Abstract
Citrus relatives are a relevant source of valuable traits for use in citrus breeding, including resistance to diseases such as Huanglongbing (HLB). Resistant rootstocks may impact tree responses to HLB. This requires graft compatibility, which has been poorly investigated within the Aurantioideae. In this study, the biometric characteristics and the anatomy of the graft union of 86 scion/rootstock combinations were assessed. This comprised 18 genotypes/species and 8 genera from Citrinae, Balsamocitrinae, and Clauseninae subtribes sensu Swingle and Reece. Most graft combinations were found to be noncompatible. Phylogenetic proximity did not ensure successful grafting as, for example, Orange jasmine autografts failed, whereas some intergeneric grafts were successful (>60% of graft-take). Plant scion height was directly related to graft-take, but the correlation between the scion and rootstock stem diameters was not a reliable indicator of graft compatibility. Rangpur/Tabog, Tabog/Rangpur, Wampee/Rangpur, Wampee/Pomeroy, Wampee/Swingle, Pomeroy/Wampee, and Swingle/Wampee were the most compatible intergeneric graft combinations. Graft-take success for this was at similar levels to those of sweet orange grafted on common citrus rootstocks. The position as a scion or rootstock in the combination affected the performance and was specific to the genotypes tested. The lack of differentiation between xylem-derived calli and the accumulation of phenolic compounds at the graft union were clear anatomical and biochemical markers, respectively, of incompatibility for most Aurantioideae combinations. In the field, within a set of the ten most promising combinations, Hamlin/Rangpur (control) was the only one that became infected by ‘Candidatus Liberibacter asiaticus’. This was first observed 12 months after planting. Overall, the assessment of biometric traits and anatomy of the graft union allowed Aurantioideae genotypes to be divided into four clusters, with respect to their graft compatibility, as follows: fully compatible with high graft-take and plant growth; potentially compatible with high graft-take but lower plant growth; partially incompatible with lower graft-take and poor plant growth; and fully incompatible with a complete absence of graft-take.
Highlights
Aurantioideae is one of the largest Rutaceae subfamilies [1,2,3]
The species used in this study were selected based on a review of literature describing responses to Candidatus Liberibacter asiaticus’ (CLas), the bacterium associated with HLB pathogenesis
Obtaining graft-compatible combinations may allow exploration of traits of interest both from citrus and citrus relatives within the subfamily Aurantioideae. These may be directly used as rootstocks to bypass biotic and abiotic problems faced in the field with commercially available scion/rootstock combinations
Summary
Aurantioideae is one of the largest Rutaceae subfamilies [1,2,3] It is divided into the Clauseneae and Citreae tribes. Citreae contains “citrus fruit trees” in the Citrinae subtribe This includes the genus Citrus, which is currently known to have a few true species and thousands of intrageneric complex citrus hybrids and types with relevant commercial importance [4,5,6]. The broad genetic and phenotypic diversity observed within Aurantioideae may be an important source of traits that could be used to improve significant attributes in commercial citrus This includes yield, abiotic stress tolerance, and pest and disease resistance [6,7,8,9]
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