Seed health testing of rice and the comparison of field incidence and laboratory counts of Drechslera oryzae (Bipolaris oryzae) and Pyricularia oryzae in Ghana

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2012-06-22
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Abstract
A study was set up to find out the prevalence and occurrence of two fungi pathogens, Bipolaris oryzae and Pyricularia oryzae on rice (oryzae sativa L) seeds. Thirty- three (33) seed samples were collected from rice growers in seven communities in the four agro-ecological zones of Ghana (Sudan Savannah, Guinea Savannah, Forest Zone and Coastal Savannah). Laboratory seed health test was conducted on all the samples by blotter method, and four varieties were selected, one each from the ecological zones and a comparable count of different fungi was obtained under near ultraviolet light before sowing and after sowing. Visual symptom of blast and brown spot were also observed on the rice plants during the field experiments. Pyricularia oryzae was not observed on any of the seed samples collected when the blotter method was used for the health test. Sudan Savannah recorded the highest infection of Bipolaris oryzae with nine numbers of infections recorded out of nine samples used with infection rate ranging from 1.5% to 29.5%, whilst Guinea Savannah recorded the least infection rate, ranging from 0 to 0.5% when one sample was used. Nerica 14 was used for Guinea Savannah zone and before sowing it recorded 0.5% of Bipolaris oryzae but recorded 0% at harvest. Jet 3 variety from the Coastal Savannah recorded 0.5% infection before sowing and recorded 9% infection level at harvest. Also Nerica 2 from the forest zone recorded 0% infection level before sowing but a recorded high infection level of 5% at harvest. Curvularia pallescens was not recorded in the forest zone (nerica 2 variety) and in the Guinea savannah (Nerica 14 variety) before sowing but recorded significantly higher percentages at harvest at 86% and 46.5% respectively.Also Sudan Savannah (Jasmine 85 variety) and Coastal Savannah recorded 8.5% and 4.5% infection of Curvularia pallescens before sowing respectively but recorded significantly higher percentages of 60% and 61% respectively.
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A Thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the Degree of Master of Science in Seed Science and Technology, August-2012
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