Biopotency of Promising Plant Extracts against Rice Sheath Rot Disease

Partially purified protein fraction of leaf extracts of Convolvulus arvensis, Acalypha indica, Catharanthus roseus and Ocimum tenuiflorum at 100, 250 and 500 ppm effectively inhibited the mycelial growth, sporulation, spore germination and germ tube elongation of Sarocladium oryzae. Non-protein fractions were less effective. In pot culture experiment, spraying of leaf extract of C. arvensis protein fraction at 500 ppm recorded the maximum disease reduction which was on par with protein fractions (500 ppm) of A. indica, O. tenuiflorum and C. roseus.

Rice sheath rot caused by Sarocladium oryzae is a serious disease affecting in all rice growing areas of Tamil Nadu and there was 85 per cent yield loss (Prabhakaran et al., 1973). The leaf extracts of Ocimum sanctum, Curcuma longa, Datura metal and Azadirachta indica inhibited the spore germination of S. oryzae (Komala et al., 1988). Selvaraj and Narayanasamy (1994) reported that the seed extract of Tribulus terrestris and leaf extract of Agave americana effectively inhibited the spore germination, germ tube elongation and mycelial growth of S. oryzae. Extract from tender stem of Euphorbia tirucalli and leaf extract of Urginea indica reduced the sporulation of S. oryzae. Dried leaf extract of Ipomoea spp. effectively inhibited the mycelial growth of S. oryzae (Rajappan et al., 1997).

Protein and non-protein fractions
Leaf extracts were mixed with equal volumes of saturated ammonium sulphate and the mixture was left to stand overnight. The protein precipitate was collected by centrifugation for 20 min at 10,000 rpm (Van Loon et al.,1987). The protein fractions were then dialysed against running tap water. Then, these fractions were lyophilized in a lyophilizer. The required amount of lyophilized protein was dissolved in 80 per cent alcohol to get 100, 250 and 500 ppm concentrations. Alcohol was allowed to evaporate and the remaining solution was made up to original volume with sterile distilled water. The effect of these solutions on the mycelial growth, sporulation, spore germination, germ tube elongation and on the disease intensity was studied. Similarly the effect of the nonproteins fraction at dilutions of 1:100, 1:50 and 1:25 were also tested.
The efficacy of protein and non-protein fractions of plant extracts on the mycelial growth and sporulation of S. oryzae was assessed by poisoned food technique (Schmitz, 1930).
The efficacy of protein and non-protein fractions of plant extracts on spore germination and germ tube elongation was assessed by the slide germination technique described by the Committee on Standardization of Fungicidal Tests (CSFT, 1947).
The effect of protein fractions at 100, 250, and 500 ppm concentrations and non-protein fractions at dilutions of 1:100, 1:50 and 1:25 on sheath rot intensity was also studied by spraying the fractions on 85 day old CO 43 rice plants under pot culture condition. After 24h, the plants were inoculated with S. oryzae. Ten days after inoculation, one more spraying was given with the same treatments on the respective groups of plants. Suitable control was also maintained for each treatment. Sheath rot intensity was assessed based on the new scoring *Corresponding author email : yesupatho@yahoo.co.in system developed by Narayanasamy and Results and Discussion Viswanathan (1990). The disease index and per Mycelial growth cent disease reduction were worked out.
The results on the efficacy of protein fractions of The protein fraction of the leaf extract of Convolvulus arvensis at 500 ppm showed the least mycelial growth (2.93cm) as against 7.47cm in the control which accounted for 60.71 per cent inhibition.
This was on par with the protein fractions (500ppm) of the leaf extract of Acalypha indica (59.38%), Catharanthus roseus (58.48%) and Ocimum tenuiflorum (56.25%). This was followed by protein fraction (250ppm) of the leaf extracts of C.arvensis (54.92%), that of (250ppm) A.indica (53.57%), 500ppm Datura stramonium (50.90%), 250ppm C.roseus (50.89%) and that of (500ppm) Ipomoea carnea (49.55%) which were all on par.The non- protein fractions from the leaf extract of all the plant species tested were less effective at all the three concentrations as compared to the protein fractions of the respective plant sources (Table 1).

Spore germination
The results on the effect of these fractions on the inhibition of spore germination of the pathogen are shown in Table 3. The protein fraction (500ppm) of C. arvensis registered the least (40.29%) spore germination as against 88.99 per cent in the control which accounted for 54.72 per cent inhibition and it was on par with protein fraction (500ppm) of A. indica (53.65%), that of (500ppm) O. tenuiflorum (52.56%), 250ppm of C. arvensis (50.55%) and 250ppm of A. indica (49.94%). The non-protein fractions of all these leaf extracts were less effective.

Germ tube elongation
The protein fraction of C. arvensis at 500ppm had the minimum (11.62mm) germ tube elongation as against 27.37mm in the control which accounted  500ppm of Datura stramonium (46.77%) which were all on par. The inhibitory effect of non-protein fractions on germ tube elongation exerted by all the leaf extracts was appreciably less than that of their protein fractions (Table 4).
In the present study, the protein fractions of the leaf extracts of C. arvensis at 500 ppm showed the maximum inhibitory effect on the mycelial growth, spore germination and germ tube elongation of S. oryzae .The protein fraction of A. indica at 500 ppm recorded the maximum antisporulant effect. In the pot culture study, the protein fraction of C. arvensis at 500 ppm recorded the highest disease reduction which was on par with protein fractions (500 ppm) of A. indica, O. tenuiflorum and C. roseus. Protein fraction of C. arvensis at 200 ppm had the maximum inhibitory effect on the germ tube elongation and the mycelial growth of S. oryzae.Protein fraction (200 ppm) of C. roseus recorded the maximum inhibition on the spore germination and sporulation of S. oryzae. Protein fraction of C. arvensis (500 ppm) registered the maximum reduction of rice sheath rot intensity. Selvaraj and Narayanasamy (1994) also documented that the protein fraction from Tribulus terrestris seed extract recorded the maximum inhibitory effect on the spore germination of S. oryzae.The present findings provides for further studies on the scope of developing an agro product using these protein fractions for the management of this important disease of rice.