Basil little leaf: a new disease associated with a phytoplasma of the 16SrI (Aster Yellows) group in Cuba

In Cuba, the development of urban and peri-urban agriculture, using a combined organic and hydroponic ('organoponic') system of intensive vegetable production, currently plays a very important role for the sustainability of food security. Basil (Ocimum basilicum) has become a very popular barrier crop for organoponic gardens, where it is commonly used to repel undesirable pests. During a survey in 2005 of weeds from the 'Alamar' organoponic in Havana province, typical phytoplasma symptoms of little leaf and witches' broom (Jones, 2002) were observed in all basil plants used as barrier crops (Fig. 1).

Leaf samples from 27 plants with symptoms and 16 apparently healthy (symptomless) plants were collected and the DNA extracted. This was used as the template in a nested PCR with universal phytoplasma rRNA primer pairs P1/P7 and R16F2n/R16R2. All 27 extracts from plants with symptoms produced a 1250 bp product, which gave typical phytoplasma profiles when digested with the restriction endonuclease HaeIII. No amplicons were produced when DNA of symptomless plants was used as the template. RFLP using RsaI and AluI gave identical profiles for all 27 samples. The P1-P7 PCR products were directly sequenced and compared by BLAST analysis with those of other phytoplasmas in GenBank. The highest similarity (99%) was to that of a 16SrI group phytoplasma (Aster Yellows; Candidatus Phytoplasma asteris) affecting watercress (GenBank accession no. AY665676). The 16S rRNA sequence from basil was deposited in GenBank (Accession no. DQ286577). This report from Cuba is the first record of a new disease for which we propose the name Basil little leaf.