Heritabilities of Sweet Potato Resistances to Root Knot Caused by Meloidogyne incognita and M. javanica1

Three greenhouse tests to determine the reactions of sweet potato ( Ipomoea batatas (L.) Lam.) breeding lines and their respective open-pollinated offspring to 2 species of root-knot nematodes were conducted. Resistances occurred in high frequency to both the southern root knot nematode ( Meloidogyne incognita (Kofoid & White) Chitwood) and the Javanese (tropical) root knot nematode ( M. javanica (Treub) Chitwood). Reaction to M. incognita was studied in 2 consecutive years with different sets of parental lines using an egg mass index. Estimated heritability (h 2 ) in 1976 was 0.75 ± 0.23 and in 1977 was 0.57 ± 0.37. Three indices of reaction to M. javanica and respective h 2 estimates were: Egg mass index, 0.69 ± 0.18; galling index, 0.78 ± 0.19; and necrosis index, 0.72 ± 0.20. Resistances to the 2 species were not correlated, indicating independent inheritance. Development of cultivars with high levels of resistance to each or to both of the above diseases is possible.