Biological Control Of Some Bacterial And Fungal Diseases On Bean (phaseolus Vulgaris L.):

Fathy Gad Mohamed

SUMMARYThe present work was carried out to study the role of the biologicalcontrol of diseases caused by Rhizoctonla solani, Sclerotium rolfsii andCorynebacterium flaccumfaciens in bean cultivars. These studies have beendone under laboratory, greenhouse and field conditions. Results obtained C8nbe summarized as follows:1- Rbizoctonia solani, S. rolfsii and C.flaccumfaciens isolates varied in theirpathogenicity against different bean cultivars.2- Different microorganisms used in these study as antagonists were isolatedfrom sclerotia of pathogenic fungi, rhizosphere of bean plants and loridentified isolates obtained from Bacterial Dis. and Biological Control Dept.Plant Pathology Inst. Agric. Res. Center, Giza, Egypt and Fungus and PlantPathology branch, Dept. Agric. Botany. Fac, of Agric. Moshtohor.3- An aggressive isolates of R. solani and S. rotfsii were used under laboratoryconditions, to study the effect of physiological factors affecting antagonismbetween pathogenic fungi isolates and different antagonistic fungi andbacteria. Reaction in mycelial growth or sclerotial formation of S. rolfsii wereused as two parameter to measure the efficacy of the antagonist.4- Data obtained under laboratory conditions show that, different antagonistsvaried in their reaction according to different physiological factors. Glucose,fructose and sucrose were the most favourable carbon source for theantagonistic effect of against R. solani. Dextrin was the least one effecting theantagonistic effect of fungi against R. solani. While, lactose, starch, dextrinwere the most favourable carbon source for the antagonistic effect against S.rotfsii. Starch, sucrose, fructose and glucose were the most favourable carbonsource for antagonistic bacteria against R. solani . On the other hand, lactose,glycerol and starch were the most effective carbon sources on the antagonismbetween antagonistic bacterial isolates and S. rol[sii.5- Ammonium tartrate and potassium nitrate were the most favourable nitrogensources for antagonism between different antagonistic fungi and R. solani andS. rolfsii. On the other hand, urea and potassium nitrate were the mostfavourable nitrogen sources for antagonism between different antagonisticbacteria and R. solani. Sodium nitrate, ammonium nitrate and potassiumnitrate were the most favourable nitrogen sources for antagonistic effects ofdifferent antagonistic bacterial isolates against S. rolfsii.6- CIN ratios 15/2 and 25/5 were the most suitable ratios for antagonisticeffect of different antagonistic fungi and R. solani, whereas CIN ratio 00/2 and25/2 were the most suitable ratios for antagonisms between differentantagonistic fungi and S. rolfsil. On the other hand, CIN ratios 1/0.5, 5/2.5 and2/1 were the most suitable ratios for antagonistic effect of differentantagonistic bacterial isolates against mycelial growth of R. solani. While CINratio 3/1.5 was the most suitable ratio for antagonism against S. rolfsii.7_ Regarding the effect of pH value on the efficacy of different antagonists, itwas clear that, at pH 6.5 and 7 were the most suitable pH values for theantagonistic effect between antagonistic fungi and pathogenic fungi (R. solaniand S. rolfsii ) causing increasing of reduction in mycelial growth andreduction in sclerotia! formation of S. rolfsii. On the other hand, pH 6.6 and7.6 were the most suitable pH value for the antagonistic effect of antagonisticbacterial isolates and R. solani. While pH 6.6 and 7.0 were the most pH valueeffects against mycelial growth of S. TolfsU.C.- 8- Regarding the effect of temperature degrees on the antagonism, 25 and300e were the most suitable degrees for antagonists effect against mycelialgrowth of R. solani. While, 20 and 25°e were the most suitable degrees forantagonisms between different antagonistic fungi and S. rolfsii. On the otherhand, 300e were more effective than 25°C on the antagonism betweendifferent antagonistic bacterial isolates and R. solani or S. Tolfsii.9- Morphological studied on the effect of antagonistic bacteria B. subtilis onmycelium of R. solani. After 4 days showed that, mycelium of R. solanishowed malformed and lytic.10- Histological studies, showed that, T. harzlanum parasitized sclerotia of S.rolfsii and absolutely destroyed it within 10 days under laboratory conditions.iI-Adding culture filtrates of different antagonistic fungi after 5, 10, 15 and 20days to the medium of R. solani and S. Tolfsii led to reduction in mycelialgrowth of the pathogenic fungi. Data obtained revealed that, positivecorrelation between the percentage of reduction and rate of adding culturefiltrate and age of culture filtrates. Culture filtrates of T. hanianum iso.No.28was the most toxic ones to R. solani mycelium while T. harzlanum iso. No.5was the most effects against S. Tol/sii. On the other hand, slight differencesbetween T. harzianum iso.No 3, 4 and NO.5 on reduction in amount ofmycelial growth of R. solani. T. harzlanum iso.No.3 was the most toxic oneagainst S. rolfsii to reduction in amount of mycelial growth was filtrates takenafter 15 days of inocubation.12- Effect of time inoculation, of the antagonists, on the mycelial growth of R.solani and S. rolfsii or sclerotial formation of S. rolfsii were also tested. Dataobtained revealed that, positive correlation between inocubation period andpercentages of reduction in mycelial growth of R. solani and S. rolfsii orsclerotial formation of S. rolfsii were recorded. All isolates of T. harzianumshowed more antagonistic effect than G.penicilloides on reduction in mycelialgrowth and sclerotia! formation of S. rolfsii. On the other hand, Bacillus. iso.No.2 and B. cereus were the most effect against R. solani, while B. subtilisiso. No.2 and Ps. jluorscens were the most effects against S. Rolfsii.13- Under greenhouse conditions inoculum potential of the aggressivepathogenic fungi and methods of inoculation for the pathogenic bacterialisolates indicated that, 6 g/kg of soil for R. solani and 75 sclerotia/kg of soilfor S. rolfsii were enough to destroy highest in % of bean plants. Whilemethods of inoculation of C.flaccumfaciens varied between different beancultivars.14- Under greenhouse conditions, c.jlaccumfaciens as a causal organismresponsible for wilt disease in bean plants, was able to infect soybean, pea,cowpea and water-melon. While broad bean, tennis, tomato, squash, rice andlettuce were not susceptible to c.jlaccumfaciens.15- Different antagonistic fungi were use as spore suspension or culturefiltrates to control disease incidence caused by R. solani and S. rolfsii in beancompared with fungicide vitavax-captan 75% under greenhouse conditions.Data obtained revealed that, spore suspension was more effective on controldisease incidence than culture filtrates or vitavax-captan and caused increasein % survival plants, fresh, dry and No. ofpodsJpot. On the other hand, T.harzianum iso.No.28 were more effective than other isolates.16- Under the same conditions, seed or soil treated with antagonistic bacterialisolates to control disease incidence caused by the same pathogenic fungi inbean cvs. Data obtained revealed that, in regard to Giza 3 cv soil treated withdifferent antagonistic bacteria was more effective on reducing in % of diseaseincidence than seed treatment which caused increase in % of survival plants.While seed treated with vitavax-captan was more effective than bio-agents inContender and Bronco cvs. On the other hand, all biological agents were mereeffective on increasing No. of pods/pot than fungicide in all bean cvs.Regarding fresh and dry weight/pot data indicate that, isolates ofantagonistic bacteria varied in their effects according to reaction between thevariety and the pathogens, and showed more or equal with chemical treatmentin increasing fresh and dry weight/pot for bean cvs.17_ Regarding the effect date of application of biocontrol agents againstpathogenic fungi on disease incidence caused by R. solani and S. rolfsii inbean cvs. under greenhouse conditions. Adding different antagonists before orat sowing were more effective on reduction of disease incidence than any otherways compared with fungicide treatment in case Giza3 and Contender cvs.when used against R. solani.Regarding No. of pods/pot B. subtilis was the most antagonistseffective in increasing No. of pods/pot when added to soil before sowing inGiza 3 cv. While T. harzianum and Ps.fluorscens increased No. of pods/potwhen added at three times or at sowing respectively. Fresh and dry weight ofbean plants was clear when different antagonists were added at three times.18- Regarding the effect of application time of adding antagonistic bacteriRlisolates on % wilt disease incidence caused by isolates of C.flaccumfaciensin bean cvs. Data obtained revealed that, adding different antagonistic bacterialisolates at 72 hrs before inoculation of pathogenic isolates were more effectiveon reducing in % wilt disease incidence in bean cvs. than adding at the sametime. On the other hand, Contender cv was the most affected by usingantagonistic bacterial isolates by only 9.2% wilt diseased. While Bronco andGiza 3 cvs were slightly affected by them and 30.3 and 42.50/0wilt diseasedwere obtained respectively. B. cereus was the most antagonists effectiveagainst isolates of C flaccum/aciens and caused only 22.5 % wilt disease.While no differences between B. subtilis iso.No.2 and Ps.Jluorscens incontrolling C. flaccum/aciens isolates in bean cvs. by caused 32.2 % wiltdiseased.19- Comparison between the effect of different antagonists as seed dresser orsoil treatment on disease incidence caused by R. solani and S. rolfsii in beancvs. Data obtained revealed that, adding different antagonists as soil treatment(granules on wheat straw) or as seed dresser were more effective than otherforms on disease incidence in Giza 3. On the other hand, T. harzianum and B.subtilis were more effective than Ps:fluorscens. Seed treated with differentantagonists increased in No. of pods/pot in Giza 3 cv. than other ways.Slightly differences between different treatments in increasing fresh and dryweight/pot.20- Under field conditions, the same three antagonists, T. harzianum, B.subtilis and Ps. fluoTscens were used as seed or soil treatment and differentapplication dates for bean cvs during 1995 and 1996 seasons. Data obtainedrevealed that, T. harzlanum and B. subtilis used as seed treating were themost effective on reduction in disease incidence and increased yield of beancvs comparing with control or fungicide vitavax-captan.21- Adding any of the tested antagonists two weeks before sowing seeds,inhibited disease incidence and increased the yield of bean cvs., moreeffectively if compared with adding at divided into two amounts or at twoweeks after sowing.22- Under the same conditions, adding different antagonists at different formsled to different degrees of protection against disease incidence in bean cvs.Also, different antagonists behaved differently according to the variety oftreated plants. In general, using antagonistic fungi as granules ( on wheat strawor bran) led to the most protection of disease incidence, and increased of yieldbean cvs. Regarding, the antagonistic bacteria, no trend was observed amongdifferent forms in most cases for controlling of disease incidence and yield ofbean cvs during 1995 and 1996 seasons.