Light Microscope Study of Pollen Tube Growth, Fertilization and Early Embryo and Endosperm Development in the Avocado Varieties Fuerte and Hass

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Abstract
Pollen tube growth, fertilization and early embryo and endosperm development were studied using light microscopy in the avocado varieties Fuerte and Hass. The ovule was penetrated by a pollen tube by 24 h after pollination. On reaching the ovary, the pollen tube grew along the surface of the inner ovary wall. It then grew around the funicle, through the micropyle in the inner integument and between the papillate cells at the apex of the nucellus. It entered the embryo sac via a synergid. Sperm nuclei were present in the embryo sac at 48 h after pollination and fusion of the polar and sperm nuclei took place before fusion of the egg and sperm. The endosperm nucleus was the first to divide and cell wall formation occurred following division. The first division of the zygote occurred at 5 or 6 days after pollination. In the variety Fuerte less than 20 per cent of the 1- and 2-day-old embryo sacs had been penetrated by a pollen tube although tubes were often observed in the integument or nucellus. In the variety Hass over 60 per cent of the embryo sacs were penetrated. In was concluded that low yields of the variety Fuerte may be partly attributable to the failure of the pollen tube to penetrate the embryo sac.