Studies On The Relationship Between The Occurrence & Development Of Bacterial Leaf Streak Of Rice And The Alteration Of The Quantities Of Phages In Paddy Field Water

The studies on the interactions of 10 strains of Xanthomonas oryzae pv. oryzicola and 20 strains of phage isolated from Hubei province showed that: there were differentiation in the susceptibilities of host bacteria to phage stains isolated from different areas. According to the interactions, 10 bacterial strains were classified into 6 susceptible groups and 20 phage strains were classified into 7 different lysotypes. 5 bacterial strains such as RP, RS, RT, RX and RY were susceptible to 20 phage strains all, so they could be used to detecting the phage in samples forecasting Bacterial Leaf Streak of Rice (BLS) with the bacteriophage technique in Hubei province.Inoculating with the suspension of X. o. pv. oryzicola on the leaves of rice plants by needle-pricking, spraying and pouring it in paddy water, the percentages of diseased plants and quantities of phages in water were checked up periodically. The results showed that three kinds of inoculation methods all causing BLS, the bacteriophages were detected in water.there were no diseased plants and phages in plots not inoculated, which indicted there was a close relationship between the pathogen and the phage. When inoculated with the natural compound strain of B-l,both diseased plants and phages were detected;but when inoculated with monocell colony strain of IV-16 of Xanthomonas oryzae pv. oryzae, although there are diseased plants, no phage was detected in paddy water, which suggested that the bacteriophages should be transmitted by the lysogenic cell among the compound strain cells in theartificial inoculation condition.Detection the quantities of the phage of X.o. pv.oryzicola in paddy water during different growth stages of rice showed that the plaques could be observed clearly formed on PSA plates mixture with host bacterium under low temperature (below 34 ,before 15th, July or after 1st, September). In high temperature periods ( higher than 34 ,between 15th, July and 1st, September in Wuhan ) .to discontaminate,the method adding the chloroform to the samples of paddy field water with ratio 1:10 was much better than filtering with bacterial filters and centrifuging,the actual quantities of phages in samples should be the counts of observed plaques divided by 40%.Investigation on the early,middle and late season rice showed that BLS was very light on early season rice and it mainly attacked middle and late season rice in Hubei Province. It was found that BLS show symptoms in a tillering stage and reached the summit of disease from heading to milking stage. Studies on relationship between the development of BLS and quantities of phages in rice fields indicated that the rapid increasing periods of phages steped with BLS diseases or ocurred ahead, so it would be feasible to forecast the development trend of BLS by periodically detecting the quantities of phages in selected rice fields on middle or late season rice for three weeks (a time per 7 days) from tillering to early heading stage, considering with the quantities and days of rainfall before the mature stage. When the quantities of phages in paddy water reached to 100 pfu/ml ,BLS would begin to appear scatteredly 10 days after. When the quantities reached to 1000 pfu/ml, BLS would be gradually serious with the increasing of the quantities of rainfall and rainy days, if the total quantities of rainfall exceeded 600mm in entire growth stages and the rainy days per week more than 4days,the disease could be very serious in heading to milking stages, otherwise it would be light or very light.