First report of phytoplasmas affecting organoponic crops in central and eastern Cuba

The organic and hydroponic (‘organoponic’) system of intensive crop production in Cuba is used to supply the increasing urban and peri-urban demands. Surveys of organoponics in Matanzas, Las Tunas and Stgo de Cuba provinces revealed the occurrence of phytoplasma diseases with a 20-30% incidence, whose patchy distribution suggested an insect vector role in disease spread.

Symptoms were observed in cabbage (Brassica oleracea), beetroot (Beta vulgaris) (Fig 1A) and cassava (Manihot esculenta), mostly associated with leaf yellowing, small fruits, and stunting. Radish (Raphanus sativus) plants showed leaf yellowing, mosaic, crinkling, and smaller leaves (Fig 1B), and carrot (Daucus carota) plants exhibited yellowing and purpling of leaf tips (Fig 1C) becoming necrotic progressively with little leaves and shortening of internodes (Fig 1D). A total of 32 symptomatic and 12 asymptomatic plants were randomly surveyed for total DNA extraction and indexing in a nested PCR with generic phytoplasma 16S rRNA primers R16mF2/R1 and fU5/rU3. Nested PCR amplicons (~880 bp) were obtained for 26/32 samples from the symptomatic species surveyed, with no amplicons from the asymptomatic plants. PCR products were purified, cloned (pGEMT-Easy Vector, Promega), and sequenced (www.dnaseq.co.uk). All samples showed Sau3AI, HpaII and HaeIII RFLP patterns identical to the 16SrI-C reference control ‘Candidatus Phytoplasma asteris’, except those from radish that were identical to the 16SrII-A reference control ‘Ca. Phytoplasma aurantifolia‘. The phytoplasma 16S rRNA sequences scored 99% identity for carrot (GenBank Accession No. EU328254), cabbage (EU328252), beetroot (EU328251), and cassava (EU328256) with those of members of group 16SrI; and for the radish phytoplasma (EU328253) with members of group 16SrII. Both groups 16SrI and 16SrII occur in Cuba (Arocha et al., 2006a, 2006b). However, this is the first report of both a 16SrI phytoplasma affecting carrot, cabbage, beetroot and cassava, as well as a 16SrII phytoplasma in radish, in organoponics in central and eastern Cuba, and raises concerns about the spread of phytoplasmas to crops cultivated under organoponic conditions.