The Complete Genome Sequence of ‘Candidatus Liberibacter solanacearum’, the Bacterium Associated with Potato Zebra Chip Disease

Zebra Chip (ZC) is an emerging plant disease that causes aboveground decline of potato shoots and generally results in unusable tubers. This disease has led to multi-million dollar losses for growers in the central and western United States over the past decade and impacts the livelihood of potato farmers in Mexico and New Zealand. ZC is associated with ‘Candidatus Liberibacter solanacearum’, a fastidious alpha-proteobacterium that is transmitted by a phloem-feeding psyllid vector, Bactericera cockerelli Sulc. Research on this disease has been hampered by a lack of robust culture methods and paucity of genome sequence information for ‘Ca. L. solanacearum’. Here we present the sequence of the 1.26 Mbp metagenome of ‘Ca. L. solanacearum’, based on DNA isolated from potato psyllids. The coding inventory of the ‘Ca. L. solanacearum’ genome was analyzed and compared to related Rhizobiaceae to better understand ‘Ca. L. solanacearum’ physiology and identify potential targets to develop improved treatment strategies. This analysis revealed a number of unique transporters and pathways, all potentially contributing to ZC pathogenesis. Some of these factors may have been acquired through horizontal gene transfer. Taxonomically, ‘Ca. L. solanacearum’ is related to ‘Ca. L. asiaticus’, a suspected causative agent of citrus huanglongbing, yet many genome rearrangements and several gene gains/losses are evident when comparing these two Liberibacter. species. Relative to ‘Ca. L. asiaticus’, ‘Ca. L. solanacearum’ probably has reduced capacity for nucleic acid modification, increased amino acid and vitamin biosynthesis functionalities, and gained a high-affinity iron transport system characteristic of several pathogenic microbes

Sensitivity and efficacy of the succinate dehydrogenase inhibitor fluxapyroxad, against raspberry spur blight fungus Didymella applanata

Didymella applanata, the causal agent of raspberry spur blight, is a destructive plant pathogen that can cause serious reductions in total yield. The use of fungicides plays a crucial role in successful control of the pathogen. The sensitivity of 94 isolates (66 collected during 2013 and 28 in 2017) of D. applanata to the succinate dehydrogenase inhibitor, fluxapyroxad, was evaluated in this study. In addition, the efficacy of fluxapyroxad in raspberry spur blight control in the field was determined. The isolates tested in this study showed different sensitivity to fluxapyroxad in vitro. The EC50 values of total number of isolates tested were ranged from 0.82 to 5.92 mu gml(-1). The ranges of EC50 values for the isolates varied between the localities where the isolates originated from and also the year of isolation. The mean EC50 values in the group of isolates obtained in 2013 were 1.95 mu gml(-1)+/- 0.81 (0.82 to 4.05 mu gml(-1)), while the EC50 values for those isolated in 2017 were ranged from 1.16 to 5.78 mu gml(-1) (mean=3.24 mu gml(-1)+/- 1.38). The efficacy trials were conducted during 2017 and 2018 in a commercial raspberry field at two locations in western part of Serbia. Applied in both concentration rates 0.02 and 0.03% of the formulated product (0.006 and 0.009% of a.i.), fluxapyroxad showed a very high efficacy in spur blight control in practical condition

Anastomosis group and pathogenicity of isolates of Rhizoctonia solani from potato crops in South Australia

Isolates of Rhizoctonia collected from the stems, roots, tuber sclerotia and soil of potato crops in Virginia and Lenswood, South Australia, were identified to anastomosis groups (AG). Of the 301 multinucleate isolates of Rhizoctonia solani tested, 90% were AG-3, 7% were AG-4 and 2% were AG-5; 12 isolates were binucleate Rhizoctonia spp. This is the first report of isolates of AG-4 and AG-5 causing disease in potato crops in South Australia. All AG-3, AG-4 and AG-5 isolates tested caused rhizoctonia disease symptoms on the potato cultivar Coliban in pathogenicity trials conducted under glasshotise conditions. Both AG-3 and AG-5 isolates caused black scurf and stem cankers, although symptoms of black scurf were less severe with AG-5. AG-4 isolates produced the most severe stem and stolon cankers of all isolates tested. The pathogenicity of tuber-borne inoculum was confirmed by growing plants from sclerotia-infested tubers. AG-8 isolates from diseased barley and wheat produced severe root cankers and caused loss of feeder roots on inoculated potato plants. Results suggest that rhizoctonia disease in potato fields in South Australia is caused by a combination of different anastomosis groups and this has important implications for crop rotations.G. R. Balali, S. M. Neate, E. S. Scott, D. L. Whisson, T. J. Wick