Responses of citrandarins (Poncirus trifoliata x Sunki mandarin) to infection by "Candidatus Liberibacter asiaticus"

Abstract

Huanglongbing (HLB or greening) is considered one of the most important citrus diseases in the world. The causative agent of HLB is the Gram-negative bacterium named Candidatus Liberibacter spp. of restricted occurrence to the sieve vessels of the host plant phloem and to the vector insect, Diaphorina citri. Although there are no reports in the literature of the existence of completely resistant genotypes, through previous studies it was possible to confirm that the multiplication of the bacteria is a contrasting characteristic among citrus species. Poncirus trifoliata and some of its hybrids have been shown to be a possible source of tolerance to the bacteria, in addition to that these genotypes have gained increasing importance as citrus rootstocks due to the qualities that confer to the fruits. In this sense, this work aims to challenge fourteen citrandarins (Citrus sunki x P. trifoliata) genotypes that showed negative results for natural infection with Candidatus Liberibacter asiaticus (CLas), according to results of previous studies, and to study the contribution of one of these genotypes when used as a rootstock for "Valencia" sweet orange infected with CLas. Two experiments will be conducted. In the experiment I, it will be evaluated the colonization of the bacterium in citrandarins grafted in plants "Valencia" sweet orange already infected with CLas. In the experiment II, one of the citrandarins, pre-selected in previous works, the TSxPT 222, will be used as a graft and intergraft for "Valencia" sweet orange, where the inoculations of CLas will be performed by grafting infected tissue. With this work it is expected to define genotypes of citrandarins that may confer less susceptibility of the scion variety to CLas when they are used as rootstocks, thus contributing to the management of HLB.