Brote Grande, a New Phytoplasma-Associated Disease of Chile Peppers.

Abstract

Chile is one of the most important crops in New Mexico, contributing both to the agricultural economy and cultural identity of the state. Chile producers in New Mexico and Arizona have reported a disorder of unknown etiology that has increased in frequency for the past several years. Affected plants have a bushy appearance, develop overly large green calyces instead of normal flowers, and fail to set fruit. This characteristic phyllody is similar to symptoms associated with other phytoplasma-caused diseases, such as tomato big bud, and has led chile producers to refer to the disorder as "brote grande", which is Spanish for "big bud". PCR analysis using the phytoplasma-specific primer pairs P1/Tint and P1/P7 (4) produced amplicons of the expected size (~1.6 kb) from symptomatic but not healthy samples. Direct sequencing of the P1/P7 PCR amplicons determined that they contained the expected 16S rRNA and internal transcribed spacer (ITS) sequences and included the tRNAIle typically found in phytoplasma ITS regions. BLAST analysis of the brote grande sequence (GenBank Accession No. FJ525437) indicated it is most closely related (99% identity) to sequences reported for previously characterized 16Sr group VI phytoplasmas, such as 'Candidatus Phytoplasma trifolii' (Accession No. AY390261) and the Vinca virescence (Accession No. AY500817) phytoplasma. 'Candidatus phytoplasma trifolii' is synonymous with beet leafhopper virescence, which was reported as a cause of tomato big bud in California during the mid 1990s (3). The brote grande phytoplasma was less related to other phytoplasmas known to affect peppers such as the 16Sr group XII stolbur of pepper phytoplasma (Accession No. AF248959) and newly described 16Sr group I phytoplasmas described in peppers in Cuba (Accession No. DQ286947) and Mexico (Accession No. DQ092321) (1,2). The brote grande phytoplasma is also distinct from other phytoplasmas, such as potato purple top and tomato little leaf that are common in Mexico, affecting solanaceous crops in the region (2). Although the disease frequency never exceeded 5% in any given field, plants displaying brote grande symptoms were observed in the majority of chile pepper fields examined from July to September of 2008. The presence of the brote grande associated phytoplasma was confirmed by PCR and sequence analysis of symptomatic plants from 10 different fields ranging from Las Cruces, NM to Tucson, AZ, indicating that brote grande disease is widespread across the major chile-producing areas of the Desert Southwest. The brote grande phytoplasma sequence was the only phytoplasma sequence detected in any of the symptomatic chile samples. Taken together, the etiology, PCR, and DNA sequence results all indicate that brote grande of chile is a new disease of chile peppers associated with infection by a novel 16Sr group VI phytoplasma and that this disease is distributed across the major chile-producing areas of the Desert Southwest.