Growth promoting effects of endophytic fungus Piriformospora indica in small cardamom (Elettaria cardamomum Maton)

Piriformospora indica, an endophytic fungus of Sebacinales, colonizes the roots of a wide range of host plants and provides various benefits to the plants. Cardamom (Elettaria cardamomum Maton) is an economically valuable spice crop of the tropics. In this work, we describe differentially expressed transcripts responding to P. indica root colonization in small cardamom for elucidation of molecular basis of growth and development. During the study, a wild genotype of cardamom was propagated under in vitro conditions using full strength Murashige and Skoog medium supplemented with 1 mg l(-1) BAP (for shoot induction) and basal MS liquid medium (for root induction). Cardamom plantlets were co-cultivated with P. indica. Microscopic observation confirmed the presence of P. indica inside the roots of cardamom plantlets. Growth parameters of control and P. indica colonized plantlets were observed for three months at an interval of 15 days. P. indica colonization resulted in a significant increase in the morpho-physiological traits of the host plant. The growth enhancement was visible after 15 days of co-culture. There was a significant increase (p < 0.05) in the number and length of leaves, height of the plant and chlorophyll content in P. indica colonized plants compared to non-colonized control plant. In addition to this, the expression levels of auxin, nitrate reductase, vegetative storage protein and phosphate transporter genes were upregulated by 3.45, 3.26, 1.62 and 1.19 times respectively by the co-cultivation of P. indica in cardamom plantlets.