Grapevine bud fertility under elevated carbon dioxide

Aims: Microscopic bud dissection is a common tool used to assess grapevine bud fertility and therefore to predict the yield of the following season. Grapevine yield has been shown to increase under elevated carbon dioxide (eCO2) concentration and was demonstrated under Free Air Carbon dioxide Enrichment (FACE) conditions. The effect of eCO2 on bud fertility in regards to this yield gain has not been investigated. However, little is understood about which yield components are affected and at what stage of development this occurs. The aim of this study was to determine the number and cross sectional area of the inflorescence primordia (IP), and the levels of primary bud necrosis (PBN) found in grapevine compound buds grown under two different CO2 conditions and relate this data to yield parameters at harvest of field grown vines.
Methods and results: Plant material was collected in February 2016 and 2017 from two Vitis vinifera cvs., Riesling and Cabernet Sauvignon growing in the VineyardFACE experimental site at Hochschule Geisenheim University (49° 59′ N, 7° 57′ E) in the Rheingau wine region, Germany. Bud dissections were performed at the University of Adelaide’s Waite Research Institute, Australia. There canes were stored at 4°C until dissection at room temperature. The first eight nodes of every cane were dissected and the compounds buds were assessed for primary bud necrosis (PBN), IP number and the cross sectional area of IP using image analysis.
No difference in IP number per node and subsequent number of bunches per shoot was observed between treatments in Riesling. However, larger cross sectional areas of IP were found in the compound buds grown under eCO2. This was not supported by higher bunch weights and yield of Riesling for the eCO2 treatment over the two years. Cabernet Sauvignon showed a higher IP number per node under eCO2 but no changes in bunch number per shoot for the two seasons. A larger cross sectional area of IP was observed under eCO2 treatment. This did translate into significantly higher bunch weights and yields of Cabernet Sauvignonover both seasons. Percentage of PBN was highest in the most basal node position along the fruiting cane. However, average PBN was not affected by eCO2 for both cultivars along the cane.
Conclusions: Microscopic bud dissection can be used as a predictive tool to capture an increased bunch size at an early stage of vine development. There was evidence of a cultivar dependent response to bud fruitfulness under eCO2. It will be of future interest to investigate whether higher carbohydrate levels could be responsible for the increase in IP area detectable at a very early stage of development under eCO2.
Significance and impact of the study:This study contributes to an improvement in ourexisting knowledge about grapevine bud fertility and yield potential particularly under changing climatic conditions.

Authors: Yvette WOHLFART1, Cassandra COLLINS2, Manfred STOLL1

(1) Hochschule Geisenheim University, Department of General and Organic Viticulture, Von-Lade-Str. 1, 65366 Geisenheim, Germany
(2) School of Agriculture, Food and Wine, University of Adelaide, Waite Research Institute, Glen Osmond, 5064, Australia


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