Effects of temperature and light (before and after budburst) on inflorescence morphology and flower number of Chardonnay grapevines (Vitis vinifera L.)

Abstract

Plastic mini-chambers were used as tiny 'glass houses' to increase bud temperature in the vineyard. Open containers, with holes cut in them for ventilation, were used as controls, and inflorescences produced in those chambers were compared with inflorescences from modified chambers where either shade cloth or reflective foil were used to alter internal levels of photosynthetically-active radiation (PAR) as well as temperature. Buds were treated for either14 days prior to budburst or for 13 days subsequent to budburst. Temperature and PAR were monitored immediately adjacent to the buds. Applied prior to budburst, the closed mini-chambers increased bud temperatures and reduced flower numbers per inflorescence. Both 'clear' and 'reflective foil' treatments resulted in similar flower numbers. However, the shading treatment increased flower numbers by approximately 13%. Prior to budburst, there was a significant but weak correlation between average temperature and flower number per inflorescence for both the basal and apical inflorescence. Average PAR was not significantly correlated with flower number on either inflorescence, and did not improve the correlation when included with temperature in a multiple linear regression. Subsequent to budburst, flower numbers per inflorescence were decreased by the closed container but were unaffected by either the shading or foil treatment. The correlation between temperature and flower number on the apical inflorescence was maintained but the correlation between temperature and flower number on the basal inflorescence was no longer apparent. These results suggest that temperatures encountered in a vineyard during budburst can influence the number of flowers per inflorescence to the extent of a 15 to 25% variation in flower number. PAR, apart from influencing bud temperature, does not appear to influence flower number. The effect of temperature on flower differentiation diminishes as budburst advances.