Response of Selected Kenyan Rice Cultivars to Infection by Root Knot Nematode (Meloidogyne incognita)

Abstract

Meloidogyne incognita causes huge yield losses in rice which is the third most important cereal crop in Kenya. The aim of this study was to identify M. incognita-resistant rice cultivars from Kenya and relate the responses to known resistance pathways with OsPR1a, OsPAL1, and OsJAMYB as marker genes in rice. Five rice cultivars BW 196, Basmati 217 (Pishori), Sindano, IR 2793-80-1 (grown in lowland irrigated fields), and NERICA 4 (grown in upland rainfed fields) were evaluated for resistance to M. incognita under greenhouse conditions in two separate trials. The number of nematode eggs, reproduction factor (RF), and the level of galling were determined. The RF was used to select resistant cultivars. There was a significant difference (P < 0.001) in the number of eggs, galling index, and RF among the cultivars. NERICA 4, BW 196, and Sindano were classified as resistant with an RF <1. There was differential expression of the three marker genes between susceptible and resistant cultivars. OsJAMYB gene was up-regulated in leaves of all rice cultivars after 1 and 3 days post inoculation (dpi). OsPAL1 was up-regulated in leaves of all varieties at 3 dpi while OsPR1a was down-regulated in leaves of resistant plants at 1 dpi and 3 dpi. These results provide an insight on sources of M. incognita resistance in Kenyan rice and it also forms an interesting starting point for further studies on defense responses of common rice varieties to root knot nematode infection.