Root and Foot Rot of Lantana Caused by Phytophthora cryptogea.

Abstract

Lantana (Lantana camara L.) is an evergreen shrub in the Verbenaceae. In some countries, this plant has been declared a noxious weed. However, a number of sterile or near-sterile forms are cultivated as attractive flowered potted and garden plants. In early spring 2004, ≈4,000 potted, small trees of lantana grown in a screenhouse in a commercial nursery of ornamentals near Giarre, Sicily, showed symptoms of chlorosis, defoliation, and sudden collapse of the entire plant. These aboveground symptoms were associated with a reduced root system, rot of feeder roots, and brown discoloration of the base of the stem. A Phytophthora sp. was isolated consistently from roots and basal stems of symptomatic plants using the selective medium of Masago et al. (3). Cardinal temperatures for radial growth of pure cultures obtained by single hypha transfer were 2°C minimum, 25°C optimum, and 30 to 35°C maximum. Sporangia produced in the saline solution of Chen and Zentmyer (3) were obpyriform, persistent, and nonpapillate. All isolates were A1 mating type and differentiated oospores with amphigynous antheridia in dual cultures with A2 reference isolates of P. cryptogea Pethybr. & Laff. and P. drechsleri Tucker (3). Electrophoretic patterns of total mycelial proteins (3) of the isolates from lantana were very similar to those of reference isolates of P. cryptogea from different hosts, but clearly distinct from those of reference isolates of other species included in Waterhouse's taxonomic group VI (3). Indeed, isolates from lantana were identified as P. cryptogea on the basis of morphological and cultural characters as well as the electrophoretic phenotype. Sequences of internal transcribed spacer (ITS) regions of rDNA (1) confirmed the identification as P. cryptogea. Pathogenicity of a representative isolate from lantana (IMI 392045) was tested in a screenhouse by transplanting 20 6-month-old rooted cuttings of lantana in pots (12 cm in diameter) filled with infested soil; the soil was prepared by mixing steam-sterilized sandy loam soil at a concentration of 4% (vol/vol) with inoculum produced on a mixture of vermiculite and autoclaved oat seeds. Twenty control plants were transplanted in pots containing noninfested soil. The soil was saturated with water by plugging the pots' drainage holes for 48 h and watering. After 40 days, all plants except the controls showed symptoms of root and foot rot, and P. cryptogea was reisolated from infected tissues. To our knowledge, this is the first report of P. cryptogea on lantana. On this host and other species in the verbena family, only P. nicotianae van Breda de Haan (= P. parasitica Dastur) has been previously reported (2,3,4). A possible cause of the high incidence of this disease in the nursery was waterlogging due to heavy rain and excessive irrigation.