*2.1.1 Adaptability of blueberry to water stress*

Drought and soil waterlogging were prone to occur due to the evident uneven distribution of rainfall in blueberry growing areas of the Yangtze river basin [15]. Therefore, it is urgent to carry out studies on adaptability of blueberry to water stress**.** Taking 2-year-old potted seedlings of cultivar "Powderblue" and "Gardenblue" of rabbiteye blueberry (*Vaccinium ashei* Reade) as research objects, changes in growth indexes of seedlings after drought or flooding stress for 14 days and recovering normal water supply for 60 days were examined and analyzed. The results showed that after drought or flooding stress for 14 days, growths of two cultivar seedlings are inhibited severely, and their root dry weight, shoot dry weight, and whole plant relative growth rate (RGR) are significantly lower than those of the control. After recovering under normal water supplying for 60 days, "Powderblue" and "Gardenblue" did not show significant differences in the root dry weight (81.4 and 83.1% of control values, respectively) between drought-stressed and control plants. Shoot dry weight of drought-stressed plants of two cultivars was still significantly lower than those of the control. RGR of drought-stressed "Powderblue" seedlings were significantly higher than that of the control, whereas "Gardenblue" did not show significant differences in RGR (75.2% of control values) between drought-stressed and control plants. Recovering under normal water supply for 60 days after flooding stress, root dry weight and shoot dry weight of the recovered "Powderblue" seedlings were significantly lower than those of the control (41.9 and 39.8% of control values, respectively), whereas recovered "Gardenblue" seedlings maintained root dry weight and shoot dry weight of 78.7 and 62.1%, respectively, of those of corresponding controls. RGR of recovered "Powderblue" seedlings were lower than that of the control, whereas RGR of "Gardenblue" was greater than that of the control seedlings (**Figure 2**). It is concluded that recovered rabbiteye blueberry seedlings preferentially partitioned assimilate to the roots during the recovery period. RGR of the recovered seedlings approached or exceeded

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*The Developing Blueberry Industry in China DOI: http://dx.doi.org/10.5772/intechopen.88225*

flooding of up to 2 weeks.

*water supply for 60 days after flooding stress.*

**Figure 2.**

recovery and 30 days after recovery.

those of the control by the end of the experiment. "Powderblue" is more droughtresistant, whereas "Gardenblue" is more flood-resistant. Our study demonstrated that rabbiteye blueberry "Powderblue" and "Gardenblue" appear to be promising cultivars for commercial planting in Yangtze river basin region prone to drought or

*Comparison on some growth indexes of "Powderblue" and "Gardenblue" of* Vaccinium ashei *after water stress for 14 days and recovering under normal water supply for 60 days. Different small letters indicate the significant difference (P* ≤ *0.05) among different treatments of the same cultivar.CK, the control; D + R, recovering under normal water supply for 60 days after drought stress; and F + R, recovering under normal* 

*2.1.2 Study on photosynthetic physiology of rabbiteye blueberry under water stress*

Study on photosynthetic response of rabbiteye blueberry to water stress was not only helpful to reveal photosynthetic adaptation to water stress in blueberry but also beneficial to selecting appropriate measures to improve the stress resistance of blueberry, creating favorable conditions for growth and yield formation of blueberry. In this study, potted, 1-year-old seedlings of rabbiteye blueberry "Brightwell" and "Gardenblue" were subjected to 14-day flooding stress, followed by a recovery for 30 days. The leaf net photosynthetic rate (*Pn*), stomatal conductance (*gs*), and intercellular CO2 concentration (*Ci*) were measured during stress, 7 days after

Repeated measures ANOVA showed that flooding treatment and duration both had a significant effect on net photosynthesis rate (*Pn*), stomatal conductance (*gs*), and intercellular CO2 concentration (*Ci*) in both cultivars (*P* ≤ 0.05). There was also a significant interaction between flooding treatment and duration (*P* ≤ 0.05), indicated that the negative effects of flooding increased over time (**Figure 3A**–**F**). The *Pn* in "Brightwell" decreased gradually after 3 days of flooding, and exhibited a significant drop by the 5th day. By day 11, the *Pn* of flooded plants in "Brightwell" dropped to the lowest values (−39% compared with that of control) and increased thereafter until the end of the experiment (**Figure 3A**). After 8 days of flooding, flooded plants in "Gardenblue" showed a significant reduction in *Pn* compared to control plants. The largest decline in *Pn* of flooded plants in "Gardenblue" was observed on days 21 (−39% compared with that of control) (**Figure 3B**). After the flooding was ended and plants were allowed to recover for 30 days, the *Pn* of both cultivars recovered to different degree (104 and 95% for "Brightwell" and "Gardenblue" with respect to control plants, respectively). Flooding-induced decline in *gs* in both cultivars were evident after 11 days of flooding (**Figures 3C** and **1D**; *P* ≤ 0.05). The largest decline in *gs* of flooded plants

in both cultivars was observed on days 14 as compared to the control

*The Developing Blueberry Industry in China DOI: http://dx.doi.org/10.5772/intechopen.88225*

**Figure 2.**

*Modern Fruit Industry*

Soil types in Changjiang (Yangtze) river basin region are red soil and yellowbrown soil, which are heavy clay with poor drainage. Moreover, there are not only heavy rain days but also drought days in summer and autumn due to monsoon climate. Therefore, soil permeability improvement by soil amelioration and soil moisture regulation by precision irrigation are the key measures of blueberry cultivation in this region. Because of the different soil texture and climate conditions, it is necessary to study the water stress tolerance and water requirement of major blueberry cultivars based on local experiments in this region. It has been found that types of blueberries that best suited to grow in Yangtze river basin region are rabbiteye (*Vaccinium ashei*) and southern highbush (*V. corymbosum*). In this study, changes in growth indexes and photosynthetic characteristics of rabbiteye blueberry seedlings after drought or flooding stressed for 14 days and recovering normal water supplying were analyzed and compared. Effects of different irrigation regimes on seedling growth and water consumption pattern of "Brightwell" rabbiteye blueberry and "Misty" southern highbush blueberry were investigated. The relationship between actual water requirement of blueberry seedlings and water surface evaporation was studied, and the water requirement model based on water surface evaporation was established. Recommendations for optimum irrigation management of blueberry grown in southern China were drawn accordingly.

**2.1 Studies on some ecophysiological responses of blueberry grown under** 

distribution of rainfall in blueberry growing areas of the Yangtze river basin [15]. Therefore, it is urgent to carry out studies on adaptability of blueberry to water stress**.** Taking 2-year-old potted seedlings of cultivar "Powderblue" and "Gardenblue" of rabbiteye blueberry (*Vaccinium ashei* Reade) as research objects, changes in growth indexes of seedlings after drought or flooding stress for 14 days and recovering normal water supply for 60 days were examined and analyzed. The results showed that after drought or flooding stress for 14 days, growths of two cultivar seedlings are inhibited severely, and their root dry weight, shoot dry weight, and whole plant relative growth rate (RGR) are significantly lower than those of the control. After recovering under normal water supplying for 60 days, "Powderblue" and "Gardenblue" did not show significant differences in the root dry weight (81.4 and 83.1% of control values, respectively) between drought-stressed and control plants. Shoot dry weight of drought-stressed plants of two cultivars was still significantly lower than those of the control. RGR of drought-stressed "Powderblue" seedlings were significantly higher than that of the control, whereas "Gardenblue" did not show significant differences in RGR (75.2% of control values) between drought-stressed and control plants. Recovering under normal water supply for 60 days after flooding stress, root dry weight and shoot dry weight of the recovered "Powderblue" seedlings were significantly lower than those of the control (41.9 and 39.8% of control values, respectively), whereas recovered "Gardenblue" seedlings maintained root dry weight and shoot dry weight of 78.7 and 62.1%, respectively, of those of corresponding controls. RGR of recovered "Powderblue" seedlings were lower than that of the control, whereas RGR of "Gardenblue" was greater than that of the control seedlings (**Figure 2**). It is concluded that recovered rabbiteye blueberry seedlings preferentially partitioned assimilate to the roots during the recovery period. RGR of the recovered seedlings approached or exceeded

Drought and soil waterlogging were prone to occur due to the evident uneven

**different water regimes in Nanjing**

*2.1.1 Adaptability of blueberry to water stress*

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*Comparison on some growth indexes of "Powderblue" and "Gardenblue" of* Vaccinium ashei *after water stress for 14 days and recovering under normal water supply for 60 days. Different small letters indicate the significant difference (P* ≤ *0.05) among different treatments of the same cultivar.CK, the control; D + R, recovering under normal water supply for 60 days after drought stress; and F + R, recovering under normal water supply for 60 days after flooding stress.*

those of the control by the end of the experiment. "Powderblue" is more droughtresistant, whereas "Gardenblue" is more flood-resistant. Our study demonstrated that rabbiteye blueberry "Powderblue" and "Gardenblue" appear to be promising cultivars for commercial planting in Yangtze river basin region prone to drought or flooding of up to 2 weeks.

#### *2.1.2 Study on photosynthetic physiology of rabbiteye blueberry under water stress*

Study on photosynthetic response of rabbiteye blueberry to water stress was not only helpful to reveal photosynthetic adaptation to water stress in blueberry but also beneficial to selecting appropriate measures to improve the stress resistance of blueberry, creating favorable conditions for growth and yield formation of blueberry. In this study, potted, 1-year-old seedlings of rabbiteye blueberry "Brightwell" and "Gardenblue" were subjected to 14-day flooding stress, followed by a recovery for 30 days. The leaf net photosynthetic rate (*Pn*), stomatal conductance (*gs*), and intercellular CO2 concentration (*Ci*) were measured during stress, 7 days after recovery and 30 days after recovery.

Repeated measures ANOVA showed that flooding treatment and duration both had a significant effect on net photosynthesis rate (*Pn*), stomatal conductance (*gs*), and intercellular CO2 concentration (*Ci*) in both cultivars (*P* ≤ 0.05). There was also a significant interaction between flooding treatment and duration (*P* ≤ 0.05), indicated that the negative effects of flooding increased over time (**Figure 3A**–**F**).

The *Pn* in "Brightwell" decreased gradually after 3 days of flooding, and exhibited a significant drop by the 5th day. By day 11, the *Pn* of flooded plants in "Brightwell" dropped to the lowest values (−39% compared with that of control) and increased thereafter until the end of the experiment (**Figure 3A**). After 8 days of flooding, flooded plants in "Gardenblue" showed a significant reduction in *Pn* compared to control plants. The largest decline in *Pn* of flooded plants in "Gardenblue" was observed on days 21 (−39% compared with that of control) (**Figure 3B**). After the flooding was ended and plants were allowed to recover for 30 days, the *Pn* of both cultivars recovered to different degree (104 and 95% for "Brightwell" and "Gardenblue" with respect to control plants, respectively).

Flooding-induced decline in *gs* in both cultivars were evident after 11 days of flooding (**Figures 3C** and **1D**; *P* ≤ 0.05). The largest decline in *gs* of flooded plants in both cultivars was observed on days 14 as compared to the control

#### **Figure 3.**

*Changes in the net photosynthesis rate (Pn), stomatal conductance (gs), and intercellular CO2 concentration (Ci) in the leaves of 1-year-old seedlings of "Brightwell" (A–C) and "Gardenblue" (D–F) under two soil conditions: Control (open circles) and flooding plus recovery (half-closed circles). Measurements were taken on days 0, 3, 5, 8, 11, and 14 (during the flooding); day 21 (7 days after flooding ended); and day 44 (30 days after flooding ended). Different lowercase letters indicate significant differences (P* ≤ *0.05) among treatments. Values are mean ± standard error.*

(−59 and −52% for "Brightwell" and "Gardenblue," respectively). When the flooding treatment ended, *gs* in both cultivars recovered gradually and reached a level similar to that of the control (100 and 102% for "Brightwell" and "Gardenblue" with respect to control plants, respectively) by the end of the experiment.

The *Ci* in both cultivars decreased gradually after 5 days of flooding. Compared with the control, the *Ci* of "Brightwell" and "Gardenblue" under flooding significantly decreased by 19.6 and 9.0%, respectively, by the 14th day (**Figures 3E** and **1F**; *P* ≤ 0.05). After the flooding was ended and plants were allowed to recover for 7 days, the *Ci* of both cultivars increased rapidly and was slightly higher than that of the control. By day 44 (30 days after flooding ended), the *Ci* in both cultivars increased to a level similar to that in the control (97.4 and 103.4% for BW and "Gardenblue" with respect to control plants, respectively).

Decreases in carbon assimilation under the flooding condition have been demonstrated in many woody fruit species [3, 4, 16, 17]. In the present study, the leaf net photosynthetic rate (*Pn*) of flooded plants in both cultivars was significantly less than those of unflooded controls after 14 days of flooding. Meanwhile, the stomatal conductance (*gs*) and intercellular CO2 concentration (*Ci*) also decreased significantly, indicating that flooding reduced photosynthesis mainly via a decrease in stomatal conductance. Photosynthetic activity decreased during flooding in both cultivars but recovered rapidly following drainage, which indicates that decreased

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**Figure 4.**

*same cultivar.*

*The Developing Blueberry Industry in China DOI: http://dx.doi.org/10.5772/intechopen.88225*

*2.1.3 Study on water requirements of blueberry*

southern China are 100 and 75% ET, respectively [21].

photosynthetic activity was temporary and that rabbiteye blueberry possessed rapid recovery ability after flood water was released. Our study demonstrated that rabbiteye blueberry could adapt to flooding stress by adjusting photosynthetic process

Reasonable water management is the basic guarantee for the high fruit yield and quality of blueberry [18–20]. Clarifying the water requirement of blueberry is a precondition for scientific management of blueberry orchard. In this study, weighing lysimeters were used to determine actual evapotranspiration (ET) of young seedlings of "Brightwell" rabbiteye blueberry and "Misty" southern highbush blueberry under different irrigation regimes. Effects of different irrigation regimes on seedling growth, total water consumption, and water-use efficiency (WUE) were also investigated. The results show that net increment of dry weight (IDW) per plant and total water consumption (TWC) per plant of two cultivar seedlings both elevate with increasing amount of irrigation, while water-use efficiency is lowest under 50% ET condition and the highest under 75% ET condition. As for "Brightwell," 125% ET treatments had similar values for IDW and WUE compared to 100% ET plants, whereas TWC was significantly higher than that of the control (100% ET). IDW and TWC in 50 and 75% ET treatments were significantly lower than that of the control, whereas no significant (*P* > 0.05) differences in WUE were observed. As for "Misty," IDW and TWC in 125% ET treatments were significantly higher than that of the control (100% ET), whereas WUE was not significantly different from that of the control (100% ET). IDW in 75% ET treatment was slightly lower than that of the control, and TWC was significantly lower than that of the control, whereas WUE was significantly higher than that of the control. IDW, TWC, and WUE in 50% ET treatment were all significantly lower than that of the control (**Figure 4**). It is concluded that the optimum irrigation treatment for "Brightwell" and "Misty" in

Water requirement estimation is one of the important aspects in crop water require-

*Effects of different irrigation treatments on net increment of dry weight per plant, total water consumption, and water-use efficiency of seedlings of* Vaccinium ashei *"Brightwell" and* V. corymbosum *"misty." different lowercases in the same column indicate the significant difference (P* ≤ *0.05) among different treatments of the* 

ment research. Crop water requirement estimation by pan evaporation has been extensively used worldwide due to simplicity and low cost of the technique [22–24]. Pan evaporation method takes into account temperature, humidity, wind speed, solar radiation, and other meteorological factors, which are the same factors that affect crop

and possess a certain extent of adaptation to flooded soil conditions.

*Modern Fruit Industry*

(−59 and −52% for "Brightwell" and "Gardenblue," respectively). When the flooding treatment ended, *gs* in both cultivars recovered gradually and reached a level similar to that of the control (100 and 102% for "Brightwell" and "Gardenblue" with respect to control plants, respectively) by the end of the experiment.

*Changes in the net photosynthesis rate (Pn), stomatal conductance (gs), and intercellular CO2 concentration (Ci) in the leaves of 1-year-old seedlings of "Brightwell" (A–C) and "Gardenblue" (D–F) under two soil conditions: Control (open circles) and flooding plus recovery (half-closed circles). Measurements were taken on days 0, 3, 5, 8, 11, and 14 (during the flooding); day 21 (7 days after flooding ended); and day 44 (30 days after flooding ended). Different lowercase letters indicate significant differences (P* ≤ *0.05) among treatments.* 

The *Ci* in both cultivars decreased gradually after 5 days of flooding. Compared with the control, the *Ci* of "Brightwell" and "Gardenblue" under flooding significantly decreased by 19.6 and 9.0%, respectively, by the 14th day (**Figures 3E** and **1F**; *P* ≤ 0.05). After the flooding was ended and plants were allowed to recover for 7 days, the *Ci* of both cultivars increased rapidly and was slightly higher than that of the control. By day 44 (30 days after flooding ended), the *Ci* in both cultivars increased to a level similar to that in the control (97.4 and 103.4% for BW and "Gardenblue" with

Decreases in carbon assimilation under the flooding condition have been demonstrated in many woody fruit species [3, 4, 16, 17]. In the present study, the leaf net photosynthetic rate (*Pn*) of flooded plants in both cultivars was significantly less than those of unflooded controls after 14 days of flooding. Meanwhile, the stomatal conductance (*gs*) and intercellular CO2 concentration (*Ci*) also decreased significantly, indicating that flooding reduced photosynthesis mainly via a decrease in stomatal conductance. Photosynthetic activity decreased during flooding in both cultivars but recovered rapidly following drainage, which indicates that decreased

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**Figure 3.**

*Values are mean ± standard error.*

respect to control plants, respectively).

photosynthetic activity was temporary and that rabbiteye blueberry possessed rapid recovery ability after flood water was released. Our study demonstrated that rabbiteye blueberry could adapt to flooding stress by adjusting photosynthetic process and possess a certain extent of adaptation to flooded soil conditions.
