Embryo Sac Development in Almond [Prunus dulcis (Mill.) D. A. Webb] as Affected by Cross-, Self- and Non-pollination

Abstract

Embryo sac development in ‘Nonpareil’ almond was studied following cross-, self- and non-pollination under field and greenhouse conditions. The embryo sac, which develops according to the Polygonum type, does not begin to differentiate until anthesis in contrast to other Prunus spp. where a well-developed embryo sac is present at the time of flower opening. The developing megagametophyte appears to be isolated from surrounding nucellar tissue by the deposition of a ring of callose, which, as indicated by aniline blue-induced fluorescence in the walls of nucellar cells, encloses the embryo sac during its elongation. Development and growth of the embryo sac following the different pollination treatments indicated that embryo sac development was stimulated by the presence of compatible pollen tubes in the style and final elongation growth of the embryo sac was promoted by cross-pollination. Irregularities in megagametophyte development, including delayed differentiation of the megaspore mother cell, embryo sac abortion and lack of polar nuclei fusion and embryo sac elongation, were frequently noted in ovules of self- and non-pollinated flowers.