Stability in chromosome number and DNA content in synthetic Tetraploids of Lolium Multiflorum after two generations of selection/Estabilidade no numero cromossomico e no conteudo de DNA em tetraploides sinteticos de Lolium multiflorum apos duas geracoes de selecao

Chromosome doubling of Italian ryegrass genotypes (Lolium multiflorum Lam.) adapted to the brazilian edaphoclimatic conditions is an important strategy used by breeders and aims to obtain more vigorous genotypes with better forage quality and disease resistance. The effectiveness of chromosome doubling can be measured by genetic stability and fertility rates of plants over generations. However, a common problem in the polyploidization process is the regeneration of mixoploid plants that have impaired fertility and genetic stability. The objective of this study was to verify ifprogenies of recently tetraploidized plants remain stable regarding DNA content and chromosome number, over two generations. Progenies of L. multiflorum plants artificially tetraploidized with colchicine treatment were evaluated. Chromosome counting and estimates of the DNA content were used to evaluate the genetic stability. The percentage of tetraploid plants (4X) increased over generations (18%, 34% and 91% in cycle 0, 1 and 2, respectively). All progenies identified as tetraploid by flow citometry showed variation in chromosome number (mixoploidy), but produced viable seeds. Results showed that stabilization in chromosome number and DNA content in tetraploidized plant progenies requires time and that the success of this procedure depends on a continuous and accurate screening and selection. Key words: chromosomal duplication, mixoploidy, Italian ryegrass, plant breeding. A duplicacao cromossomica de genotipos de azevem anual (Lolium multiflorum Lam.) adaptados as condicoes edafoclimaticas brasileira e uma estrategia importante usada pelos melhoristas e visa a obtencao de genotipos mais vigorosos com melhor qualidade de forragem e resistncia a doencas. A eficincia da duplicacao cromossomica pode ser medida pela estabilidade genetica e taxas de fertilidade das plantas ao longo das geracoes. No entanto, um dos problemas comumente encontrados no processo de poliploidizacao e a regeneracao de plantas mixoploides que apresentam comprometimento na fertilidade e instabilidade genetica. O objetivo deste estudo foi verificar se prognies oriundas de plantas tetraploidizadas recentemente se mantm estaveis quanto ao conteudo de DNA e ao numero cromossomico, ao longo de duas geracoes. Foram avaliadas prognies de plantas de L. multiflorum tetraploidizadas artificialmente com tratamento de colchicina. A estabilidade genetica foi avaliada por meio de contagens cromossomicas e estimativa da quantid