**4. Climatic change and chilling requirement**

Global warming, the phenomenon of sustainable rise in ocean and atmospheric temperatures, is the main form of climate change. Terrestrial temperature measurements made during the twentieth century show an increase in the average temperature. This warming would have taken place during the twentieth century in two phases, the first from 1910 to 1945, and the second from 1976 to the present [21].

Human activities are therefore the dominant cause of the warming observed over the last 50 years on Earth [22]. This climate change is already having consequences on the biodiversity and ecosystems [8]. Temperature is an influencing factor on the development and growth of plants. Climate change can therefore have a major impact on their phenology. Changes in the phenological stages such as the date of leaf coloring [23] and blooming [24] have already been observed. The advance of the growing period has been linked to climate [25, 26].

Phenology is the main biological parameter of climate change and is one of the main key characteristics of the adaptability of species to these changes.

The exposure to these cold temperatures and the satisfaction of chilling requirements is necessary in several species by the resumption of growth in the spring. Predicting the break of dormancy in fruit trees is essential for producers. Knowing the date of budding makes it possible to estimate the length of the growing season and the risk of frost damage. Global warming can cause a decrease in the number of chill units for certain regions, which will have an impact on the date of bud burst [27]. A limited supply of chill units decreases fruit production [28].

#### **4.1 Chill accumulation in the three studied sites**

Sweet cherry trees develop their vegetative and fruiting buds in summer. As winter approaches, the already developed buds remain dormant to protect themselves from the cold. These buds remain dormant until they have accumulated sufficient chill units. They break up in response to high temperatures and following a sufficient accumulation of chill. If the buds do not receive a sufficient chilling requirement during the winter, the trees will develop one or more of the physiological symptoms such as heterogeneous and spreading flowering, a reduction in the quality of fruit (degree of firmness, size of the fruit) and the fruit set rate.

**Table 4** shows the mean chilling accumulation registered in Ain-Draham, Bousalem, and Tibar from October 1 to March 1 during the three consecutive years (2012–2013, 2013–2014, and 2014–2015). The chill accumulation is expressed in chill units (CU) (Utah model), chill portions (CP) (Dynamic model), and hours below 7°C (Weinberger model). A noteworthy difference between chill accumulations in three experimental areas was found using any of the three described models.

Under field conditions, the coefficients of variation between October 1 and March 1 during the 3 years at Bousalem were relatively high when using the Utah and Dynamic models (CV = 13.98, 5. 42%, respectively), which indicates that the chill accumulation varies from year to year (**Table 4**). The Ain-Draham station presented CV values slightly lower than those of Tibar. Using the three models, chill accumulation is low in Bousalem, intermediate in Tibar, and significantly higher in Ain-Draham.

The three studied areas registered a different chill accumulation explained by altitude location which is in accordance with results obtained by Alburquerque et al. [29] and geographic distance between sites. Bousalem is at a lower altitude (127 m above sea level). Nevertheless, Ain-Draham is at a higher altitude (800 m above sea level). Tibar is at an intermediate altitude (328 m above sea level).


#### **Table 4.**

*Chill accumulation in the period November-March between 2012 and 2015 in Ain-Draham, Bousalem, and Tibar. Results are expressed in chill units (Utah model), chill portions (dynamic model), and hours below 7°C(Weinberger model).*

**69**

**Table 5.**

**Figure 5.**

*Stage 53 (Bud burst) [30].*

*(CP) for the cultivars in Bousalem site.*

*Flowering of Sweet Cherries "*Prunus avium*" in Tunisia DOI: http://dx.doi.org/10.5772/intechopen.93234*

with less average chill accumulation (**Table 4**).

branches [30, 31].

date of dormancy release.

Mediterranean conditions [29].

**4.2 Chilling requirement for breaking dormancy**

The Bousalem site is characterized by a mild winter with less chill accumulation calculated according to the three models. The Tibar site is milder than Ain-Draham

From the beginning of the chilling accumulation (first week of November), five branches of each cultivar (length of 40 cm, base diameter of 8–10 mm) were picked every 3–4 days from trees in the orchards and the bases were placed in a 5% sucrose solution in a growth chamber, making a fresh cut at the base of the

The branches were maintained at 25 ± 1°C under white fluorescent tubes (55 mol m−2 s−1) with a photoperiod of 16 h and at 18 ± 1°C during a dark period of 8 h, with a constant relative humidity of 70%. The sucrose solution was refreshed and changed every 5 days. Branches were maintained for 10 days for forcing in the growth chamber. The date of breaking dormancy was established when, after 10 days in the growth chamber, 30% of the flower buds had reached the phenological growth stage 53–55 (**Figure 5**) according to the international BBCH scale [32]. The chilling requirements (CRs) coincided with the chilling accumulated until the

The chilling requirements for breaking dormancy of the sweet cherry cultivars planted in Ain-Draham, Tibar [31], and Bousalem (**Table 5**) showed different chilling requirements (CR) compared to the geographic area and climatic conditions of the year according to the three models. The Dynamic model is used to determine the chill requirements of different cultivars since it is the adequate model for

Bousalem Mean 23.33b 50.66a 26b 53.66a 54.33a

*Chilling requirements (mean; coefficient of variation, %) for breaking of dormancy expressed in chill portions* 

*Different small letters in the same row indicate significantly different values within cultivars at* α *≤ 0.05.*

**V1 V2 V3 V4 V5**

CV 24.74 6.02 19.98 5.69 6.46

Prunus

Phenology is the main biological parameter of climate change and is one of the

The exposure to these cold temperatures and the satisfaction of chilling requirements is necessary in several species by the resumption of growth in the spring. Predicting the break of dormancy in fruit trees is essential for producers. Knowing the date of budding makes it possible to estimate the length of the growing season and the risk of frost damage. Global warming can cause a decrease in the number of chill units for certain regions, which will have an impact on the date of bud burst

Sweet cherry trees develop their vegetative and fruiting buds in summer. As winter approaches, the already developed buds remain dormant to protect themselves from the cold. These buds remain dormant until they have accumulated sufficient chill units. They break up in response to high temperatures and following a sufficient accumulation of chill. If the buds do not receive a sufficient chilling requirement during the winter, the trees will develop one or more of the physiological symptoms such as heterogeneous and spreading flowering, a reduction in the quality of fruit (degree of firmness, size of the fruit) and the fruit set rate. **Table 4** shows the mean chilling accumulation registered in Ain-Draham, Bousalem, and Tibar from October 1 to March 1 during the three consecutive years (2012–2013, 2013–2014, and 2014–2015). The chill accumulation is expressed in chill units (CU) (Utah model), chill portions (CP) (Dynamic model), and hours below 7°C (Weinberger model). A noteworthy difference between chill accumulations in three experimental areas was found using any of the three described models.

Under field conditions, the coefficients of variation between October 1 and March 1 during the 3 years at Bousalem were relatively high when using the Utah and Dynamic models (CV = 13.98, 5. 42%, respectively), which indicates that the chill accumulation varies from year to year (**Table 4**). The Ain-Draham station presented CV values slightly lower than those of Tibar. Using the three models, chill accumulation is low in

The three studied areas registered a different chill accumulation explained by altitude location which is in accordance with results obtained by Alburquerque et al. [29] and geographic distance between sites. Bousalem is at a lower altitude (127 m above sea level). Nevertheless, Ain-Draham is at a higher altitude (800 m above sea

**Dynamic model Utah model Weinberger model**

80.17 2.32 1.86 1840 3.79 69.77 1044 4.36 45.61

Tibar 62.82 2.99 1.88 1014 4.21 42.71 480\* 10.42 50.08 Bousalem 55.11 5.42 2.9 767.33\* 13.98 107 296.33 3.6 10.96

*Chill accumulation in the period November-March between 2012 and 2015 in Ain-Draham, Bousalem, and Tibar. Results are expressed in chill units (Utah model), chill portions (dynamic model), and hours below* 

**CV% SD Mean** 

**(H < 7°C)**

**CV% SD**

Bousalem, intermediate in Tibar, and significantly higher in Ain-Draham.

**(CU)**

level). Tibar is at an intermediate altitude (328 m above sea level).

**CV% SD Mean** 

**Mean (CP)**

main key characteristics of the adaptability of species to these changes.

[27]. A limited supply of chill units decreases fruit production [28].

**4.1 Chill accumulation in the three studied sites**

**68**

*\**

**Table 4.**

Ain-Draham

*Significant at ≤0.05.*

*7°C(Weinberger model).*

The Bousalem site is characterized by a mild winter with less chill accumulation calculated according to the three models. The Tibar site is milder than Ain-Draham with less average chill accumulation (**Table 4**).

### **4.2 Chilling requirement for breaking dormancy**

From the beginning of the chilling accumulation (first week of November), five branches of each cultivar (length of 40 cm, base diameter of 8–10 mm) were picked every 3–4 days from trees in the orchards and the bases were placed in a 5% sucrose solution in a growth chamber, making a fresh cut at the base of the branches [30, 31].

The branches were maintained at 25 ± 1°C under white fluorescent tubes (55 mol m−2 s−1) with a photoperiod of 16 h and at 18 ± 1°C during a dark period of 8 h, with a constant relative humidity of 70%. The sucrose solution was refreshed and changed every 5 days. Branches were maintained for 10 days for forcing in the growth chamber. The date of breaking dormancy was established when, after 10 days in the growth chamber, 30% of the flower buds had reached the phenological growth stage 53–55 (**Figure 5**) according to the international BBCH scale [32]. The chilling requirements (CRs) coincided with the chilling accumulated until the date of dormancy release.

The chilling requirements for breaking dormancy of the sweet cherry cultivars planted in Ain-Draham, Tibar [31], and Bousalem (**Table 5**) showed different chilling requirements (CR) compared to the geographic area and climatic conditions of the year according to the three models. The Dynamic model is used to determine the chill requirements of different cultivars since it is the adequate model for Mediterranean conditions [29].

**Figure 5.** *Stage 53 (Bud burst) [30].*


#### **Table 5.**

*Chilling requirements (mean; coefficient of variation, %) for breaking of dormancy expressed in chill portions (CP) for the cultivars in Bousalem site.*

These results and the study of Azizi-Gannouni et al. [31] showed that the cultivars "Bouargoub," V1, and V3 registered less chill requirements than the other cultivars.

If we compare our results with those found by Alburqurque et al. [29] in Murcia (southeastern Spain), we can find some cultivars close to that cultivated in Bousalem using the Dynamic model. "V2" required the same chill requirements (48 CP) as "Ruby," "Somerst," and "Burlat." "V4" required the same CP as New Star (53.5 CP). "V1" and "V3" were almost close to Cristobalina (30 CP).

According to the three models, the cultivars "V1" and "V3" do not need a large amount of chill and are better favored in the north of Tunisia. However, "V2," "V4," and "V5" can be grown in this region provided they meet their chilling requirements (CR). Our results suggested that chilling requirements are the main factor for determining the date of flowering in sweet cherry. The date of flowering of the cherry tree in the north of Tunisia was influenced by the cold rather than by the heat and probably, by other biochemical factors of the plant.

In terms of low chilling requirement, "V1" and "V3" were the best cultivars, but they recorded the lowest yield. However, "V2" and "V4" need to accumulate a large amount of chill (CR) to register the highest fruit yield. "V5" was poorly adapted to the North Tunisian climate. It needs large chilling requirements and it has generated the lowest yield. For future improvement programs, we can choose "V1" and "V3" for their low chilling requirements, "V4" and "V2" for their high yields.

## **5. Determination of flowering date**

Phenological monitoring of flowering was carried out on five trees per cultivar per site during the 2012–2013, 2013–2014, and 2014–2015 seasons. Flowering (**Figure 6**) was observed from mid-March to mid-April depending on the region, cultivars, and climatic conditions. The start of blooming was taken as the day on which 10% of the flowers on the tree were opened, full blooming was when 75% of the flowers were opened, and the end of blooming was when 95% of the petals fell [33]. Periodical checks (every 2–3 days) were carried out on the trees for this purpose.

The graphical representations of the different phases of flowering for the three sites during the years 2012–2013, 2013–2014, and 2014–2015 are shown in **Figures 7**–**9**, respectively.

**71**

**Figure 9.**

**Figure 8.**

**Figure 7.**

*Flowering of Sweet Cherries "*Prunus avium*" in Tunisia DOI: http://dx.doi.org/10.5772/intechopen.93234*

*Spreading of sweet cherry blooming at the three sites during 2013.*

*Spreading of sweet cherry blooming at the three sites during 2014.*

*Spreading of sweet cherry blooming at the three sites during 2015.*

**Figure 6.** *Blooming of "Bouargoub" cultivar.*

#### *Flowering of Sweet Cherries "*Prunus avium*" in Tunisia DOI: http://dx.doi.org/10.5772/intechopen.93234*

#### **Figure 7.**

Prunus

These results and the study of Azizi-Gannouni et al. [31] showed that the cultivars "Bouargoub," V1, and V3 registered less chill requirements than the other cultivars. If we compare our results with those found by Alburqurque et al. [29] in Murcia (southeastern Spain), we can find some cultivars close to that cultivated in Bousalem using the Dynamic model. "V2" required the same chill requirements (48 CP) as "Ruby," "Somerst," and "Burlat." "V4" required the same CP as New Star (53.5

According to the three models, the cultivars "V1" and "V3" do not need a large amount of chill and are better favored in the north of Tunisia. However, "V2," "V4," and "V5" can be grown in this region provided they meet their chilling requirements (CR). Our results suggested that chilling requirements are the main factor for determining the date of flowering in sweet cherry. The date of flowering of the cherry tree in the north of Tunisia was influenced by the cold rather than by the

In terms of low chilling requirement, "V1" and "V3" were the best cultivars, but they recorded the lowest yield. However, "V2" and "V4" need to accumulate a large amount of chill (CR) to register the highest fruit yield. "V5" was poorly adapted to the North Tunisian climate. It needs large chilling requirements and it has generated the lowest yield. For future improvement programs, we can choose "V1" and "V3"

Phenological monitoring of flowering was carried out on five trees per cultivar per site during the 2012–2013, 2013–2014, and 2014–2015 seasons. Flowering (**Figure 6**) was observed from mid-March to mid-April depending on the region, cultivars, and climatic conditions. The start of blooming was taken as the day on which 10% of the flowers on the tree were opened, full blooming was when 75% of the flowers were opened, and the end of blooming was when 95% of the petals fell [33]. Periodical checks (every 2–3 days) were carried out on the trees

The graphical representations of the different phases of flowering for the three sites during the years 2012–2013, 2013–2014, and 2014–2015 are shown in

CP). "V1" and "V3" were almost close to Cristobalina (30 CP).

heat and probably, by other biochemical factors of the plant.

**5. Determination of flowering date**

for their low chilling requirements, "V4" and "V2" for their high yields.

**70**

**Figure 6.**

for this purpose.

**Figures 7**–**9**, respectively.

*Blooming of "Bouargoub" cultivar.*

*Spreading of sweet cherry blooming at the three sites during 2013.*

#### **Figure 8.**

*Spreading of sweet cherry blooming at the three sites during 2014.*


**Figure 9.**

*Spreading of sweet cherry blooming at the three sites during 2015.*

#### **5.1 Blooming in Ain-Draham site**

The date of blooming of the different cultivars in the Ain-Draham site is offset from Tibar and Bousalem. The local cultivar "Bouargoub" showed an early flowering followed by "Napoleon" during the 3 years of study. The blooming period for "Bouargoub" is more spread out than the other cultivars (18–24 days).

In 2015, the blooming period was reduced, and it was between 11 and 17 days for "Stella" and "Moreau," respectively. The blooming period of all cultivars was reduced during 2015 with the exception of "Bouargoub" which keeps the same period as 2013. "Van" has the same blooming period during 2013 and 2015, with a shortening of 2 days during 2014 (**Figures 7**–**9**).

#### **5.2 Blooming in Tibar site**

Blooming was advanced in the Tibar site compared to the Ain-Draham site for the same cultivars and during the 3 studied years. "Sunburst" was characterized by the shortest blooming period and a moderately late start to blooming, while "Napoleon" had the longest period between 15 and 22 days and an early blooming start.

With a high monthly temperature in Tibar, blooming started earlier than in Ain-Draham. Observations of the blooming periods, "Napoleon," "Van," and "Moreau," registered longer periods than that in Ain-Draham. "Sunburst" kept almost the same blooming period (13 days) in 2013 and 2014, with 11 days in 2015 (**Figures 7**–**9**).

#### **5.3 Blooming in Bousalem site**

During the 3 years of study, "V1" and "V3" were the earliest, "V2" and "V4" triggered an intermediate blooming date, while "V5" was the last. The blooming period was spread out for all cultivars during the 2015 year and was shortened for the 2 years (2013 and 2014).

The blooming period was between 10 and 14 days during 2013 for "V1" and "V5," respectively. This period was extended during 2014 and varied from 17 to 22 days for "V2" and "V5," respectively. However, during 2015, the blooming period varied from 9 ("V4") to 16 ("V2") days. Flowering began early in 2014, late in 2015, and intermediate in 2013 for all cultivars (**Figures 7**–**9**).

#### **5.4 Comparison of blooming period in the three sites**

The dates and period of blooming for the 11 studied cultivars varied between the sites, cultivars of the same site, and between the years of study. The blooming periods of the different studied cultivars were superimposed on each other, which created the conditions for possible pollination between compatible or semi-compatible cultivars. Full blooming was between 6 and 16 days for all early and late cultivars in the three study sites. The cultivars of Bousalem showed a shortened blooming period during 2013 and a spread-out blooming period during 2014, explained by the difference of temperature between the years and the low chill accumulation during 2014. The Ain-Draham site is characterized by the highest chill accumulation and late blooming during the 3 years, which is explained by the effect of climatic conditions on blooming according to Westwood [14]. At each site, the blooming periods of all cultivars overlapped with each other except for the local one "Bouargoub," which was ahead during 2014 and 2015.

For this reason, the latter is not recommended as a pollinating cultivar for the others grown in Ain-Draham. According to Nyeki [34], for the sweet cherry tree, a

**73**

*Flowering of Sweet Cherries "*Prunus avium*" in Tunisia DOI: http://dx.doi.org/10.5772/intechopen.93234*

vars except for "Bouargoub" during 2015 and 2014.

temperature).

**fruit yield**

(18, 19°C) (**Figure 10**).

(**Figure 11**).

blooming period of 10–14 days, with at least 4–6 days of full blooming, is necessary. This author mentioned that for stone fruits, a period of 3 days of overlap in full blooming is adequate, which is the case of our study in the three sites for all culti-

In the Ain-Draham site, full blooming can vary from 5 to 16 days. Generally, it occurs during the month of April and rarely extends to the beginning of May. In Tibar, full blooming overlaps between the third week of March and the second week of April. The four cultuvars "Napoleon," "Van," "Moreau," and "Sunburst" behave differently in the two sites which can exclude the genetic potential factor in the triggering and the duration of flowering assuming that this phenomenon depends on the physiological state, age, rootstock, expression of cultivar genes, and other external factors (photoperiod, soil, nutrient supply, rainfall, and

The difference in the date and duration of blooming among the receiving cultivars (to be pollinated) and the pollinating cultivars is the cause of a fruit set failure, which is confirmed by the works of Bekefi [35], Tosun and Koyuncu [36], Beyhan and Karakaş [37], and Moghadam et al. [38]. These authors have shown that in addition to the gameto-phytic self-incompatibility (GSI), the efficiency of pollination and fertilization in the cherry tree is also affected by the availability of pollinating insects and weather conditions in particular temperature during flowering.

**6. Effect of temperature (maximum) during blooming period on** 

period characterized by a low temperature (13.37°C) (**Figure 4**).

19.8–18.85°C, respectively) and record low yield.

The maximum temperature during the flowering period has a negative effect on the yield at the Ain-Draham site. The cultivar "Van" is characterized by the lowest yield (3.2 Kg/tree) during 2013 and a highest temperature during blooming (17.43°C), while "Bouargoub" produced 8 Kg/tree in 2015 and bloomed during a

In Tibar site, the year 2015 was characterized by a low temperature during blooming and by a better yield. The cultivars "Moreau" and "Sunburst" registered 6.5 and 7 Kg/tree and a maximum blooming temperature of 20 and 22°C, respectively. While "Napoleon" records the lowest yield and a low blooming temperature

Bousalem site, the blooming periods of the cultivars "V2" and "V5" in 2013 and 2014 were characterized by almost the same maximum temperature. The cultivars "V3" and "V1" were also characterized by the same blooming temperature, whereas they showed a difference in yield throughout the 3 studied years. The cultivar "V4" was characterized by the highest yield during the 2 years, 2014 and 2015, while its flowering period was overlapping with that of "V2"

The temperature at the blooming period is a determining parameter for the yield. If the blooming period coincides with a low mean maximum temperature the yield is high, whereas if the blooming coincides with a high mean maximum temperature the yield will be low, which is the case for the local cultivar "Bouargoub" in the site of Ain-Draham and the cultivar "V5" in the Bousalem site. "V5" is characterized by spreading blooming and a low yield despite the highest number of stamens. However, the other cultivars such as "V1" and "V3" bloom during a period characterized by a low mean maximum temperature (19.61–17.51°C and

These results show that the temperature during blooming determines the fruit yield in the sweet cherry tree, but there are other factors that influence

Prunus

**5.1 Blooming in Ain-Draham site**

**5.2 Blooming in Tibar site**

**5.3 Blooming in Bousalem site**

the 2 years (2013 and 2014).

(**Figures 7**–**9**).

shortening of 2 days during 2014 (**Figures 7**–**9**).

The date of blooming of the different cultivars in the Ain-Draham site is offset from Tibar and Bousalem. The local cultivar "Bouargoub" showed an early flowering followed by "Napoleon" during the 3 years of study. The blooming period for

In 2015, the blooming period was reduced, and it was between 11 and 17 days for "Stella" and "Moreau," respectively. The blooming period of all cultivars was reduced during 2015 with the exception of "Bouargoub" which keeps the same period as 2013. "Van" has the same blooming period during 2013 and 2015, with a

Blooming was advanced in the Tibar site compared to the Ain-Draham site for the same cultivars and during the 3 studied years. "Sunburst" was characterized by the shortest blooming period and a moderately late start to blooming, while "Napoleon"

had the longest period between 15 and 22 days and an early blooming start.

With a high monthly temperature in Tibar, blooming started earlier than in Ain-Draham. Observations of the blooming periods, "Napoleon," "Van," and "Moreau," registered longer periods than that in Ain-Draham. "Sunburst" kept almost the same blooming period (13 days) in 2013 and 2014, with 11 days in 2015

During the 3 years of study, "V1" and "V3" were the earliest, "V2" and "V4" triggered an intermediate blooming date, while "V5" was the last. The blooming period was spread out for all cultivars during the 2015 year and was shortened for

The blooming period was between 10 and 14 days during 2013 for "V1" and "V5," respectively. This period was extended during 2014 and varied from 17 to 22 days for "V2" and "V5," respectively. However, during 2015, the blooming period varied from 9 ("V4") to 16 ("V2") days. Flowering began early in 2014, late in 2015,

The dates and period of blooming for the 11 studied cultivars varied between the sites, cultivars of the same site, and between the years of study. The blooming periods of the different studied cultivars were superimposed on each other, which created the conditions for possible pollination between compatible or semi-compatible cultivars. Full blooming was between 6 and 16 days for all early and late cultivars in the three study sites. The cultivars of Bousalem showed a shortened blooming period during 2013 and a spread-out blooming period during 2014, explained by the difference of temperature between the years and the low chill accumulation during 2014. The Ain-Draham site is characterized by the highest chill accumulation and late blooming during the 3 years, which is explained by the effect of climatic conditions on blooming according to Westwood [14]. At each site, the blooming periods of all cultivars overlapped with each other except for the local one "Bouargoub,"

For this reason, the latter is not recommended as a pollinating cultivar for the others grown in Ain-Draham. According to Nyeki [34], for the sweet cherry tree, a

and intermediate in 2013 for all cultivars (**Figures 7**–**9**).

**5.4 Comparison of blooming period in the three sites**

which was ahead during 2014 and 2015.

"Bouargoub" is more spread out than the other cultivars (18–24 days).

**72**

blooming period of 10–14 days, with at least 4–6 days of full blooming, is necessary. This author mentioned that for stone fruits, a period of 3 days of overlap in full blooming is adequate, which is the case of our study in the three sites for all cultivars except for "Bouargoub" during 2015 and 2014.

In the Ain-Draham site, full blooming can vary from 5 to 16 days. Generally, it occurs during the month of April and rarely extends to the beginning of May. In Tibar, full blooming overlaps between the third week of March and the second week of April. The four cultuvars "Napoleon," "Van," "Moreau," and "Sunburst" behave differently in the two sites which can exclude the genetic potential factor in the triggering and the duration of flowering assuming that this phenomenon depends on the physiological state, age, rootstock, expression of cultivar genes, and other external factors (photoperiod, soil, nutrient supply, rainfall, and temperature).

The difference in the date and duration of blooming among the receiving cultivars (to be pollinated) and the pollinating cultivars is the cause of a fruit set failure, which is confirmed by the works of Bekefi [35], Tosun and Koyuncu [36], Beyhan and Karakaş [37], and Moghadam et al. [38]. These authors have shown that in addition to the gameto-phytic self-incompatibility (GSI), the efficiency of pollination and fertilization in the cherry tree is also affected by the availability of pollinating insects and weather conditions in particular temperature during flowering.
