Grapevine reproductive performance: the role of amines, and the effects of salt and silicon.

Abstract

Optimising reproductive performance of the grapevine is one of the major difficulties faced by Australian viticulturists due to a physically and economically challenging environment. It is well-documented that salt stress is one of the challenges that causes significant damage to grapevine vegetative and reproductive performance. One of this project’s aims was to investigate the yield reduction caused by salt stress during and post flowering. While the ability of silicon (Si) to enhance salt tolerance and yield performance is well-known in many crops especially cereals, the use of Si as a tool for improving grapevine reproduction under saline conditions is inconclusive. This study demonstrated that salt stress reduces fruit set by increasing flower abscission and interrupting normal berry development, which results in more live green ovaries and seedless berries in a bunch. The poor berry development due to impaired fertilization correlated with poor pollen tube growth in the style, while pollen viability and stigma receptivity were not affected by salinity. A significantly higher amount of Na⁺ and Cl⁻ was found both in leaves and flowers after salt treatment and was not affected by additional Si application. The inability of Si to restrict Na⁺ and Cl⁻ ions in the reproductive organs of grapevines correlated with its inability to ameliorate the deleterious effects of salinity on the reproductive performance of grapevines. However, this study identified the possible role of Si in improving water use efficiency of non-stressed vines. Bioactive amines are a group of growth regulators which are reported to have major roles in many aspects of grapevine reproductive development as well as stress tolerance. The reproductive performance of three red winegrape cultivars commonly used in Australian viticulture; Shiraz, Cabernet Sauvignon and Merlot were investigated in relation to the occurrence of different amines in the reproductive organs. Amine profiles of the flowers and developing berries significantly differed among these three cultivars. Significantly higher amounts of diaminopropane (DAP) were found in Merlot and Cabernet Sauvignon and correlated with a higher proportion of underdeveloped berries. An aromatic amine phenylethylamine (PEA) not previously reported for grapevine was found to be the major free amine in the flowers of Merlot, which is a cultivar susceptible to poor fruit set. To the best of our knowledge, this is the first study to indicate that PEA may have a role in the reproductive performance of grapevines. Exogenous application of amines was also investigated as a way to manipulate the endogenous levels of each targeted amine and to manipulate fruit set. Results from this investigation were inconclusive and as such further studies are required to determine the concentration and timing of application that have an effect on different cultivars. To undertake controlled environmental experiments small fruiting grapevines were used; we further developed a method described by Mullins and Rajasekaran (1981) into a technique designed to obtain optimal growth in controlled conditions to produce experimental grapevine plants with optimal nutrition and adequate and consistent reproductive performance. This research led to significant advances in our understanding of grapevine reproductive biology, the impact that salt stress has upon flowering, fruit set and ultimately yield, and the involvement of amines in the reproductive performance of grapevines. Based on these results new research avenues are proposed to further our understanding.