El Brazilian Huanglongbing disease-associated phytoplasma está presente en Citrus spp en Hidalgo, México

Este trabajo tuvo la finalidad de investigar la presencia de fitoplasmas asociados a síntomas similares al HLB, enfermedad causada por CLas, con el propósito de optimizar los procesos de muestreo y diagnóstico en el marco de acciones fitosanitarias oficiales en la citricultura Mexicana. A partir de alertas de resultados negativos a CLas en árboles de Citrus spp con síntomas putativos de HLB se realizaron muestreos dirigidos en huertos comerciales y traspatios en Hidalgo, Colima, Puebla y Veracruz en 2012, 2013 y 2018. El ADN total se analizó por PCR con los iniciadores P1/P7 anidados con R16F2/R16R2 y D7f2/D7r2. La infección de CLas se determinó con los iniciadores A2/ J5. Se confirmó en México la presencia del Brazilian Huanglongbing disease-associated phytoplasma, miembro del grupo 16Sr IX, asociado a C. latifolia (NCBI, MK282760) y C. aurantifolia (NCBI, MK282761) induciendo síntomas similares pero contrastantes a los causados por CLas. Estos hospederos se reportan por primera vez en adición al original reporte en C. sinensis en Brasil. También se reporta a Bidens odorata y Cajanus cajan como probables hospederos arvenses alternos y la presencia de especímenes de Graphocephala y Acinopterus (Cicadellidae), géneros reconocidos con especies vectoras de fitoplasmas de los grupos 16Sr III-A y Aster Yellow, respectivamente.

A Phytoplasma Associated with an Outbreak of an Unusual Disease of Chrysanthemum in China in 2008

In August of 2008, a disease of chrysanthemum (Dendranthema morifolium (Ramat.) Tzvel) caused losses of 70 to 80% in one of the largest chrysanthemum gardens in Yangling, Shanxi Province, China. Chrysanthemum plants in nearby areas also were affected to various degrees. Symptoms included flattened stems, shortening of internodes, yellowing of leaf margins, root death, and dwarfing of plants. Affected plants eventually collapsed. On the basis of these symptoms, a phytoplasma was suspected. Total nucleic acids were extracted from 0.5 g of phloem tissue from stems of eight symptomatic and eight asymptomatic plants by the cetyltrimethylammoniumbromide (CTAB) method (1). To amplify phytoplasma DNA, primer pairs R16mF2/R16mR1, followed by R16F2n/R16R1 (2), were used in a nested PCR. A final amplicon product (1.2 kb) was obtained from all symptomatic plants but not from asymptomatic ones. Restriction fragment length polymorphism (RFLP) analyses of R16F2n/R16R1 amplicons with MseI, AluI, HhaI, HaeIII, KpnI, RsaI, and HpaII endonucleases indicated that all symptomatic plants, but none of the asymptomatic plants, contained a phytoplasma strain of group 16SrI, subgroup B (3). A search of rDNA sequences in GenBank revealed a similarity (>99%) to aster yellow phytoplasma, 16SrI group, thereby confirming strain identity based on RFLP analysis. These results indicate the disease of chrysanthemum is associated with a phytoplasma related to the aster yellow phytoplasma group. Sequences were deposited in GenBank (Accession No. FJ543467). A vector of this phytoplasma in chrysanthemum has not been identified. References: (1) E. Angelini et al. Vitis 40:79, 2001. (2) D. E. Gundersen and I.-M. Lee. Phytopathol. Mediterr. 35:144, 1996. (3) I. M. Lee et al. Int. J. Syst. Evol. Microbiol. 48:1153, 1998.

THE SIX-SPOTTED LEAFHOPPER, MACROSTELES FASCIFRONS (STÅL.) AND ASTER YELLOWS IN MANITOBA

The six-spotted leafhopper overwintered in the egg stage only. Adults migrated into Manitoba in substantial numbers on strong south winds in mid-May. The migrant population reached a peak of about 80 leafhoppers per 100 sweeps in mid-June on cereals. There was a high mortality of migrants in late June and early July. The non-migrant population originated partly from overwintered eggs but mostly from eggs laid by migrants. New generation adults appeared in late June. Distinct broods were not apparent in the field because generations overlapped. The peak of population, about 400 leafhoppers per 100 sweeps, was reached about mid-August. Four generations were reared in a year. In general field collections the percentage of leafhoppers transmitting the aster yellow virus did not exceed 1 per cent. The percentage transmission was highest in the migrant population but dropped in July and August with the increase in local population. The rate of virus transmission was low in June and July but reached a peak in August in conjunction with the peak in population. Some weeds are a source of aster yellows virus. In Manitoba, early maturing crops generally escape severe aster yellows infection but it is often a problem on late crops.