Hasnain Alam, Muhammad Razaq, and Salahuddin

1Department of Biotechnology, International Islamic University, Islamabad

2Department of Silviculture, Northeast Forestry University, Harbin 150040, China

Induced Polyploidy as a Tool for Increasing Tea (Camellia sinensis L.) Production

Hasnain Alam1, Muhammad Razaq2, and Salahuddin2

1Department of Biotechnology, International Islamic University, Islamabad

2Department of Silviculture, Northeast Forestry University, Harbin 150040, China

Tea (Camellia sinensis L.) represents different ploidy levels. In the present paper, we reviewed the recent data on the diploid, aneuploid and polyploid formed their origin and chemically induced polyploidy and predicted it role in teagenetic improvement for better yield. Different polidy levels had different effects on tea physiology. Tetraploid and triploid had more vigour and hardness due to increased size of cells, while triploid could have even more vigours due to increased size of cells and sterilities. Chemically induced polyploidy had been found an important tool for improving plant physiology and production, therefore, induced polyploids should be produced to overcome the problem of low yield and limited rainfall in tea growing areas.

tea, Camellia sinensis, polyploidy

Introduction

Tea (Camellia sinensis (L.) O. Kuntze) belongs to family Theaceae and evergreen tree or shrub that grows up to 10-15 m tall in the wild and 0.6-1.5 m under cultivation. The leaves are short stalked, light green, coriaceous, alternate, elliptic-obovate or lanceolate, with serrate margin, glabrous, or sometimes pubescent beneath, varying in length from 5 to 30 and about 4 cm wide. Mature leaves are brighter green in color, leathery and smooth. Flowers are white, fragrant, 2.5-4 cm in diameter, solitary or in clusters of two to four. They have numerous stamens with yellow anthers and produces brownish-red, one- to four-lobed capsules. Each lobe contains one to three spherical or flattened brown seeds (Ross, 2005).

Commercial tea population contains the following three spices and hybrid between them (Wood and Barua, 1958), China type (Camellia sinensis (L.) O. Kuntze), Assam type (Camellia assamica (Masters) and Cambod type (Camellia assamica sub ssp. Lasiocalyx (planchon.ex.watt) (Mondal et al., 2004).

It is the oldest non-alcoholic caffeine containing beverage in the world. Chinese were the first to use tea as medicinal drink, later as beverage and have been doing so for the past 3 000 years, recorded first in Chinese literature 2 700 years ago (Eden, 1958).

It spread to Japan in 1 000 AD and was introduced in Europe in the middle of 17th century. The British started tea cultivation in the middle of 18th century. The Indians (South East sub-continent) got familiar with tea, due to British rulers in 18th century (Yamanishi, 1991).

Tea is grown in about 30 countries, but consumed worldwide. Although at greatly varying levels, it is the most widely consumed beverage aside from water with a per capita worldwide consumption of approximately0.12 liter per year (Graham, 1992).

Polyploidy

Polyploidy was first discovered in 1907 and was defined as the heritable increase in genome copy number. Polyploidy is the presence of more than two genomes per cell (Lutz, 1907). Polyploidy occurs in nature due to adverse environmental conditions like temperature and it was observed in Vicia and Pisum plants treated with hot water at 40℃ (Randolph, 1932).

Polyploidy is a central feature of plant diversification. Thirty to seventy of angiosperms, including many important crop plants, are estimated to have polyploidy in their lineages (Grant, 1981). The success of polyploid species had been attributed to their ability to colonize a wider range of habitats and to survive better in unstable climates compared with their diploid progenitors, presumably due to increase heterozygosity and flexibility provided by the presence of additional alleles (Lewis, 1980). During polyploidy only cell size increase and without change in the nuclear genome (Song, 1995). In various plant genera, the rate at which polyploids arise and persist is on the order of 0.01 per lineage per million years, roughly 1/10ththe rate of speciation (Meyers and Levin, 2006). With such a high rate of polyploidization per speciation, one would expect a large fraction of plant species to have undergone polyploidization at some points in their evolutionary past. Previous studies had suggested that polyploidy occurred sometime in the past of 57% to 70% of flowering plants, based solely on chromosome numbers among extant species (Goldblatt, 1980; Masterson, 1994).

Polyploidy might cause morphological differences; most important of them is the larger size. Polyploid animals tend to preserve the same body size as diploids in spite of an increase in cell size by reducing the overall numbers of cells and are often morphologically indistinguishable from their diploid progenitors (Bogart, 1980), but polyploid plants more often have larger bodies and thus could be ecologically or reproductively altered compared with diploids (Otto and Whitton, 2000). This process is also used to produce the causes or consequences of such developmental differences for the adaptive potential of polyploids in new environments. Therefore, tolerance of polyploids is generally greater than the diploids and can adapt to a wider range of adverse environmental conditions (Estilai and Shannon, 1993).

Role in Crop Genetic Improvement

Obtaining polyploid plant is widely used to increase the cold resistance and bigger flowering species in ornamental breeding. For medicinal plants, polyploids are usually more valuable because they exhibit increased biomass and content of effective compounds (Gao et al., 1996). Their dark green color is the result of bigger cells and more chlorophyll content. Photosynthesis potential is even higher than diploids (Molin et al., 1982). In the flavonol biosynthetic pathway of Petunia 'Mitchell', polyploid had been found a differential effect of increasing the relative concentration of the major metabolite quercetin-3-sophoroside and decreasing the relative concentration of the minor metabolite quercetin-3, 7-diglucoside (Griesbach and Kamo, 1996). The characteristics of being bigger species increased their commercial interests through increasing agricultural production. Although cell size typically is larger in polyploids, adult size may or may not be altered; as a rough generalization, polyploidization is more likely to increase adult body size in plants and invertebrates than in vertebrates (Gregory and Mable, 2005; Otto and Whitton, 2000). Polyploidy is of interest not only to researchers who have been worked on plants to utilize for vegetative part but also researchers specialized on ornamental plant breeding (Rose and Tobutt, 2000; Vainole and Repo, 2000).

Tea Cytology and Polyploidy

The chromosome number in Camellia sinensis is15 (n=15) (Morinaga et al., 1929) and saprophytic chromosome count is n=30 (Morinaga and Fukushima, 1931) Karasawa (1932) first reported polyploidy in camellia (n=45). Karyo type of Thea sinensis, var. macyophylla was examined that was grown at the Kobotoke Pass, and found that the variety was triploid form having 45 somatic chromosomes (three times as many as the 15 basic chromosome numbers). Extensive investigation in Camellia's polyploidy began in early 1950's (Janaki, 1952).

In South East Asia, out of 100 different clones of verity assamica, all but two plants are found regular diploid and only one C. sasanqa as a hexaploid with 2n=90. Schimawallichi which is common in North East India contains 36 chromosomes with n=18 (Bazbaruah, 1968).

Different aneoploidy chromosome numbers among inter specific and inter generic hybrid may also be found (Ackerman, 1973; Kondo, 1977) like Meng 38 Long Shu Cha had only 28 chromosomes found in China (Li, 1996). Similar results were also observed that Guangdong tea varieties Ruyuan Baimao and Taishan Baiyun which have chromosome number 2n=2x=30 (diploid) but cells with fewer than 30 chromosomes and also a haploid cell was also observed in Ruyuan Baimao (Li et al., 1996). Open pollinated progenies of triploid tea which ranged from diploid aneuploid to tetraploid and rear pentaploid (Chaudhurai, 1979).

Attempts have also been made to create triploids artificially by hybridizing tetraploids with diploids tea in Japan (Osone, 1958), India (Chaudhurai, 1979) and Bangladesh (Rashid et al., 1985), but success was low.

Effect of Polidy Level on Tea

Polyploidy may cause phenotypic variation in the same Camellia species. Triploids, in general, are more vigorous, hardier and tolerant to cold than diploids (Simurah, 1956a). Some triploids and aneoploids had been found to have superior vigour. Morphological and anatomical studies on polyploids revealed a wide range of phenotypic variations and anatomical characteristics like frequency and size of stomata and sclereids (Chaudhurai, 1979). Chromosome number is also correlated to the pollen size in genus Camellia (Ackerman and Kondo, 1980) and to the stomatical guard cells of leaf the mean number/stomata being 21.9±2. 07 for diploids, 32.5±3.15 for triploids and 41.4±4.26 for t tetraploids (Ahmed and Sing, 1993). A simple and effective method to distinguish the polyploidy of tea is to count the chloroplast numbers per guard cell. Chloroplast numbers per guard cell of diploid, triploid and tetraploid were generally equal or a slightly less than 16, 24 and 32, respectively (Dapeng, 1989).

Though Bazbaruah (1971) reported that the quality of the tetraplods and natural triploids were inferior to the diploids but yet the two commercial clones UPASI-1 and TV-29 were triploids which produced acceptable quality of tea. Genetic variations or mutations of diploid tea plants into polyploids are therefore expected to improve the vigour and hardness. Out of different types of tea polyploids produced so far, dry weights, leaf size and rooting ability of triploids were higher by 14% and 109%, respectively, over diploids. Pentapoids and aneuploids were, however, poor rooters and had smaller leaves than diploids, triploids and tetraploids. Consequently breeding might have to be concentrated mostly on the production of vigorous triploids (3n=3x= 45) or perhaps tetraploids (2n=4x=60), providing that the quality aspects do not deteriorate (Singh, 1980).

Induced Polyploidy

Induced polyploidy was first observed in the seedlings grown in close association with disintegrating pieces of the corms of Colchicum autumnale. It was suggested that the sites of colonies of this species might prove fruitful sources of polyploids (Bates, 1939). Polyploidy can be induced by hydrostatic pressure (Lou and Purdom, 1984) and oryzaline (Bouvier et al., 1994).

When young protocorms were treated in liquid culture with 50 mg · L-1colchicine about 50% of the proto corms Phalaenopsi sorchids developed into tetraploids. Lavandula angustifolia (lavender) seed germinated in the presence of colchicine at concentrations of 125 mg · L-1resulted in polyploid plants carrying sports with larger flowers (Nigel et al., 2007). Seeds of V. villosa (hairy vetch) were obtained treated with 0.005% colchicine and 12% tetraploid plants (2n=4x=28) (Tulay and Unal, 2010).

Miscanthus species produced 55% polyploid treated with 313 μmol · L-1colchicine for 18 h (G?owacka et al., 2009a). Miscanthus sinensis and Miscanthus x giganteus by plant colchicine treatment showed 20% efficiency of doubling of the chromosome numbers when treated with 1 252 μmol · L-1colchicine, supplemented with dimethyl sulphoxide for 18 h (G?owacka et al., 2009b).

Treating shoot-tips of Centella asiatica (L.) with colchicine concentrations ranging from 0.050%-0.200% for 12-24 h promoted induction of tetraploids. Tetraploid plants demonstrated significantly longer stomata and a higher stomatal index compared to those of the diploid control plants. Furthermore, a positive trend in both biomass and triterpenoid production was obtained with the tetraploid and mixoploid plants of C. asiatica (Kaensaksiri et al., 2011).

Conclusions

Tea production in Pakistan was very low and its cultivation was not feasible to the farmer due to poor genetic makeup. Pakistan produced about 400-800 kg per acre production that was much lower as compare to other tea producing countries about 3 000 kg per acre. Thus, there was a great need to increase production per unit area with acceptable tea quality. We could increase its production by selecting high yielding bushes. Chemically induced polyploidy could also increase its production 40%-60%. Since tea polyploids are scare under natural conditions and their artificial production had become a necessity. Breeding of the tea polyploids had been advocated by some workers. The aim of tea breeding was to develop high yielding tea per unit area of bush surface with acceptable quality under different agroclimatic conditions. Tea was valued for its vegetative parts (two leaves and a bud) which offered the greatest chance of success to induce polyploidy.

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Received 10 July 2015

Hasnain Alam, E-mail: agrian369@gmail.com