Abstract
Huanglongbing (HLB) disease is the most serious threat to citrus production in Indonesia. Commonly, the planted rootstocks/scion varieties expressed severely damaged to HLB. This research aimed to study effects of six citrus rootstock/scion combination of varieties on intensity of HLB disease, presence of Candidatus Liberibacter asiaticus (CLas), and growth of the seedlings. The grafting combination of three rootstock varieties: Japansche citroen (Citrus limonia Osbeck), Volkamer lemon (C. volkameriana V. Ten & Pasq), ‘Salam’ (local name), and two scions varieties: ‘Siem Pontianak’ (C. nobilis Lour) and ‘Keprok Tejakula’. ‘Keprok Tejakula’ (C. reticulata Blanco) were used for examination the effect rootstock/scion combination to HLB. Based on symptoms, the onset of disease intensity was observed in eight months after CLas inoculation, except on ‘Salam’ rootstock. The status of CLas inoculation, rootstock/scions varieties and the duration of plant infection influenced to CLas titers. There were inconsistency between HLB symptoms and CLas titers. According to measurement of plant height, and diameter of rootstocks and scion stem, the plant growth of Volkamer lemon rootstock grafted with ‘Siam Purworejo’ scion or ‘Keprok Tejakula’ scion was better than grafted with Japansche citroen and ‘Salam’ rootstocks. Japansche citroen rootstock was more susceptible to HLB than Volkamer lemon and ‘Salam’ rootstocks. Combination of rootstock/scion varieties affected plant tolerance against HLB.
Highlights
Citrus huanglongbing (HLB) is caused by a phloem-limited gram-negative bacterium, Candidatus Liberibacter asiaticus (CLas)
The objective of this study was to study the effect of six citrus rootstock/scion combinations of varieties on huanglongbing disease intensity, presence of Candidatus Liberibacter asiaticus (CLas), and growth of citrus seedling
The success of transmission of CLas in each rootstock/scions variety was not related to the rate of symptoms expression (Figure 1)
Summary
Citrus huanglongbing (HLB) is caused by a phloem-limited gram-negative bacterium, Candidatus Liberibacter asiaticus (CLas). HLB is one of the most serious citrus diseases worldwide, because it still has no effective control method and citrus yield is greatly declined while the disease spreads rapidly in orchards. Grafting could be effective to transmit the bacteria with the rate of infection level reached 100% in 120 days after inoculation. CLas might be propagated by buds taken from non-symptomatic but infected branches and multiplication occurred most quickly in young citrus plants. Folimonova et al (2009) grouped citrus genotypes into four categories (sensitive, moderately tolerant, tolerant and variable) based on severity of HLB symptoms and continuous growth of the CLas-inoculated plants. While, according to reaction with HLB pathogen, Ahmad et al (2011) classified citrus species into very susceptible, susceptible, and tolerant
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