Effect of Thinning Practices on Fruit Yield and Quality of Ruzeiz Date Palm Cultivar (Phoenix dactylifera L.) in Al-Ahsa Saudi Arabia
Mohamed Salem Al-Saikhan
A field study was carried out to determine
the effect of thinning fruiting bunches on fruit yield and quality of
Ruzeiz date palm trees (Phoenix dactylifera L.) at Date Palm Research
Center, Al-Ahsa, Kingdom of Saudi Arabia. Four thinning treatments included
control, no thinning of strands (T1), 1/3 shortening of the
total strands from the tips (T2), 1/3 removal of the central
strands (T3), 1/3 shortening plus 1/3 removal of central strands
(T4). All the thinning treatments improved the fruit quality
with respect to fresh fruit weight, fruit flesh weight, reducing sugar
and non-reducing sugar contents as compared to the control treatment.
Among the various thinning treatments, T4 (combination of 1/3
shortening and 1/3 removal of central strands) produced the best fruit
weight, flesh percentage, reducing and non-reducing sugars contents of
date fruit. Whereas the total date palm yield and bunch weight were significantly
reduced by the same treatment (combination of the shortening and central
removal of strands). However, the date fruit quality was identical for
T2 and T3 (i.e., 1/3 removal of central strands
and 1/3 shortening of total strands) treatments. There was no significant
difference of date palm yield and bunch weight obtained in control treatment
than that of strands removing and shortening treatments. Overall, the
removing and shortening of strands treatments showed promising results
for adoption at large scale to improve Ruzeiz fruit yield and quality.
Date palm is the major fruit tree in the Kingdom of Saudi
Arabia and the annual production is expected to surpass million tons in
the coming years (Annual Agricultural Statistics Book, 2004). Presently,
the date growers are facing many difficulties to produce high quality
date fruit for economical reasons and to compete with the international
market. Among the different date growing management practices, thinning
practice is an important managerial approach in date palm to improve fruit
size, fruit weight, fruit quality and reduce chances of bunch breaking
and alternate bearing (Ibrahim and Khalif, 1998; Alkhateeb and Ali-Dinar,
2002; Ali-Dinar et al., 2002). Several methods were used to thin
date palm trees, namely: bunch thinning (Ali-Dinar et al., 2002),
bunch strands thinning (Nixon and Carpenter, 1978) and individual fruit
removal (Osman and Abdulrida, 1989). Combination of removal of individual
fruits and strands had substantially improved fruit quality in Majdool
date palm (Osman and Abdulrida, 1989). In early studies, Nixon (1940,
1956) found that thinning improved fruit weight and quality, however,
severe thinning should be avoided in certain cultivars due to possible
occurrence of physiological and black nose diseases (Nixon, 1956; Nixon
and Carpenter, 1978). In Sewi date palm fruit physical and chemical characteristics
were substantially improved with thinning by progressive removal of strands
while bunch and palm yields were reduced (Mustafa, 1993). Removing 30%
of entire spikelets from bunch center was the most promising treatment,
which gave a reasonable yield and the best fruit quality of Nabtet Ali
cultivar as compared with the other used treatments (El-Shazly, 1999).
Recently, Al-Joumayly (2003) concluded that bunch thinning by heading
back of strands for Khadrawi cultivar at chemiry stage was useful to produce
high quality dates.
In spite of profuse production, most date growers rarely
pay any attention to fruit quality and in many cases prices are extremely
low and marketing channels are limited. At the same time, certain date
growers who adopt management practices to improve fruit physical and chemical
characteristics, normally fetch good prices and their produce is highly
demanded and easily marketed. The main objective of this study was to
evaluate some thinning practices and their possible effects on fruit yield
and fruit quality with respect to certain physical and chemical characteristics
of Ruzeiz date palm cultivar.
MATERIALS AND METHODS
The experiment was conducted at the Date Palm Research
Center, Al-Ahsa, Kingdom of Saudi Arabia. Ruzeiz date palm trees of approximately
uniform size were used for the study. All the date trees received optimum
management practices such as irrigation water and fertilizer etc. Thinning
practices were applied few days after pollination and proper fruit setting.
Thinning treatments were as followed.
||Control (no thinning of strands).
||1/3 shortening of total strands from terminal tips.
||1/3 removal of the central strands.
||1/3 shortening and 1/3 removal of total strands.
The experiment was laid out by following A Complete Randomized
Block Design with 4 replications according to Gomez and Gomez (1984).
Date fruits were harvested during August 2002 and 2003.
Date palm yield and yield components included bunch weight, fruit weight,
flesh percentage, reducing and non-reducing sugar contents of date fruit.
A sample of randomly selected 25 dates was used to determine different
yield components. Reducing and non-reducing sugar contents were determined
according to Lane and Eynon (1975).
Data were subjected to statistical analysis according
to Gomez and Gomez (1984). The treatment means were compared using Least
Significant Difference (LSD) at 5% level of probability according to Waller
and Duncan (1969). All statistical analysis was performed using the facility
of computer and SAS software package (SAS, 2001).
RESULTS AND DISCUSSION
Fruit weight: Mean fruit weight ranged between
11.25- 16.00 g per fruit in different fruit bunch thinning treatments
(Table 1). Mean fruit weight was significantly more
in different thinning treatments than the control treatment (LSD0.05
= 0.998). The fruit weight was significantly higher in T4 than
other thinning treatments but the difference in weight was not significant
between T2 and T3 treatments. Similar results were
reported by Mustafa (1993) who concluded that in Sewi date palm fruit
physical and chemical characteristics were substantially improved with
thinning by progressive removal of strands while bunch and palm yields
were reduced. Also, El-Shazly (1999) stated that by removing 30% of entire
spikelets from bunch center was the most promising treatment which gave
a reasonable yield and the best fruit quality of Nabtet Ali cultivar as
compared with the other treatments.
Fruit flesh: The mean fruit flesh (expressed on
percent basis relative to control treatment) ranged between 86-93% in
different thinning treatments (Table 1). The fruit flesh
percentage was significantly higher in the thinning treatments as compared
to the control treatment (LSD0.05 = 0.005). Although, mean
flesh percentage showed increasing trend in T4 than T2
and T3 treatments but the difference was not significant among
different thinning treatments. Similar views were stated by Nixon and
Carpenter (1978), Ali-Dinar et al. (2002) and Hammam et al.
(2002) who concluded that increase of fruit and flesh weights in treatments
of strands removing and tips thinning may be attributed to an internal
adjustment mechanism that makes the remaining fruits capable to efficiently
use assimilates and improve their chemical and physical qualities in reduced
competitive environments However, in contrast to the study results, many
similar studies showed that fruit parameters were not affected by different
bunch thinning treatments (Godara et al., 1990).
Fruit yield: Mean date fruit yield ranged between
80-89 kg per tree under different thinning treatments (Table
1). Mean fruit yield was significantly affected by different thinning
treatments (LSD0.05 = 2.514). Unexpectedly, the mean fruit
yield was significantly less in T4 (1/3 shortening and 1/3
removing strands) than other treatments. However, the difference in yield
was not significant among T1, T2, T3
and T4 thinning treatments. The low yield in T4
could be attributed to the removal of sizable number of fruit bunches
that makes up the total fruit yield. The results were identical to those
reported by Osman and Abdulrida (1989) and Mustafa (1993) who reported
that severe thinning led to great reduction in date palm yield and bunch
|| Effect of different thinning practices on date fruit
yield and fruit quality
|The values in a column followed by the same letter(s)
are not significantly different by LSD0.05
Bunch weight: Mean date fruit bunch weight ranged
between 8.30-12.00 kg per tree under different thinning treatments (Table
1). Mean bunch weight was significantly affected by different thinning
treatments (LSD0.05 = 0.998). The mean fruit bunch weight was
significantly less in T4 (1/3 shortening and 1/3 removing strands)
than other treatments. Whereas, the difference in bunch weight was not
significant among T1, T2, T3 and T4
thinning treatments. These results were identical to those of Tavakkoli
et al. (2006) on Shahani date cultivar. Because developing fruits
normally act as strong sink to tree nutrient sources (Leopold, 1964).
Several studies have demonstrated that less date fruits in proper managed
trees have always better chances to increase size, weight and other fruit
quality variables (El-Hamady et al., 1983; El-Gassas, 1986). This
is mainly due to abundance of photosynthates to remaining fruits (Ali-Dinar
et al., 2002).
Reducing and non-reducing sugar contents of fruit:
Mean sugar contents of date fruit ranged between 46.25-48.65 and 20.50-22.25%
for reducing and non-reducing sugar, respectively in different thinning
treatments (Table 1). The sugar contents were significantly
affected by different thinning treatments (LSD0.05 = 0.005
for reducing sugar and LSD0.05 = 0.007 for non-reducing sugar).
The difference in both the sugar contents (reducing and non-reducing)
were significant among different thinning treatments and increased in
ascending order from T1 to T4 treatments. The higher
sugar contents in T4 could be attributed to overall low total
fruit yield in T4 than other treatments that might have caused
concentration factor in total sugar accumulation. The increase of sugar
contents in treatments of strands removing and tips thinning may be attributed
to an internal adjustment mechanism that makes the remaining fruits capable
to efficiently use assimilates and improve their chemical and physical
qualities in reduced competitive environments (Nixon and Carpenter, 1978;
Ali-Dinar et al., 2002; Hammam et al., 2002). On the other
hand, many similar studies showed that fruit parameters were not affected
(Godara et al., 1990) by thinning treatments when compared to the
study results. It is quite obvious that a balanced removal of bunch strands
reduces the inter competition between the remaining fruits for nutrients
Mean date fresh fruit weight, fruit flesh percent, reducing
and non-reducing sugars increased with thinning treatments. Besides, total
date fruit and individual date fruit bunch yield reduced significantly
with application of various thinning treatments. In conclusion, application
of thinning practices in date palm production seems to play a significantly
in improving date fruit quality. This practice can be held true only if
the date palm trees are properly managed and the leaves are optimally
functioning and efficiently providing assimilates. Based on the study
results, it was found that thinning 1/3 of bunch strands from tips and
1/3 removal of the central bunch strands are appropriate approaches to
improve Ruzeiz date palm fruit quality and ensures reasonable incomes
to date growers. The study provided an excellent potential for the application
of thinning practices to produce high quality dates in the Kingdom. Further
studies are required to study in detail all the physical and chemical
characteristics of date fruit under different managing practices.
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