Abdul Ghaffar

Biological control of root rot-root knot disease complex of tomato.

Efficacy of Pseudomonas aeruginosa alone or in combination with Paecilomyces lilacinus was evaluated in the control of root-knot nematode and root-infecting fungi under laboratory and field conditions. Ethyl acetate extract (1 mg/ml) of P. lilacinus and P. aeruginosa,respectively, caused 100 and 64% mortality of Meloidogyne javanica larvae after 24 h. Ethyl acetate fractions of biocontrol agents were more effective than hexane extracts in the suppression of M. javanica larvae, indicating that active nematicidal compounds are intermediary in polarity. In field experiments, biocontrol fungus and bacterium significantly suppressed soilborne root-infecting fungi including Macrophomina phaseolina, Fusarium oxysporum, Fusarium solani, Rhizoctonia solani and Meloidogyne javanica, the root-knot nematode. P. lilacinus parasitized eggs and female of M. javanica and this parasitism was not significantly influenced in the presence of P. aeruginosa. P. aeruginosa was reisolated from the inner root tissues of tomato, whereas P. lilacinusdid not colonize tomato roots.

Biological control of white rot of onion

Interactions of 123 isolates of fungi, 17 of bacteria and 22 of actinomycetes, respectively, withSclerotium cepivorum were studied in agar culture. They were grouped into 4 different types of reactions. Amongst themTrichoderma viride, Fusarium graminearum, Coniothyrium minitans andGliocladium roseum inhibited the growth ofS. cepivorum and later grew over its colony.T. viride showed a characteristic coiling around the hyphae ofS. cepivorum. T. viride andF. graminearum prevented the development of sclerotia.C. minitans was found to parasitize the sclerotia ofS. cepivorum and produced its pycnidia within them.Aleurisma carnis, Cladosporium elatum, Penicillium expansum, P. nigricans, P. notatum, P. piscarium, P. puberulum, P. rolfsii, P. urticae, P. variabile, Tilachlidium humicola andHelminthosporium sp. inhibited the growth ofS. cepivorum at a distance. Eleven isolates of bacteria and 3 ofStreptomyces sp. showed pronounced antagonistic properties againstS. cepivorum. Experiments were carried out to study the effects on white rot development in soil of organisms selected from agar plate tests. None of the antagonistic micro organisms had any deleterious effects on onion growth. Of the organisms testedP. nigricans gave the best results in controlling white rot infection.

Biological control of white rot of onion: II. Effectiveness of penicillium nigricans (Bain.) Thom

A study has been made of the persistence of the effects ofPenicillium nigricans, in garden loam, on the control of white rot disease of onion. Twenty days old cultures ofP. nigricans, diluted up to 0.25 strength, remained effective up to 5 days. Further additions of maize meal to the soil prolonged its effectiveness. The control of white rot was associated with a concentration of 80µg of griseofulvin per g of soil. Loss of activity in controlling white rot was related to decline in griseofulvin concentration, which in turn was associated with the build ofPseudomonas sp. in soil.Pseudomonas had no effect onS. cepivorum. Decline in control byP. nigricans was followed by a second period of control which was related to increase in number of bacteria antogonistic toS. cepivorum. In agar culture griseofulvin produced a fungistatic effect on the growth ofS. cepivorum. Similarly in the presence of griseofulvin in soil, the appearance of white rot infection was delayed. Evidence was obtained to the fact that a fungistatic effect onS. cepivorum is effected by griseofulvin, complete control of white rot was related to increase in population of microorganisms antagonistic toS. cepivorum.

Inhibition of fungi, actinomycetes and bacteria by Stachybotrys atra

The effect ofStachybotrys atra on fungi, actinomycetes and bacteria was studied in agar culture. Of the 27 genera and 52 species of fungi, 6 species of actinomycetes and 5 genera and 10 species of bacteria tested,S. atra was found to inhibit 95.7 % fungi, all the actinomycetes and 83.3 % of bacteria.Aspergillus ustus, 2 unidentified species ofFusarium, Rhizobium trifolii andPseudomonas spp. were however not inhibited. In experiments in soil,S. atra inhibited the growth ofTrichoderma viride. S atra was ineffective whereT. viride andS. atra were inoculated simultaneously or whereT. viride was added 7 days earlier. Besides,S. atra was not found to controlMacrophomina phaseoli infection on cotton. Soil culture ofS. atra showed phytotoxic effect on cotton seedlings.S. atra produced a dark brown to black thermostable toxic metabolite in the medium. The culture filtrate retarded the growth ofM. phaseoli in agar culture. Despite the importance ofS. atra as a fungistatic agent with wide antimicrobial spectrum, the use ofS. atra as a protectant against plant pathogens seems to be limited because of its phytotoxicity on cotton.

SURVIVAL OF MACROPHOMINA PHASEOLI (MAUBL.) ASHBY ON CUCURBIT ROOTS

Experiments on the survival ofM. phaseoli on cucurbit root pieces were carried out. The sclerotia ofM. phaseoli were almost unaffected by 10 months dry storage in the laboratory. Under dry to moderately moist soil conditions it survived for 2 months with little loss of viability. In wet soils however, the buried root pieces were colonized by other soil microorganisms which prevented the growth ofM. phaseoli.

Interactions of soil fungi with Macrophomina phaseoli (Maubl.) ashby, the cause of root rot of cotton

Interactions of 46 isolates of fungi with an isolate ofM. phaseoli from cotton, was studied in agar culture. They were grouped into 4 different types of reactions.T. viride was found to inhibit the growth ofM. phaseoli and grow over its colony. The hyphae ofT. viride were observed to coil around the hyphae ofM. phaseoli. A majority of the isolates tested had no effect on the growth ofM. phaseoli. M. phaseoli, however, was found to overgrow the test fungi.

Interactions of actinomycetes with Macrophomina phaseoli (Maubl.) Ashby; The cause of root rot of cotton

Macrophomina phaseoli, the cause of root rot of cotton, was inhibited byStreptomyces albus, S. griseus andS. noursei in agar culture.S. aureofaciens, S. flaveolus, S. rimosus, S. scabies andS. venezuelae were non-antagonistic. Only the antagonisticStreptomyces were found to reduceMacrophomina infection on cotton seedlings in soil without any deleterious effect on cotton growth.

Colonization of cotton roots by soil micro-organisms

An experiment was carried out to study the colonization of soil microorganisms on cotton roots buried in the soil.Fusarium culmorum, F. solani, F. oxysporum, Macrophomina phaseoli andBacillus sp. were found to be the predominant colonizers followed byBotryodiplodia theobromae, Fusarium acuminatum, Aspergillus niger, A. flavus, Stachybotrys atra, Tilachlidium humicola andRhizopus sp. The practice of leaving cotton roots in the soil would therefore add to the building up of the inoculum potential of the soil inhabiting fungi several of which are serious root pathogens.

Effect of certain physico-chemical factors on growth and antifungal property of Stachybotrys atra

Summary Stachybotrys atra was found to utilize sucrose and asparagine as the best carbon and nitrogen sources. A temperature of 30°C and pH 5.6 was found to be optimum for its growth. The fungus secretes a dark brown to black thermostable toxic metabolite in the medium. Maximum production of antifungal substance was observed at 26°C and at pH 5.0 using maltose and sodium nitrate as the carbon and nitrogen sources. Importance of the metabolite produced by S. atra is discussed.

Effect of some antibiotics on Sclerotium cepivorum Berk., the cause of white rot of onion.

The effect of some antibiotics onSclerotium cepivorum, the cause of white rot of onion was studied in agar culture and soil. The growth ofS. cepivorum was inhibited in Czapek Dox yeast agar containing 50µg of gliotoxin, viridin, actidione and 100µg of patulin per ml of the medium. Lower concentrations of the antibiotics retarded the growth of the fungus. In soil, patulin had no effect in the control ofS. cepivorum infection of onion seedlings. Concentration of actidione of 5µg/g of soil completely controlled white rot infection but severely stunted the growth of onion seedlings; 40µg/g of actidione killed the seedlings. Despite the importance of actidione as a fungistatic agent its use on onion is limited by its phytotoxicity.