5.2.57
EVALUATION OF ANTAGONISTIC ACTIVITY OF SOME TRICHODERMA SPECIES ON RHIZOCTONIA SOLANI, CAUSAL AGENT OF RICE SHEATH BLIGHT, IN THE FIELD AND COMPARISON WITH A COMMERCIAL PRODUCT, PROMOT

M IZADYAR1, F PADASHT2 and M BAHRAMI3

1Plant Pests and Diseases Research Institute, PO Box 1454, Tehran 19395, Iran; 2Rice Research Institute, Rasht, Iran; 3Rice Research Institute, Amol, Iran

Background and objectives
Rice sheath blight became a big problem after cultivation of high yielding varieties in the north of Iran, in the Caspian Sea area. Chemical control of rice sheath blight is popular in Iran because there are no resistant, high yielding varieties against sheath blight so far. Investigations on biological control of rice sheath blight started from the beginning of 1970 [1-5]. The first step in developing a biological control system is to isolate and identify organisms with high potential for disease suppression. Therefore, the search for biological control agents should be in the same system in which they will be applied.

After isolation and identification of some Trichoderma species and evaluation of their antagonistic activity in different tests in vitro and in the greenhouse, T. harzianum, T. viride and T. koningii were selected for field trials.

Materials and methods
Field experiments were conducted during the 1995 and 1996 growing seasons at Rasht and Amol Mazandaran Province. In each year, two similar experiments were established in infested fields with additional artificial infection; each field was a separate experiment and no statistical comparisons could be made between the two fields. Within each field the experiment design was split plot with randomized complete block design, with treatments: Bl=T. viride, B2=T. koningii, B3=T. harzianum, B4=Promot (commercial product from Biotec Co. USA), B5=Tilt (propicanazole 25% from Ciba), and B6=no-treatment control). The times of application were A1=one application at beginning of heading, A2=two applications at booting stage and beginning of heading, and A3=one application at booting stage. For evaluation of disease intensity and comparison of effectiveness of antagonists, isolates were taken from rice fields in Gilan province grown with a recommended fungicide and Promot on rice sheath blight: 10 hills were cut randomly from each plot 1 day before harvesting time. The degree of damage (DD) and the percentage degree of severity (DS) were calculated according to Ono, 1953 and Yushimura, 1954, respectively . A yield of 5 m2 was harvested from each plot and after separation the grain weighed with 14% relative humidity. All data were analyzed by IRRISTAT Software.

Results and conclusions The results showed that T. harzianum and Tilt were in the first group, T. koningii and Promot were in the second group and T. viride and control were in the last group, with one application at the beginning of heading, one application at booting stage and two applications at booting and heading. No significant differences were seen in 1995 at Rasht and Amol, but experiments in 1996 showed that there are significant differences between treatments in sub-plot and main-plot. In these experiments Tilt was the most effective while T. harziantim, T. koningii and Promot had the same effective as Tilt. T. viride and control were in the last group. None of the treatments failed to increase yield significantly over the 2 years, because the severity of infection was not very high, however during all experiments the yield of control was lower than other treatments. The same results were obtained from experiments at Amol over 2 years. Two applications, at booting and heading, of T. harzianum, T. koningii, Promot and Tilt, reduced disease severity significantly.

References
1. Anon., 1982. Annual Report of IRRI. Manila, The Philippines.
2. Baby and Manibhusharao K, 1993. Tropical Agriculture, 70, 240-244.
3. Hashika and Fukita, 1969. Tottori Mycological lnstitute 7, 8-18.
4. Izadyar M, Padasht F, 1993. 6th International Plant Pathology Congress.
5. Kanjananeesathian M, Caunt RE, Oharigkapakorn N, Phetchart V, Taveechai N, 1993. 6th IPPC.