The stress index is defined as an objective atmospheric indicator that allows determining and quantifying through its accumulation, by means of a correlative number, and its direct relationship between the atmosphere and the plant. The accumulation of stress units is conditioned by the relationship of two climatic variables, such as ambient temperature (T/°C) and relative humidity (RH/%), where to accumulate stress units the following condition must be met in each of the variables: temperatures must be equal to or greater than 10°C and relative humidity must be at a percentage equal to or less than 75%; if any of the variables does not present this condition, there is no accumulation of stress units.
It has been observed that in most cases the main trigger in the accumulation of stress units is the percentage of relative humidity in the environment, since, when comparing areas with similar ambient temperatures, the area that presented a lower percentage of relative humidity obtained a greater accumulation of stress units.
This method of stress unit accumulation comes from the simplification of the vapor pressure deficit (VPD) formula, which calculates the difference between the saturation pressure and the current pressure; the greater the difference between the two, the greater the water demand by the plant.
The concept and calculation of this method can be complex, however, the stress index formula helps us to estimate and interpret stress conditions in an easier way.
The accumulation of stress units in cherry cultivation directly affects the physiological behavior of plants, because there is a direct relationship in the generation of carbon structures through photosynthesis, that is, the greater the accumulation of stress units, the lower the photosynthetic rate and carbohydrate reserves for the following season, given that when plants encounter situations of atmospheric stress they tend to use part of their reserves to recover their damaged photosystems.
Given the above, for cherry cultivation it is important to be able to build the plants for the following season, which implies keeping the plants in low stress conditions, this is because until at least the phenological state of petal fall, the plants only work with the carbon reserves that they managed to accumulate during the previous season both in their roots and in their vegetative structures in the post-harvest period.
Since the accumulation of stress units is directly related to the climatic conditions that may occur during the season, our only way to cope with this condition is to mitigate this environmental stress through cultural management aimed at reducing this effect and the problems associated with it, which will translate into a better accumulation of reserves for the following season.
Cultural management to mitigate problems attributed to the stress index (Sepúlveda, 2020).
- Avoid excessive fruit load and weak leaf development of the tree. This will provide fewer carbohydrates for the plant's defense systems.
- Maintain the tree in an adequate water status. Greater damage has been shown in trees with a lack of irrigation.
- Maintain the health of the garden. Any biotic stress (pests, diseases, weeds) will compete for photosynthesis assimilates.
- Applications of algae and/or sunblock during periods of greater stress accumulation.
Sepúlveda, A., Arenas, L., Yuri, J. 2019. Climate and Quality of Apples. Pome Center-University of Talca.
Sepúlveda, A. 2020. Environmental stress and fruit production. Climate newsletter No. 54, Pomaceous Center-University of Talca.
