Observações citológicas em Coffea: XIV - Microsporogênese em Coffea arabica L. Var. rugosa K.M.C.

Abstract

<abstract language="eng">Only one plant of Coffea arabica L. var. rugosa K.M.C., is available for study Its fruit production is very low. Of the progeny observed, none has reproduced th rugose condition of the leaves characteristic of the parent plant. Previous study ha shown that the rugose condition of the leaves could not be considered a somatic chimer because the tissues have a normal number (2n=44) of chromosomes. The present cytological study was undertaken in order to find out if the low yiel of the rugose variety could be related to abnormalities in microsporogenesis. The structure of the chromosomes in early prophase is difficult to study. In diaki nesis two pairs and sometimes three pairs of chromosomes appear to be attached to th nucleolus. Also in diakinesis it is possible to locate the centromere in the chromosoni pairs and to count the chiasmata. It was observed that an average of 6.6 bivalent show one single chiasma, 12.3 bivalents show two chiamata and 3.0 bivalents shoM three chiasmata. The average total number of chiasmata per cell at this phase is o 40.0, while at metaphase this number is reduced to 34.7. The first division in the mi crospore is normal and the resulting two nuclei differ in size and also in the size o their nucleolus. The polen grains are normal, giving 69% germination on a medium containinj 0,5% of agar and 15% of sucrose. It is concluded that microsporogenesis is normal and would not appear to be relate< to the low production of fruits of the rugosa variety. The fact that none of the progen¹ has reproduced the rugose condition might be due to the limited number of plants observed

Microsporogênese em Coffea stenophylla G. Don e C. salvatrix Swynn et Phil

“…Assim, pois, das observações feitas em diferentes plantas da coleção deste Instituto, sabe-se que a espécie C. arábica L., apesar de tetraplóide em relação ao número básico x= 11, comporta-se como diplóide e que o processo da microsporogênese apresenta poucas irregularidades (8,16). A meiose, nas formas monosperma (i 1 ?)…”

Cytogenetics of coffee

“…These studies indicated a uniform number of chromosomes (2n=44) for all varieties of C. arabica, and it was demonstrated for the first time that, despite the tetraploid condition, this species shows normal meiotic behavior. Subsequently, many other species, varieties, cultivars, and interspecific hybrids, with different levels of ploidy, such as triploids, tetraploids, hexaploids and octoploids, also had their chromosome number established (Krug, 1937, Mendes, 1938Medina, 1950Medina, , 1952Medina, , 1972.…”

“…He analyzed the number of nucleolar chromosomes, number of chiasmata per cell, pairing of bivalents and the pollen formation, and concluded that microsporogenesis in these varieties was normal. Medina (1950) also analyzed the microsporogenesis of C. arabica L. var. rugosa to explain the low productivity of this variety and the lack of the wrinkled (rugosa) characteristic in the progenies of these plants.…”

“…Although morphologically quite distinct, Coffea species present some common genetical features, such as the small variation in the chiasmata number (Mendes, A.J.T., 1950;Mendes C.H.T., 1950;Medina, 1950Medina, , 1952Conagin, 1961;Medina and Rijo, 1969;Medina et al, 1977) and the high frequency of bivalents in interspecific hybrids (Medina, 1972). Several studies have been carried out to establish precisely the relationships between species in the genus Coffea (Carvalho and Mônaco, 1967;Chinnappa, 1981;Lashermes et al, 1996Lashermes et al, , 1997, but interspecific relationships in this genus are still controversial since the affinities among species based on morphological characteristics and/or geographical distributions conflict with the relationships indicated by hybridizations and the cytological analyses of such hybrids (Carvalho and Mônaco, 1967;Medina 1972).…”

Taxonomia de Coffea arabica L. VI: caracteres morfológicos dos haplóides

“…• 4-6 tempo, a julgar pelos estudos da meiose (25,29) e resultados das análises genéticas (19). Do cruzamento entre as diversas variedades de C. arábica com a variedade typica dessa espécie, considerada como tipo padrão, têm-se obtido relações simples, correspondentes a segregações de um a dois pares de fatores genéticos.…”