Evaluation of Antifungal Potential of Macro-Algae for Controlling Leaf Spot of Tuberose (Polianthus tuberosa L.) Incited by Alternaria polianthi

Tuberose (Polianthes tuberosa L.) is one of the major commercial flower crops cultivated in Tamil Nadu. Although it has been cultivated for a long time, the significant increase in productivity is yet to be achieved. It is well recognized that the disease constitutes a major constraint in increasing the flower production. The incidence of leaf spot disease caused by the fungal pathogen Alternaria polianthi is a severe problem that leads to reduced growth and flower yield. The occurrence of seaweeds viz., Sargassum myricocystum (Brown algae), Kappaphycus alvarezii, Gracilaria edulis (Red algae), Caulorpa racemosa (Green algae) and Ulva lactuca (Green algae) from Munakkadu, Thonithurai, and Vedhalai at Mandapam, Rameshwaram taluk where as in Chennai Chaetomorpha antennia were collected. In vitro evaluation of seaweeds revealed that methanol extract of Sargassum myricocystum (5%) found to be effectively inhibited the mycelial growth of Alternaria polianthi which showed 70.33 per cent inhibition over control. A pot culture experiment was conducted to evaluate the efficacy of seaweeds on incidence of leaf spot was revealed that foliar spray of Sargassum myricocystum @ 3% two spray at 45 and 60 days after planting was significantly reduced the leaf spot which recorded disease incidence of 21.65 PDI.