Abstract:

Groundnut rosette virus disease (GRVD) is the most destructive disease of groundnut (Arachis hypogaea) in Uganda and across sub-Saharan Africa. Epidemics are sporadic and unpredictable, causing substantial losses which significantly reduce groundnut production and can potentially cripple the rural economy. The disease is principally transmitted by aphids (Aphis craccivora Koch.). There has been an increase in understanding of GRVD since its discovery in 1907. However, gaps still remain in the available knowledge on key epidemiological aspects of the disease. This study was aimed at establishing the influence of ambient ecology and farmers’ practices on the incidence and severity patterns of GRVD in Uganda. Trials were established for three planting seasons (1st and 2nd season 201 1 and 2nd season 2012) season 201 1 and 2nd in four groundnut growing locations each situated in different agro-ecological zones in Uganda. Four groundnut genotypes (2 susceptible and 2 resistant to GRVD) were used as treatments in a randomized complete block design that had four replicates. Disease progress was assessed at 4. 8 and 12 weeks after planting. Data on environmental factors; particularly rainfall, temperature and wind speed were obtained from standard meteorological stations located at/near the study sites. Aphid populations were assessed at regular intervals during the trial. Soil samples and yield data were also obtained for each planting season at each location. The study revealed that GRVD incidence and severity were significantly affected by season, location and variety as well as their three way interactions (P<0.05). This was also true for groundnut yields. Levels of GRVD infection were found to be influenced by rainfall and wind speed. Disease incidence, severity and AUDPC values were generally higher in conditions of lower rainfall and wind speeds. The Pearson’s two tailed correlation between total rainfall and GRVD incidence for all trial sites in all the three seasons was negative and highly significant (r = -0.280, P<0.01; N=144). This was also true for wind speed and GRVD incidence (r = -0.476, P<0.01; N=48). However, there was no conclusive trend between temperature and GRVD incidence with the Pearson’s two tailed correlation showing significantly positive and negative trends depending on location. The rate of GRVD development was also observed to be different for the four groundnut varieties, the three seasons and the different locations. A survey was also conducted within five major agro-ecological zones in Uganda. In this survey, 105 farmers were interviewed using a structured questionnaire with the aim of obtaining information on the various practices they employed in the field. Disease severity was scored in each farmer’s field. Results of the survey showed that farmers were employing a range of practices in groundnut production, including: early sowing, intercropping, use of improved groundnut genotypes, crop rotation; and uprooting and burning diseased plants among others. However, only two management practices: early sowing and use of improved varieties were found to significantly (P<0.05) reduce rosette severity in groundnut fields. It can be concluded, therefore, that ecological factors (such as rainfall, temperature, wind speed and soil), farmers’ practices and their consequential interactions, are ultimately the main influencing factors of GRVD severity in groundnut fields. This knowledge will guide the future development and promotion of more sustainable integrated GRVD management packages within the different agro-ecologies of Uganda.