Pollination and pollen-pistil interaction in oil palm, Elaeis guineensis

Abstract

Structural and cytochemical aspects of the pistil and details of pollination and pollen-pistil interaction were investigated in the African oil palm (Elaeis guineensis Jacq.), an important perennial oil crop. The stigma is trilobed, wet and papillate. The branched papillae are confined to a narrow linear zone on each stigmatic lobe. Each stigmatic lobe harbours a deep stigmatic groove, which runs adaxially along the surface. The stigmatic groove is bordered by a well-defined layer of glandular cells, each of which has a pectinaceous cap on the inner tangential wall. The style is hollow. The canal cells show thickenings on the inner tangential wall. The stigmatic groove and stylar canal contain an extracellular matrix secreted by the canal cells which is rich in proteins, acidic polysaccharides and pectins. The canal cells at the base of the style are papillate and loosely fill the stylar canal. The stigma becomes receptive when the stigmatic lobes separate, and remains so for 24 h. Pollination is mediated by weevils as well as by the wind. Under natural conditions the pollination efficiency was 100%. Pollination induces additional secretion in the stigmatic groove and stylar canal. During post-pollination secretion, the pectinaceous caps of the cells lining the stigmatic groove are degraded. Pollen grains germinate on the stigmatic papillae and tubes grow on the surface of the papillae, entering the stigmatic groove and advancing along it into the stylar canal to eventually gain access to the locules. Pollen tubes are seen in the ovules 18-20 h after pollination.