A hypersensitivity-like response to meloidogyne graminicola in rice (Oryza sativa)

Abstract

Mdoidogyne granunicola is a major plant-parasitic nematode affecting rice cultivation in Asia. Resistance to this nematode was found in the African rice genotypes Oryza glaberrima and O. longistaminata; however, due to intcrspocific hybrid sterility, the introgrcssion of resistance genes in the widely consumed O. sativa varieties rcmaias challenging. Recently, resistance was found in O. sativa and here, we report for the first time the histological and genetic characterization of the resistance to M. graminicola in Zhonghua 11, an O. sativa variety. Bright-light microscopy and fluorescence observations of the root tissue of this variety revealed that the root cells surrounding the nematode displayed a hypcrscnsitivity-likc reaction with necrotic celLs at early stages of infection when nematodes are migrating in the root's mesoderm. An accumulation of presumably phenolic compounds in the nematodes' neighboring root cells was also observed. In addition, at a later stage of infection, not only were few feeding sites observed but also the giant cells were underdeveloped, underlining an incompatible interaction. Furthermore, we generated a hybrid O. saliva population by crossing Zhonghua 11 with the susceptible O. saliva variety 1R64 in order to describe the genetic background of this resistance. Our data suggested that the resistance to M. gratninicola infection was qualitative rather than quantitative and. therefore, major resistance genes must be involved in this infection process. The full characterization of the defense mechanism and the preliminary study of the genetic inheritance of novel sources of resistance to Mcloidogyne spp. in rice coastitutc a major step toward their use in crop breeding.