Rice (Oryza sativa (2n = 24) is a monocot plant and belongs to the Poaceae family and Oryzoidea subfamily. It occupies almost one-fifth of the total land area under world cereals. It covers about 148 million hectares annually that is roughly 11 percent of the world-cultivated land.
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It is life for more than half of humanity and in past, it shaped the cultures, diets, and economies of billions of people in the world (Farooq et al., 2009). More than 90 percent of the world’s rice is grown and consumed in Asia where 60 percent of the world population lives. The world major rice consuming countries are China, India, Egypt, Indonesia, Malaysia, Bangladesh, Vietnam, Thailand, Myanmar, Philippines, Japan, Brazil, South Korea and USA that consume 135, 85, 39, 37, 26, 18, 10, 10, 9.7, 8.7, 8.1, 5.0 and 3.9 million metric ton, respectively (Meng et al., 2005; USDA, 2003-04).
Rice is a major source of macro and micronutrients for human being. It feeds more than two billion people worldwide and is the number one staple food in Asia. It provides over 21 percent of the calorific needs of the world’s population and up to 76 percent of the calorific intake of the population of South East (SE) Asia (Fitzgerald et al., 2009). It is mostly consumed as a polished grain, which usually lacks its nutritional components such as minerals and vitamins 41 P. Lucca et al., Genetic engineering approaches to enrich rice with iron and vitamin A, Physiol. Plant. 126 (2006), pp. 291-303. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (7)( Lucca et al., 2006). Since the advent of molecular techniques, recently genetically modified rice verities have been developed, which contains more nutritional aspects like minerals and vitamins in endosperm (Vasconcelos et al., 2003; Paine et al., 2005; Fitzgerald et al., 2009). The major value-added nutritional protein constituents of the rice.
In Pakistan, besides its importance as a food crop, rice is the second important component of daily diet of bulk of the population after wheat. About 23% of the total foreign exchange earnings is shared by rice and thus called as ‘Golden Grain of Pakistan’ (Shah et al., 1999). Around one third of total production is annually exported and two third is locally consumed to meet food needs. Rice is also used in dishes for special occasions (Sagar et al., 1988). Pakistan is the third largest rice exporting country. In Pakistan, rice occupies about 10% of the total cultivated area, accounts for 6.1% of value added in agriculture and 1.3% in gross domestic product. Production of rice during 2007-08 was estimated at 5,540 thousand tones, 10.4% higher than last year with 6.1% increase in yield per hectare (Anonymous, 2006).
Area, production and yield of rice for the last 5 years are shown in Fig. 1. Varieties of basmati rice, sub-species of indica, are economically important due to the high quality of the grain and constitute an important source of revenue for two major rice-growing countries in Asia (Pakistan and India). The international market for basmati rice has always been higher than that of the moderate varieties. Pakistan’s annual rice export stands at about 2.5 million tons, which earn a total of 513.0 million dollars for the country (Anonymous, 1998). During the year 2005-2006 rice export was about one billion US$ (Bashir et al., 2007).
Depending upon the irrigation water availability, rice can be grown in any part of the country from sea level up to 2500m height. Pakistan has a climate and a potential in soil that permits the expectations of a most bright future for the productions of rice. Considering temperature difference, optimum sowing seasons and the varietals performance, rice growing areas can be divided in four ecological zones (Salim et al., 2003; Table-1.2).
Rice is grown in all four provinces of Pakistan. However, the acreage under rice varies greatly from one province to another. The Punjab and Sindh are the major rice growing provinces with about 59% and 33%, respectively of the total rice in the country. The remaining 5% of the area is planted in Baulochistan and 3% in NWFP (Bhatti and Anwar, 1994). Despite the fact that it’s cultivated area is far smaller than wheat (more than 7.24 million), it has a great impact on national economy due to two reasons. Firstly, rice is the only crop which can be grown successfully in vast chunks of salt-ridden and water-logged areas where it facilitates not only the reclamation of land for the cultivation of other crops but also provide food.
Secondly, superior quality basmati has a consistently increasing demand in the foreign countries. Consequently, there is a great scope for augmenting the foreign exchange earning by exporting it in bigger quantity. In view of these facts, it is highly desirable to increase the production and improve the quality of rice the quality is particularly more important from the “trade view point, as it is instrument entail in increasing and then sustaining the demand in the foreign market in competition with other rising exporting countries. There in no denying the fact that purity is the very sole of quality. The impurities not only restrict the export trade, but also inflict losses to the growers, millers and the consumers alike. Therefore, these should possibly be minimized (Saleem et al., 2003).
More than 20 rice varieties have been released for general cultivation in Pakistan (Bashir et al., 2007). A general description of agronomical and physiochemical characteristics of these varieties.
There are thousands of rice varieties and landraces, which differ with respect to plant and grain characteristics. Of these, aromatic (Basmati) rice constitutes a small but special group that is regarded as best in grain quality, superior aroma and usually used for special dish preparation (Khush and dela Cruz, 2001). Quality of rice may be considered from the view point of size, shape and appearance of grain, milling quality and cooking properties (Dela Cruz and Khush, 2000). Pakistan is famous for the production and export of Basmati rice. The origin of the word “Basmati” can be trade to the word “Basmati” meaning earth recognized by its fragrance. The Hindi word “Bas” was derived from the Pakrit word “BAS” and has a Sanskrit root” Vassy” (Aroma), while “Mati” originated from “Mayup” (ingrained from the origin). In common usage Vas is pronounced as “Bas” and while combining “Bas and Mayup”, the later changed to “Mati’ thus the word Basmati (Ahuja et al., 1995; Gupta, 1995).
The fragrance of basmati rice is most closely associated with the presence of 2-acetyl-1-pyrroline (Buttery et al., 1983; Lorieux et al., 1996; Widjaja et al., 1996; Yoshihashi et al., 2002). Although many other compounds are also found in the headspace of fragrant rice varieties (Widjaja et al., 1996) possibly due to secondary effects related to the genetic background of the rice variety, 2-acetyl-1-pyrroline is widely known to be the main cause of the distinctive basmati and jasmine fragrance. The desirability of fragrance has resulted in strong human preference and selection for this trait. Non-fragrant rice varieties contain very low levels of 2-acetyl-1-pyrroline, while the levels in fragrant genotypes are much higher (Widjaja et al., 1996).
Basmati rice occupies a prime position in the Indian subcontinent and is becoming increasingly popular in Middle East, Europe, USA and even in non-traditional rice growing countries such as Australia (Bhasin, 2000). High-quality, traditional Basmati rice varieties command premium prices, more than three times that of non-Bamati rices in the world market due to its exquisite aroma, superfine grain characteristics and excellent cooking (extra elongation, soft and flaky texture) qualities (Bhasin, 2000; Singh et al., 2000a; Khush and dela Cruz, 2002). Basmati rice traditionally grown in the Himalayan foothills regions of Pakistan and India, and the name is traditionally associated with this region. Basmati rice is the result of centuries of selection and cultivation by farmers (Khush, 2000).
Cultivation of basmati rice in mainly confined to the Kallar tract (Gujranwala, Sheikhupura and Sialkot districts) of Punjab province. Basmati rice always fetch a higher price in the domestic as well as in the international market due to their peculiar quality features such as pleasant aroma, fine grain, extreme grain elongation (7.6mm long) and soft texture on cooking. In spite of hard competition from India, Thailand and the United States, Pakistan enjoys a good position in the global trade of aromatic rice and every year earns a lot of foreign exchange (Akram and Sagar, 1997).
Diversity among organisms is a result of variations in DNA sequences and of environmental effects. The diversity in crop varieties is essential for agricultural development for increasing food production, poverty alleviation and promoting economic growth. The available diversity in the germplasm also serves as an insurance against unknown future needs and conditions, thereby contributing to the stability of farming systems at local, national and global levels (Singh et al, 2000). In crop improvement program, genetic variability for agronomic traits as well as quality traits in almost all the crops is important, since this component is transmitted to the next generation (Singh, 1996). Study of genetic divergence among the plant materials is a vital tool to the plant breeders for an efficient choice of parents for plant improvement. Genetically diverse parents are likely to contribute desirable segregants and/or to produce high heterotic crosses. Parents identified on the basis of divergence for any breeding program would be more promising (Arunachalam, 1981). In early 1970’s, public authorities felt the need that genetic resources should be collected, maintained and conserved, especial focus was on important food crops e.g wheat, rice, barley etc (Hawkes 1983; Bellon et al., 1998; Barry et al., 2007). This was the first official attempt to preserve genetic diversity. Currently different genetic diversity assessment methods including morphological, biochemical and molecular markers are available.
Morphological evaluation is the oldest and considered as the first hand tool for detection of genetic variation in germplasm (Smith and Smith, 1989). It is cheap and convenient. It requires not any in depth knowledge at genomic or proteomic level. However, morphological markers are relatively less effective for genetic diversity analysis due to sensitivity to environmental influences and developmental stage of the plant (Werlemark et al., 1999). It takes long time, requires seasonal changes and quite laborious. The genetic variability for some of the traits needed for high yield performance and stress tolerance is limited in cultivated germplasm. This is because a small core of adapted progenitors has been used repeatedly in rice breeding programs such that the genetic base of rice has become narrow (Moncada et al. 2001; Hargrove et al. 1980; Dilday 1990). Introgression of genes from other rice species can provide genetic variation to improve rice and meet the challenges affecting rice production. Morphological traits including both qualitative and quantitative ones are used to evaluate genetic relationship among genotypes (Goodman 1972; Bajracharya et al., 2006). Fida et al. (1995) reported the evaluation of elite rice genotypes for agronomic traits during 1992 at NARC, Islamabad. All the genotypes possessed similar grain quality. Agronomic evaluation was used for screening of lines with desired performance by Akram et al. (1995), in field leading to the identification of varieties possessing longer and fine grains as donors for utilization in breeding programmes aimed for the improvement of grain length in Basmati rice. Iqbal et al. (2001) morphologically evaluated selected landraces for paddy yield and other important agronomic traits as a propose to select parents for hybridization program. All the landraces possessed some desirable agronomic traits so these proved effective in rice breeding programmes. Koutroubas et al. (2004) described variation in grain quality traits among some European rice lines. They concluded that these lines could be used as parents for introgression of desired traits into different rice cultivars grown in Europe. They also suggested that the interrelations among grain quality traits found in these lines could be useful to study the relationship among their grain quality components and for improving selection criteria. Nabeela et al. (2004) evaluated fifteen agronomical important traits in landrace genotypes of rice collected from various parts of Pakistan. A significant amount of genetic variation was displayed for most of the traits examined. The coefficient of variation was more than 10% for all the characters with exception of grain length. Seven accessions with best performance for individual character were identified, by exploiting their genetic potential. These genotypes can have a beneficial use in the breeding programs. Nepali rice landrace diversity was evaluated by Bajracharya et al. (2005) by using morphological traits as one of the parameter for selection. The genotypes varied only for few quantitative traits controlled by major genes; husk color, seed coat and panicle traits. Agronomic characterization also helped to decide which traits need to be improved for further crop improvements. Zaman et al. (2005) studied fifteen different rice varieties which showed that the different morphological characteristics such as the yield, tiller number per hill and filled grains per panicle did not contribute towards the total divergence. This suggested that the breeding improvement of these morphological characteristics have the little possibility. Little phenotypic variation at farm level was observed in Vietnamese rice by Fukuoka et al. 2006, which was considered to be the result of genetic drift and selection by the farmers, on farm conservation of the landraces of rice is considered to be under a force to decrease phenotypic diversity. Different phenotypic profiles contribute to the conservation of regional genetic diversity of the landraces of rice. Veasey and colleagues (2008) investigated the genetic variability among different rice species from South in a greenhouse experiment. They showed a significant difference (p
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