Journal of Citrus Pathology

Having bacteria grown in pure culture has been the foundation of bacteriology, by allowing a wide range of microbiological studies towards understanding the functionality of a specific bacterium. However, most bacteria have not been axenically cultured to date, thus hindering the understanding of their role in the context of their host or environment. One of these unculturable bacteria are the recently emergent plant pathogens ‘Candidatus Liberibacter spp.’. This group is comprised by dynamic psyllid-vectored, phloem-limited plant pathogens and endophytes that harm a wide range of economically important crops worldwide. ‘Candidatus Liberibacter asiaticus’ (CLas) is associated with Huanglongbing (HLB) in most of the main citrus-producing areas globally, a disease causing severe economic damages. Although the establishment of axenic cultures of CLas remains a major scientific challenge, many research groups have devoted efforts to culture this bacterium to aid in elucidating its virulence mechanism and contribute towards effective HLB management. This led to the development of innovative systems to culture and grow CLas, however different authors have approached the concepts of bacterial culture and axenic culture in different manners, leading to confusion in the terminology used. In this review, we provide the scientific definitions of important terms in bacteriology, while critically reviewing the contribution of each of these important CLas culturing studies.

Might Toxoptera citricida (BrCA) be a citrus psorosis virus (CPsV) vector? We examined CPsV transmission by the BrCA throughout two experiments. In experiment 1, 4 CPsV-infected plants bearing BrCA colonies were introduced in separated cages with 12 healthy 'Madame Vinous' sweet orange (MV) seedlings in each one (48 in total). In experiment 2, 5 BrCAs collected from each CPsV-infected plant were transferred into 3 MV seedlings for each one (12 in total) and left for a 72-h inoculation period. Both experiments were replicated once. No psorosis symptoms or CPsV detection evidences a BrCA inability for CPsV transmission under our controlled conditions.

Citrus dwarfing viroid (CDVd) infection of navel orange trees (Citrus sinensis (L.) Osb.) on ‘Rich 16-6’ trifoliate orange (Poncirus trifoliata (L.) Raf.) rootstock has been previously reported to reduce canopy volume by approximately 50%. We demonstrated that the reduction in tree size of CDVd-infected citrus resulted from a >20% reduction in the apical growth of individual shoots within the tree canopy. We also demonstrated that the reduced canopy volume of the CDVd-infected trees is a long lasting phenotype comparable to that of ‘Flying Dragon’ rootstock, which is known to reduce citrus tree size.

This document sets forth the California Department of Food and Agriculture (CDFA), Citrus Pest and Disease Prevention Division (CPDPD) statewide Action Plan for Asian citrus psyllid (ACP) and Huanglongbing (HLB).  This document details the program implemented by CPDPD to sustain and protect California’s commercial citrus production, residential citrus plantings, and natural resources.