The Impact of Summer Rainfall on Alternate Bearing of Mangosteen (Garcinia mangostana L.) in Southern Thailand
S. Sdoodee1 and N. Sakdiseata2
1 Department of Plant Science, Faculty of Natural Resources, Prince of Songkla University, Hat Yai, Songkla, 90112, Thailand
2 Department of Plant Science, Faculty of Agriculture, Rajamangala University of Technology Srivijaya, Toungsong, Nakhon Sri Thammarat, 80240, Thailand Keywords: alternate bearing index, crop load, fruit quality, pre-flowering period Abstract
Southern Thailand normally has rainfall conditions which favour mangosteen production. However, mangosteen trees also require a certain degree of water stress during summer or during the pre-flowering period for flower induction. Recently, unusual rainfall during summer has caused strong vegetative growth of tree in the off- year leading to irregular yielding. This may have been due to the effects of climatic change. Therefore, the effects of rainfall distribution on alternate bearing of mangosteen were investigated in Nakhon Sri Thammarat Province, southern Thailand during four consecutive years (2004-2007). It was evident that the yields of the off-year (2004 and 2006) trees were relatively low because of summer rainfall. While the on- year (2005 and 2007) trees exposed to water stress during summer produced high yield. In 2007, an extreme on-year with profuse flowering occurred, but low fruit- quality was greatly influenced by the high crop load. With the assessment of an alternate bearing index [ABI = (year 1 yield-year 2 yield) ÷ (year 1 yield + year 2 yield)], ABI of year 1-2, year 2-3 and year 3-4 were 0.25, 0.38 and 0.57, respectively.
This indicates that severity of alternate bearing in mangosteen progressively increases over time. Therefore, the improvement of cultural management strategies is needed to minimize alternate bearing.
INTRODUCTION
In Thailand, mangosteen is a fruit that has high potential for export. The main areas of production are on the East and in the South. The humid tropical climate of southern Thailand normally favours mangosteen production. However, evidence of climate change on phenological development of fruit trees has recently been increasingly obvious (Chmielewski et al., 2004). There has been a distinct increase in air temperature in southern Thailand, leading to change in the precipitation pattern and to phenological change in mangosteen (Sdoodee, 2007). Normally, mangosteen requires a dry period of around 3 weeks followed by irrigation application to induce flowering. In southern Thailand, a dry period normally occurs during January-February in summer. However, summer rainfall induces strong vegetative growth leading to alternate bearing in the off- year. Therefore, mangosteen has been reported to flower in alternate years (Yaacob and Tindall, 1995). The average annual yield of mangosteen trees prone to alternation is considerably lower than those with regular yielding (Ruangying, 2005). Recently, the impact of climate change has tended to be more severe, with unpredictable summer rainfall causing strong shoot developing of mangosteen more than flowering induction.
Racskó et al. (2006) also reported that strong vegetative growth of fruit trees in the off- year makes the tree more prone to irregular yielding. Therefore, the aim of this study was to investigate the impact of summer rainfall on alternate bearing of mangosteen in southern Thailand during 4-years of on-off cycles.
MATERIALS AND METHODS
The experiment was conducted in the Nakhon Sri Thammarat province, southern Thailand. Ten mangosteen orchards with 13-year-old trees (in year 2004) were used. The orchards sampled for investigation were located within 5 km of the Nakhon Sri
Thammarat Meteorological Station. The phenological development of mangosteen trees was continuously recorded from 2004 to 2007. Current climate during 2004-2007 was measured and recorded by the meteorological station. Rainfall and evaporation trends were used for the assessment of water deficit in summer during the 4-year cycles. The phenophases of mangosteen in each year were recorded as bloom and fruit development periods. Ten trees in each orchard were sampled for the determination of fruit yield per tree.
Alternate bearing index (ABI) was calculated for each sequential 2-year period using the equation (Lovatt, 2005):
ABI = (year 1 yield – year 2 yield) ÷ (year 1 yield + year 2 yield) (1) For the assessment of fruit quality, 30 harvested fruit were sampled from each of 10 trees. Average fruit weight, peel thickness and total soluble solids concentration (TSS) were determined. Fruit disorders, particularly translucent flesh disorder and gamboges, were also assessed.
RESULTS
Average maximum and minimum temperature at Nakhon Si Thammarat were approximately 34 and 25°C, respectively (Fig. 1). In 2004, total rainfall in Nakhon Si Thammarat province was only 1941 mm, which was lower than average annual rainfall.
However, there was some rainfall during January and February followed by a water deficit in March that caused flower induction. Prolonged stress occurred during early summer in 2005 from January to February, leading to profuse flowering. During harvesting, there was high rainfall, particularly in May. At the end of 2005, there was severe flooding because of heavy rainfall during October and December. Rainfall also continued into January and February in 2006. The dry period in summer in 2006 was delayed until March, and the bloom stage of mangosteen was delayed until April, and flowering was sparce. There was high rainfall in June during the harvest period. There was a long dry period in the summer of 2007, particularly in February, which caused an extreme on-year with profuse flowering. Furthermore, there was high rainfall during harvesting.
There were clear differences in phenology among the four years as assessed by the two phenophases (Fig. 2). In 2004, flowering of mangosteen started in March. The effect of prolonged stress in 2005 caused early flowering in February. However, the flowering was delayed until April in 2006, because of summer rainfall. This caused late harvesting in year 2006. Flowering of mangosteen in 2007 was similar to 2005 because of the regular dry period in summer.
The impact of summer rainfall had a marked impact (decrease) on yield in 2004 and 2006 (Fig. 3). Average yield of mangosteen in 2004 and 2006 was 23.6 and 17.92 kg tree-1, respectively which were both significantly less than yields in 2005 and 2006. The mangosteen trees in 2007 exhibited heavy fruiting with the highest average yield (64.62 kg tree-1), which it was also significantly different from the average yield in 2005 (39.64 kg tree-1).
The ABI calculated from 2004 (year 1) and 2005 (year 2) was 0.25 (Table 1).
However, a marked decrease of yield in 2006 (year 3) caused ABI of year 2-3 to be 0.38.
In 2007 (year 4), extreme on-year led to a marked increase of ABI (year 3-4) to 0.57.
During the 4-year on-off cycles, the average ABI of mangosteen was 0.40.
Fruit quality was different between the on-year trees and off-year trees. Average fruit weight in 2006 was significantly higher (107.56 g fruit-1) compared to those in the other years (Table 2). Peel thickness of the fruits in on-year trees was significantly higher than those in off-year trees. However, there was a non-significant difference in total soluble solids of fruit between on-year trees and off-year trees. In addition, high rainfall during harvest resulted in the highest percentage of TFD in fruit in 2005, followed by those in 2007. The incidence of GB in each year was around 5%.
DISCUSSION
It was evident that summer rainfall caused a marked decrease in fruit yield in the off-year. Conversely, a prolonged dry period in summer led to extreme on-years with profuse flowering and heavy fruiting. This indicated that the mangosteen tree needs a dry period to induce flowering. If the dry period is delayed, it will also cause a delay in both bloom and fruit development.
This study showed that the magnitude of ABI of mangosteen is moderate ranging from 0.25-0.57. Lovatt (2005) reported that alternate bearing in avocado is a serious problem, with the ABI ranging from 0.57-0.92. With the alternation of average yield during 2004-2007, high crop load in an on-year also affected fruit quality, particularly fruit weight and peel thickness. Ruangying (2005) suggested that the reduction in fruit size is an adverse effect of excessive crop load in mangosteen. It was also reported in mandarins that excessively heavy crops cause a decrease in fruit size. This was due to competition between fruitlets for water and nutrients. As fruit size is a major determinant of market price, fruit must be thinned to maximise returns (Vock et al., 1997). Link (2000) suggested that a reasonably balanced compromise between quality and quantity is essential in the improvement of fruit quality. Therefore, thinning is needed to optimize crop load of mangosteen in on-years where heavy fruit loads occur. Stover et al. (2005) reported that the trees with heavy cropping will often result in a light bloom and low crop load in the following year. Heavy crop load causes a reduction of dry matter accumulation in trees, where vegetative and root growth are poor leading to adverse effects in the following year (Inglese et al., 2001). In mangosteen, Ruangying (2005) also found that trees that produce high crop loads have a low crop load in the following year. Therefore, optimizing crop load in the on-year is needed to alleviate alternate bearing and to increase yields of standard fruit size. It was also found that the incidence of TFD in on-year trees was significantly higher than that in off-year trees. This was due to high rainfall during pre-harvest. Sdoodee and Limpum-Udom (2002) suggested that excess water causes the incidence of translucent flesh disorder of mangosteen fruits.
The incidence of summer rainfall is tending to become more severe and, consequently, research on this impact has to increase. Improvements in cultural management practices to alleviate alternate bearing of mangosteen is necessary under the influence of climate change. Recently, some effective methods have been reported in mangosteen; such as optimizing crop load (Ruangying, 2006), canopy management by topping (Sakdiseata et al., 2000) and chemical application to induce flowering (Omran and Semiah, 2006).
CONCLUSION
The impact of summer rainfall on alternate bearing of mangosteen in southern Thailand is becoming more severe. Therefore, in the future, impacts on crop yield have to be investigated further. Improvement in cultural management strategies to minimize alternate bearing are also needed.
Literature Cited
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Tables
Table 1. Effect of summer rainfall on alternate-bearing index of mangosteen in Nakhon Sri Thammarat Province, Southern Thailand during 2004-2007.
Each sequential 2-year period Alternate-bearing index
Year 1-2 0.25
Year 2-3 0.38
Year 3-4 0.57
Average 0.40
Table 2. Average fruit weight, peel thickness, total soluble solids concentration (TSS) and percentage fruit disorder (translucent flesh disorder (TFD) and gamboges (GB)) of mangosteen in Nakhon Sri Thammarat Province, Southern Thailand during 2004- 2007.
Years Fruit weight (g fruit-1)
Peel thickness (cm)
Fruit quality TSS
(°Brix)
Fruit disorder (%)
TFD GB
2004 87.21b* 0.84a 17.23ns 9.39c 4.50
2005 81.71b 0.68b 18.46 16.60a 5.44
2006 107.56a 0.86a 17.58 9.71c 5.50
2007 78.96b 0.67b 17.91 13.25b 5.17
* = Means with different superscripts in each column are significant different (P≤0.05) by DMRT.
ns = non-significant difference.
Figurese
Fig. 1. Monthly rainfall, evaporation, maximum and minimum temperature during 2004- 2007. Data from Nakhon Si Thammarat Meteorological Station, Nakhon Sri Thammarat Province, Thailand.
0 200 400 600 800 1000 1200
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 0 5 10 15 20 25 30 35 40 2004
0 200 400 600 800 1000 1200
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 0 5 10 15 20 25 30 35 2005 40
0 200 400 600 800 1000 1200
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 0 5 10 15 20 25 30 35 2006 40
Monthly rainfall and evaporation (mm) Average maximum and minimum ( 0 c)
0 200 400 600 800 1000 1200
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 0 5 10 15 20 25 30 35 2007 40
Rainfall Evaporation Maximum temperature Minimum temperature
Month
Fig. 2. Bloom and fruit development periods of mangosteen trees in Nakhon Sri Thammarat Province, Southern Thailand during 2004-2007.
Fig. 3. Fruit yield of mangosteen (kg tree-1) averaged from the 10 orchards in Nakhon Sri Thammarat Province, Southern Thailand during 2004-2007. Bars with different letters are significant different (P≤0.05) by DMRT.
2004
Year
Bloom
Fruit development
2006
2007
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 2005
0 10 20 30 40 50 60 70
2004 2005 2006 2007
c*
b
c
a
Years Average fruit yield (kg tree-1 )
