Cucurbit Genetics Cooperative Report 10:35-36 (article 21) 1987
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.
Table 1. Results of the identification of apomictic propagation.
Figure 1. Generative apospory embryo sacs in C. ficifolius.
Figure 2. Beginning of automixis in C.ficifolius.
