Morphology and morphogenesis of female reproductive organs in some walnut (Juglans regia L.) genotypes

Abstract

The morphological characteristics of female flowers and their parts in six walnut genotypes were described. The number of female flowers per inflorescence ranged from 1.9 to 2.7. The length and width of female flowers were 8.0–10.1 mm, and 3.4–3.8 mm, respectively. The average length and width of the ovule for all genotypes was 0.55 mm. The largest width of the ovule was 0.59 mm in the cultivar ‘Sheynovo’, and the smallest 0.51 mm in the cultivar ‘Geisenheim 139’. A significant positive correlation was found between the length and width of female flowers (r = 0.34⁎) and between the length and width of ovules (r = 0.57⁎⁎). Also, a significant negative correlations were found between the length of female flowers and the number of female flowers in the inflorescence (−0.58⁎⁎), and between the beginning of flowering and the duration of flowering (r = −0.66⁎⁎). The average width of the megaspore for all genotypes was 13.7 μm and of the mature embryo sac 70.2 μm. The average length of the mature embryo sac was 78.1 μm. The female flower morphogenesis occurred successively and in the same order in all examined genotypes. The differences by years and between genotypes referred to the time of onset and duration of the development stages. The characteristic phases of the female flower morphogenesis are described, and their dynamics are shown graphically for each genotype. The type of dichogamy had a significant influence on the rate of flower development. A high degree of concordance was found between the phases of female flower development and the stages of megasporogenesis and megagametogenesis. The paper presents photographs of comparative developmental stages that enable the assessment of the phases of megasporogenesis and megagametogenesis according to external morphological changes on female flowers and ovules.