ArbuscularMycorrhizal Fungi (AMF) induced hardening of micropropagated pomegranate (Punicagranatum L.) plantlets

Abstract

Improper hardening leads to high field mortality and poor growth of in vitro raised plantlets which posesa major hurdle in utilization of in vitro propagation for pomegranate. In this study four arbuscular mycor-rhizal fungi (AMF) strains namely, Glomus mosseae, Acaulospora laevis, Glomus manihotis and a mixed AMFstrain were used as biohardening agents to improve survival and growth of in vitro raised pomegranateplantlets. Plantlets inoculated with G. mosseae gave highest survival (90.40% and 88.00% at 60 and 90 DAI,respectively) and root colonization per cent (47.40 and 87.60 at 60 and 90 DAI, respectively). The pre-dominant effect of G. mosseae was also evident on increased plant height (24.96 and 30.50 cm at 60 and90 DAI, respectively) and root length (23.42 and 27.68 cm at 60 and 90 DAI, respectively) of the inoculatedplantlets. G. mosseae and G. manihotis were found more effective in improving most of the growth, phys-iological and biochemical attributes of inoculated tissue culture raised plantlets. However, total phenol(24.94 and 28.62 g/g at 60 and 90 DAI, respectively) and total chlorophyll (3.70 and 3.96 mg/g at 60 and90 DAI, respectively) were found highest in mixed AMF inoculated plantlets.© 2012 Elsevier B.V. All rights reserved.1. IntroductionPomergranate (Punica granatum L.) is one of the favouritefruit crops of the world grown widely under tropical andsubtropical regions (Jalikop, 2007). It is suitable for grow-ing under arid and semiarid regions due to its hardy nature,low cost maintenance and high returns which make its culti-vation sustainable in long run particularly in resource deficitareas. The crop is also well known for its anti-cancerous,anti-microbial, anti-oxidant and anti-inflammatory properties(Albrecht et al., 2004; Lansky and Newman, 2007; Opara et al.,2009).In general, it is propagated by stem cuttings and air layering atefficiencies varying from 40% to 80%. However, in some parts ofIndia seedling plants are still used, but such seedlings show widevariation in growth and yield. At present, commercial orchardsin the world are established by stem cuttings. Air-layered plantsare commonly used for the cultivation of pomegranate in the Dec-can Plateau of India. All these conventional propagation methods∗Corresponding author.E-mail address: nripendras72@gmail.com (N.V. Singh).are less efficient as compared to in vitro propagation which pro-duces more propagules in lesser space and time. Besides these,in vitro raised plants are more uniform, come to synchronized flow-ering and fruiting and originally free from diseases. However, thepropagation by tissue culture has become difficult due to highfield mortality and slow growth rate of tender plantlets duringacclimatization phase due to poorly formed and weak root system(Hazarika, 2003), unfavourable nutritional and environmental con-ditions (Schubert et al., 1990), poorly developed cuticle (Louro et al.,1999) and/or non functional stomata (Lee and Wetzstein, 1988;Hazarika, 2003). The success rate of tissue culture raised plantletscan effectively be improved by proper hardening using bioagentslike arbuscular mycorrhizal fungi (Rupnawar and Navale, 2000).Many fruit crops develop a symbiotic mycorrhizal relationship andexhibit a high degree of dependence on this symbiosis for normaldevelopment and improved field performance (Aseri et al., 2008).Furthermore, AMF can mitigate the effects of extreme variationin temperature and water stress by improving water and nutri-ents uptake through increased rhizosphere exploring area (Krishnaet al., 2006). In the present study, different AMF strains were usedand their inoculation impact on survival, growth, physiologicaland biochemical attributes of in vitro raised plantlets had beenstudied