Observações citológicas em Coffea: XVI - Microsporogênese em Coffea canephora Pierre ex Froehner

Abstract

<abstract language="eng">This paper presents the results of cytological observations on microsporogenesis in the self-sterile species Coffea canephora. It was found difficult to study chromosome structure in the first stages of meiosis because the chromosomes do not stain well with aceto carmine and could be seen only as long faintly threads with some heteropycnotic regions. In many observations of the pachytene stage it was possible to observe and study a chromosome attached to the nucleolus. This chromosome characteristically had a visible centromere which divided it into two arms of different sizes. The short arm was attached to the nucleolus and had several heteropycnotic regions. In the long arm the heteropycnotic regions were observed to be close to the centromere ; the distal portion of this arm was only faintly stained. Other chromosomes in the pachytene stage were found to have a conspicuous centromere located between two highly heteropycnotic regions. The heteropycnotic regions in some chromosomes were located near the centromere while in others they were observed to be scattered throughout the chromosome. In diakinesis the chiasmata were counted and there were found seven chromosomes with one chiasma, three chromosomes with two chiasmata and one chromosome with three chiasmata. The average number of chiasmata per cell was 15.88. In metaphase the average number of chiasmata per cell was found to be 14.57, which is less than the average per cell in diakinesis. Anaphase I appeared normal as did all subsequent phases of meiosis, that resulted finally in the development of four microspores with eleven chromosomes each. Very few pollen mother cells with abnormal numbers of chromosomes were observed. On the basis of this study, it is concluded that microsporogenesis in Coffea canephora is normal

Meiosis in hybrids between tree coffees (C. liberica, C. dewevrei) and Nandi coffee (C. eugenioides)

“…Mendes (1950) considers univalent formation in Coffeu to be generally due to precocious separation. This is in line with our observation of a reduction of frequency of observed chiasmata from early stages to MI.…”

Microsporogênese de Coffea canephora Pierre ex Froehner com número duplicado de cromossomos

“…Devido à grande regularidade na divisão meiótica das células de C. canephora dipióide (93,68%), MENDES (1950) concluiu que o pólen era normal. Em C. canephora tetraplóide, apenas 21,0% dos grãos de pólen são viáveis, o que é esperado em uma planta que teve o número de cromossomos duplicado.…”

Melhoramento do cafeeiro: V - Melhoramento por hibridação

“…Iniciaram-se depois as análises genéticas dos característicos das principais variedades dessa espécie (10) e realizaram-se também observações quanto à biologia da flor (2) e contagem de cromosômios das formas existentes (12,18). Efetuaram-se pesquisas relativas à micro e megasporogênese (14,19,21,22,23), desenvolvimento do endosperma (16) e, em alguns casos, sobre a morfologia dos cromosômios (15).…”