The effect of crop rotation on bacterial wilt incidence and potato tuber yield

Abstract

To determine the effects of crop rotation on potato bacterial wilt incidence and tuber yields, one-and two-season rotation experiments were conducted during 1995-1999 at Kachwekano Agricultural Research and Development Centre located at an altitude of 2200 meters in southwestern Uganda. Pulses, cereals, root crops and vegetables commonly grown in the area were included in different sets of rotation experiments. Each time, prior to planting the experiment, the field was planted to a bacterial wilt susceptible potato variety and artificial inoculation was also done, when needed, to achieve a somewhat uniform distribution of Ralstonia solanacearum. A one-season rotation in heavily infested field (>90% wilt incidence) with wheat and maize did not significantly reduce wilt but increased ware tuber yield, while the effects of phaseolus beans were not significant. On the contrary, a one-season rotation in mildly infested field (about 15-20% infestation) resulted in a significant reduction in wilt incidence as compared to the control. The highest wilt incidence under rotation was below 13% as compared to 62% in the control. Finger millet and sweetpotatoes reduced wilt the most, while carrots and onions reduced the least. There were no significant yield differences among the rotation treatments except for the control. A two-season rotation on heavily infested soil reduced wilt to 22% - 49% as compared to 81% in the control. The highest wilt reduction was obtained with potato-beans-maize-potato treatment, while the lowest reduction was with potato-maize-maize-potato. Total yields and ware potatoes increased from 3.2 t ha-1 with the control monocrop to 9.3 - 11 t ha-1 with rotation and marketable yields increased from 1.8 t ha-1 to 6.7 - 9.2 t ha-1. Planting different crops in two consecutive seasons performed better than planting the same crop. Interestingly, sweetpotato, which is a major staple food in the area this experiment was conducted, was found to be a good rotation crop for reducing wilt. Beans, the most important food crop and a protein source, but probably a symptom less carrier of Ralstonia solanacearum can be a good rotation crop if used before or after cereals in a potato rotation scheme.



Key Words: Crop rotation, infestations, marketable yield, Solanum tuberosum, ware potatoes, wilt incidence


(African Crop Science Journal 2001 9(1): 257-266)