Cucurbit Genetics Cooperative Report 10:35-36 (article 21) 1987
Autonomous Apomictic Propagation of Cucumis
ficifolius A. Rich and C. anguria L.
L. Zagorcheva Maritsa
Vegetable Crops Research Institute, Plovdiv, Bulgaria
The incompatibility barrier of C. ficifolius with C.
sativus was studied in 1985 under greenhouse conditions. Treatments
included sib- and self- pollination and unpollinated female flowers to check
apomictic seed production (Table 1.). The reason for this check was the
in vitro investigation regarding pollen tube behavior observed
under ultraviolet microscope of diallel crosses between wild species of
Cucumis and C.sativus. After self-pollination of C.
ficifolius, the pollen tubes either widened or branched in an unusual
way just above the embryo sac.
The results obtained were unexpected, showing both in C. ficifolius
and C. anguria that 100% of the isolated female flowers produced
fruits and 100% of their fruits had numerous seeds (122 to 270 in C. ficifolius
compared to 249 in C. anguria). The high percentage of fruits
with seeds following hybridization of C. ficifolius and C.
anguria with C. sativus (Table 1) confirms also the
presence of apomictic propagation in these species. Obviously, both C.
ficifolius and C. anguria are species with autonomous
apomictic propagation, i.e. propagation independent of pollination and the
effect of pollen tubes.
To establish the apomictic propagation type in these species, we investigated
the way the embryo sac and the embryo are formed. It was found that C.
ficifolius and C. anguria form two female flower types:
embryo sacs of the Polygonum type are formed in the first type, and diploid
generative apospory embryo sacs (prevailing) (Fig. 1) and embryo sacs of
the Polygonum type are formed in the second type. The generative apospory
embryo sacs have 8 nuclei. Their egg-apparatus is three-celled, but their
synergids have no vacuoles and their nuclei are located at the chalazal
end near the egg nucleus. The behavior of one of the synergids of the generative
apospory embryo sacs is quite impressive. It grows fast and leaves behind
the other synergid and egg (Fig. 2). It is evident that it will divide and
form an embryo. This kind of behavior of some embryo sac cells is characteristic
of automixis. We think that automixis is one of the mechanisms of apomictic
propagation with C. ficifolius and C. anguria.
Fig. 1. Generative apospory embryo sacs in C. ficifolius.
Fig. 2. Beginning of automixis in C.ficifolius.