Int.J.Curr.Microbiol.App.Sci (2019) 8(2): 884-889 884 Original Research Article https://doi.org/10.20546/ijcmas.2019.802.100 Effect of Hardening Media and Different Cross Combinations on Leaf Gas Exchange Parameters of in vitro Cultured Citrus Plantlets Anjali Soni 1 *, A.K. Dubey 1 , R.M. Sharma 1 , O.P. Awasthi 1 and Bharadwaj Chellapilla 2 1 Division of Fruits and Horticultural Technology, 2 Division of Genetics, ICAR- Indian Agricultural Research Institute, New Delhi- 110012, India *Corresponding author ABSTRACT Introduction One of the major impediments to the success of micropropagation is the low survival rates and poor growth of tissue culture derived plantlets either during the acclimatization phase or at transfer to field conditions (Moraes et al., 2004). Therefore, commercial utilization of micropropagation requires a successful acclimatization (Deccetti et al., 2008; Dobránszki et al., 2010). In the whole process of successful plantlet transfer from in vitro to ex vitro conditions is difficult because of significant environmental differences (Hazarika, 2003). Pospíšilová et al., 2007 reported that plantlets raisedin vitro are exposed to diminished gas exchange, high air humidity, low irradiance, and use of sugar as energy source, which could cause inhibition of photosynthesis, abnormal stomatal structure, and generally could lead to high plantlet mortality during acclimatization. Therefore, acclimatization to new environmental conditions, such as increased irradiance and low air humidity, requires that plants undergo physical and anatomical International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 8 Number 02 (2019) Journal homepage: http://www.ijcmas.com The present investigation entitled as “Effect of hardening media and different cross combinations on physiological parameters of in vitro cultured citrus plantlets” was carried out in the Division of Fruits and Horticultural Technology, ICAR-IARI, New Delhi. The experiment consisted of embryo rescued plantlets from cross pollination (control pollination) and open pollination (uncontrolled pollination) and two hardening media HM1(Coco peat: Perlite: Vermiculite, 1:1:1) and HM2 (Coco peat: Perlite: Vermiculite, 2:1:1). The results revealed that the progenies of ALC-2 x Kagzi Kalan had highest values of leaf gas exchange traits like internal CO 2 concentration (Ci), transpiration rate (E), stomatal conductance (g s ) and photosynthesis rate (A) which was followed by progenies of PusaUdit x KagziKalan. However, it was least in progenies of Troyer citrange (Open pollinated). Considering the hardening media, there was a general trend of the higher leaf gas exchange in the HM1media (Coco peat: Perlite: Vermiculite, 1:1:1) compare to HM2 media (Coco peat: Perlite: Vermiculite, 2:1:1). Keywords Hardening media, in vitro, Cocopeat and leaf gas exchange Accepted: 10 January 2019 Available Online: 10 February 2019 Article Info