INTRA-SPECIES VARIATION IN NUCLEAR DNA CONTENT OF TURMERIC VARIETY OF NORTH EAST INDIA
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This chapter gives information of the nuclear DNA content variation of the cultivated turmeric varieties.
CHAPTER 5C
INTRA-SPECIES VARIATION IN NUCLEAR DNA CONTENT OF TURMERIC VARIETY OF NORTH EAST INDIA
5C.1 Introduction
Turmeric (C. longa L. Zingiberaceae), is widely cultivated and extremely marketable spice in Asian country, having distinctive chemical and physical properties. The plant has wide industrial applications, like manufacture of canned beverages, baked product, farm product, ice cream, yogurt, yellow cakes, fruit crush, biscuits, popcorn color, sweets, cake icings, cereals, sauces, gelatins, and curry powders etc. Turmeric is employed as an additive, preservative and coloring agent in Asian countries (Antunes and Araujo 2000;
Cecílio-Filho et al 2000).In addition, turmeric has a wide range of medicinal activities, with recent findings that shows that curcumin, the yellow color pigment of turmeric, may be a powerful inhibitor, anti-parasitic, antispasmodic agent and anti-inflammatory compound, which can inhibit carcinogenesis (Araujo & Leon 2001; Ravindran 2007).Indian enjoys monopoly in turmeric production and export. Owing to its ever- increasing demand in food and pharmaceutical industries, there is an urgent need to increase the productivity of turmeric. However, attainment of increase in productivity, data concerning the crop’s genetic diversity is crucial for breeding programs (Nass 2001). Moreover, McMurphy & Rayburn (1991) noted that the more intensive the breeding programme involved in the development of a cultivar, the lower the association between DNA variability and agronomic characteristics.
While at first this looks to be of very little consequence, it should be realized that nuclear DNA content variation in crop species (or their primitive relatives) is being lost because of the slender variety of nucleotides within the breeding pool. This nucleotypic variation may play a vital role within the adaptation of crop species to dynamical environmental conditions. It's been documented that the eukaryotic DNA will adapt to
numerous stresses by DNA amplification in each animal and plant cells. Sequence amplification is purported to be a conducive mechanism to the fluidity of the organism genome (Bachmann 1993). Additionally, if a breeding concept induced unwanted DNA content variation into a plant choice, this variability may well beharmful to the breeding programme. Such surprising DNA content variation has been seen throughout the assembly of F" hybrid maize (Rayburn et al 1993). The nuclear DNA content variation of 15.1 % has already been documented in Indian accessions of turmeric (Skornickova et al 2007). The cytophotometric estimation of nuclear DNA content of 17 varieties of C.
longa ranged from 4.30 to 8.84 pg (Nayak et al 2006). In addition, flow-cytometric nuclear DNA amounts for16 taxa (including the above-mentioned species and one undetermined sample) from Bangladesh is given in the unpublished PhD thesis of Islam (2004). The genome size variation of 1.07 fold has been documented for C. zedoaria from the wild accessions of Bangladesh. In this current study, the nuclear DNA content variation in cultivated variety of turmeric has been studied.
5C.2 Materials and methods 5C.2.1 Plant materials
For details section 4A.2.1 can be referred.
5C.2.2 Standards for flow cytometric estimation of nuclear DNA content
Seeds of O. sativa ‘IR36’ (2C = 1.01 pg, Price and Johnston 1996), S. lycopersicum cv.
Stupicke (2C = 1.96 pg, Dolezel et al 1992), were used as the standards for flow cytometric estimation of nuclear DNA content in the turmeric germplasm of NE India.
5C.2.3 Sample preparation and flow cytometric estimation
The details of the sample preparations and flow cytometric estimation were discussed in section 5A.2.3 and section 5A.2.8, respectively.
5C.3 Results and discussion
5C.3.1 Inter-varietal variation in nuclear DNA content
The nuclear DNA content of the 19 cultivated turmeric varieties against one internal standards (O. sativa) is shown in Figure 5C.1 and presented in tabular format (Table 5C.1). There were significant differences (p < 0.05) in nuclear DNA content. Eleven groupings of turmeric varieties with significant differences in nuclear DNA content were identified against O. sativa as an internal standard including four different ploidy levels (5x, 6x, 7x and 9x).
The DNA content of cultivated variety of turmeric2 & 6 were significantly higher than that of any other cultivated varieties (group j in Table 5C.1) (2C -value = 2.76-2.81 pg, p- value = 0.116). Considering 1-C value of turmeric to be 0.30 (Skornickova et al 2007), the ploidy level of the germplasm 2 and 6 is 9x. These nona-ploid varieties were followed by low-nonaploid groups of statistically similar nuclear DNA content [group i (5 &13): 2C-value = 2.60-2.63 pg, p-value = 0.961; group h (5 & 10):2C = 2.56-2.60, pg, p-value = 0.391; and g (3 & 10): 2C-value = 2.54-2.56 pg, p-value = 0.989] (Table 5C.1). So, the percentage of nonaploids in the studied turmeric cultivars is 30.0%. This is followed by the heptaploid group of solitary cultivated turmeric variety having 2C value of 2.20 pg found in Assam (Cultivated variety 1) providing 5 % coverage of the studied cultivated varieties. The next statistically similar and the largest groupings (58 % of the studied varieties) was of hexaploid varieties [group e (7, 8, 9, 16, 17 and 19): 2C- value = 1.82 - 1.87 pg, p-value = 0.182; group d (8, 9, 11, 12, 16, 17, 18 and 19) 2C- value = 1.80 - 1.86 pg, p-value = 0.116; group c (9,11,12,14, 16, 17, 18 and 19) 2C-value
= 1.80 - 1.84 pg, p-value = 0.672)]. The next statistical solitary group was observed to be the turmeric variety 4 having 2C-value of 1.60 pg with low hexaploidy status. One variety from Meghalaya (variety no 15 with 2C= 1.36 pg) was found to be having pentaploidy status (5x).
Fig 5C.1 Histogram of fluorescence intensity of the nuclear DNA content of 19 turmeric variety estimated by internal standardization with O. sativa ‘IR36’. A. Turmeric variety of Assam (12951, 12953, 12955, 12950, 12956); B. Arunachal Pradesh (12952, 12940, 12949, 12947, 122931); C. Manipur (12957, 12978, 12989,12939, 12910); D. Meghalaya (12980, 12944, 12990, 12985)
Among the all studied turmeric varieties, the highest nuclear DNA content was found to be 2.83 pg and the lowest nuclear DNA content was found to be 1.35 pg with the fold variation of 2.10. The mean nuclear DNA content of turmeric was observed to be 2.08 pg. Positive correlation (r = 0.63) was observed between the average nuclear DNA content of each variety and Shannon’s information index (Refer to Table 4A.3), implying genetic diversity increases with increase in nuclear DNA content. Significant variation of 4C DNA content was recorded at the intra-specific level with values ranging from 4.30 to 8.84 pg. The differential DNA content observed among 17 different cultivars of C. longa comprising same (2n = 48) chromosome number could be attributed to the loss or addition of highly repetitive sequences in the genome (Nayak et al 2006). Skornickova et al (2007) showed the nonaploids (9x) with 15.1% intra-specific variation for their turmeric variety analysed from India. If polyploids are the reasons for the production of turmeric, the polyploids (9x is 60%) studied in the turmeric production were less compared to hexaploids. This is one of the predicted reasons of low productivity of the north eastern turmeric varieties.
India is responsible for around 90% of turmeric production worldwideand this species has been widely used in India since Vedic times. Perhaps the variation may have adaptive value, as previously documented in another crop, Zea mays (Rayburn & Auger 1990). The reasons for intra-specific genome size variation in Curcuma remain unknown.
Aneuploidy or presence of B-chromosomes may lead to heterogeneity in nuclear DNA amount, but this explanation seems rather unlikely as only euploid numbers were revealed and more importantly, two accessions of C. longa with more than 9% genome size variation possessed the same number of chromosomes (Skornickova et al 2007).
Plausibly, intra-specific variation may be related to a long-term cultivation and targeted selection of desirable genotypes in several Curcuma species (Skornickova et al 2007).
Table 5C.1 Variation in nuclear DNA content as estimated using flow cytometry
The super-scripts of the same letters have statistically similar nuclear DNA content (p=0.05)
5C.3.2 Intra- varietal variation in nuclear DNA content
The highest nuclear DNA content of the turmeric variety (2) of Assam was found to be 2.74 pg (9x) and the lowest nuclear DNA content of the same (3) was found to be 1.58 (6x) pg with the fold variation of 1.36. Among the five varieties screened from Assam the 9x ploidy stature was observed for three cases and the rest varieties were 6x and 7x.
The highest nuclear DNA content of Arunachal varieties of turmeric (6) was found to be 2.83 pg (9x) and the lowest nuclear DNA content (9) of the same was found
Population Code 2C-DNA content (pg)
CV Ploidy status Minimum–
Maximum (range)
(2C)
Fold variation
Assam
1 2.21f± 0.018 3.21 7x
1.58-2.74 1.73
2 2.74j± 0.002 2.81 9x
3 2.56g± 0.010 2.83 9x
4 1.58b± 0.032 2.47 6x
5 2.59h,i± 0.021 3.00 9x
Arunachal
6 2.83j± 0.021 2.86 9x
1.84-2.83 1.73
7 1.87e± 0.012 3.73 6x
8 1.87d,e± 0.009 3.29 6x
9 1.84c,d,e± 0.011 3.29 6x
10 2.56g,h±0.018 3.06 9x
Manipur
11 1.83c,d± 0.021 2.76 6x
1.35-2.63
1.95
12 1.79c,d±0.018 2.98 6x
13 2.63i± 0.021 3.05 9x
14 1.79c±0.018 3.14 6x
15 1.35a ± 0.021 2.23 5x
Meghalaya
16 1.86c,d,e±0.002 2.96 6x
1.83-1.85
1.01
17 1.84c,d,e±0.018 3.39 6x
18 1.83c,d± 0.012 4.02 6x
19 1.83c,d,e±0.018 2.80 6x
Mean 2.08 ± 0.43 1.35 – 2.83 2.10
to be 1.84 pg (6x) with the fold variation of 1.73 fold. Two nonaploids and three hexaploids varieties were observed among the studied species of the state.
The highest and the lowest nuclear DNA content observed for Manipur varieties was 2.63 pg and 1.35 pg, respectively. The fold variation was found to be 1.95. One nonaploid, three hexaploid varieties and one pentaploid variety was observed.
The fold variation of nuclear DNA content was low in Meghalaya varieties of turmeric. It is 1.01 fold. The maximum nuclear DNA content was observed to be 1.96 pg and the minimum nuclear DNA content was found to be 1.83 pg. Skornickova et al (2007) observed that for the genus Curcuma, most of the varieties are hexaploid in nature. This allows them to hypothesize that these hexaploids have played a key role in the evolution of polyploidy in Indian Curcuma spp. Nonaploid cytotypes probably originated by a fusion of reduced and unreduced gametes of hexaploids, either within or between species, giving rise to auto - or allopolyploids (Skornickova et al 2007).
Having the lowest fold variation of nuclear DNA content for Meghalaya variety could point to the temperature of the hilly states and over exploitation of the varieties for turmeric production. The fold variation in nuclear DNA content was found to be minimum for varieties occurring in Manipur.
5C.4 Conclusion
It was observed in current study that an overall 2.10 fold variation exist among the turmeric (C. longa) varieties. Turmeric varieties of state Meghalaya was less varying compared to the rest of the varieties. The ploidy status of the studied turmeric varieties varied from 5x to 9x type. This is the first study on the nuclear DNA content of turmeric varieties of NE India. The study will help in assessing the ploidy status of the turmeric varieties. The correlation study of the productivity and the ploidy status shall further help in devising the strategy whether ploidy screening could be potential marker for crop productivity.
NUCLEAR DNA CONTENT ESTIMATION OF ZINGIBEROIDEAE .
This chapter describes the nuclear DNA content estimation of Zingiberoideae species by internal standardisation.