Nature of Sweet Potato Resistance to Meloidogyne incognita and the Effects of Temperature on Parasitism.

Penetration, rate of development, and total population of Meloidogyne incognita in roots of susceptible 'Allgold' and resistant 'Nemagold' sweet potatoes increased with temperature 24-32 C. Rate of larval penetration in 'Allgold' was significantly higher than in 'Nemagold' after 48 hr of root exposure at 24, 28, and 32 C. At 24, 28, and 32 C (16 hr) day and 20 C (8 hr) night temperature the life cycle of M. incognita required 42, 32, and 28 days in 'Allgold', and 44, 33, and 31 days in 'Nemagold'; mature females in the first generation were 40, 40, 40, and 10, 22, 20 respectively. The correlation between the length of time roots were allowed to grow in the soil prior to inoculation and number of larvae recovered from the roots after inoculation was positive for 'Allgold' and negative for 'Nemagold'. Therefore, a root exudate repellent to M. incognita larvae is proposed as a hypothetical basis for resistance to M. incognita in sweet potatoes.