Field Evaluations of Two Citrus Interspecific Hybrid Populations Using Desert Lime (Citrus glauca (Lindl.) Burkill) Identify Presumed Resistance and Tolerance to Huanglongbing

Huanglongbing (HLB), associated with the bacterial pathogen Candidatus Liberibacter asiaticus (CLas), is one of the most destructive diseases affecting citrus. Although some citrus cultivars are tolerant of the disease, no commercially resistant varieties exist to date. Resistance, however, has been identified in the sexually compatible distant relative, the Australian desert lime (C. glauca) and its F1 hybrids. In an effort to develop commercial varieties with resistance to HLB, we produced interspecific hybrid populations between an HLB-resistant C. glauca × C. maxima F1 hybrid and two mandarins (C. reticulata). The progenies were evaluated under natural CLas infection conditions in Florida for infection status, disease symptom severity, and growth to determine whether resistance or tolerance was manifested. After four years of evaluations, using two cluster analyses (K-means and hierarchical cluster), three groups were identified: (1) progeny that was uninfected, had very low infection levels or recovered from infection, and also had low defoliation and above average growth, (2) progeny that was infected and showed high defoliation and below average growth, and (3) progeny that was infected with generally high titters, low defoliation and above average growth. Overall, these results indicate the interspecific hybrid progeny in the field segregated into apparent resistant, susceptible and tolerant trees.