Screening and Identification of Potential Striga [Striga Hermonthica (Del.)] Suppressing Rhizobacteria Associated With Sorghum [Sorghum Bicolor (L.) Moench] in Northern Ethiopia
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Date
2020-06-06
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Addis Ababa University
Abstract
Sorghum (Sorghum bicolor (L.) Moench) is one of the globally important cereal crops well adapted to Sub-Saharan Africa (SSA) agro-ecologies. However, the productivity of sorghum is hindered by both abiotic and biotic factors including drought, Striga, insect pests, poor soil fertility and diseases. Among the constraints, Striga (genus), also called witch weed is the most important production problem in the area. Out of Striga species, Striga hermonthica can cause a complete yield loss making it the most economically important weed. Control methods including cultural, chemical, biological and breeding for resistance have been practiced for years. To date, none of these strategies have become practically effective to eradicate Striga. Some of the existing control methods mentioned are not easily accessible for small holder farmers, while still some are not environmentally friendly. Therefore, this thesis focused on an alternate control of Striga hermonthica that employ rhizobacteria whose application is scanty in the study area. Hence, study was designed with the objective of identifying potential Striga suppressing rhizobacteria associated with sorghum. Soil samples were collected from three Striga infested sorghum fields with different levels of Striga infestation in northern Ethiopia. In order to activate the microbes, the sample was mechanically homogenized and various sorghum varieties grown on it in the greenhouse for four weeks. One hundred seventeen rhizobacteria were isolated from the root surface of the sorghum and these were then screened for their Striga suppressive traits, namely hydrogen cyanide and indole acetic acid production ability. Accordingly, 40.2% and 46.8% were capable of producing hydrogen cyanide and indole acetic acid, respectively. Twenty two isolates (18.8%) could produce both hydrogen cyanide and indole acetic acid in common. These elites were considered for further in vitro effect on Striga seed germination, in the presence and absence of susceptible host plant, and all of them, with varying ranges, showed a statistically significant germination inhibition. Finally, shortlisted most effective isolates RI6, RI9, RI19, RI23, RI26, RI38, RI54 and RI72 were morphologically and biochemically identified to belong to the genera of Pseudomonas, Klebssiella, Bacillus and Entrobacter. The result of the study demonstrated the existence of promising soil born bacteria that could be exploited as a bioherbicides to control Striga infestation on sorghum provided that broader samples from various parts of the country are explored.
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Biotic Factor, Germination Inhibition, Rhizosphere, Striga Infestation, Susceptible Host