Study on the Effects of Selected Plant Extracts on Sugarcane Smut Pathogen (Ustilago scitaminea)

Abstract

Commercially grown sugarcanes (Saccharum Hybrid spp.) are perennial grasses belongs to the

family Poaceae. It is a C4 plant which utilizes sun light very efficiently and grows well in tropical and frost-free warm temperate areas (Jalaja, 2001). Sugarcane Smut (Ustilago

scitaminea) is one of the most devastating diseases in Sri Lankan sugarcane plantations among

major sugarcane diseases. (Annual report SRI, 1997). The Sugarcane Smut disease is caused

significant yield losses to sugarcane plantation (Agnihothi, 1990). Although, Smut resistant

varieties are grown in the plantations, this particular disease could not be eliminated completely because there is a probability to appear this disease in some extent even in resistant varieties due to the nature of field resistance (Comstock, 1989). This situation can be further anticipated

where resistant varieties are introduced into the areas with high inoculum density. Botanical

control methods like antifungal plant spp. acclaimed as effective, eco-friendly and cheap,

nullifying the ill effects of chemicals. Plant extracts like, Calendula officinalis, Solanum

nigrum etc., have been found antagonistic to Ustilago scitaminea (Ji Lal.et al.2009). However, the information on use of botanicals for the management of the disease under field condition is entirely lacking (Ji Lal.et al. 2009). Therefore, considering the cost of chemical pesticides and

the probable hazards involved in the use of chemical fungicides, biological control of plant

diseases appears to be an effective and eco-friendly approach to increase crop yield. Therefore,

the present study was to identify the possible plant species and their optimal concentration with fungicide to control Smut disease (Ustilago scitaminea).

Methodology

The twenty five plants species viz., Azadirachta indica, Psidium guajava, Lantana camara L., Gliricidia maculate, Cinnamomun sp., Raphanus sativus, Tagetes erecta L., Solanum nigrum, Ricinus communis, Cyprus herbacea, Piper betle, Kaempferia spp., Alostonia scholaris, Zinger officinale Roscoe, glorisa superba, Cassia alata, Plectranthus zeylanicus, Carrica papaya,

Elettaria cardamomum, Euphorbia heterophylla Syzygium aromaticum, were used to obtain plant extracts for evaluation against Smut pathogen (Ustilago scitaminea) under in-vitro conditions. Leaf extracts of the above plant species were prepared by crushing surface sterilized leaves with sterilized distilled water (1:1 w/v) using cleaned sterilized, motor and pestle. The extract of each plant was filtered through a sterilized double layered muslin cloth. Then the filtrate was centrifuged at 2000 rpm for 10 -15 minutes at 20 C to get the supernatant. The smut whips which were collected from the Uda Walawe Research Farm were rubbed and fungal spores were collected. The spores were inoculated on PDA plates and were incubated at 28  1 C for four (04) days and continued sub cultures until getting pure cultures. Plant Extracts were tested in- vitro against Smut pathogen (Ustilago scitaminea) using dual culture method (Morton and Stroube.1955) with control. The plates were incubated at 28  1 C temperature for 48 hours. The growth of the pathogen was measured up to 15 days and was expressed as Percentage of Mycelia growth Inhibition (MGI) of smut.