Mutagenic treatment of pollen to obtain an inbred generation from self-incompatible cultivars of apple (Malus domestica Borkh.) and pear (Pyrus communis L.)

Abstract

Aims. The information analysis on the gene expression of self-incompatibility in apple (Malus domestica Borkh.) and pear (Pyrus communis L.) cultivars and the generalization with our research results on overcoming self-incompatibility by pollen mutagenic treatments were determined to be the aim of this article. Methods. The studies of the controlled geitonogamy were conducted at the orchards of the National Dendrological Park “Sofiyivka” of the NAS of Ukraine (NDP “Sofiyivka”) and the Uman National University of Horticulture (UNUH). The experiments were performed on 10- to 20-year-old apple trees Golden Delicious’, ‘Zymove lymonne’, ‘Cortland’ and ‘Slava Peremozhcyam’, as well as pear trees ‘Bere Desiatova’ and ‘Clapp's Favorite’. Castrated flowers of these cultivars were pollinated with pollen from other flowers of the same tree, i.e. geitonogamy was performed (one of the variants of inbred pollination), and also а number of variants of geitonogamy by mature pollen preliminarily treated with gamma rays in doses of 5; 20 and 50 gray (Gy) and chemical mutagens vapours: nitrosodimethylurea (NDMU—50 mg per desiccator; dimethyl sulfate (DMS) and ethylene oxide (EO)—both 12 drops per ten-litre sealed desiccators. The statistical analyses were carried out using the methods of Ronald Fisher. Results. The efficiency of the mutagens used for increasing the percentage of fruit set and seeds per fruit was confirmed in most variants of the experiments with apple (M. domestica) and pear (P. communis). We assumed that after geitonogamous pollination by many mutagenized pollen grains with mutant and non-mutant alleles of the S-gene, the inhibition in the stigma and/or in the ovary mainly may show for pollen grains without mutant alleles of the S-gene. Analysis of the fruit set showed that in all variants with mutagens, the fruit set and also the number of seeds per fruit significantly exceeded variants of "geitonogamy without mutagens". It also was revealed that the average fruit set and the average number of seeds per fruit in apple cultivars were much higher than in pear cultivars. Conclusions Studies have shown that treatment of apple and pear pollen with mutagens promotes fruit setting and the number of seeds per fruit in geitonogamous pollination, possibly due to the natural selection of mutant microspores by the egg apparatus of the female gametophyte and the germination inhibition of non-mutant pollen. The technique of geitonogamous pollination by pollen pre-treated with gamma rays and chemical mutagens for obtaining an inbred generation can be recommended for apple and pear breeding, and also deserves to be studied in other cultivated plants with self-incompatibility genes.