Management of bacterial wilt of potato using rotation crops in southwestern Uganda

Studies were conducted in the field, shade house and laboratory to explore different Ralstonia solanacearum management options for southwestern Uganda. The major objectives were to determine the effect of the crops commonly grown in rotation with potato, on a) wilt incidence and the days to on-set of wilt, b) R.solanacearum latent infection in tubers, c) R. solanacearum inoculum level in the soil after harvest, and d) yields of the tubers in the successive seasons. The field experiments were carried out in naturally wilt-infested plots at Kachwekano (2,200 meters above sea level). Potato was grown during the first rains of 2000 and 2001(referred to as 2000A and 2001A). the eight commonly grown rotating crops (sorghum, wheat, finger millet, maize, sweet potato, carrots, common beans and potato) were raised in the same experimental plots during the second rain of 2000 (referred to as 2000B). Continuous potato cultivation and served as the control. The shade house studies were to investigate the efficiency of a grass pasture (panicum maximum), four cereal crops (sorghum, wheat, finger millet maize) and a herbaceous weed (Bidens pilosa) as fallow/intervention crops in the management of bacterial wilt of potato in a shortened (one-season) rotation. Sterile soil was artificially infested with 4 levels of R.solanacearum inoculum (10*, 10 The shade house studies were to investigate the efficiency of a grass pasture (panicum maximum), four cereal crops (sorghum, wheat, finger millet maize) and a herbaceous weed (Bidens pilosa) as fallow/intervention crops in the management of bacterial wilt of potato in a shortened (one-season) rotation. Sterile soil was artificially infested with 4 levels of R.solanacearum inoculum by drenching. The Bidens pilosa grown in the CFU/gm soil was the control treatment. The third experiment was conducted in the laboratory, it investigated latent unfection of seed tubers produced from different short-rotation areas and used as planting material in various locations. All three experiments were replicated three times and conducted for three consecutive seasons. In the field study, all the rotation crops significantly (P>0.05) affected the initial R.solanacearum inoculum compared to the control. They reduced wilt incidence, increased the days to on-set of wilt, lowered the R.solanacearum inoculum level in the soil and led to higher potato tuber yields in the subsequent season. Sorghum was the best followed by wheat, then maize and finger millet. In the shade house study, irrespective of the initial level of R.solanacearum inoculum, use of fallow/intervention crop especially Panucum maximum followed by cereals (sorghum, wheat, finger millet and maize) let to a significant (P>0.05) reduction in latent tuber infection. Treatments with lower levels of R.solanacearum inoculum in soil led to significantly (P.0.05) higher tuber yields. The laboratory studies showed that most of the potato tubers being used as planting material in the short rotation areas were latently infected with R.solanacearum. Results from the current study indicate that use of commonly grown non-host rotation crops coupled with healthy seed tubers, boosts productivity in bacterial wilt infested soils. In view of the fat that rotation crops will neither require a change in the farming systems nor food habits, manipulating rotation crops is a potential strategy in the management of bacterial wilt of potato in south western Uganda where the disease is wide spread and farmers face cash and land constraints.