Abstract: The penetrat ion and dynamics of Ditylenchus destructor in sweet potato were studied in a natural filed condition with an in oculation method. The results showed that the nematodes penetrated to the seedling from its tip (6cm deep from soil surface) and then migrated to upside in the seedling. The nematodes could migrate in underground stem closing to ground 8 weeks later. The nematodes reached to the aerial stem of a plant and caused damage 10 weeks after transplanting. The nematodes migrated to the new tuber roots and caused the damage 12 weeks after transplant ing, but henematodes were not extracted from the fiber roots. The nematode dynamics in the sweet plants were determined with a series of inoculation densities. The disease incidences were 40% and disease indexes were 10 in the treatments of 1 g soil containing 1- 2 nematodes in 24 d after transplanting (DAT), and disease incidences reached to 100% in 60 DAT, the disease indexes were 52- 60 in 120 DAT, while the disease incidences were 60%- 80% and disease indexes were 20 in the treatments of 1 g soil containing 16- 64 nematodes in 24 DAT, and the disease indexes reached as high as 60- 100 in 120 DAT. The disease incidences reached 100% in 24 DAT and disease indexes were 100 in 96 DAT in the highest inoculation densities (256 nematodes per gram soil). Generally, the numbers of nematodes increased in the plants with both of increasing nematode densities and culture times. The numbers of nematode per stem were 49- 56 in the treatments of 1 g soil containing 1- 2 nematodes in 60 DAT, while its numbers were more than 200 in the treatments 1 g soil containing more than 16 nematodes. The numbers of nematode started to decline in 96 DAT in the treatments of 1 g soil containing more than 2 nematodes. Our studies determined the nematodes penetration site D. destructor to the sweet potato seedling and the linear relation between the numbers of nematode in the soil and disease indexes. Our data providedmore information in the selection of control strategy and measure for managing D. destructor in sweet potato.

Key words: Ditylenchus destructor , Penetration, Population dynamics

CLC Number: 

• S435.31