Date Palm Fruit Set and Quality as Influenced by Variations in Inflorescence Bagging Material following Pollination

Bagging of female inflorescence following pollination has recently received growers attention. Although this process occurs early in the season but affects fruit quality, yield, and marketability. Date palm growers have used to use grocery paper bags for this bagging process. Since inflorescence bagging causes what is called the greenhouse effect, it was very important to investigate the effect of the bagging materials on fruit set and quality early in the season. This study was conducted during the two successive seasons 2002 and 2003 using Barhi date palm cultivar. Female inflorescence was bagged with one of the following treatments: paper bags, clear (transparent) – nonperforated plastic bags, clearperforated plastic bags, blackperforated plastic bags, in addition to the control (no bagging). Bagging continued for 65 days since the area was not humid. After that period, fruit set and fruit quality parameters were determined. Fruit set was not significantly affected by various bagging materials as compared with the control. Use of paper bags or blackperforated plastic bags proved to be the most effective materials in terms of their effect on increasing fruit weight, fruit size, and flesh weight consistently in both seasons. Furthermore, clearnonperforated led to a significant reduction in such above characteristics. Various bagging materials protected the fruit from mechanical damage. Transparent or clearperforated plastic bags were not consistent in affecting fruit characteristics. Thus, bagging female inflorescence with J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.4 (2)2005 115 either paper bags or blackperforated plastic bags following pollination is recommended. INTRODUCTION Date palm is the most important crop in the gulf area. The Egyptian production of date palm ranks second world wide after Iran (El-Sherif, 2002). Fruit quality is influenced by early events such as fruit set and development. Before bunch bending, it is easy to damage small date fruits by friction with the pinnae bases. This mechanical damage adversely affect fruit marketability. Inflorescence bagging following pollination just started to be a cultural practice for date palm. Growers focus on using brown paper bags or also called small grocery bags. This bagging process raises the temperature around the bunch because the bag works like a small greenhouse. Thus, the bag traps the sun heat. Bagging also preserves the stigma moisture, protects small fruits against the damage of dry wind and insects, and avoids direct injury by rain. Al-Jabbouri (1993) found that bunch bagging near maturity (beginning of coloration) can even accelerate fruit coloration and uniformity in the same bunch. Al-Abboudi (2002) reported that using craft paper bags following pollination of female inflorescence resulted in accelerating the maturity of date balm fruits. There are no available studies on the effects of bagging materials on fruit growth and development. The objectives of this study were to increase fruit set and development, to enhance the growth rate of fruits, and to protect bunches against mechanical damage and rain. J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.4 (2)2005 116 MATERIALS AND METHODS This study was conducted during the two successive seasons 2002 and 2003 on Barhi date palms grown in AlAin city, AlKwaitat farm that belongs to the Dept. of Agriculture and Live stocks, United Arab Emirates. Barhi trees were healthy, uniform, thirty years old, grown in sandy soil, and under standard cultural practices and free of defects. “Barhi” female flowers were pollinated by using mechanical pollination on March 3 and Feb.27 in the two seasons respectively. Each pollinated bunch was covered with a bag of different material for 65 days. Treatments were: the control (no bagging), perforated paper bags (or called craft papers), nonperforated clear (transparent), plastic bags, perforated clear (transparent) plastic bags and perforated black plastic bags. Treatments were randomly distributed on many trees. After the bagging duration, five strands were collected from each bunch for the determination of some physical and chemical characteristics of fruits. The following parameters were taken: fruit weight, fruit size., and flesh weight ( each for 20 fruits), rag (seed + fruit cap) weight of 20 fruits (gm) number of fruits per strand, length of fruiting zone on the strand (cm), total soluble solids using a hand refractometer, tifratable acidity (%,), and vitamin C (expressed as mg/100 ml). The twenty fruits used in measurement were collected as a random sample after pooling the fruit of the five strands. A completely randomized design was used with three replications. One bunch represented on replication. Three replications were used with each treatment. Mstat computer software was used for obtaining the analysis of variance (ANOVA) and Duncan’s. Multiple Range Test was used to compare the means at 0.05 level. RESULTS AND DISCUSSION The results in Table 1 indicated that fruit set was not significantly increased by various materials used for inflorescence bagging in the two seasons. However, there was a consistent trend of more fruits per strand when the inflorescence was bagged with paper bags. Morever, used bagging materials varied in their effect on fruit set. For example, using paper bags resulted in significantly more fruits J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.4 (2)2005 117 per strand as compared with inflorescence bagging using clear (transparent) nonperforated plastic bags in the two seasons (Fig. 1). Similarly, inflorescence bagging with paper bags led to the formation of more fruits per strand as compared with using black perforated plastic bags especially in the first season. It is worth mentioning that even if the number of fruits per strand did not significantly increase but the process of bagging protected the fruits from mechanical damage usually induced by friction with leaf petioles.(Fig. 2) With regard to the length of fruiting zone, it was found that fruits were generally distributed on similar space on the strand regardless the material used for inflorescence bagging in the first season. However, the use of clearnonperforated plastic bags resulted in significantly shorter fruiting zone per strand as compared with clearperforated plastic bags in the two studied season. In the second season, it was obvious again that the least space carrying fruits on the strand was obtained with the use of clear-nonperforated plastic bags while other materials and control had significantly longer fruiting zone on the strand than that of clearnonperforated plastic bags (Table 1). Fruit characteristics by the end of the bagging process are shown in Table 2. It was found that the weight of 20 small fruits was significantly increased as a result of using paper bags for inflorescence bagging as compared with the control. In a similar way, bunch bagging by using black-perforated plastic bags resulted in higher fruit weight than the control. These trends were consistent in both seasons. On the contrary the use of clear-perforated plastic bags resulted in inconsistent increase in fruit weight since the significant increase was in, the second season only. Moreover, there was an adverse effect on fruit weight which resulted from the use clear-nonperforated plastic bags. The data indicated that using such bags led to a significant retardation of fruit growth which reflected on reduced fruit weight as compared with all other treatments including the control. Similar pattern was obtained for fruit size. Again, fruit size was significantly increased as a result of using paper bags and blackperforated plastic bags when compared with the control. Meanwhile, inflorescence bagging by clear-perforated plastic bags increased fruit size ,in the second season while the use of clear-nonperforated plastic J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.4 (2)2005 118 bags caused a significant reduction in fruit size as compared with all other treatments in both seasons. Results of flesh weight also came consistent with previous characteristics. There was a significant and consistent increase in flesh weight when paper bags or black-perforated plastic bags were used as compared with the control. Moreover, using clear-perforated plastic bags caused an increase in flesh weight only in the second season. Furthermore, the two inflorescence bagging materials that resulted in positive results on fruit characteristics, namely paper bags and black-perforated plastic bags did not significantly vary from each other in term of their effect on flesh weight (Table 2). The use of clear-nonperorated plastic bags resulted in a significant reduction of flesh weight in both seasons. Rag weight, which included the seed and fruit cap, was also influenced by the variations in inflorescence bagging materials. The smallest rag weight was obtained when the bunch was bagged with clear-nonperforated plastic bags that were correlated to the retardation in fruit growth as explained above. Moreover, rag weight as a result of other used bagging materials did not vary significantly from the control in both seasons. Total soluble solids (TSS) were not greatly affected by the change in inflorescence bagging materials. There was a slight but significant reduction in TSS with the use of paper bags, clearperforated plastic bags, and black-perforated plastic bags, while in the second season all treatments resulted in similar TSS values as compared with the control. In a similar manner, there were slight changes in fruit acidity at this stage due to the variations in inflorescence bagging materials. The use of paper bags and black perforated plastic caused a reduction in acidity as compared with the control in both seasons. The use of clear-perforated plastic bags also led to a reduction in fruit acidity in both seasons. Meanwhile, there was no significant difference in fruit acidity between inflorescence bagging by paper bags and black-perforated plastic bags. There was no consistent pattern with regard to vitamin C content. Inflorescence bagged with paper bags gave significantly higher vitamin C content than those bagged with clear-perforated plastic and black-perforated plastic bags in the first season.. However, there were no significant J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.4 (2)2005 119 differences in vitamin C content in the second season due to the changes in inflorescence bagging materials. This study provided evidences about some beneficial effects of inflorescence bagging on “Barhi” dates fruit set and quality. To the best of our knowledge, no previous studies were accomplished using different inflorescence bagging materials. Where inflorescence bagging is done, the focus was on the use of craft or grocery paper bags. The bunch cover with papper bags provides what is called “greenhouse effect” where light energy is converted to heat energy. This energy is trapped around the bunch. Thus, it was important to investigate the effect of inflorescence bagging materials on the microenvironment around this bunch. It was reported that placing paper bags over the female inflorescence at the time of pollination increased fruit set especially when the weather was cold early in the season (Zaid and de Wet, 1999). Bagging female spadices using paper bags (40-70 cm) immediately after pollination and during the first four weeks was also found to have a significant increase in fruit set, yield and fruit dimension of Hallawy cultivar (Galib et al.,1988). Furthermore, growth of the pollination carpels in the bagging treatment was faster than with the nonbagged one. Reurther and Crawford, (1946) supported the idea of raising temperature to a suitable limit in order to increase the germination percentage. Further evidence for the role of bunch bagging of female inflorescence on improving fruit set, delaying the dryness of the style and permitting the normal progress of pollen tube into the ovule even at relatively low temperature was provided by (Reuveni et al., 1986). Due to the warm temperature in the region of this experiment, various inflorescence bagging materials did not have a positive effect on fruit set. Moreover, clear (transparent) nonperforated plastic bags might have accumulated excessive heat around the female inflorescence and caused some undesired effects as mentioned in the results. It should be noticed that the duration of inflorescence bagging depends on the area. In dry areas where relative humidity is low, bagging could continue for longer period as was the case in this study. In some regions of Saudi Arabia, the date palm fiber sheath has been used to cover pollinated female inflorescence for 3035 days (AlJabbouri, 1993). In humid regions these bags must be removed after two to three weeks only. J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.4 (2)2005 120 This study assessed the role of various bagging materials for female inflorescence following pollination. Paper bags and blackperorated plastic bags were the most efficient materials affecting fruit quality, while clear-nonperforated plastic bags damaged the fruits and adversely affected fruit quality. REFERENCES AlAbboudi. 2002. Situation of date palm culture in United Arab Emirates. In: Proceedings of the Date Palm Global Network. Establishment Meeting, United Arab Emirates University, Held in April 7-9. PP. 8194. AlJabbouri, H., J. 1993. Data Palm United Arab Emirates University. AlAin Modern Press. PP. 369. ElSherif, F. S. 2002. Situation of date palm culture in Egypt. In: Proceedings of the Date Palm Global Network Establishment Meeting, United Arab Emirates University, Held in April 7-9. PP. 6070. Galib, H. A., E. A. Mawlood and H. H. Hamood. 1988. The Influence of bagging on fruit set and fruit characteristics in date palm cv. Hallawi. Date Palm Journal. 6: 238254. Reuther, W. and C. L. Crawford. 1946. The Effect of temperature and bagging on fruit set of dates. Date Grower’s Inst. Report. 23: 37. Reuveni, O., S. Abu and S. Golobavitz. 1986. Date palm pollen germination and tube elongation on pistillate flowers cultured at different temperatures. Acta Horticulturae 175: 9195. Zaid, A. and P. F. de Wet. 1999. Pollination and Bunch Management. In: Date Palm Cultivation. Zaid. A. and Jimenez, E. J. (eds.) FAO Plant and Protection Paper 156. PP. 290. J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.4 (2)2005 121 Fig. 1. Barhi date fruits resulting from using various inflorescence bagging materials in the first season (Top) and in the second one (Bottom). J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.4 (2)2005 122 Fig. 2. Close up graphs of Barhi date palm fruits resulting from using various inflorescence bagging materials in a, b, c, d plus the uncovered control (e). D C E B Paper Bags A Perforated clear plastic J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.4 (2)2005 123 Table 1: Fruit Set and the length of fruiting zone per strand of Barhi dates as influenced by the variations in inflorescence bagging materials following pollination during the two successive seasons 2002 and 2003 Treatments* Fruit set (expressed as the number of fruits /strand) Length of fruiting zone per strand