Pre-budburst temperature influences the inner and outer arm morphology, phenology, flower number, fruitset, TSS accumulation and variability ofVitis viniferaL. Sauvignon Blanc bunches

Abstract

Background and Aims: Inflorescence morphology, flower formation and subsequent fruit development of grapevines are influenced by genetic, environmental and cultural practices. While the effect of temperature on inflorescence primordia number per bud is documented, its effect during dormancy and budburst (BB) on floral development is less clear. In our study, winter dormant buds were passively heated for different periods of time from mid‐winter (July) to BB (October). Methods and Results: Individual canes were heated pre‐BB for different periods in polyethylene tunnels. Heating during winter dormancy had no effect on the number or position of inflorescences on the shoot, or on the type of structure occurring at the outer arm position of the inflorescence. Heating buds for either July or August to BB advanced the date of BB and the start date of flowering by 12–14 and 14 days, respectively, compared with that of the unheated Control treatment. There was a significant (P < 0.05) negative correlation between the mean temperature 12 days pre‐BB and flower number per shoot. The time between 50% flowering and the fruit TSS reaching 14°Brix was not influenced by winter heating or the date of flowering; the difference in this time interval, however, between the inner and outer arm components increased as shoot node number increased. Conclusions: Flower number per inflorescence had the greatest influence on the proportion of fruitset. The date of flowering of the outer arm was later at higher inflorescence positions on the shoot and later than that of the inner arm. Likewise, the outer arms of bunches higher up the shoot took longer from flowering to accumulate a fruit TSS of 14°Brix. Significance of the Study: Much of the within‐vine variability in berry composition at harvest can be attributed to the position of bunches on the shoot and the presence of an outer arm. The outer arm on apical bunches took significantly longer to progress from flowering to a fruit TSS of 14°Brix, suggesting that removal would significantly reduce within‐vine fruit variability.

What do we know about grapevine bunch compactness? A state-of-the-art review

“…In addition, some cultivars present a lateral wing (also called outer arm or shoulder) (May ) which is differentiated from the main bunch already in the bud during the first growing season (Srinivasan and Mullins ). The lateral wing may have different morphologies, from a highly branched bunch‐like structure rivalling the main bunch in size, to just a tendril with no flowers/berries (Carmona et al , Eltom et al ).…”

“…The degree of branching decreases acropetally within the developing bud, and will have an influence on the degree of branching that can occur at the start of season two and on the future number of flowers in the inflorescence (Dunn and Martin ). During the second season, secondary and tertiary branching starts during budswell before budburst, ending in the flower initiation or formation of floral primordia in small groups, normally three (Dunn and Martin , Carmona et al , Eltom et al ). Major differences in the rachis elongation rate between cultivars have been described during the period of inflorescence development prior to flowering time, whereas little growth exists after flowering (Coombe , Shavrukov et al ).…”

“…In the inflorescence, flower differentiation (floral organogenesis) starts after budburst and ends with the formation of the pistil about 2 weeks before flowering (May ). The number of flowers per inflorescence is highly variable, being influenced by environmental, genetic and cultural factors (Dry et al , Eltom et al ). In addition, strong differences can be appreciated in the diverse branches of the inflorescence at flowering, with final branches presenting the lowest number of flowers (Dunn and Martin ).…”

“…The final number of berries in the bunch is mainly established during fruitset, 1 or 2 weeks after flowering, as in the grapevine a delayed drop usually does not happen (May ). The proportion of flowers converting into berries (fruitset rate) greatly depends on the number of flowers in the inflorescence (May , Eltom et al ), and large differences exist for both between cultivars (Dry et al ).…”

“…Temperature is another factor suggested to influence bunch architecture, and high temperature during budburst can significantly reduce flower number in different cultivars (Buttrose and Hale , Pouget , Ezzili , Dunn and Martin , Petrie and Clingeleffer ). Interestingly, Eltom et al () have indicated that the later heating of buds before budburst can accelerate budburst and decrease flower number per inflorescence, but increase fruitset and bunch mass in cv. Sauvignon Blanc.…”