Without a doubt, the 2023-24 season has been one of the most challenging for the entire Chilean fruit sector. The different edaphoclimatic variables had a transversal impact on all fruit species in the country.
In the case of the cherry tree, it is known that it is a species that, in order to express its maximum flowering and subsequent fruiting potential, directly depends on the accumulation of reserves from the previous season and on adequate climatic conditions in its reproductive phase. Although the flowering potential is given by a series of factors and events that occurred during the previous season, the fruiting potential is closely linked to the process of pollination and fertilization.
These processes are highly dependent on the prevailing climatic variables during the season, and these factors are impossible to control. In this regard, it is important to consider the following technical aspects:
- Floral biology.
The process of flower and later fruit development involves an interaction between genetic and environmental factors that regulate the transition from vegetative buds to mature floral structures. This process requires a long period of time, ranging from the previous spring/summer to late winter and early spring of the following season.
According to Fadón et al., in their work carried out between 2015 and 2018, floral induction occurs during the summer, and floral differentiation begins before dormancy, in late summer and autumn, and after breaking latency, the flowers complete differentiation when temperatures progressively increase.
- Floral Induction.
The floral induction process is crucial to reach the maximum productive potential, as it balances floral and vegetative development, ensuring both the quantity and quality of the fruit; in other words, it is when the buds pass from a state of vegetative growth to a state of floral development (Roversi & Alessandro. 2002). This process, influenced by genetic and environmental factors such as light, temperature, nutrition, irrigation and phytohormones, determines the number and quality of the flowers. In the case of sweet cherry, floral induction begins approximately 70 days after full flowering, marking the beginning of the next year's production stage. Proper management of these factors is crucial to optimize fruit yield and quality.
- Floral differentiation.
Floral differentiation in cherry trees is essential for the construction of productive potential. This process, influenced by genetic, hormonal and environmental factors, determines the identity and quantity of flowers. Plant hormones, such as auxins and gibberellins, regulate floral growth and morphogenesis (Ayala, M. 2008). The interaction between floral differentiation and other physiological processes, both aerial and root, can impact fruit production and quality. Understanding and effectively managing this process is crucial to optimize cherry yield and quality, implying the consideration of adequate nutrition, light management, irrigation and hormonal regulation to ensure successful harvests over time.
- Effective pollination period (EP).
The effective pollination period is defined as the number of days of pollination necessary for a fruit to be produced (Sanzol, J., & Herrero, M. 2001). In other words, it corresponds to the difference in days between the viability of the ovule and the growth of the pollen tube.
This variable is closely linked to the climatic conditions present in the season and is conditioned by three fundamental processes, which are: stigmatic receptivity, pollen tube kinetics and development.
This effective period of pollination, as shown in Figures 1 and 2, was strongly affected by the climatic conditions that occurred during the flowering stage, mainly in areas and early-flowering varieties, where low temperatures affected floral receptivity, causing a lethargic growth of the pollen tube, dehiscence of the anthers and a degeneration of the ovule. This is also demonstrated by works carried out by Toyama (1980) and Sanzol and Herrero (2001).
Figure 1. Hours with radiation over 300 W/m2. Last 4 seasons.
Figure 2. Hours with temperatures above 15 °C. Last 4 seasons.
- Flight of bees.
For species that require cross-pollination to ensure fruit set, it is essential that environmental conditions favour the activity of the vector agents. In this sense, the work of bees (Apis Melífera) as a pollinating agent is vital to ensure the transfer of pollen grains from the anthers to the stigma of the flower.
Bee flight (BF) is defined by the period when temperatures are above 15°C and solar radiation is above 300 W m2.
During the 2023/24 season, conditions were very unfavorable for optimal VA. Figure 2 shows the flight behavior of bees from the 2021/22 season to the 2023/24 season.
If we assume that the solid blue line, which represents the average of all seasons, is the optimal number of hours per week of VA, the first three weeks of September are below the expected threshold, that is, there was not the amount of VA necessary for pollination to occur. This largely explains the low production of early flowering varieties located in early harvest areas. Then, the last week of September is very close to the inter-season average and above it the first two weeks of October.
It must be considered that, although the fourth week of September the VA is very close to the inter-season average (optimal), the climatic conditions prior to the full flower that occurred during this week were not adequate to have good quality structures, therefore, there could have been VA but with degenerated floral structures.
Figure 3. Hours with temperatures above 15°C and solar radiation above 300 W m2. Station located in the commune of Requinoa VI Regón, Chile.
- Final comments.
It is essential to closely monitor the interaction of different climatic variables and how they impact the work of the vector agents during the flowering period. If we are concerned, it is possible to implement strategies that can mitigate or reduce the negative impacts of climatic adversities, such as, for example, increasing the number of hives per hectare, using bee attractants, complementary flower/fruit retention strategies, handling plastic covers, etc.
In summary, the data presented reveal a direct influence of climatic conditions on VA during the months of September and October. This behaviour is crucial, especially in early harvest areas, where temperature and radiation play a fundamental role in the pollination process.
- Quotes.
Ayala, M. 2008. Dwarfing combinations of cherry: the challenges of rootstocks. Faculty of Agronomy and Forestry Engineering of the Pontifical Catholic University of Chile. Journal of Extension Agronomy and Forestry UC 34: 12-16.
Fadon, E., & Rodrigo, J. (2018). Unveiling winter dormancy through empirical experiments. Environmental and Experimental Botany, 152, 28–36.
Fadón, E., Herrero, M., & Rodrigo, J. (2015). Flower development in sweet cherry framed in the BBCH scale. Scientia Hortícolae (Amsterdam), 192, 141–147. https://doi.org/10.1016/j.
Fadón, E., Herrero, M., & Rodrigo, J. (2018a). Dormant flower buds actively accumulate starch over winter. Frontiers in Plant Science, 9, 171.
Fadón, E., Rodrigo, J., & Herrero, M. (2018b). Is there a specific stage to rest? Flower bud development and winter dormancy in sweet cherry (Prunus avium L.). Trees – Structure and Function, 32, 1583–1594. https://doi.org/10.1007/s00468-018-1735-7.
Roversi, Alessandro (2002) Floral and fruiting biology of sweet cherry [online]. Coyhaique: INIA. Proceedings Series – Institute of Agricultural Research. no. 18.
Sanzol, J., & Herrero, M. (2001). The “effective pollination period” in fruit trees. Scientia Hortícolae (Amsterdam), 90, 1–17.
Toyama, TK 1980. The pollen receptivity period and its relationship to fruit setting in the stone fruits. Fruits Varieties Journal, 34, 2-4.
