Studies on the effects of cropping system on fusarium wilt of pigeonpea

Studies on the effects of crop rotation and intercropping on the soil borne wilt [ Fusarium udum (Butler)] of pigeonpea were conducted in a wilt-sick plot at ICRISAT Center, India, from 1979 to 1983. The wilt incidence in a continuous sole pigeonpea treatment was 64% in the year 1981 and 80–90% or more in the remaining three years. One-year breaks of sorghum and fallow produced substantial reductions in wilt incidence in the following pigeonpea crop. After two cycles of break crop followed by pigeonpea, wilt incidence was only 16% in the sorghum rotation and 31% in the fallow rotation. Averaged over these two cycles, pigeonpea seed yields were increased from only 93 kg/ha to 340 and 495 kg/ha after the sorghum and fallow breaks, respectively. A break with tobacco caused less reduction in wilt incidence than with other break crops, but pigeonpea yield was increased to 398 kg/ha. A one-year break of cotton or one year of a wilt-resistant line of pigeonpea delayed wilt development, but did not reduce final wilt incidence or significantly afftect yield. Wilt incidence increased again in the second successive pigeonpea crop ater a one-year sorghum break, although it was still significantly less than that in the continuous pigeonpea. After a two-year sorghum break, the effects lasted longer, the wilt incidence being only 24% in the second successive pigeonpea crop. Intercropping with sorghum produced a large reduction in wilt incidence in pigeonpea in the first year (down to 55%) and thereafter it stabilised at about 20–30%. Although intercropped pigeonpea yields were greater than the partial yields normally expected in intercropping, they were no higher than the sole crop yields. The reduced wilt incidence due to a sorghum intercrop was found to be consistent across 14 susceptible pigeonpea genotypes grown in another experiment, but did not occur with maize as the intercop.