Phytophthora palmivora : causal agent of peach palm stem base rot in Brazil

摘要

The area planted with peach palm ( Bactris gasipaes ) for the production of palm heart has increased in the Brazilian states of Bahia, Espírito Santo, Rio de Janeiro, Tocantins, S?o Paulo, Paraná and Santa Catarina. In these regions, the crops are attacked by stipe basal rot (SBR), a disease associated with the oomycete Phytophthora palmivora . There are few studies on this disease, and some doubts about the species Phytophthora palmivora remain. Thus, the objective of this study was to identify and morphologically, physiologically and molecularly characterize Phytophthora sp. isolates obtained from three peach palm plantation sites in order to elucidate its etiology. The 31 Phytophthora isolates were obtained from peach palm crops in the states of S?o Paulo (Eldorado, Cajati and Registro), Paraná (Paranaguá and Morretes) and Santa Catarina (Massaranduba, Garuva and Joinville). Mycelial growth of isolates was evaluated at eight temperatures (8, 12, 16, 20, 24, 28, 32 and 36 °C), as well as the aspect of the colony and the production of sporangia, chlamydospores and oospores. Fifty structures of each isolate were measured, as well as molecular analysis based on the regions ITS1 and ITS2 and Cox 1 and Cox 2. Three colony patterns were found: slightly starry, starry and cottony, and the first pattern was most frequent. There was no growth at 8 °C and 36 °C and the optimal growth temperature was 23.7 °C. The sporangia formed on sympodial ontogeny were papillate, predominantly ellipsoid, showing 21.1 – 84.8 μm length and 17.4 – 41.7 μm width, caducous, with a short pedicel of 0.4 - 6.6 μm and a length-to-width ratio varying from 1.3 to 1.9. The papillae measured between 0.9 – 11.2 μm length and 0.5 – 11.4 μm width. Chlamydospores were globose, terminal and interpolate, showing 20.0 – 53.6 μm diameter and 0.3 – 4.4 μm wall thickness. All isolates were heterothalic of the compatible mating type A1. Oospores were globose and aplerotic with no ornamented walls, measuring 26.0 – 63.6 μm, and showing amphigynous antheridia. Based on these morphological and molecular characteristics, the peach palm isolates were identified as Phytophthora palmivora (Butler) Butler .