Observations on the morphology and development of star flowers of 'Vitis vinifera' L. cvs Chardonnay and Shiraz

Abstract

Background and Aims: Following our original discovery of star flowers on grapevines in Australia, further variants of the star flower phenotype have been discovered on other varieties in South Australia. The objective of this report was to describe star flowers on 'Vitis vinifera' L. cvs Chardonnay and Shiraz. Methods and Results: Field and microscopic observations revealed that star flowers on both varieties opened precociously; there was neither pollen nor pollen tubes on the stigmas of the star flowers, and both Chardonnay and Shiraz star flowers contained aberrant ovules. The Chardonnay vines with star flowers produced bunches with an abundance of seedless berries; however, star flowers on Shiraz vines did not develop into berries. Conclusions: The inability of the Shiraz star flowers to develop into berries suggests that either there are two different mutations affecting these two varieties, or else the difference lies in their contrasting parthenocarpic tendencies. Significance of the Study: The star flower variants described here and previously may be the result of deviations to the normal molecular pathway for flower development in 'Vitis' species. The identification of star flowers on numerous varieties and in several different regions suggests that the occurrence of star flowers may be more widespread than previously realised, and the association of star flowers with the production of seedless berries and poor fruitset suggests that star flowers may also play a significant role in the problem of poor fruitset.