858. Morphological Dissimilarity Between Tetrapoloid and Diploid Watermelon (Citrullus lanatus Thunb.) Ishtiaq Ahmad, Tanveer Hussain, Muhammad Nafees, ...
World Applied Sciences Journal 21 (6): 858-861, 2013 ISSN 1818-4952 © IDOSI Publications, 2013 DOI: 10.5829/idosi.wasj.2013.21.6.169
Morphological Dissimilarity Between Tetrapoloid and Diploid Watermelon (Citrullus lanatus Thunb.) Ishtiaq Ahmad, 1Tanveer Hussain, 1Muhammad Nafees, 2Maryam, Moazam Jamil, 1Irfan Ashraf, 1Muhammad Fakhar-u-Zaman Akhtar, 1 Muhammad Iqbal, 1Muhammad Rafay, 1Tahira Ruby and 1Liaqat Ali 1
1
University College of Agriculture and Environmental Sciences, Islamia University of Bahawlpur, Pakistan 2 Institute of Horticultural Sciences, University of Agriculture Faisalabad, Pakistan 1
Abstract: Polyploidy plays an important role in plant morphology and an important tool to create genetic and morphological variation. The idea of this investigation was to differentiate the tetrapoloid and diploid morphologically. Three lines tetrapoloids were used to differentiate diploid from triploids on morphological basis. In present study morphological parameters observed include chloroplast count, pollen colpi, seedling mortality (%), fruit set (%), fruit weight (kg), TSS, rind thickness and number of seed per fruit. Chloroplast count per guard cell was higher (9.0) in tetrapoloid-2, rind thickness was also more (14.7 mm) while fruit set (%) was more in diploids with 94.3 (%). Key words: Watermelon
Pollen colpi
Chloroplast
Morphology
INTRODUCTION
reported for many plant species [6] and has potential application to establish a large number of new watermelon tetraploid breeding lines [7]. The identification of tetraploid plants may require morphological, cytological and even molecular techniques. Chromosome counting is the usual method to determine ploidy but this is difficult in watermelon due to small chromosome size. The method is not practical for non-dividing cells in differentiated tissues, such as leaves [8]. Flow cytometry is a rapid and exact method for estimating nuclear DNA content [9]. It can be efficiently used for ploidy determination in plants growing in the field and in the greenhouse and has already been well established in watermelon [10, 11]. induced tetraploid plants of watermelon are identified by counting the number of chloroplasts per guard cell pair of fully expanded leaves [12]. Studies have shown that diploid and tetraploid watermelon plants possess variable number of chloroplasts in guard cells of stomata. Ploidy can be estimated by examining plant morphological traits such as leaf and flower size Confirmation of tetraploidy can be obtained by comparing the size of the pollen grains (about 1.44 X larger than diploid pollen) and the number of colpi (4 versus 3) [13].
Seedlessness is an important and desirable breeding goal in horticultural crops. In watermelon polyploidy is utilized to produce seedless fruits. Most watermelon cultivars are diploid and produce fruit that have a striped/green rind, red flesh with small black seeds and weigh 20-30 lbs at maturity. Tetraploid breeding lines have been created for use in producing triploid hybrids [1]. Triploid watermelons were first developed in the early 1950’s at Kyoto University in Japan [2]. Difficulties with seed germination have retarded the expansion of tetraploid cultivation. High seed cost has generally attributed to difficulties in obtaining a sufficient number of tetraploid plants as they exhibit low fertility and generally require at least 8-10 years of self pollination before enough plants are obtained for commercial triploid seed production [3]. Traditionally, tetraploid parents have been obtained by treating newly emerged diploid seedlings with colchicine [4]. However, it produces a limited number of tetraploids and mostly chimeric seedlings that possess vines of mixed ploidy [5]. The production of polyploid regenerants from tissue culture colchiploids has been
Corresponding Author: Ishtiaq Ahmad, University College of Agriculture and Environmental Sciences, Islamia University of Bahawlpur, Pakistan.
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World Appl. Sci. J., 21 (6): 858-861, 2013
MATERIALS AND METHODS
The results regarding pollen colpi showed significant differences among terapoloid and diploids the mean values ranged as 3.0-3.9 (Table 1). The highest mean pollen colpi per pollen grain was found in tetrapoloid-2 (3.9) while minimum pollen colpi was observed in diploid (3.0). Results revealed that number of pollen colpi/pollen grain increased with increase in ploidy level. Our results are also in line with the findings of [13] who observed 3 vs 4 pollen colpi in tetraploid and diploid plants, respectively. Maximum number of fruit set was recorded in diploid (94.3%) that was statistically different from all tetrpoloids. Our findings are also supported by the work of [15] who reported low fertility in autotetraploid watermelon.
The present research project was planned to study characterization of tetraploid plants of watermelon. Seeds of three different tetraploid watermelon cultivars were soaked in water for 3 hours. The seeds were spread uniformly in a tray on wet towel and covered with aluminum foil. The tray was shifted to an incubator at 30°C for 54 hours for seed germination. The plastic cups (8x6 inches) were filled with compost and saw dust 50:50 (%) proportion and watered with the help of shower before 8 hours of seeds plantation. After the sowing of germinated seeds, the plastic cups were covered with polythene sheet until seedlings emergence. Following observations were recorded on these seedlings. Mortality rate (%) in tetraploid watermelon seedlings, chloroplast count/stomata guard cell, pollen colpi per pollen grain, fruit set (%), fruit analysis (fruit weight, total soluble solids and rind thickness) and number of seeds/fruit. The collected data was analyzed using LSD test at 5% level of significance for comparing the difference among three strains mean.
Fruit Weight, TSS and Rind Thickness: The statistical analysis of data regarding the fruit weight (kg) revealed significant differences among tetrapoloid and diploids as shown in Table 2. The highest fruit weight was noted (3.3 kg) in tetraploid-1 followed by tetrapoloid-2 (2.2 kg) while lowest fruit weight was recorded in diploids (1.7 kg). Results of [16] were also similar who recorded similar size of fruits in tetraploid and diploids. The mean values for TSS (Total Soluble Solids) of watermelon fruits are given in Table 2. It was observed that the tetrepoloid-2 (11.4%) was at top followed by tetrepoloid-1 (9.8%) while in diploid had lowest TSS. The current study explains that tetraploids had higher TSS. These results collaborate with the findings of [17] who observed higher total sugar content in tetrapoloid than diploid fruits. The rind thickness was high in tetrapoloid-2 (14.7 mm). The results indicated that the highest rind thickness was in tetrapoloids. Our results are in accordance with the findings of [18].
RESULTS AND DISCUSSION Mortality Rate, Chloroplast Count and Pollen Colpi: An over view of Table 1 shows that the highest mortality rate was recorded in tetrapoloid-3 (26.3%) followed by tetrapoloid-2 (20.0) while lowest mortality rate was observed in diploid (5.0%). Our results were found in correlation with that of [14] who reported that colchicine had a negative effect on the regeneration of plants. The chloroplast number ranged 6.0-9.0 in one side of stomata guard cell, highest chloroplast count was observed in tetrapoloid-2 (9.0). The minimum value for the chloroplast count was recorded in diploid (6.0). It is clear from the results that the tetraploids had more chloroplast count per stomata guard cell as compared to diploid leaves. Our results are consistent with the findings of [12] who observed the high number of chloroplast per guard cell pair of stomata.
Number of Seed Set, Developed Seeds and Shriveled Seeds /Fruit: Mean values for the total number of developed seeds was minimum in Tetraploid-3 (133.3) while maximum number of developed seeds/ fruit (464.7). The number of shriveled seeds was maximum in Tetraploid-2 while minimum number of shriveled seeds
Table 1: Difference between tetrapolod and diploid on Chloroplast count, Pollen colpi and Seedling mortality (%) Ploidy level
Chloroplast count
Pollen colpi
Tetraploid 1
7.8 B
3.7 AB
14.0 B
66.0 B
Tetraploid 2
9.0 A
3.9 A
20.0 AB
54.7 B
Tetraploid 3
8.0 AB
3.3 B
26.3 A
55.3 B
Diploid
6.0 C
3.0 C
5.0 C
94.3A
859
Seedling mortality (%)
Fruit set (%)
World Appl. Sci. J., 21 (6): 858-861, 2013
5.
Table 2: Difference between tetrapolod and diploid on fruit weight, TSS and rind thickness in watermelon Ploidy level
Fruit weight
TSS
Rind thickness
Tetraploid 1 Tetraploid 2 Tetraploid 3 Diploid
3.3 A 2.2 AB 2.1 B 1.7 B
9.8 B 11.4 A 9.5 B 8.0 C
12.0 BC 14.7 A 13.0 B 10.7 C
6.
Table 3: Difference between tetrapolod and diploid on Seed Set, Developed seed and shriveled seeds.
Polidy level
Mean (no. seed /fruit) --------------------------------------------------------------Seed Set / Developed shriveled Fruit seed /Fruit seeds /Fruit
Tetraploid 1 Tetraploid 2 Tetraploid 3 Diploid
323.0 B 289.3 BC 233.0 C 486.7 A
184.7 A 140.3 B 133.3 B 464.7 AB
7.
8.
129.3 AB 145.0 A 99.7 B 22.0 C
9.
was observed in diploids. These results are in line with [19] who found that tetraploid water partially sterile and generally produce more undeveloped (shriveled) seeds compared to their diploid varieties [20].
10.
11.
CONCLUSIONS In this study, tatraploids plants differed from diploid plants in growth rate and morphology with broader leaves, more number of chloroplast, bigger flowers and larger seeds. In conclusion, application of colchicine to diploid seeds of watermelon to induce polyploids particularly tetraploids. The higher concentration of colchicine is lethal for plants and is of no use for induction of polyploids. The suitable concentration of colchicine for the induction was 0.4% for tetraploids.
12.
13. 14.
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