Observações citológicas em Coffea: XIX - Microsporogênese em Coffea dewevrei

Abstract

<abstract language="eng">Coffea Dewevrei De Wild, et Th. Dur. is a diploid species with 2n = 22 chromosomes. Details on the microsporogenesis are presented in this paper. From pachynema to diakynesis the 11 bivalents were well differentiated into achromatic and chromatic regions : the centromere was in all chromosomes surrounded by deeply chromatic zones. Only one pair of chromosomes was found to be attached to the nucleolus; it has a submedian centromere, the organizing region seeming to be located in the short arm. Chiasmata were seen in diakynesis and metaphase I; in this later stage they were studied in detail and the chromosomes were classified as follows : a) 1 longer pair with 3 chiasmata; b) 2.7 pairs (average) with 2 chiasmata ; c) 7.3 pairs (average) with 1 chiasma. The 2-chiasmata chromosomes were of two kinds : "symmetric" and "assymmetric", depending on the position of their chiasmata in relation to the centromere. The anaphase is normal, pollen grains having 11 chromosomes. Very seldon are pollen grains formed with 10 or 12 chromosomes. First mitosis in the microspores occurs before pollen shedding. It was concluded that microsporogenesis in the coffee plants studied is normal

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.…”

“…rugosa to explain the low productivity of this variety and the lack of the wrinkled (rugosa) characteristic in the progenies of these plants. In addition to these varieties of C. arabica, similar analyses on microsporogenesis were made for several diploid species of Coffea, mainly those used in interspecific hybridizations with C. arabica Medina, 1952;Conagin, 1961;Medina and Rijo, 1969;Medina et al, 1977;Boaventura and Cruz, 1987). However, despite these studies on meiotic behavior, the characterization of individual chromosomes remained an important desideratum for progress with cytological research on coffee.…”

“…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).…”

Relationship between meiotic instability and fertility in F2 generation Arabusta coffee plants

“…Hybrids between the species C. arabica and C. canephora have been obtained on different occasions, and they are called "Arabusta" (Mendes 1950). Because of its importance, meiotic behavior had already been studied to some F 1 hybrids and also to parental plants in order to explore the genetic resources of these hybrids (Mendes 1950;Medina 1952;Medina 1963;Mônaco and Medina 1965;Medina and Rijo 1969;Reddy and Narayan 1981;Owuor 1985;Boaventura and Cruz 1987;Boaventura 1990).…”