Alternaria alternata is recorded as the causal agent of seed discoloration of Amaranthus caudatus ssp. mantegazzianus for the first time in Argentina.

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In Argentina, amaranth is a promising crop due to high nutritional quality and ability to grow in a diversity of environments. In areas cultivated with amaranth, were observed plants exhibiting slow growth, deformed leaves, proliferation of shoots and malformed lateral panicles. Field survey revealed up to 96% disease incidence and 92% of the seeds collected from mother plants produced diseased seedlings. A phytoplasma was detected in association with seedlings and adult plants using nested PCR assays. Molecular identification by computer‐simulated RFLP and phylogenetic analysis evidenced the occurrence of a ‘Candidatus Phytoplasma hispanicum’‐related strain, affiliated with 16SrXIII‐A subgroup. The findings implicate amaranth as a new host for this subgroup and as a potential reservoir of the pathogen for other cultivated species. In addition, to the best of our knowledge, this study reports for the first time the presence of 16SrXIII‐A phytoplasma in Argentina and in South America. Furthermore, transmission assays pointed that naturally infected seed is an important vehicle of dissemination of the pathogen, threatening the expansion of the crop for new geographical areas.

Amaranth is an ancient crop originating in the Americas that can be used as a high-protein grain (12-17%) or as a leafy vegetable, and has potential as a forage crop (Putnam et al., 1989). Grain amaranth species have been important in different parts of the world and at different times for several thousand years (Meyers & Putnam, 1988 (Fig. 3) (Noelting et al., 2009a(Noelting et al., , 2009b (Perelló et al., 2007). This disease could significantly reduce the production and the quality of amaranth due to seed transmission and its possible effects on other plant parts.

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