Flower abnormalities cause abnormal fruit setting in tissue culture-propagated date palm (Phoenix dactylifera L.)

Off-types are quite common among tissue culture-produced date palm trees. The present study characterises a low fruit setting phenotype, found widely. among tissue culture-produced date palms of the cultivar 'Barhee'. Most flowers in such trees turn into parthenocarpic fruitlets having three carpels. In severe cases supernumerary carpels are formed. Other flower abnormalities include distortions of carpels and stigmas. The phenotype is alleviated in older trees, with about 50% of trees reverting to normal within 10 years from planting. Many flowers on the abnormal trees have impaired pollen tube elongation, with growth being limited to the stigma or to regions near its point of joining the carpel. Directional growth of pollen tubes ceases and tubes grow in different directions or stop growing completely. Possible mechanisms for this off-type phenotype, and its resemblance to other cases of somaclonal variation are discussed.