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International Journal of Plant Pathology

Year: 2011 | Volume: 2 | Issue: 1 | Page No.: 15-25
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Authors

Dennis Ochola

Geoffrey Tusiime

Keywords

Research Article

Survey on Incidences and Severity of Rice Yellow Mottle Virus Disease in Eastern Uganda

Dennis Ochola and Geoffrey Tusiime
The present study was conducted to assess the incidences and severities of Rice Yellow Mottle Virus (RYMV) disease in Eastern Uganda. In September 2009, a field survey was conducted in 11 rice-growing districts by randomly selecting rice fields along main roads and occasionally on feeder roads. Symptoms assessment and Enzyme-Linked Immunosorbent Assay (ELISA) were used as tools of disease diagnosis. The collected 49 samples showed a strong positive reaction with polyclonal antiserum raised against an S4 isolate from Madagascar. Narrow serological and biological variability among samples confirmed that the S4 strain was prevalent in all surveyed lowland rice-growing districts. Disease incidence and severity were high with mean values of 72% and 2.3 respectively but did not vary significantly (p = 0.05) among districts, varieties, altitudes and cultivation ecologies. Bugiri recorded the highest disease incidence (80%) and severity (2.5) respectively, while Namutumba had the lowest incidence (62%) and severity (2.1), respectively. Moreover, disease was most severe in districts closest to the Lake Victoria Basin. The farmer-preferred varieties showed varying degrees of susceptibility. The highest levels of disease occurred in variety K5, whereas the variety K85 had the lowest levels of disease. The results indicate that the continuous cultivation of susceptible varieties has lent impetus for the widespread of a highly infectious RYMV strain in Eastern Uganda. Plant breeders should provide significant agronomical protection against adverse effects of the virus by identification of different sources of durable resistance genes to be pyramided into the farmer preferred lowland varieties that possess good culinary traits.
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Comments

Waswa moses Reply

HOW DID THE AUTHOR CALCULATE ANOVA

Dennis Ochola

Dear Waswa Moses,
Although not described in detail in the methodology of this study, the unbalanced ANOVA function in Genstat allowed us to fit completely general models to unbalanced data that was derived from the 49 surveyed fields in 11 district.

WASWA MOSES

Thanks alot for the reply,

Am requesting you to send me a copy of your raw data and i see how to collect my data too, because am doing the same work but on potato viruses

Dennis Ochola Reply

Dear Waswa Moses,
I will gladly look around among my stuff if I can find the data sheet I used. I recently relocated from NaCRRI to Bioversity International so during the move I misplaced a lot of stuff. In the meanwhile, please feel free to contact me using the e-mail on this very article. Best regards.

Chibuikem I. N. Unamba Reply

Please can you explain in full details how the incidence and severity was calculated. I don't fully understand

Dennis Ochola

Dear Chibuikem I. N. Unamba,
I am glad that you have read our manuscript and would like some clarifications regarding the incidence and severity. However, I would kindly request you read through the field survey section of this manuscript therein you will find the answers to your question. The severity results are scores derived from a modification of the original scale by Raymundo et al (1979)through the addition of intermediate scores i.e. 1.5 and 2.5. Incidence is a visual estimate of area of field that is symptomatic. You can divide the entire field into strata and visually estimate the percentage of each strata that displays symptoms. Then find the average of the different strata. Hope this answers your queries. Most important be conversant with the disease symptoms, for RYMV it is similar to nitrogen deficiency. Be careful. Best regards.

Norehan Arifin Reply

Hello. happy new year. May i know further about symptoms assessment and Enzyme-Linked Immunosorbent Assay (ELISA) were used as tools of disease diagnosis in this study?

Dennis Ochola

Dear Norehan Arifin,

Happy new year.
Thanks for your question above. Symptom assessment in this article involved field assessment and screen house assessment. For the field, I modified the scale by Raymundo et al. 1979 by adding intermediate scores. Assessment was conducted diagonally in each rice field on 15 plants. ELISA was important especially to prove whether the samples picked where indeed RYMV infected and not necessarily nitrogen deficiency symptoms as is common. For further reading refer to my other paper 'Pathogenicity of Rice Yellow Mottle Virus and the Potential Sources of Resistance against the Disease in Eastern Uganda'.

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