Hydroponic seed germination technique for Rangpur Lime (Citrus Limonia)

S Romen Singh, L Wangchu, Barun Singh and BN Hazarika
Introduction
Citrus is a long lived perennial evergreen tree and it is the world’s leading tree fruit crop due to its adaptability to a wide range of soil, terrain, planting and cultural management. In North East India, Khasi mandarins (Citrus reticulata Blanc.) are generally grown in Assam, Manipur, Tripura, Arunachal Pradesh and Meghalaya. Out of the total production of mandarin production in India, Assam contributes (5%), Manipur, Tripura and Meghalaya (1% Each) contributed in the national mandarin production. Although the area for the citrus growing is increasing rapidly but after production fruits for about 15-20 years, it is facing the citrus decline problem due to tristeza virus (quick decline in citrus) or improper maintenance of soil fertility, irrigation, insect pest and diseases resulting the slow decline in citrus. In order to control such problems, rootstocks viz. Rangpur Lime (Citrus Limonia) and Rough Lemon (Citrus Jambheri) play an important role since Rangpur lime is resistant to citrus tristeza virus (CTV) and  tolerant to drought, high saline and calcareous soil condition and rough Lemon is tolerant to salts and tristeza virus (CTV), citrus exocortices viroid (CEV) (CEV) and citrus xyloporosis viroid. However, seed of such rootstock ae recalcitrant in nature and germination in the field condition is poor and also need regular irrigation to break the dormancy which is laborious and difficult to control weed infestation also. Therefore, in order to evaluate a better seed germination and easy for maintenance a comparison seed sowing of in-situ (Hydroponic) or ex-situ (field) condition, this investigation was conducted.
Seed treatment before sowing
Khasi mandarin is popularly grown in NE India. However, there are certain important khasi mandarin growing belts viz. in Assam (Tinsukia, NC Hills, KarbiAnglong), Tripura (Jampui hill), Meghalaya (East & West Khasi, Ri-Bhoi, Garo Hills, Jaintia Hills), Manipur (Tamenglong, Senapati) and Arunachal Pradesh (East Siang). They are the main producing zones of this fruit crop. Fruits of Rangpur lime were cut into two halves with a sterile knife and seeds were collected over sieves. Extracted seeds were washed in running tap water several times to remove the mucilage. Seeds were dried over filter paper. Its seed being recalcitrant nature seed sowing is done immediately after extraction from the fruit. Extracted seeds were treated with fungicide (Captan fungicide) @ 1% for about 1 hour to protect against fungal attack and kept drying in the shade condition for seed sowing.
Hydroponic seed germination
Seeds are kept inside the BOD for 250C during winter period after keeping the fungicide treated seed in the plastic tray (30x30cm size) which has the capacity around 2200 seeds per tray.
Seed of Rangpur lime (Recalcitrant seed)
Water absorption (Hydration phase) through blotting paper absorption Synthesis and activation of enzyme (convert complex food material into simpler forms)
Cell elongation resulting emergence of radical
Translocation stage (Food material are converted into simpler forms & translocated to the growing points of embryo)
(To be contd)