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Fusarium wilt caused by Fusarium oxysporum f. sp. ciceri causes considerable yield loss of chickpea. Pseudomonas fluorescens4-92 (Pf4-92) strain can suppress the disease. Amendment of zinc EDTA and copper EDTA could not suppress the disease significantly when used alone; however, they significantly suppressed the disease in presence of Pf4-92. In vitro observation showed that at 40, 30 and 20microgml(-1) concentrations of these minerals, i.e. Zn, Cu and Zn plus Cu, respectively, completely repressed the production of the phytotoxin, fusaric acid (FA). FA concentration (0.5microgml(-1)) has been shown to suppress the production of 2,4-diacetylphloroglucinol (DAPG) by Pf4-92, and DAPG, salicylic acid, pyochelin and pyoluteorin production was enhanced by these mineral amendments. In rockwool bioassays, Zn, Cu and Zn plus Cu amendments reduced FA production and enhanced DAPG production. This study demonstrates that Zn and Cu enhance biocontrol activity by reducing FA produced by the pathogen, F. oxysporum f. sp. ciceri.

Selected isolates of Pseudomonas fluorescens (Pf1-94, Pf4-92, Pf12-94, Pf151-94 and Pf179-94) and chemical resistance inducers (salicylic acid, acetylsalicylic acid, DL-norvaline, indole-3-carbinol and lichenan) were examined for growth promotion and induced systemic resistance against Fusarium wilt of chickpea. A marked increase in shoot and root length was observed in P. fluorescens treated plants. The isolates of P. fluorescens systemically induced resistance against Fusarium wilt of chickpea caused by Fusarium. oxysporum f.sp. ciceri (FocRs1), and significantly (P = 0.05) reduced the wilt disease by 26-50% as compared to control. Varied degree of protection against Fusarium wilt was recorded with chemical inducers. The reduction in disease was more pronounced when chemical inducers were applied with P. fluorescens. Among chemical inducers, SA showed the highest protection of chickpea seedlings against wilting. Fifty two- to 64% reduction of wilting was observed in soil treated with isolate Pf4-92 along with chemical inducers. A significant (P = 0.05; r = -0.946) negative correlation was observed in concentration of salicylic acid and mycelial growth of FocRs1 and at a concentration of 2000 microg ml(-1) mycelial growth was completely arrested. Exogenously supplied SA also stimulated systemic resistance against wilt and reduced the disease severity by 23% and 43% in the plants treated with 40 and 80 microg ml(-1) of SA through root application. All the isolates of P. fluorescens produced SA in synthetic medium and in root tissues. HPLC analysis indicated that Pf4-92 produced comparatively more SA than the other isolates. 1700 to 2000 nanog SA g(-1) fresh root was detected from the application site of root after one day of bacterization whereas, the amount of SA at distant site ranged between 400-500 nanog. After three days of bacterization the SA level decreased and was found more or less equal at both the detection sites.

The role of motility and cell surface hydrophobicity in transport and dispersal of Pseudomonas fluorescens strains LAM1-hydrophilic, LAM2-hydrophobic and LAM(NM) (non-motile mutant of LAM2) under different soil conditions was studied. Maximum adhesion was recorded for LAM2 in clay loam (70%), followed by sandy loam (68%) and sandy soil (40%). Vertical migration of P fluorescens isolates in soils was recorded at 5 and 25 cm flow of wafer or M. phaseolina exudate. In all the treatments, LAM1 exhibited maximum migration followed, by LAM2 and LAM(NM). The rate of migration of such isolates was lowered in water irrigated soils compared to those irrigated with M. phaseolina exudate. In sandy soil, cells of LAM1 migrated up to 13 cm in comparison to LAM2 (11 cm) and LAN(NM) (9 cm) at 5 cm flow of fungal exudate. Population of LAM1, LAM2 and LAM(NM) was 5.7, 5.68 and 5.61 log cfu g(-1) soil at 1 cm depth, but it decreased to 2.56, 2.21 and 1.99 log cfu during migration up to 11 cm in sandy soil at 5 cm flow of fungal exudate. Greater motility was observed in sandy soil irrigated with water or fungal exudate, followed by sandy loam and clay loam. In general, filtration coefficient (lambda) of P. fluorescens was higher in soils irrigated with 5 cm of water or exudate than with 25 cm of irrigation. The horizontal movement of P. fluorescens strains in sandy soil adjusted at different psi m showed marked reduction with decrease in psi m. The non-motile LAN(NM) did not show chemotactic response and migrated up to a maximum of 3 mm in saturated soils (0 kPa). After 96 h, LAM1 and LAM2 migrated upto 35 and 29 mm respectively in sandy soil. Motile isolates had significantly greater colonization of M. phaseolina sclerotia over the non-motile mutant.

Plant protection through siderophore producing rhizobacteria (SPR) has emerged as a sustainable approach for crop health management. In present study, 220 bacteria isolated from tomato rhizosphere were screened for in vitro antagonistic activity against Rhizoctonia solani AG-4. Nine potent antagonistic strains viz., Alcaligenes sp. (MUN1, MB21, and MPF37), Enterobacter sp. (MPM1), Pseudomonas sp. (M10A and MB65), P. aeruginosa (MPF14 and MB123) and P. fluorescens (MPF47) were identified on the basis of physiological characters and 16S rDNA sequencing. These strains were able to produce hydrolytic enzymes, hydrogen cyanide, indole acetic acid, although, only few strains were able to solubilize phosphate. Two strains (MB123 and MPF47) showed significant disease reduction in glasshouse conditions were further evaluated under field conditions using three different application methods. Application of P. fluorescens (MPF47) in nursery as soil mix + seedling root treatments prior to transplantation resulted in significant disease reduction compared to control. Total chlorophyll and available iron were significantly higher in the MPF47 treated plants in contrast to infected control. In conclusion, siderophore producing bacteria MPF47 have strong biocontrol abilities and its application as soil mix + seedling root treatments provided strong shield to plant roots against R. solani and could be used for effective bio-management of pathogen. [ABSTRACT FROM AUTHOR]

Pseudomonas fluorescens isolate 4-92 induced systemic resistance against charcoal rot disease in chickpea (Cicer arietinum L.) caused by Macrophomina phaseolina (Tassi) Goidanich. Time-course accumulation of pathogenesis-related (PR) proteins (chitinases and glucanases) in chickpea plants inoculated with P. fluorescens was significantly (P = 0.05) higher than in control plants. The level of chitinases and glucanases increased by 6.6- to 7-fold up to 4 days postinoculation; thereafter, little decrease in the activity of PR proteins was observed. Root-colonizing populations of P. fluorescens were at a maximum 2 days after transplantation at different inoculum concentrations, and decreased over time. Inoculation of root tips of chickpea by P. fluorescens, 2,6-dichloroisonicotinic acid, and o-acetylsalicylic acid induced systemic resistance against charcoal rot. Disease was 33 to 55.5% higher in control plants than in plants inoculated with chemical inducers or P. fluorescens. Single treatment of plants with P. fluorescens increased disease resistance by 33%, whereas combined application of P. fluorescens with either of the chemical inducers was most effective in inducing the resistance by 2- to 2.25-fold. The time-course study shows that an interval of at least 2 days was required between induction treatment and challenge inoculation. Biocontrol efficacy of P. fluorescens against charcoal rot disease in chickpea was demonstrated under greenhouse conditions.Key words: biological control, induced resistance, Macrophomina phaseolina, Pseudomonas fluorescens.L'isolat 4-92 du Pseudomonas fluorescens induit une résistance systémique contre la pourriture charbonneuse causée par le Macrophomina phaseolina (Tassi) Goidanich chez le pois chiche (Cicer arietinum L.). L'accumulation dans le temps de protéines PR (chitinases et glucanases) chez des plants de pois chiche inoculés avec le P. fluorescens est significativement plus élevée que chez les plants témoins. Les teneurs en chitinases et glucanases augmentent de 6,6 à 7 fois jusqu'à 4 jours après l'inoculation; par après, on observe peu de diminution dans l'activité des protéines PR. Les populations du P. fluorescens colonisant les racines atteignent un maximum 2 jours après la transplantation en présence de différentes concentrations d'inoculum, et diminuent avec le temps. L'inoculation des apex racinaires de pois chiches avec le P. fluorescens, l'acide 2,6-dichloroisonicotinic et l'acide o-acétylsalicylique induit une résistance systémique contre la pourriture charbonneuse. Chez les plantes témoins, la maladie est de 33 à 55,5% plus élevée que chez les plantes inoculées avec les inducteurs chimiques ou le P. fluorescens. Un seul traitement avec le P. fluorescens augmente la résistance à la maladie de 33%, alors qu'une application combinée du P. fluorescens avec un des deux inducteurs chimiques est la plus efficace, augmentant la résistance induite de 2 à 2,25 fois. L'étude dans le temps montre qu'il faut une intervalle d'au moins 2 jours entre le traitement d'induction et l'inoculation avec le pathogène. On a ainsi démontré l'efficacité du P. fluorescens, en serre, comme agent de lutte biologique contre la pourriture charbonneuse chez le pois chiche.Mots clés : lutte biologique, résistance induite, Macrophomina phaseolina, Pseudomonas fluorescens.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]