Frost resistance

The main issue in breeding for frost resistance is the assessment of the result obtained, in particular, the minimum temperature that a seedling can withstand in winter.

The most reliable will be long-term observations of grape bushes in the field. Since winter hardiness is no less important than frost resistance. But, this method is very long and not very suitable for modern breeding.

Therefore, various methods for assessing frost resistance and winter hardiness have long been developed, tested and put into practice by vine growers: direct and indirect.

One of the direct methods for testing the frost resistance of seedlings is hardening and freezing cuttings in a freezer. This process is well described in the works of great scientists: “Winter hardiness of grapes” by A.G. Mishurenko, V.A. Sherer, L.F. Ovchinnikova, 1975.

The latest scientific works in this direction can be found in the works of scientists of the NSC "IV&V named after V.E. Tairov": "Peculiarities of the grape plant and methods for assessing the indicators of organs and tissues" V.A. Sherer, N.N. Zelenyanskaya, 2011. ,

- and NIViV "Magarach": Frost resistance of a genetically heterogeneous gene pool of grapes. Volynkin V.A., Zlenko V.A., Oleinikov N.P., Likhovsky V.V., Modonkaeva A.E. 2011.

I will give a brief description of the process. For hardening and freezing of cuttings, a low-temperature chamber is used (up to -35, - 45 gr.c), which has the ability to change the temperature in steps of one degree from plus to minus temperatures.

Freezing of cuttings is carried out in December - February, when the grape vine is in a dormant period. Well-ripened cuttings are selected, of medium diameter, not overloaded with the crop this year, clean from diseases and damage.

For reliable analysis, it is desirable to have at least ten cuttings. If we are talking about seedlings, then it is possible to use a smaller amount to understand the perspective. Before the freezing process begins, the cuttings are stored in a cellar or refrigerator at a temperature of 0 to + 4 °C.

Before use, the cuttings are sorted, signed, wrapped in film to prevent moisture loss, and placed in a freezer. You can not soak the cuttings.

Since grapes are a southern plant, they do not have the genetic ability to withstand severe frosts like garden trees. Therefore, I would like to draw your attention and note that grapes can withstand the maximum minus temperature only when passing through all stages of hardening, with a gradual decrease in temperature.

During hardening, the cells are freed from excess water, starch is converted into glucose, and the intracellular substance and intercellular fluid are compacted. A sharp decrease in temperature is detrimental to the tissue cells of grapes.

There are three important stages of grapevine hardening: low positive temperatures (from + 5°C to 0°C), low negative temperatures (from 0 to -5°C, -10°C) and a gradual decrease in temperature no more than two degrees per day to a predetermined negative threshold.

Scientists have developed several freezing systems with different time exposures. After reaching the set temperature, the thawing process is performed. It is no less important, since a sharp rise in temperature is also detrimental to cells. Increase the temperature at a rate of 2-4 degrees per day and bring to + 10 gr.s.

The whole process of freezing and thawing takes approximately 20-25 days. After freezing on the cuttings, the sections are renewed, and completely immersed in water, they are soaked for 1-2 days. Then put in water for germination.

After 3-4 weeks, according to the results of germination, the number of whole and damaged eyes, germinated buds, the number of inflorescences, as well as damage to the tissues of the bast and core are taken into account. All data are recorded, the results of freezing are analyzed.

To test my seedlings for frost resistance in 2013, I purchased a special low-temperature chest:  TEFCOLD SE10-45 (-45c).

    

All cuttings of grape varieties (control): Talisman, Vostorg, Agat Donskoy, etc., Amur varieties and forms of grapes, as well as cuttings of my seedlings, I take out of the cellar, sign, pack in a film of 2-3 pcs. and put it in to freeze.

I use the following freezing technology: I lower the temperature in the chamber at a rate of 2 degrees per day from + 10 degrees C to a predetermined minus maximum (for example: - 27 degrees C).

If the goal is to conduct comprehensive studies in several stages (for example: up to - 25 gr.s, up to - 27 gr.s, up to - 29 gr.s, etc.), then it is necessary to prepare several batches of cuttings for each stage separately. Such studies will increase the reliability of determining the true frost resistance.

Further, after freezing, I soak the cuttings completely immersed in water for 1-2 days. After soaking, I update the cuts on the cuttings and put them in jars for germination, sorting them  by frost resistance (for comparison) and pour a little wate.

During germination, it is necessary to rinse the lower end of the cutting several times or renew the cut so that the vessels below do not clog and the result of freezing is not distorted.

Usually, bud break begins after 14-21 days. On some cuttings there are not only shoots, but also inflorescences. Some cuttings give roots. Accounting for blossoming buds, the number of inflorescences, etc. can be done after 45-60 days. It is useless to wait any longer. Unblown buds are easily broken off, damage to the bast and core is visible at the ends of the cuttings.

I conducted the first experiments on freezing cuttings in the winter of 2013-2014. Freezing of all cuttings was done in four batches: - 25 gr.s, - 27 gr.s, - 29 gr.s, - 31 gr.s. Each stage took about 20-25 days.

Since the fourth batch was frozen in February-March, many varieties and forms had already come out of dormancy and were killed by frost. Other technological errors were also made. Therefore, I consider the first freezing season to be a test and verification season.

At the end of the first year, I made the following conclusions:

1. Freezing cuttings at the highest temperature should be done first of all, when the cuttings are still in a state of natural dormancy (December - January). Freeze all other batches as the set temperature decreases (- 31, - 29, - 27, - 25 gr.s).

2. For freezing, it is necessary to choose well-ripened, healthy cuttings not damaged by diseases or hail. The diameter of the cuttings should be within 8 - 14 mm, no more and no less. It is necessary to cut the cuttings from unloaded bushes and shoots without clusters.

3.Even in the first year of the experiment, the frost resistance of the control institute grape varieties was unequivocally confirmed: Agat Donskoy (higher - 26 gr.s), Vostorg (-25 gr.s), Talisman (-25 gr.s), etc. Rootstocks Kober-5BB and RR-101-14 (over - 31 gr.s), Garant and Dobrynya (about - 28, - 29 gr.s). Among the table grape varieties that participated in the tests, only Elegia (Donetsk) withstood - 31 gr.s.

(The results of freezing in 2015 and subsequent years, with tables and conclusions, will be presented in the section "Experiments- Frost resistance test".)

Continuation: Reproduction, rootstocks.