing cycles, starting from a parental generation of tetraploid red clover plants (female parent), and diploids from the Quiniqueli cultivar, selected for production of more than 1% of giant pollen grains (male parent) aiming to obtain tetraploid plants to be used in red clover breeding programs. Crosses in the next generations were performed by mutual cross-pollinations. Chromosome number chimerism and high pollen sterility were detected in F1, F2 and F3, but there was a trend towards increasing seed production and seed viability along the generations, probably due to successful competition between fertile and sterile gametes. The identification of fertile triploids, as well as their recurrent formation along the generations, indicates that triploid block is not complete in red clover, and that triploids may be successfully used as a bridge for the production of sexual polyploids.

Tolerância ao frio e caracterização de híbridos entre leucaena leucocephala e L. diversifolia

The objective of this experiment was to identify material to be used as an alternative forage in the conditions of Southern Brazil. A population of hybrids between L. leucocephala and L. diversifolia (both tetraploid species, with 2n=104 chromosomes) in advanced generations was evaluated. The rate of growth in height, duration of flowering and frutification, number of flowers and legumes per inflorescence, seeds per legume, cold tolerance (expressed as foliage retention during winter) and regrowth ability in early spring were evaluated. A great intrapopulational variability was detected for all evaluated characteristics. Some individuals allying cold tolerance and desirable characteristics were identified to be used for further selection and breeding, which confirms the potentiality of Leucaena as a forage for Southern Brazil.

A model for floral color inheritance in Leucaena (Leguminosae)

A population of 513 hybrids of Leucaena leucocephala (4x) and L. diversifolia ssp. diversifolia (4x), that is being analyzed for several morphological and agronomical characteristics, aiming at selecting cold tolerant plants, was also analyzed for floral color. A model of additive dominant inheritance (pink color dominant over white color, or presence versus absence of pigment, and the number of dominant alleles present determining the intensity of the pink color) is proposed. The action of two independent locus sets is also suggested, one for the male (with two main structural genes) and another for the female floral organs (one main structural gene). It is suggested that an undetermined number of regulatory genes affect color expression.

Valor forrageiro de híbridos interespecíficos superiores de Paspalum

O objetivo deste estudo foi avaliar a expressao de caracteres agronomicos e a tolerância ao frio de hibridos apomiticos de Paspalum plicatulum x P. guenoarum, bem como estimar suas correlacoes fenotipicas, em duas regioes edafoclimaticas distintas. O estudo foi conduzido em diferentes locais e anos de avaliacao, em delineamento de blocos ao acaso, com tres repeticoes. Foram avaliados quatro hibridos interespecificos de Paspalum, dois genotipos de P. guenoarum e a cv. Aruana (Panicum maximum), utilizada como testemunha. Os hibridos H12, H13, H20 e H22 apresentaram superioridade para os caracteres agronomicos avaliados e tolerância ao frio, em relacao as cvs. Rojas e Aruana e ao ecotipo Azulao, e sao indicados para novas etapas de avaliacao, como estimativas da producao de sementes e estudos de DHE e VCU, visando o lancamento como novas cultivares. As estimativas de correlacoes fenotipicas sao importantes ferramentas para a selecao de progenies, com destaque para o carater MSF que apresentou alta correlacao positiva com os caracteres MST, DPP, rebrote e altura, indicando ser desnecessaria a realizacao de separacao morfologica, economizando tempo e mao de obra em um programa de melhoramento de forrageiras.