Maximising postharvest carbohydrate storage

Growing a crop is exhausting – for the grapevine. Nurturing vines through autumn helps maximise their performance in spring.

After growing a heavy crop, table grape vines need to recover and start storing carbohydrate and
nutrient reserves, so postharvest care is an important consideration.

How can you assess carbohydrate reserves?

Starch is stored as tiny granules in the plant’s transport system (in xylem and phloem cells) in roots
and in wood. Usually there is more stored in roots than wood. A simple test in the vineyard can show whether starch has been stored in the wood.

Use 1% iodine from the pharmacy and carefully apply drops to exposed cut wood. The iodine turns starch black, and it becomes visible as strings of tiny black granules within the xylem and phloem ray cells. Unfortunately, this doesn’t quantify how much starch is present, but it does show presence or absence.

Note that the iodine does not stain sugars, just starch.

Some laboratories offer carbohydrate testing of grapevines. Two different approaches focus on either:

  1. Testing wood – either as cores extracted from the trunk, or as sawdust extracted after inserting
    a drill bit into the trunk. Results after testing wood are expressed in terms of how much carbohydrate was present as a percent of the total dry weight (%DW).
  2. Testing foliage and fine roots – the laboratory will want a sequence of samples sent at critical growth stages during the season. Results are expressed as an index of sugars and starch, in roots and shoots at specific phenological stages.

The ATGA acknowledges that content for this article was drawn from a GWRDC Factsheet by Jason Smith, Charles Sturt University and Bruno Holzapfel, NSW DPI (April 2014) “Post-harvest care of grapevines: Irrigation and nutrition”, and other references.

Other useful references

Bei, R., Fuentes, S., Sullivan, W., Pech, J., & Edwards, E., McCarthy, M. & Tyerman, S. (2011). Carbohydrate dynamics of Chardonnay grapevines affected by irrigation reduction and recovering regimes. 267-269.

Dahal, K.C.; Bhattarai, S.P.; Midmore, D.J.; Oag, D.; Sapkota, R.; Walsh, K.B. (2024) In Situ Sucrose Injection for Alteration of Carbohydrate Reserve Dynamics in Grapevine. Agronomy 2024, 14, 425. https:// doi.org/10.3390/agronomy14030425.

Ferrara, G., Magarelli, A., Palasciano, M., Coletta, A., Crupi, P., Tarantino, A., and Mazzeo, A. (2022) Effects of different winter pruning times on table grape vines performance and starch reserves to face climate changes. Scientia Horticulturae, Volume 305, 2022, ISSN 0304-4238, https://doi.org/10.1016/j.scienta.2022.111385.

Martínez-Lüscher J and Kurtural SK (2021). Same Season and Carry-Over Effects of Source-Sink Adjustments on Grapevine Yields and Non-structural Carbohydrates. Front. Plant Sci. 12:695319. doi: 10.3389/fpls.2021.695319.

Rossouw, G. (2017) Grapevine carbohydrate and nitrogen allocation during berry maturation: Implications of source-sink relations and water supply. Thesis submitted for fulfilment of Doctor of Philosophy. Charles Sturt University Faculty of Science Wagga Wagga, NSW, Australia.

Rossouw, G., Smith, J., Barril, C., Deloire, A., Holzapfel, B. (2017) Carbohydrate distribution during berry ripening of potted grapevines: Impact of water availability and leaf-to-fruit ratio, Scientia Horticulturae, Volume 216, 2017, Pages 215-225, ISSN 0304-4238, https://doi.org/10.1016/j.scienta.2017.01.008.

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