Multiple phytoplasmas associated with potato diseases in Mexico.

In recent years, the potato crop in Mexico has been notably affected by diseases recognized as potato purple top (PPT) in foliage and potato hair sprouts (PHS) in germinating tubers. In both cases, these syndromes reduce production by affecting viability of the tubers used as seeds. There is evidence indicating that phytoplasmas are associated with these syndromes. This study presents data on the molecular detection, characterization, and ecology of the pathogens related to PPT and PHS. Restriction fragment length polymorphism (RFLP) and sequence analysis indicated that PPT phytoplasma belongs to the 16SrI group and PHS phytoplasma fits in the 16SrII group. In this paper, we report that the two different phytoplasmas have been found coexisting in the same potato plant, which demonstrates the presence of mixed infection in the field. These phytoplasmas were also detected in weeds surrounding potato fields; therefore they should be considered as alternative hosts or natural reservoirs of PPT and PHS phytoplasmas.