AN ASSESSMENT OF SOME GROWTH AND YIELD INDICES OF SIX VARIETIES OF WATERMELON (CITRULUS LANATUS THUMB) IN ASABA AREA OF DELTA STATE, NIGERIA

Field experiments were conducted in 2011 and 2012 cropping seasons in the Teaching and Research Farm of Delta State University, Asaba Campus, Nigeria to assess some growth and yield indices of six varieties of watermelon (Sugar baby, Charleston gray, Crimson sweet, Green gold, Jubilee, and Ice box) in Asaba area of Delta State, Nigeria. The experiments were carried out in a Randomized Complete Block Design (RCBD) with three replicates. Four parameters were assessed to achieve the objectives of the study-vine length, number of leaves/plant, number of branches /plant, and weight of fruits at 75 days after sowing. The results of the two-year evaluation indicated that Sugar baby variety was superior at 4, 6, and 8 weeks in the parameters tested with mean vine length of 63.4 cm, 133.1 cm, and 181.1 cm, respectively; mean number of leaves/plant of 30.5, 33.5 and 40.4 respectively; mean number of branches/plant of 5.0, 6.0, and 7.0, respectively; and mean weight of fruits of 1315.43 t ha -1 at 75 days after sowing in 2011 and 2012. Based on the findings of this study, it was recommended that farmers in the study area grow Sugar baby variety for increased growth and yield of watermelon.


INTRODUCTION
Watermelon (Citrullus lanatus Thumb) is a member of the cucurbitaceae family. It is believed to have originated from the Kalahari and Sahara deserts in Africa (Jarret et al. 1996). In Nigeria, its cultivation which was originally confined to the drier savannah regions of the North, is now gradually gaining ground in the southern parts of the country. It is a crop with huge economic importance to man. The fresh fruit is relished by many people across the world because it is known not only to be low in calories but highly nutritious, sweet and thirstquenching (Mangila et al. 2007). It is commonly used to make a variety of salads, most notably fruit salad. It is a popular cash crop grown by farmers during summer due to its high returns in investment, especially those residing near the urban areas. Watermelon contains Vitamin C and A in form of the disease fighting beta-carotene. Potassium is also available in it, which is believed to help in the control of blood pressure and possibly prevent stroke (IITA, 2013). *Corresponding author: enujeke@yahoo.com Water melon production in Nigeria is not enough for local demand. Declining soil fertility is one reason for low production. Identification of high yielding varieties best adapted or most suitable to each agro-ecological zone is a must to increase melon production. Iken and Anusa (2004) reported that because of the differences in yield potential of different ecological zones, testing of new crop varieties across the country became an established practice in plant breeding. The report further argued that though high yielding crop varieties can only express their full genetic resources, the yield advantages and special traits of hybrids appear to be sufficiently large enough to attract the attention of farmers. The report also recommended the right choice of site, timely and appropriate establishment, nutrition; disease and pest control, proper harvesting procedure and produce disposal and/or storage. Varietal differences affect or determine the growth and yield of crops. Majanbu et al. (1996) and Sajjan et al. (2002) reported that growth characters of crops such as plant height, vine length, leaf area, number of leaves or branches, and fruit production were influenced by genetic factors of the different varieties. Ibrahim et al. (2000) reported that the differences in growth indices of crops are normally attributed to their genetic constitution. Akinfoesoye et al. (1997); Odeleye and Odeleye (2001) indicated that growth characters, yield and its component differed among crop varieties and therefore suggested that breeders must select most promising combiners in their breeding programmes. Ray and Sinclair (1997) attributed differences between the growth characters of crop genotypes to photosynthetic activity of leaves i.e. internal factors and/or to the differences in high distribution on leaf surface of the crop canopy, leaf arrangement, differences in chlorophyll content, activity of photosynthetic enzymes and differences in stomatal conductance values. Costa and Campos (1990); Gardner et al. (1990) and Zaki et al. (1999) attributed yield differences in crop cultivars to stomata conductance value and to differences between genotypes in partitioning of photosynthetic materials towards economic yield. Clark et al. (1997) reported that the genotypes differences in yield and its components may be due to variations in genetic structure, mineral concentration and potentials to transport photosynthetic materials within plants.
At present, no variety of watermelon has been identified as best adapted or most suitable for Asaba area of Delta State, Nigeria. The objective of this study, therefore, was to assess the growth and yield indices of six different varieties of watermelon with a view to identifying the best adapted or most suitable variety for the study area.

MATERIALS AND METHODS
Field experiments were carried out at the Research and Teaching Farms of Anwai Campus of the Delta State University. The experimental site is located within latitude 06°14' N and longitude 06°49' E of the equator. The experiment was conducted during the 2011/2012 cropping seasons in a typical humid environment that is characterized by a bimodal rainfall pattern with peaks in July and September and an interrupted dry spell in August otherwise called (Harmattan). The annual mean rainfall is about 1,650 mm, the mean annual temperature is 37.3°C and a mean relative humidity of 73.2% (NIMET, 2011). By nature of its geomorphological settings, the study area falls within the classification of Ancient metamorphic crystalline basement complex formation which are more acid than base (Egbuchua, 2007). They are essentially gneisses and pegmatites that gave rise to coarse-textured soils that are deficient in dark ferromagnessium minerals (Egbuchua, 2007).The topography is undulating with pockets of hills and land use is typically based on rain -fed agriculture with root, tuber, spices, pulses and vegetables prominently cultivated. The vegetation is of rainforest origin but has been drastically reduced to derived savanna due to continuous use of the land. The land measured388.85 m 2 (38.5 m x 10.1m). It was ploughed and harrowed using a tractor, and marked out according to the experimental layout. Eighteen plots of 6.0m x 2.7m each were made and composite samples collected from the plots at 0-15 cm depth in order to assess the initial physio-chemical properties of the soil. The composite soil samples collected from the individual plots were air-dried in a room temperature of 27°C for three days, crushed and sieved using 2mm aperture. The parameters evaluated include the particle size distribution by hydrometer method (Gee and Bauder, 1986). The pH was determined using PyeUnican model MK2 pH meter in a 1:2:5 soil/water suspension ratio. Organic carbon was determined by Walkley-Black wet oxidation method (Nelson and Sommers, 1982). Total nitrogen was determined by micro-Kjeldahl distillation technique as described by Breminer and Mulvaney (1982). Available phosphorus was determined by Bray No. 1 method (IITA, 1979). Exchangeable potassium was determined by flame photometer, while cation exchange capacity (CEC) was determined by Amnonium acetate saturation method (Roades, 1982).
The experiment was carried out in a Randomized Complete Block Design (RCBD) with three replicates. Six varieties of watermelon were sown-Sugar baby, Charleston gray, Crimson sweet, Green gold, Jubilee, and Ice box. Poultry manure was uniformly incorporated at the rate of 30 t ha -1 into the soil 2 weeks before planting. The six watermelon associated erosion and leaching in the environment.  Wahua (1999).

Initial soil properties
The data on the initial physico-chemical properties of the soils used for the study is presented in Table 1. The particle size fracture showed that the soils were sandy loam in texture and low in fertility as reflected by the low content of organic matter (15.5 g kg -1 ), and total nitrogen (0.87 g kg -1 ). Soil pH was strongly acid with a mean value of 5.3. The available phosphorus (P) and water soluble, potassium (K) with mean values of 5.35 mg kg -1 and 0.17 cmol kg -1 were seemingly low based on the ratings of FMANR (1996) for the ecological zone. The low fertility status of the soils is a true reflection of most ultisols of humid environment that are strongly weathered of low activity clay mineralogy and high acidity due to intense precipitation with its

Vine length (cm) of six watermelon varieties at different weeks after sowing in 2011 and 2012
The vine length of six watermelon varieties from 4-8 weeks after sowing in 2011 and 2012 is shown in Table 2. Vine length of watermelon gradually increased from 4-8 weeks after sowing. There were significant differences in vine length of the varieties investigated. At 4 weeks after sowing in both years of evaluation, Sugar baby variety had the highest vine length with a mean value of 63.4 cm, while Ice box variety had the lowest vine length with a mean value of 43.2 cm. During the 6 th week of both years, Sugar baby variety also had the highest vine length with a mean value of 133.1 cm, while Ice box variety also had the lowest vine length with mean value of 76.2 cm. The trend did not change during the 8 th week. Sugar baby variety was also superior in vine length with mean value of 181.1 cm, while Ice box variety which had a mean value of 92.3 cm was lowest. The order of superiority in vine length of watermelon based on varieties investigated was Sugar baby > Charleston gray > Crimson sweet > Green gold> Jubilee > Ice box.
The higher mean value of vine length of Sugar baby variety over other watermelon varieties tested may be attributed to differences in its genetic constitution with respect to  Sajjan et al. (2002), who reported that genetic constitution of crop varieties influence their growth characters. It is also in harmony with the findings of Iken and Anusa (2004) who attributed the growth and yield differences among crop varieties to right choice of suitable agro-ecological zone.

Number of leaves/plant of six watermelon varieties at different weeks after sowing in 2011 and 2012
The number of leaves of six varieties of watermelon at different weeks after sowing in 2011and 2012 cropping seasons is shown in  The number of leaves/plant of Sugar baby variety was higher than that of other varieties investigated possibly because Sugar baby had higher photosynthetic activities, better distribution of leaf surface, superior leaf arrangement and chlorophyll content, and more active photosynthetic enzymes. This is in harmony with the findings of Ray and Sinclair (1997) and Enujeke (2013) who attributed the differences between the growth characters of crop varieties to photosynthetic activities of leaves, differences in distribution of leaf surface and crop canopy, leaf arrangement, differences in chlorophyll content and activity of photosynthetic enzymes.

Number of branches/plant of six watermelon varieties at different weeks after sowing in 2011 and 2012
The number of branches/plant of watermelon from 4-8 weeks after sowing in 2011 and 2012 is shown in Table 4. There were significant differences in the number of branches/ ety which had a mean value of 2.0 had the lowest number of branches/plant. During the 6 th week of both years, Sugar baby variety also had the highest number of branches/plant with a mean value of 6.0, while Ice box variety with a mean value of 3.0 had the lowest number of branches/plant. The trend did not change during the 8 th week. Sugar baby variety also had the highest number of branches/ plant with a mean value of 7.0, while Ice box variety which had a mean value of 4.0 had the lowest number of branches/plant. Based on variety, the order of superiority in number of branches/plant of watermelon was Sugar baby > Charleston gray > Crimson sweet > Green gold > Jubilee > Ice box.
Higher number of branches/plant was observed in Sugar baby variety possibly because that particular variety combined its good genetic make-up to exploit the newly found favourable agro-ecological conditions of the study area for rapid growth and branching. This is in harmony with the reports of Akinfoesoye et al. (1997) and Ray and Sinclair (1997) who attributed the growth characters of crop species not only to genetic constitution of the crop but also to the suitable agro-

Weight of fruits (t ha -1 ) of watermelon varieties at 75 days after sowing in 2011 and 2012
The weight of fruits of watermelon at 75 days after sowing in 2011 and 2012 cropping seasons is shown in Table 5. There were significant differences in weight of fruits of the varieties investigated. In both years of evaluation, Sugar baby variety had the highest weight of fruits with a mean value of 1315.43 tha -1 while Ice box variety had the lowest weight of fruits with a mean value of 756.30 t ha -1 .Based on variety, the order of superiority in weight of fruits of watermelon was Sugar baby > Charleston gray > Crimson sweet > Green gold > Jubilee > Ice box.  (1997) who attributed the differences in yield and its components between crop genotypes to variations in genetic structure, mineral concentration and potentials to transport photosynthetic materials within plants.

CONCLUSION
This study was carried out to assess some growth and yield indices of six watermelon varieties in Asaba Area of Delta State, Nigeria. The results obtained showed that Sugar baby variety was superior in the parameters investigated. Based on the findings of the study, it was recommended that farmers in the study area plant Sugar baby variety of watermelon for enhanced growth and yield. The higher weight of fruits observed in Sugar baby variety over other varieties investigated may be attributed to possibility of possession of higher stomatal conductance, better partitioning of photosynthetic materials towards economic yield, better genetic structure and higher potential to transport photosynthetic material within plants. This is in harmony with the reports of Costa and Campos (1990); Gardner et al., (1990) and Zaki et al. (1999) which attributed the yield differences in crop cultivars to stomatal conductance value and to differences in partitioning of photosynthetic materials towards economic yield. It is also in consonance with the findings of Clark et al.