Abstract: The present investigation was carried out to evaluate and compare agronomical characteristics of jojoba clones under Central Region of Saudi Arabia, using seven diverse female jojoba genotypes. Survival rats ranged between 91.7 to 98.0%. Highly significant differences among time periods, clones and their interaction were found for plant height and number of branches per plant. Plant height ranged from 30.5 cm in April 1st 2009 to 52.8 cm in February 1st, 2010 and branches ranged from 11.9 to 58.7 branches per plant in same period. The clones significantly differed in all studied traits. Genotypes, HA9 and HD1 recorded the highest and lowest values for plant height, respectively. For number of branches per plant, genotype HB2 had the highest value while, genotype HD1 had the lowest one. Clones HB8 and MD8 had almost similar values in most traits. For stem diameter clone HB2 recorded the highest value, while HD1 had the lowest one. Chlorophyll content ranged from 62.5 (HB2) to 73.9 (HB6). Genotype HB6 recorded the largest leaf area, the heaviest dry leaf and lowest value of specific leaf area while, genotype HA9 had the smallest leaf. Clone HB2 recorded the lowest and highest values of leaf dry weight and specific leaf area; respectively the genotypes HB8, MD8 and HD1 flowered early, while clones HA9 and HB2 were late in flowering. The results obtained in this work indicate that there is a large genetic variability among jojoba clones established at Al-Qassim Region which could permit improvement by selection and breeding.
INTRODUCTION
Jojoba (Simmondsia chinensis (Link) Schneider) is an evergreen shrub that is native to northern México and the southwestern United States. Its natural distribution falls between latitudes 25 and 34 in an area which closely approximates the Sonorant Desert (Gentry, 1958). The jojoba plant has economic value because its seeds contain about 50% of a light yellow, odorless wax ester commonly referred to as jojoba oil, which is extensively used in the cosmetic industry due to dermatological properties. Its great resistance to drought allows this shrub to produce a crop with significantly less water than is necessary for traditional crops. According to Yermanos (1982), 250-450 mm of annual rainfall was adequate for survival of natural jojoba population. In experimental farms, however, vegetative growth and its components were reported to vary with the intensity of drought stress (Nerd et al., 1982; Benzioni and Nerd, 1985; Nerd and Benzioni,1985; Malende, 1989; Nelson et al.,1993; Nelson, 1996; Osman and Abo-Hassan, 2002). Moreover, Jojoba is relatively salt tolerant, Roussos et al. (2007) reported that jojoba explants tolerate salinity up to a level of sodium chloride concentration (113 mM), without showing any stress symptoms. In addition, Roussos et al. (2006) found that, jojoba shoots deriving from explants growing under saline conditions rooted as well as those growing under salt free conditions.
It is well known, shortage of irrigation water is one of the main factors that limits crop production in arid and semi arid environment. Consequently, utilization of drought tolerant shrubs in sand stabilization and landscaping and greenification projects, in establishing open natural range lands and national parks will save adequate amounts of fresh water that can be used for cultivation of traditional field crops. Osman and Abohassan (1997) reported that jojoba in Western Saudi Arabia, as its original habitat had maintained positive growth under high drought stress. The ability to withstand drought could be attributed to its capability to cope with environmental changes through morphological modification such as reduction in leaf area and increase in leaf thickness or leaf weight. The growth of jojoba is controlled by various agro-climatic factors e.g., temperature, soil type, salinity level of soil, water and methods of sowing (Rana et al., 2003). Many researchers studied growth characters in jojoba (Nelson and Bartels, 1998; Benzioni et al., 1999; Tobares et al., 2004; Bashir et al., 2007, 2009; Prat et al., 2008).
As occurs in other crops, the jojoba industry faces the challenge of finding ways to improve productivity and quality of the products. Jojoba is a difficult species to domesticate because it is highly variable as a result of its being dioecious and an obligatory cross- pollinated species. Only a small proportion (less than 1%) of the plant population originating from seeds of native plants has the potential of yielding economically acceptable yields (Purcell and Purcell, 1988). Hence, the best method for jojoba improvement, in the short term, is the selection of plants with desirable characteristics and propagating them asexually. Our objective was to evaluate and compare agronomical characteristics of jojoba clones with the purpose of selecting the superior jojoba genotypes under Al-Qassim Region in Saudi Arabia.
MATERIALS AND METHODS
Field experiment: The field experiment cared out in the Experimental Farm of the College of Agriculture and Veterinary Medicine, Al-Qassim University. 26° 18' N latitude and 43° 58' E longitude and 725 m above sea level, in central Saudi Arabia, from Oct. 2008 to February 2010 Meteorological data at experimental site during the growing seasons are shown in Table 1.
Plant material and experimental design: Plant material (male and female) were provided by Faculty of Meteorology-King Abdulaziz University. The materials for this study comprised seven diverse female jojoba genotypes (Simmondsia chinensis.) selected for their characters. In the last decade, a comprehensive jojoba selection program was conducted at Faculty of Meteorology-King Abdulaziz University. In this program, promising individual plants were vegetatively propagated and planted at some regions in Saudi Arabia (Al-Medinah, Hail, Hada Al-Sham). The most promising clones, based on the selection criteria, were propagated by cuttings. Seven clones were chosen based on their desirable characters. The female genotypes HD1, HA9, HB2, HB4, HB6, HB8 and MD8 were planted. The plants were established in the field experiment between October 27 and 30, 2008. Sixty plants per clones were planted in completely randomized block design with five replication to study the growth of jojoba cultivars. Each replicate consisted of 4 rows, each containing 26 plants (21plants represent seven clones, two and three plant as border for west and east direction, respectively). Distances between rows and within plants in rows were 3 and 2 m, respectively. Rows ran in an east-west direction. Male plants were repeated one row every six female rows of mixed males and female plants developed from seeds derived from a mixed population.
| Table 1: | Monthly mean air temperature (At °C), mean relative humidity (RH%) and rainfed (mm/month) at the experimental sites from Oct. 2008 to February 2010* |
| *Source, according to Presidency of Meteorology and Environmental Protection | |
Before sowing, an irrigation drip system was installed in the experimental area. Fertilizer and weed control were done as necessary.
Parameters
Survival: Survival was defined as the percentage of established plants
in the end week of October 2008 of the total number of living plants 3 months
after planting (end week of January 2009) for each clone.
Growth analysis: For each genotype, five plants per block (from the inner rows) were randomly chosen and tagged for growth measurements. At March 1st 2009, measurements were taken and repeated monthly, for Plant height above the ground and branching. Branching was defined as the total number of branches (with leaves longer than 1 cm) per shrub. In addition stem diameter at 5 cm above the ground was measured once in the first week of February 2010 only.
Physiological measurements: In the first week of February 2010, from the five plants, five leaves were collected (The 5th leaves from the top of the shoot) and measurements of leaf area and leaf dry weight were recorded. Leaf area was measured using a LI-3100 (LI-COR, Lincoln, Nebraska, USA) leaf area meter. Leaf dry weight was determined by weighed and dried at 70°C. The drying process was repeated until the difference between two successive weightings was less than 1 mg. Specific leaf area (i.e. leaf area leaf-1 dry weight) was also determined. Chlorophyll pigment was measuring on the 5th leaf from the top of the shoot using a SPAD-501 Chlorophyll Meter (Konica Minolta, Co. Ltd., Japan).
Flowering percentage: In December 1st 2009, every 10-12 days, the number of plants which bearing open floral buds (with a visible stigma) of each clone were recorded until February 10, 2010. Then, the flowering percentage was calculated and presented as cumulative percentage of flower plants.
Statistical analysis: The original data of branching were transformed
using square root scale
RESULTS AND DISCUSSION
Survival rats: Survival rats ranged between 91.7 to 98.0% for the seven clones, absent holes were replanted from the stock for each clone.
Growth analysis: Growth and development of a plant is considered the result of a number of ontogenetic processes which regarded as a reflection of direct and accumulated metabolic reactions. Therefore, such information on the growth can help to understand the genetic variation in growth and jojoba development.
Effects of growth period (the months) on plant height above ground and number of branches per plant ate 12 dates in seven jojoba genotypes are presented in Table 2. Based on the combined analysis of variance, the results revealed the presence of highly significant differences among months (M and) clones (C) for the two studied traits. These indicate that, the behavior of the same genotype differed from month to another and at the same month, the genotypes differed in their traits.
Data in Table 2 revealed that, plant height ranged from 30.5 cm (April 1st) to 52.8 cm (February 1st). Moreover, in this period number of branches per plant ranged from 11.9 to 58.7 branches per shrub. The average growth increment of plant height from April 1st 2009 to February 1st 2010 was 22.3 cm (about 73.1%). Meanwhile, the average growth increment number of branches per plant in same period was 46.8 branch per plant (about 393%).
| Table 2: | Effect of growth period and genotypes on plant height above ground and number of branch per plant, for seven jojoba genotypes from March 1st 2009 to Feb 1st 2010 |
| Means in column within each factor designated by the same latter are not statistically different at p<0.05 level according to Duncan’s multiple range test | |
The maximum growth increment values of plant height and number of branches per plant were through October and May for two characters, respectively. For plant height, no significant differences (p<0.05) among months from March 1st to June 1st. This result might be due to plant growth was on the direction of produce high number of branches and/or death plants were replanted and data were recorded on some plants differed in their age.
In this connection, Bashir et al. (2007) recorded different growth parameters among jojoba strains; they found that there was different response to auxins application between jojoba strains. Also, Prat et al. (2008) studied the effect of plant growth regulators on Jojoba and recorded that, the total growth increment of plant height ranged from 18.6 to 26.8 cm at 360 days post-application. Moreover, Nelson and Bartels (1998) reported that, Plant height measurements showed that growth was rapid in April and May, decreased in June and July and then generally remained slow until the following spring. The conflicting reports about the period which growth rate is rapid of plant height measurements by earlier workers may be due to differences in the environments and materials used in those studies.
The genotypes were significantly differed in plant height and number of branches per plant based on average of all months (Table 2). Therefore, the comparisons between genotypic means are valid. Plant height above ground presented significant variation among jojoba genotypes and ranged from 35.6 cm (clone HD1) to 41.4 (clone HA9), based on average over months (Table 2). Genotypes, HA9 and HD1 recorded the highest and lowest values for plant height, respectively. No significant differences among clones HB4, HB8 and MD8 were detected.
For number of branches per plant genotype HB2 had the highest value (47.7) while, genotype HD1 had the lowest one (24.3). No significant differences among clones HB2, HB8 and MD8 were detected. The clones HB8 and MD8 were possessed same values for plant height and number of branches per plant (Table 2).
Genetic differences among genotypes in plant height and branches have previously been reported (Botti et al., 1998; Benzioni et al., 1999; Tobares et al., 2004; Prat et al., 2008).
Benzioni et al. (1999) found that, some clones exhibited excellent vegetative traits related to yield potential, such as, rapid growth and extensive branching.
Significant variation among genotypes was observed within each month from July 1st 2009 to February 2010 (Table 3). Clone HA9 was tallest genotype in most months while, clone HD1 was shortest one in most cases. Clones HB8 and MD8 had almost similar values in most cases. Rana et al. (2003) stated that the germination and growth of jojoba is controlled by various agro-climatic factors such as temperature, soil type, salinity level, water and method of sowing.
Significant variation among genotypes was observed for number of branches per plant within each month (Table 4). Genotype HB3 had the highest values at most dates, while genotype HD1 and HB4 had the lowest values. No significant differences between the two clones MB8 and MB8 were detected for all growth periods. This result confirmed the previous finding which indicated that, these two clones had similar values for plant height and number of branches per plant.
Table 5 shows the mean performance of stem diameter for seven jojoba clones. Significant differences were observed among genotypes. Clone HB2 recorded the highest value (5.3 cm) while HD1 had the lowest one (4.1 cm). These results are similar to report on the presence of significant differences among clones on stem diameter (Botti et al., 1998).
Physiological measurements: Table 5 shows the mean performance of chlorophyll content, leaf area, leaf dry weight and specific leaf area (leaf area per unit dry weight) for seven jojoba clones. Significant differences were observed among genotypes for these characters. Chlorophyll content presented significant variation among jojoba genotypes and ranged from 62.5 (HB2) to 73.9 (HB6).
Significant differences were observed among genotypes for leaf area (Table 5). Genotype HB6 recorded the largest leaf (8.2 cm2), the heaviest dry leaf (0.248 g) and lowest value of specific leaf area (33.1 cm2g ¯1) while, genotype HA9 had the smallest leaf (5.16 cm2). Clone HB2 recorded the lowest and highest values of leaf dry weight and specific leaf area, respectively (Table 5). No significant differences were detected between clones HB8 and MB8 for the five studied traits.
The observed significant variation for growth and physiological characters among the genotypes might reflect, partially, their different genetic backgrounds.
These results are similar to reports on the presence of significant differences among clones on leaf dry weight and specific leaf area (Osman and Abohassan,1997) and leaf area (Botti et al., 1998).
Flowering percentage: Flowering percentage varied among the genotypes (Fig. 1). The genotypes HB8, MD8 and HD1 flowered early, reaching about 93, 83 and 83% flowering respectively, in the January 1st 2010. Meanwhile, clones HA9 and HB2 reaching about 17 and 57% flowering, respectively, in the same period. Ulger et al. (2002), found that, the selected male and female plants flowered between 20 February and 25 March. They also concluded that, each type has a different genetic character and their responses vary with climatic and soil conditions depending on genetic type.
| Table 3: | Mean performance of plant height above ground for seven jojoba genotypes from March 1st 2009 to Feb. 1st 2010 |
| Means in each row designated by the same latter are not statistically different at p<0.05 level according to Duncan’s multiple range test | |
| Table 4: | Mean performance of number of branch per plant for seven jojoba genotypes from March 1st 2009 to Feb. 1st 2010 |
| Means in each row designated by the same latter are not statistically different at p<0.05 level according to Duncan’s Multiple Range Test | |
| Table 5: | Mean performance of stem diameter, chlorophyll content, leaf area, leaf dray weight (g) and specific leaf area for seven jojoba genotypes |
| Means in each column designated by the same latter are not statistically different at p<0.05 level according to Duncan’s Multiple Range Test | |
| Fig. 1: | Flowering pattern of jojoba clones in the field during December 1st 2009 to February 10, 2010 |
Different response among jojoba varieties in flowering was observed for water salinity levels (Rana et al., 2003).
CONCLUSIONS
The variations observed in the studied characters were principally due to clone differences. We conclude that jojoba shows good establishment under Al-Qassim Region in Saudi Arabia. Genotypes, HA9 recorded the highest value for plant height. For number of branches per plant, genotype HB2 had the highest. Clones HB8 and MD8 had almost similar values in most traits. For stem diameter clone HB2 recorded the highest value. Genotype HB6 recorded the largest leaf area, the heaviest dry leaf and lowest value of specific leaf area. Clone HB2 recorded the lowest and highest values of leaf dry weight and specific leaf area; respectively the genotypes HB8, MD8 and HD1 flowered early. The results obtained in this work indicate that there is a large genetic variability among jojoba clones established at Al-Qassim Region which could permit improvement by selection and breeding.
ACKNOWLEDGMENTS
Funding support for the work described here was provided by King Abdulaziz City for Science and Technology (KACST) as a part of project No. AT 27-27, Application of Biotechnology as DNA fingerprinting and Micropropagation of Jojoba and Study of its Growth and Yield under the Environmental Conditions of The Central Region of Saudi Arabia. The author is also very grateful to Dr. Abdulsalam M. Menshawy for his help especially in statistical analysis.