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Kitaibelia vol. 4 – no. 1. (1999) p.11-16.
Sorbus-fajok embriológiai-sejttani és származási vizsgálata
The paper deals with the reproductive strategies of eight Sorbus species of horticulture importance. 2300 ovule sections as samples provided data to study the possibility of agamospermy. We stated that Sorbus torminalis, S. rotundifolia, and the S. aria produce seeds exclusively on sexual way. Sorbus Degenii yields seed-clones with diploid aposporic embryos in the fruits. In the ovules of Sorbus borosiana besides the aposporic embryos a sexual embryo sac can evolve too. All studied Sorbus aria × aucuparia hybrids except S. Filarszkyana are apomictic species.
On studying the sections, we registered cases when proembryos had developed (in both sexual and asexual embryo sacs) without the fertilisation of the polar nucleus. They decayed later, so these ovules continued to develop into seeds without embryos. It was experienced at the apomictic species that the presence of more than normal number of polar nucleus also prohibited the development of the proembryos.
As pollination is necessary to both fertilisation and endosperm development, the author made compatibility experiments too.The presence of trees producing suitable pollens is always important in the gardens. As the microscopic studies of ovules appeared that by the time of anthesis the embryo sacs are yet undeveloped, the fertilisation can not take place in a short time. As the vitality of the male and female gametes are various, we propose to plant Sorbus species of different flowering time together, somehow we have to imitate the natural conditions.
There were no significant difference between the seed yield of sexual and apomictic species. The species studied produce only about two (l.l – 2.7) viable seeds per fruits owing to the different irregularities discussed in the paper.