ABSTRACT
Psyllids (Hemiptera: Psylloidea) can transmit the phloem restricted bacterium 'Candidatus Liberibacter solanacearum' (Lso). In Europe, Lso causes severe losses to carrot and represents a threat to the potato industry. A rising concern is Lso transmission from carrot to potato and within potato, and this has driven the need for monitoring populations of psyllid species which could serve as vectors on both crops. This would provide a fundamental understanding of the epidemiology of Lso. Different sampling methods were used to survey populations of psyllid species in commercial carrot and potato fields in central and eastern mainland Spain from 2015 to 2017. Two psyllid species, Bactericera trigonica and Bactericera nigricornis were found on carrot and potato crops. In carrot fields the most abundant species was B. trigonica (occurring from crop emergence to harvest); whereas in potato crops the most abundant psyllid species was B. nigricornis. Depending on field location, the maximum psyllid populations occurred between June and October. Since B. nigricornis was found on both carrot and potato and is the only psyllid species able to feed and reproduce on both these crops in Europe, there is the potential risk of Lso transmission from carrot to potato.
ABSTRACT
The phytosanitary emergency caused by the spread of Xylella fastidiosa in the Mediterranean has raised demands for a better understanding of the ecology of its presumed and candidate insect vectors. Here, we present the results of a two-year survey carried out in olive groves across southern, eastern and Central Spain and northeastern Portugal. Several sampling methods were tested and compared to select the most appropriate to estimate population levels of potential vectors of X. fastidiosa. The spittlebugs Philaenus spumarius and Neophilaenus campestris (Hemiptera: Aphrophoridae) were the main species associated with olive groves. Both species were widely present on herbaceous ground vegetation within the olive groves; P. spumarius mainly associated with Asteraceae and N. campestris with Poaceae. Due to the patchy distribution of spittlebugs within the olive groves, sweep nets were the most effective and least time-consuming sampling method for the estimation of population size both in the ground cover and tree canopies. Trends in population density showed that spittlebugs can be abundant on ground vegetation but very rare on olive canopies. Spittlebugs disperse in late spring to non-cultivated hosts that act as natural reservoirs. In late fall, adults return to the olive groves for oviposition. However, olive trees may act as transient hosts for spittlebugs and high population densities of these insect vectors should be avoided in areas where X. fastidiosa is present.
ABSTRACT
A new symptomatology was observed in celery (Apium graveolens) in Villena, Spain in 2008. Symptomatology included an abnormal amount of shoots per plant and curled stems. These vegetative disorders were associated with 'Candidatus Liberibacter solanacearum' and not with phytoplasmas. Samples from plant sap were immobilized on membranes based on the spot procedure and tested using a newly developed real-time polymerase chain reaction assay to detect 'Ca. L. solanacearum'. Then, a test kit was developed and validated by intralaboratory assays with an accuracy of 100%. Bacterial-like cells with typical morphology of 'Ca. Liberibacter' were observed using electron microscopy in celery plant tissues. A fifth haplotype of 'Ca. L. solanacearum', named E, was identified in celery and in carrot after analyzing partial sequences of 16S and 50S ribosomal RNA genes. From our results, celery (family Apiaceae) can be listed as a new natural host of this emerging bacterium.
