Cucurbit Genetics Cooperative Report 10:37-38 (article 22) 1987
Pollen Mother Cell Meiosis in the Haploid of Cucumis
ficifolius A. Rich
L. Zagorcheva, M. Alexandrova and C. Kichukova
Maritsa Vegetable Crops Research Institute, Plovdiv, Bulgaria
Haploid forms in the genus Cucumis ficifolius have not
been reported previously in the literature. Tetraploid (2n=48) (1,2) and
hexaploid (2n=72) forms (1) have been established. With C. ficifolius
(2n=24) autonomous apomictic propagation has been found (3), both after
the isolation of non- fertilized female flowers and when hybridized with
C. sativus, C. melo var. flexuosus, etc.
Progenies resulting from crosses of C. ficifolius with C.
sativus and C. melo var. flexuosus appeared
to be matromorphic. In the progeny of isolated non-fertilized female flowers
of C. ficifolius, one out of eight plants had a chromosome
number of 2n=12. it is evident that besides the unreduced egg cells, egg
cells with reduced chromosome number in C. ficifolius embryo
sacs are capable of apomictic development as well.
These haploids develop slowly, but preserve the species traits. Plants
are as tall as the original diploids, but its leaves are smaller and deeper
cut. Staminate and pistillate flowers are smaller, with shorter petioles,
and have petals that are not joined at the base.
Meiosis in pollen mother cells of the haploids is characterized by disturbances.
During diakinesis, 12 non-spiralized chromosomes are established. During
Metaphase I they are strongly spiralized and in 92.9% of pollen mother cells,
they are scattered along the divisional spindle that is most often considerably
elongated and twisted (Fig. 1). It is followed by mitosis and diad formation
of microspores (Fig. 2). It is evident that the haploid has inherited from
the parent plant the ability to form unreduced gametes. In 7% of pollen
mother cells chromosomes are incorporated into the metaphase plate, and
from Metaphase I through Anaphase I, 1 to 10 chromosomes are divided into
chromatids. Through Anaphase I different numbers of chromosomes move in
the direction of the divisional spindle poles, but most often it is 6+6.
In Metaphase II and Anaphase II, the location and division of chromosomes
is irregular. In a part of the pollen mother cells, three-pole divisional
spindles are formed. Microspore types consisted of diads (66.7%), tetrads
(18.6%), polyads (11.0%) and triads (3.7%). Only 28% of the pollen is fertile.
When self -pollinated, the haploid did not set fruits. When crossed with
C. sativus, 80% of the pollinated flowers set fruits with
seeds. The average seed number per fruit was 3.5. The embryo takes up half
of the volume of the seed. On an artificial medium in culture, the white
part of the seed formed plants that died of secondary infections. The haploid
can be maintained through in vitro propagation from apical
meristems.
This is the first case we know of where the incompatibility barrier between
the wild species of Cucumis in the melo group and Cucumis
sativus L. has been overcome.
Fig. 1. Pollen mother cells with 12 chromosomes MI-AI).
Fig. 2. Dyad from microspores.
Literature Cited
- Dane, F. and T. Tsuchiya, 1976. Chromosome studies in the genus Cucumis. Euphytica 25:367-374.
- Shimotsuma, M., 1965. Chromosome studies of some Cucumis species. Seiken Ziho 17:11-16.
- Zagorcheva, L., 1985. Autonomous apomictic propagation of Cucumis
ficifolius A. Rich and C. anguria. Genetics and Breeding: 18 no. 5.
