Evaluation of the antagonistic effects of some actinomycetes species isolated from Maseno Soils on Pyricularia grisea infecting finger millet (Eleusine coracana (L.) Gaertn).

Abstract

Finger millet (Eleusine coracana (L.) Gaertn) is one of the most important crops among the small millets. In Kenya yields are generally low, because of blast caused by the fungus Pyricularia grisea. Low finger-millet production accelerates incidences of malnutrition. Management has been challenging with cultural approach showing minimal success. Comparatively the use of actinomycetes species as a bio-control agent in management of rice blast caused by a similar pathogen, has shown some success hence a need to look at its candidacy as agent in the control of finger millet blast. Little is known about success of such a control strategy in Maseno University area using soil actinomycetes extracts. The objective was to isolate actinomycetes from soils collected in Maseno area, test against Pyricularia grisea and fungicidal ones characterized. The P. grisea were isolated from infected finger millet earlier grown in Maseno University’s botanical garden. Soil samples were collected a long a line transect drawn from Siriba-Main campus road. Soil samples collected were pre-treated by air drying at room temperature for 3 days, after which they were dissolved in distilled water, homogenized and spread over modified Kuster’s agar from where colonies were isolated. The actinomycetes cultures were grown together with the fungus, in a fresh Kuster’s agar and incubated for 4 days at 28°C. The species with the inhibitory ability such as AT2 and AT4 were characterized using classical approach according to Bergy’s manual of Determinative bacteriology. Then AT2, AT4 and AT6 were grown in Kuster’s broth in a shaker incubator at 28°C and 200 rpm for six days, and extracts obtained from each tested for inhibitory effect against the pathogen. 50mg/ml of AT2, AT4, AT6 extracts and Probenazole were mixed with the pathogen spores at 7.2 x106 spores/ml of corn oil and used as treatments. Five Treatments were replicated three times in a Randomized design and Disease severity (DS) scored using a 1-5 visual scale. Area under disease progress stairs (AUDPS) indicating efficacy based upon the records were obtained by calculating the area of each step function, and then adding up the areas. The Data collected was subjected to analysis of variance (ANOVA). The means were separated and compared using LSD at P≤ 0.05. Fifteen Actinomycetes (AT1, AT2, AT3, AT4, AT5, AT6, AT7, AT8, AT9, AT10, AT11, AT12, AT13, AT14 and AT15) were isolated from the samples and picked for invitro tests against Pyricularia grisea. When the actinomycetes cultures were grown together with the fungus, AT2 had a mean inhibition distance of 10 mm, AT4 had 8 mm, AT1, AT3 and AT6 had less than 1.0mm. Extracts of AT4 and AT6 had no fungicidal effects while extracts of AT2 showed fungicidal effects against Pyricularia grisea. AT 2 was identified as Streptomyces sindeneusis and AT 4, Streptomyces plicatus. Plants exposed to the mixture of pathogen and AT6 showed no significant difference in disease incidence with the plants exposed to the Pyricularia grisea alone. AT2 treatment had highest resistance at AUDPS of 24.8, however there was a significant difference between it and the spores exposed to Probenazole, AUDPS of 13.5. AT4 at AUDPS of 40.2 had a weak resistance; however it was significantly different from either AT6 at 47.5 AUDPS or pathogen alone at 50.5 AUDPS. Maseno soils have actinomycetes, some of which have inhibitory ability against finger millet blast. A few produce extracts that can resist spread of Pyricularia grisea in host plant. Streptomyces sindeneusis in this study had a significant ability in the control of finger millet blast both invitro and invivo. The findings of this study will be useful to any work involving isolation of actinomycetes within Maseno. It has also pointed at a possibility of formulating a bio-control agent among the actinomycetes isolates for many other pathogenic fungi.