Introduction

Citrus belongs to the subfamily Aurantioideae of the family Rutaceae, is considered to originate from the North East region of India eastward through the Malay Archipelago, north into China and Japan and south to Australia and also to New Caledonia and New Guinea (Roose et al., 1995). Taxonomy of Citrus fruit are complex, confusing and controversial due to the genetic heterogeneity of the genus, high rate of bud mutation, sexual compatibility between citrus and related genera as well as its polyembryonic nature (Pang et al., 2006). Citrus classification of Swingle and Tanaka are the most commonly accepted. Due to degree difference in giving species status, the number of species recognized also different as in Swingle recognizing only 16 species where as Tanaka recognized 162 species.

Citrus cultivation is repeatedly expanded in the recent past due to its large economic value and now citrus growing regions is  distributed between 400 N and 400 S, up to 1800m altitude in tropics and up to 750 m altitude in the subtropics. The total diversity of Citrus and its wild relative’s world over is spread over 33 genera and 224 species (Swingle and Reece, 1967). In India 27 species of Citrus is being reported (Anonymous, 1950) of which 23 species is available in North East Region of India. The rich wealth of Citrus genetic resources makes India to enjoy a remarkable position in the ‘‘Citrus belt of the world’’. The North-East region of India and the parts of North-Western India is considered the best locations for collecting primitive Citrus germplasm (Singh 1981).

The rich Citrus germplasm available in the NEH region is reflected by 23 species and a subspecies and 68 varieties (Sharma et.al. 2004). Citrus diversity in Manipur and NEH region is favoured by the prevailing agro-climatic and soil-physiographic setup of the region which is further added by easy hybridization amongst different species and genera leading to availability of numerous forms growing in wild and semi-wild forms (Singh et al. 2001).  Citrus plants in the NE region are still growing in deep forests undisturbed by biotic factors. Manipur  and its neighbouring states of NEH region is described by the past explorers as hotspots with respect to Citrus as the rich germplasm available here is threatened by the various biotic and abiotic stresses and  due to farmers preference for other crops of high economic returns.

Even though there is availability of large germplasm and suitable conditions of NER that favours the growth, Citrus industry of the region is in poor shape as its productivity is extremely low. Absence of disease free planting material, plantation of nucellar plantlets, plantation at slopes without taking up measures of nutrient conservation, high rainfall leading to soil acidity, higher incidence of various insects and pests due to high humidity and rainfall conditions are major factors for low productivity of the region.  Development of natural enemies such as parasitoids for controlling the insect and pest population under economic and threshold level is required.(Singh et al. 2001b)

Citrus crops are associated with socio-cultural activities of people of Manipur.  Important Citrus species present in Manipur are Citrus grandis, Citrus jambhiri, Citrus medica, Citrus macroptera, Citrus pseudolimon, Citrus reticulata, Citrus sinensis and other Citrus species which are not properly known (Singh 2004). There is availability of rich germplasm of pumelos in Manipur but it is not properly exploited for its useful traits and industrial purpose. Kachai lime a high yielding land race is cultivated in the whole village of Kachai village of Ukhrul District, Manipur as community garden thereby conserving (Singh et al., 2003). Conserving by doing community gardening must be extended to other citrus species with giving importance to rarely available or endangered ones.

 

 

 

Citrus is valued for the fruit, which is either eaten alone as fresh fruit, processed into juice, pickles or added to dishes and beverages. Citrus is known for good sources of bioactive compounds such as citric acid, flavonoids, phenolics, pectins, limonoids, ascorbic acids etc. having properties of antimicrobial, anti antioxidant, antimutagenic effect, analgesic, anti-inflammatory properties. Bioactive compounds known for treatment of degenerative diseases have wide variation in content among the citrus species (Garg et al. 2001; Dugo and Giacomo 2002). The rich Citrus germplasm can also be exploited for finding new antibiotic compounds that can use as drug for treatment of multi drug tolerant pathogens that become resistant to existing antibiotic compounds.

The gene pool of Citrus requires systematic approach for its collection, conservation and characterization for incorporating the useful agronomical important traits present in this large gene pool in breeding programs. Large gene pool of Citrus is also potential source of important traits to face the unforeseen changes in climate and any further soil degradation, the sudden appearance of insect and virulent forms of pathogens. Developing rootstock suitable to the agro-climatic conditions of NEH region and cultivars of high economic value will be very helpful by using the large gene pool of Citrus through conventional and biotechnological tools. The rich germplasm of Citrus but most of them without exploring properly can give us some view of a potential Citrus based industry in the state of Manipur. In this study, the morphological characters of the different Citrus species can give a valuable information of its shape, size and gives an idea of the diverse gene pool of Citrus available in the state. The information provided also helps in differentiating among various Citrus species easily by seeing based on the phenotypes which are highly heritable and equally expressed in all environments. So far there is very less information of diverse germplasm of Citrus reported from the state. This will certainly very helpful in further exploring the Citrus germplasm for its improvement and conservation measures.