Study On The Screening Of Microorganism Against Digitaria Sanguinalis

The purpose of using microorganisms to control weeds is not causing them death but keeping their abundance at a proper level that can be acceptted on economics or esthetics according to colony ecology principle. Microorganisms used as bio-herbicides are mainly on two aspects: one is DRB (deleterious rhizobacteria);the other is making a profit of their metabolized products which are toxic to the weeds. We try to isolate special DRB from illed Digitaria Sanguinalis and improve their ability to control the growth of Digitaria Sanguinalis in order to make successful bio-herbicides used in corn regions in the northern of China.This paper studies mainly on the problems of bio-control of Digitaria Sanguinalis . Conclusions are got from the studies of bacteri-herbicide including its screening methods and its results and its toxin conditions and its physiological and biochemical appraisal:1. Active components of filtrate of S₄, H₁₁,S(21), S₃₃ are tested by leafage soakage in vitro and bourgeoning inhibit and root inhibit. Because we have conquered the biggest disadvantage of seed vigor,the method of roots inhibiting is the best way for choosing the most strong toxic strain: according to the checking aspects of S^<sub>, H₁₁ S₂₁ S₃₃ that they all can excrete more or less toxins. S4 and H₁₁ are prior to the other two. Bourgeoning inhibiting rate of S4 is over 93% and sprouts' is 53% and roots' is 90% and live weights's is 58%. H₁₁''s are 70% and 47% and 85% and 61% respectively. So we choose S₄ as the probably strain to be done a further experiments.2. According to the experiments of S₄ we know that the the optional conditions for its growth and producing toxins are liquid PB medium 30ml in 250ml trigonal bottle with its primal pH 6.5-7.5 inoculated 5% young cultures 28℃ and 210r/min 24h. Also we can get the same results if we only change a double factors accordingly. For example, improving PB enhydrous medium to 60ml in 250ml trigonal bottle while the shaking speed is 250r/min. So toxins are accumulated as time goes by according to its cells' growth. Culturing temperature of S4 affects its growth a lot but its toxins a little. If it is the latter, 25℃³0℃will be ok. The only thing that needed to be changed is its growing time. After 24h's growing, S4 has enough cells to produce toxins against Digitaria Sanguinalis. As time goes by, the bacterium will die while its toxins are never lost. The toxins has an obvious effect on roots of Digitaria Sanguinalis while a little on sprouts. They were degraded slowly when were put in dark corner and covered. From the data we know, two formulas were got: y=0.9325x^0.0477,R²=0.9566, x stands for time, y stands for inhibiting rate on roots;y=0.3327x-0.3606,R2=0.9781,x stands for time, ystands for inhibiting rate on sprouts..3. Bacteria identifying: As a result of identifying S4 ,we found that its colony is round and red and its surface is smooth;there is a little tuber. And it is not translucent on PB solid-medium which is little yellow. It is G'and can move. Also it hasn't bores. It is aerobic and anaerobic. It can take advantage of sucrose and maltose and glucose and methyl alcohol and dextrine and citrate and DL-malic acid well. It uses lactose poor and n-Butanol not at all. Also it can use urea and peptone and ammonium molybdate as N-sources but cannot use ammonium chloride and sodium nitrate and potassium nitrate. Sodium chloride is necessary to its growth because of its infiltrative press. Osculant enzyme is positive. M.R. is negative. V-P is negative. According to all the factors we tested, we found that S4 belongs to Chromobacterium.4. There are 7 kinds of bacteria that have been reported as DRB, including (1) Pseudomonas;(2) Enterobacter;(3) Flavobacterium;(4) Citrobacter;(5) Achromobacter;(6) Alcaligenes;(7)Xanthomonas .We haven't found Chromobacterium reported as DRB which has side effect on weeds. This may be the biggest innovation in the paper.