Abstract
The early ripening date of mid-April for rabbiteye blueberries in Chengjiang signals a bright future, with a total of 338 kg of fruit harvested from 780 2-year-old plants on 0.1 ha of paddy land. In Lishui, a 0.65 ha rabbiteye blueberry orchard produced 6,000, 8,000, and 12,000 kg of fruit in the fourth, fifth, and sixth year, respectively. In 2009, in Shandong Peninsula, fruit development time was shortened by about 4 weeks because of a very late spring and sudden high summer temperature, and the fruit were difficult to separate from the peduncle and were greenish flesh. The insect pest, Sardoscelis sphenias Mayrickin, was found in mainland China for the first time.
INTRODUCTION
Blueberries were first introduced into China in the 1980s, and the test and cultivation regions were vast, from 24°N to 50°N, including central-subtropics, northern-subtropics, and temperate zone. Currently, there are four major growing regions: the Northeast, Shandong province, Southeast, and Southwest, with a total acreage of over 1,300 ha and a production of over 800 tons in 2009 (CitationHe et al., 2009). Some initial observations on these plantings are reported in this article.
MATERIALS AND METHODS
This report is based on data collected in the different production regions in China from 2005 to 2010.
RESULTS AND DISCUSSION
Extremely Early Ripening
Rabbiteye blueberry plants are generally adapted to regions around the 32° latitudes both north and south of the equator, and in higher elevations at lower latitudes with a cooler climate (CitationAustin, 1994). In lower latitude areas, fruit ripen earlier due to higher temperatures in early spring. Fruit going to the market earlier can receive higher prices, so pursuing early ripening fruit is one of the foci of producers. In cultivar trials, blueberries in Chengjiang, Yunnan province, in the southwestern part of China appear to have early ripening potential.
Chengjiang is located at 24° 20′ N, 102° 54′ E, and altitude 1,820 m. Average annual temperature, average temperature of the coldest month, absolute maximum temperature, and absolute minimum temperature are 20.5, 9.2, 33.9, and −4.4°C, respectively. Average temperature, average maximum temperature, average minimum temperature, and average precipitation in every month are shown in . Temperatures are high enough to allow plants to grow almost all year, except the end of December and the beginning of January. The other unique climatic characteristics of the region are the distinct dry and rainy seasons. Annual precipitation is 1,029.3 mm with the percentage in the dry season (November–April) and rainy season (May–October) being 12.73 and 87.27%, respectively. Annual evaporation is 1,533.7 mm. The soils are latosols and plateau red earths with a low pH.
TABLE 1 Temperatures (°C) in Chengjiang
Rabbiteye blueberries were first established on 3.33 ha on hill slopes in the spring of 2005, and another 3 ha were planted in the following year. Total plant number was 13,300, and the varieties planted were ‘Baldwin’, ‘Brightwell’, ‘Climax’, ‘Gardenblue’, ‘Powderblue’, and ‘Premier’. The blooming period has been from the middle of February to the middle of March, while the fruit developing period has been from the last ten days of March to the first ten days of May, and the fruit development period has been from the middle of April to the middle of July. The harvest season has started with ‘Climax’ and ‘Premier’. ‘Brightwell’ was harvested beginning in the middle of May, while ‘Powderblue’ and ‘Gardenblue’ were picked a few days later. ‘Baldwin’ was the last one ripening, beginning in the middle of June.
In the second and third years after planting, the productivity of ‘Brightwell’ was the best with 0.60 kg per plant and an average weight of 1.0 g per fruits, while the fruit size of ‘Premier’ was the largest with an average weight of 1.5 g per fruit. Growth and development among the cultivars were different, e.g., ‘Gardenblue’ had more off-season flowers especially as juveniles. Even at the end of December there were a few fruits scattered on the plant, while ‘Brightwell’ had just a little off-season bloom.
Southern highbush blueberries were planted in 2007, including ‘Misty’, ‘O'Neal’, and ‘Sharpblue’. Fruits were harvested from these cultivars in the middle of April. Average yield per plant was 0.5 kg, and the average weight of fruit was 3.0 g.
Compared to the harvesting time of southern-highbush and rabbiteye blueberries south of Changjiang river (Southeastern China Region), which usually begins around May 20 and June 26, respectively, the ripening date of southern-highbush and rabbiteye blueberries planted in Chengjiang was 30–60 days earlier. The very early ripening date for blueberries represents a bright future for this region.
Early-Cropping and Rice Paddy Land Cultivation for Blueberries in Yunnan
Because of the long growing season in Chengjiang, early-cropping (in years one and two) can be accomplished if water availability is sufficient. A 0.1 ha research planting was established on rice paddy land at the bottom of the valley in January 2009, where irrigation water was readily available. Seven hundred eighty ‘Brightwell’ plants were tested that were 2-year-old container stock with a bush height of 0.7–0.8 m and crown width of 0.4–0.5 m. Raised beds 0.2 m high were formed prior to planting. The spacing in row was 1.5 m. Distance between plants was 1 m. Mountainous red soil was mixed to lower the soil pH.
All the seedlings were flowering and fruiting in the first year, with a bush height of about 1.5 m and a crown width of 0.5–0.6 m in July. A total of 338 kg of fruit were harvested, averaging 0.42 kg of fruits per plant. Due to the comparatively intensive cultivation, especially abundant irrigation, fruit size was larger than that from mountain slopes with an average weight of 3.0 g per fruit. In 2010, with a bush height of about 1.8 m and a crown width of 0.5–0.6 m in July, the yield was two times that in the first year.
It was thought that paddy fields could not be used for blueberry growing owing to their high pH and high ground water table. Our study showed that by adopting some specific measures, blueberries can be successfully grown in paddy fields. Because the Yunnan province is characterized by a dry season (November–April), irrigation is necessary for blueberry cultivation in these areas. So the planting sites must be near a source of water, such as a paddy field. This trial is just a beginning, but it seems that this region has the potential to be a new blueberry growing area.
Fast Growing and High Yield
It is well known that rabbiteye blueberry plants can grow well on nearly every soil type, but do best on light, well-drained, acid soils. The results of an experimental plantation in southeastern China showed that the growth and development of a number of rabbiteye blueberry cultivars were normal and strong. Generally, under the common cultural conditions, rabbiteye blueberries gave a yield of 7 or 8 tons per ha at the age of 8-years-old (CitationGu and He, 2001).
To date, a rabbiteye blueberry orchard of two-third hectares located in Lishui County, southeastern part of Jiangsu province (established in the spring of 2004) is generally recognized as one of the best in China. The total plant number is 2,560, and ‘Brightwell’, ‘Gardenblue’, ‘Powderblue’, and ‘Premier’ are included. In 2007, 2008, and 2009, the yields were 6,000, 8,000, and 12,000 kg, respectively. That means that the yield per hectare could be more than 15 tons. In 2008, the size of the bushes were >2 m high and >2 m in width.
The climatic conditions of heavy precipitation and high temperatures in spring and summer in the subtropical areas in southeastern China are good for shoot growth, and large crowns are easy to form. High and stable yields can be obtained by solving the problem of low precipitation in autumn and winter, which limits plant growth, especially of the root system.
Forced Ripening Phenomenon
The Shandong Province located in northern China is a great horticultural province in China. The ecological conditions are suitable for many deciduous fruit trees and vegetables, but not perfect for blueberries. The sunshine and physical features of soils and day-night temperature differentials are very good for blueberry growing; however, the soil pH is not low enough and water quality is sometimes not appropriate. In addition, the low air humidity is also a problem. Although this area belongs to a warm, humid monsoon climate, the climatic characters are actually approaching a continental climate that is arid in early summer with only a few rainy days and many hot days. More than 10 mm of rain will occur only one or two days in May, and about two days in June, while temperature can be quite high even above 30°C, and the absolute maximum temperature is 40.0°C. This region also suffers from dry, hot wind three or four times in every ten years (CitationChina Natural Geography Editorial Committee, 1984). So, besides the high soil pH, hot and drought weather is also a problem for blueberry growing in this region. Even so, this region possesses a considerable acreage of blueberries and produces most of the blueberry fruit in the country.
Up until now, the main production region in Shandong province is in Rizhao County, where the average annual temperature is 12.7°C. Here the orchards were planted in 2005 on an area of 22 ha, with several highbush varieties, including ‘Bluecrop’, ‘Darrow’, ‘Duke’, ‘Elliot’, and a few southern highbush and rabbiteye blueberry varieties, such as ‘Diana’, ‘Sharpblue’, and ‘Gardenblue’.
Generally, the buds begin to develop in late March; flowering is from late April to early May, and fruit ripening is from the end of June to early July. In 2009, spring came later than usual by about 4 weeks in Shandong Peninsula and flowering was later than usual by 7–10 days. The fruit ripening season was also earlier than usual by about 7–10 days. The duration of fruit development was shortened by about 2 or 3 weeks. During ripening, the pericarp became black or blue-purple, but the flesh remained hard and green and had a very sour taste. Some fruit were difficult to separate from the fruit stalk, as the abscission layer had not fully formed.
If we look at the meteorological data in 2009, it shows that the rainfall in Rizhao County was 249.0 mm from January to June, which is close to the average precipitation (249.2 mm) across years. But the rainfall distribution was extremely uneven, with two drought periods in early spring and the beginning of summer. The average monthly temperature was 1.8°C higher than the corresponding month of a normal year, and temperature in February, May, and June was 2.0°C higher. Precipitation fell mainly during a few days, including March 12, April 20, May 11, May 15, June 8, June 20, and June 21. Dry, hot windy weather conditions occurred in the early and late days of June. For example, temperatures above 32°C appeared on May 31, June 1, and June 2, respectively. High temperatures again appeared from June 23–27, and reached 35.8, 37.8, and 35.4°C on June 24, 25, and 26, respectively (CitationCong et al., 2009; CitationSong et al., 2009).
So, it appears that the hot and dry weather baked the fruit, forcing the fruit to “ripen” with a dark color outside and relatively hard and greenish meat inside. The authors concluded that the climate in that region is likley to cause more problems in the future.
A New Record of Insect Sardoscelis Sphenias Mayrickin
Up to now, 150 kinds of harmful insects have been found on blueberries, among these, 94 species have been identified in southern China including 54 leaf pests. Sardoscelis sphenias Mayrickin was found in the continental region for the first time (CitationHu et al., 2009).
This insect has not been reported in the continental region before. The larva was found in Lishui and Nanjing, Jiangsu Province in 1994, and also in Ganyu, Jiangsu Province in 2007.
Nymph larvae eat the twigs first, causing them to wilt and die-back above their feeding hole. Sometimes tip mortality can be more than 80%. According to the field observation and analysis of indoor feeding, there can be four generations of the worm in Jiangsu per year. The fourth generation emergence is in early and middle October.
CONCLUSIONS
In 2009, there were more than 3,000 ha of blueberry orchards in China, producing more than 3,000 tons of fresh fruit. The ecological condition in each growing area has its own advantages and disadvantages. Suitable varieties and appropriate cultural practice must be utilized in each region to maximize productivity.
ACKNOWLEDGMENTS
We wish to thank Shi Zhongming and Hong Benqiao for their assistance in Yunnan and Dave Creech for his kindness in English smoothing. This work was supported by China Agricultural Ministry Project nyhyzx07-028.
LITERATURE CITED
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