Abstract
The poor set of normal seeded berries in 'Pione' grapes is attributed to the small number of fertilized eggs in the ovules. To examine the effect of nutrients and phytohormones on ovule development and pollen tube growth, young florets, about one week before bloom, were cultured in vitro on several media. Florets of 'Muscat of Alexandria', which is known to be a good setting cultivar, were cultured for comparison.
The ovary size became larger in both cultivars as the concentration of inorganic components of Nitsch and MS media or only KNO3 of the Nitsch medium was increased. Ovule development and pollen tube growth, however, were inhibited in these enlarged ovaries, especially in 'Pione' pistils. The addition of 110 ppm NAA, GA or BA to the Nitsch medium inhibited ovule development and pollen tube growth in pistils of 'Pione', but we observed no significant change in ovary size. Pollen tube growth was inhibited in pistils of 'Muscat of Alexandria' cultured on medium containing water extracts of 'Pione' pistils; however, ovary growth and ovule development were not affected.
From these results, we concluded that in florets of 'Pione', an excess of nitrogenous nutrients leads to severe inhibition of ovule development and pollen tube growth. Pollen tube growth inhibitors, detected abundantly in 'Pione' pistil extracts, do not appear to be inorganic or hormonal substances.
