This work was carried out during 2009 and 2010 seasons, in a private orchard located in Kafr El-Sheikh Governorate-Egypt, to study the influence of pollen quantity (PQ) on the anatomy and fruit quality of ’Zaghloul’ dates. Twelve bunches of each female were selected for four different treatments (three bunches for each treatment), as follow; PQ0 (by nature pollination; control), PQ1 (four strands/bunch), PQ2 (eight strands/bunch) and PQ3 (16 strands/bunch). PQ2 gave the highest bunch weight, fruit weight, fruit length, SSC and lowest tannins content and total acidity as compared to the control and other treatments. Also, PQ2recorded the lowest number of layers in epiderm cells, stone cells, outer mesocarp cells and tannins cells (14.67, 63.33, 1041.67 and 533.33 μ, respectively), additional highest layer in inter mesocarp (4500.67 μ). Control fruits recorded the highest numbers of layers in epiderm, hypoderm and tannins (20.00, 48.22 and 1072.22μ, respectively). PQ1 and PQ2 recorded the highest number of layers in outer mesocarp cells and stone cells (1700.00 and 90.00 μ, respectively). Results showed that the amount of pollen play an important role in fruit quality of “Zaghloul” date palm fruits through some changes in the number of cell layers.
Date palm, Quality, Anatomy, Pollen quantity
Dates are considered as one of the most important crops in the Middle East region, and an important nutritional element contributing to food security. ’Zaghloul’ dates is one of the main soft dates cultivars in Egypt. According to the statistics of the Ministry of Agriculture in 2012, there are 12.521.212 female date palms in Egypt and the total production of date fruits is about 1.400.000 tons/year (FAO, 2012). Date palm is dioecious plant, and pollens have to transfer from the male to the female tree. Pollination is a very important process in date palm since it affects the percentage of fruit set and fruit characteristics. Several date palm growers believe that different cultivars require different amount of pollen in order to get high percentage of fruit set (Godara et al, 1994; Nail, 1994; Metwaly, 1999; Hussein et al., 2001; Soliman, 2002; El-Agamy et al, 2003; Rizkalla et al, 2007). Dowsen (1982) stated that a lower fruit set percentage was achieved when a lower pollen deposits were transferred to the female inflorescence. The transversal section at the equatorial zone of a developed date fruit, showed three main regions; exocarp, mesocarp and endocarp. The exocarp is a one layer of epidermal cells. Under this layer, there are two to three layers of hypodermal cells containing tannins, and next to them, there is a layer of three to four parenchyma cells. The endocarp consists of one layer of small cells, which can be distinguished in fertilized fruit only at the first stages of fruit development. At a later stage, these cells die together with few layers of the inner mesocarp and form the papery envelope of the mature seed (Hass and Bliss, 1935; Turrell et al,1940; Long, 1943; Schroeder and Nixon, 1958; Gefen, 1966; Coggins et al,1967; Reuveni, 1967; Reuveni, 1970; Osman et al, 1974; Al-Jarrah and Al-Ani, 1981). Long (1943) studied the pericarp development, and divided it into six layers (or seven layers when including the period of softening which follows maturation). Reuveni 1967 studied pericarp and seed development in fertilized and unfertilized fruit, cv. Zaghloul, and divided the pericarp into six stages, but the length of each stage was different to some extent from that found by Long (1943). These differences may be due to the differences in growing conditions. There are no much information on the effect of pollination and pollen source on the anatomical structure, and physical and chemical characteristics of date fruit. This study aims to add some new information in that regard, how many strands/bunch sufficient for good fruit yield and quality through changes in fruit anatomy?
Materials and Methods
Plant material and experimental design: This work was carried out during 2009 and 2010 seasons, in a private orchard, located in Kafr El-Sheikh Governorate, Egypt. One male date palm of unknown cultivar, which called ‘Meghal’ and four healthy, 17 years female date palms of cultivar ‘Zaghloul” were selected Palms were grown in a loamy soil, 8 meters apart, and receiving the regular horticultural practices recommended by the Ministry of Agriculture. The experiment was designed as a randomized complete blocks, with four treatments and each treatment was represented by three replicates, Twelve bunches (each bunch as replicate) on each female were selected for four different treatments (three bunches for each treatment), as follow; PQ0 (by nature pollination; control), PQ1 (4 strands/bunch), PQ2 (8 strands/bunch) and PQ3 (16 strands/bunch). Pollination was made after 2 or 4 days from the opening of spathes.
Bunch weight (Kg) was weighted by digital balance (kg), according to (A.O.A.C.1995).
Fruit physical characteristics: A samples of 60 fruit per treatment 20 fruit per replicate) were randomly collected to measure fruit weight (g), flesh weight (g), and fruit dimensions (length and diameter “cm”) according to (A.O.A.C.1995).
Fruit chemical characteristics: Same fruit samples were used to determine fruit acidity, total soluble solids and tannins content, according to (A.O.A.C.1995)
Fruit anatomy: Fruit samples were collected from each treatment during the first week of September (Bisir stage). Each fruit sample includes 18 fruit; 6 fruit/replicate. Fruit were stored in vials. The ordinary paraffin method was followed for preparing the samples using the formalin acetic alcohol fluid (FAA [70%]) as a killing and fixing agent (Yeni et al., 2006). Butyl alcohol was used for dehydration. Paraffin wax (56E-58EC m.p.) was used for infiltration and embedding (Johansen, 1940). Longitudinal and cross sections of 10 micron were taken using a rotary microtome, and sections were stained using safranin dye and light green technique according to the schedule of Sharman (1943) and mounted in Canada balsam. An Olympus compound microscope (BX-51) magnifications of 200-1200x (Al-Atawi., 2010) were used to examined the sections for measure the cell layer (μ) of the following; epidermis, hypodermis, stone cells, outer mesocarp, tannins cells, and inner mesocarp.
Fig. 1. Cross section of “Zaghloul “ datepalmfruit showing theeffectofpollen quantity. A – Control (PQ0 ), B – 3 strands/bunch (PQ1 ), C- 6 strands/bunch (PQ2 ) and D -12strands/bunch (PQ3)
Experimental design and statistical analysis: The experiment was designed in a complete randomized model with three replicates (bunch as replicate) per treatment. One way ANOVA was run using SAS program (2000). Means were compared using least significant differences (LSD) at P≤0.05 (Schanderi 1970).
Bunch weight (kg): Data in table (1) showed that, in both seasons the highest bunch weight was recorded with PQ2 (eight strands/bunch). Bunch weight was 23.67 kg in 2009 and – 24.87 kg in 2010, these values were significantly higher than the control, which recorded the lowest bunch weight; 16.52 and 17.73 kg in 2009 and 2010, respectively.
Fruit weight (g): Treatment PQ2 significantly increased fruit weight compared to the control and other treatments in both seasons. The highest fruit weights were 40.99 and 35.11g by PQ2 during 2009 and 2010, respectively (Table1).
Flesh weight (g): Treatment PQ2 recorded the highest significant flesh weight (36.78 and 34.80g) in 2009 and 2010, respectively, compared to the control and other treatments as shown in Table (1).
Fruit dimensions (length and diameter) (cm): No significant differences were recorded between treatments or the control in both seasons (Table 1).
Acidity (%): Treatment PQ2 had more pronounced effect on fruit acidity compared to other treatment (except PQ1 in 2009) and the control in both seasons; 0.11 and 0.28 in 2009 and 2010, respectively (Table 2).
SSC (%): As acidity decreased, SSC increased significantly with PQ2 compared to the control and the other treatments. SSC recorded 36.85 and 37.37% in 2009 and 2010, respectively (Table 2).
Tannins (%): Control recorded the highest and significant tannins percentage compared to other treatments in both seasons (0.150 and 0.341% in 2009 and 2010, respectively) (Table 2).
Fruit anatomy:Microscope images revealed some effects on fruit anatomy as results of pollen quantity
Epidermis cells layer (μ): Data in table 3 and Fig.1 showed that all treatments significantly reduce epidermis cells layer as compared with control and treatment 4 (PQ3) and recorded 20.00 and 17.00μ respectively.
Hypodermal cells layer (μ):All pollination treatments reduced significantly the cells layer of hypodermal as compared with control except PQ2 (Table, 3 and Fig 1). The lowest cells layer was 38.33μ, while the highest were 48.22 and 47.67μ recorded by Treatments 2, 3 and 1(PQ2, PQ1and PQ3) respectively.
Table1. Effectofpollen quantity onbunchweight(kg/bunch) and fruit physicalcharacteristics of `Zaghloul`datepalmfruit in 2009and2010s.
Means not sharing any letter in each colum differ significantly at p≤0.05.
Table 2. Effect of pollen quantity on some chemical characteristics of `Zaghloul` date palm fruit in 2009 and 2010 seasons.
Means not sharing any letter in each colum differ significantly at p≤0.05.
Table 3. Effect of pollen quantity on some cell layers of Zaghloul fruit anatomy.
Means not sharing any letter in each column differ significantly at p≤0.05.
Stone Cell layer (μ):Treatment PQ3 recorded the highest stone cells layer (90.00μ) as compared with other treatments, while PQ3 and control recorded the lowest values (63.33 and 66.10μ (Table 3 and Fig 1).
Outermesocarp cells layer (μ): The outer mesocarp cells recorded the highest significant thickness (1700.00μ) with PQ1, while the lowest outermesocarp cells layer was recorded by control as compared to other treatments (Table 3 and Fig 1)
Tannin Cells layer (μ): All pollination treatments reduced significant the dimension/thickness of tannin cell layer, compared to the control (Table 3 and Fig 1). Treatment PQ2 recorded the lowest value (533.33μ) compared the control (PQ0) which recorded the highest value (1072.22 μ).
Intermesocarp Cells (μ): Treatment PQ2 recorded the highest significant value (4500.67μ) compared to the control (3481.97μ) and other treatments (Table 3 and Fig 1).
Many factors can affect fruit anatomy and consequence physical and chemical characteristics. These factors, such as temperature (Summerville, 1944, Fahn et al. 1961, Fortescue and Turner 2005), fruit cluster or bunch thinning (Nixon and Crawford, 1942), crop load (Salvador et al. 2006). Also, the amount of pollens can affect fruit quality through increasing bunch weight, fruit weight and dimensions, and SSC, in addition to reducing tannins and total acidity content. These changes were mainly noticed with six strands /bunch as compared with other treatments and the control in both seasons (Omar2004). Through this study, there were variations between pollen quantity effects on fruit quality and fruit anatomy, since treatment PQ2 recorded the lowest layers dimensions/thickness in epiderm cells, stone cells, outer mesocarp cells, tannin cells and inner mesocarp. On the other hand, control fruits had the highest layers in epiderm, hypoderm and tannin cell layers. Application of three or nine strands/bunch had lower effect than six strands/bunch in fruit quality of “Hayany” date fruit (Omar, 2004). These changes in fruit quality may be due to some changes in some enzymes or biochemical processes El-Mardi et al.,(2006) found that low pollen concentration applied to “Farad“ date palm resulted in the same effect on the pectin content as high pollen concentration affect. This is indicating that pollen quantity has no effect on the activation of pectinase, which indicate the importance of reducing the amount of pollen used in pollination. Both pollens and developing seeds contain plant hormones, and they may serve as sources of some important hormones that affect fruit growth and development (Talon et al., 1990; Garcia-Martinez et al., 1991; Ben-Cheikh et al., 1997; Ozga et al., 2002). However, the fruit quality of Zaghloul dates improved as amount of pollens added, may be through changes in cells layer of fruit and movement of hormones from pollen and seeds directly into fruit progenitor tissues has not to our knowledge been demonstrated. Zaghloul date palm anatomy showed that increase or decrease of some cells in some layers such as increase of stone and tannin cells in control and lower amount of pollen as compared with other pollination treatments and reflects on fruit quality. These results go partial withShabana et al., (2001),who reported that pollination of date palm cultivars gave the highest fruit set percentage and quality, also Howpage et al., (2001) found that the lack of amount of pollen in kiwifruit reduce of fruit quality under Australian conditions, Yong Seub Shin et al., (2007) investigate the effect of amount of pollen on development and sugar content of melon fruits.
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