Huanglongbing incidence, canopy volume, and sprouting dynamics of ‘Valencia’ sweet orange grafted onto 16 rootstocks

Abstract

Huanglongbing (HLB), the most important citrus disease worldwide, is associated with bacteria transmitted by the Asian citrus psyllid (ACP) preferably through new shoots present in the canopy. In a commercial citrus plant, the vegetative growth of the scion is influenced by the rootstock variety in which it is grafted. Although all commercial citrus varieties planted in recent years are susceptible to HLB, the dynamics of the rootstock in grafted plant could influence the progress of HLB, whether at the plant or grove scale. In this work, HLB incidence in 'Valencia' sweet orange grafted onto 16 rootstocks and its relationship to the tree canopy volume and flushing dynamics were evaluated in a field trial under ACP control. The experiment was conducted under rainfed conditions in Bebedouro, state of São Paulo, Brazil, from 2011 to 2019. 'Flying Dragon' trifoliate orange known for its dwarfing characteristics was used as the rootstock. A reduction in canopy volume by 77% at 8 years of age were observed compared to the most vigorous rootstocks. The frequency of flush shoots of 'Valencia' sweet orange was not influenced by the rootstock, but the abundance of flush shoots was lower on three semi-dwarfing rootstocks and as well as 'Flying Dragon'. Although HLB incidence on 'Flying Dragon' was lower than on 'Rangpur' lime and other three semi-standard rootstocks (trees with canopy volume between 51 and 75% of the 'Rangpur' lime canopy volume), all other combinations had similar HLB disease progress regardless of the canopy volume and flushing dynamics. Moreover, under field conditions, variations on the cumulative HLB incidence greater than 26% were necessary to significantly separate rootstocks. Therefore, the results suggest that true dwarfing rootstocks have potential to integrate the management program for HLB and that mechanisms in addition to tree vigor appear to be involved in the host-vector relationship.

Different Sweet Orange‒Rootstock Combinations Infected by Candidatus Liberibacter asiaticus under Greenhouse Conditions: Effects on the Roots

“…In contrast to most scions, tolerance to HLB was observed in several citrus relatives commonly used as rootstocks, particularly in trifoliate orange and some of its hybrids (Albrecht and Bowman, 2012;Boava et al, 2015). Using tolerant rootstocks is therefore one way to reduce the detrimental effects of HLB on the grafted scion (Bowman and McCollum, 2015;Bowman et al, 2016aBowman et al, , 2016bRodrigues et al, 2020;Shokrollah et al, 2011;Stover et al, 2016;Viteri et al, 2021).…”

Late-Season Sweet Orange Selections Under Huanglongbing and Citrus Canker Endemic Conditions in the Brazilian Humid Subtropical Region

“…All tested sweet orange selections were susceptible to the infection by the CLas bacterium. Although there are no citrus cultivars immune to CLas (Rodrigues et al, 2020), significant differences (p ≤ 0.001) were found within the sweet orange selections in relation to the cumulative incidence of HLB (Figure 5). Natal IAC and Folha Murcha IAC had the lowest cumulative CLas-infected trees (Figure 5) over nine-year of field evaluation.…”

Tree Growth and Production of Rainfed Valencia Sweet Orange Grafted onto Trifoliate Orange Hybrid Rootstocks under Aw Climate

“…In other experimental areas under evaluation, a similar behavior has been observed, indicating that drought tolerance of tetraploid citrus rootstocks still remains to be clearly elucidated in field conditions. Tetraploid citranges controlled the tree size of Valencia sweet orange and Ponkan mandarin to some extent but production was not satisfactory [22,46,47]. Nevertheless, several new tetraploid genotypes are promising as dwarfing rootstocks for sweet orange as well [48].…”