Abstract
Influences of nematodes on the growth and formation of root system were studied using sweetpotatoes grown in the framed plots infected with a root-knot nematode, Melidogyne incognia, in 1999. Nematode densities in the infected plot have reached to the level that could raise severe damage to sweetpotato roots by the late August. The growth of top and roots in the infected plot were markedly restricted and the yield of storage roots in October sharply decreased. In the root system of sweetpotatoes in the infected plot, the amount of roots not larger than 1mm in diameter was definitely little. The damage of nematodes to the root system was considered to be not only a reduction in root amount but also a reduction in feeder roots caused by inhibiting the growth of high dimensional lateral roots. It is considered that the change in the structure of root system brought about the retardation of the top growth and moreover, it led to a large reduction in the yield.
