Zamioculcas zamiifolia (Lodd.) Engl., commonly called ‘ZZ’ plant, is a monocotyledonous plant in the Araceae. It is a new introduction in the foliage plant industry worldwide and is an increasing popular ornamental foliage plant in Taiwan. In 2003, basal petiole rot and death of ZZ plants were found in two nurseries in southern Taiwan with 18% of the plants diseased at one nursery. Early symptoms were water soaking of the petiole base and a slight yellowing of the leaflets followed by browning of leaflets. As the disease progressed, the petiole base became dark brown, shriveled, collapsed, and eventually rotted. The surface of the roots and rhizomes of diseased plants were initially blackish brown followed by root rots and mortality of plants. A Phytophthora species was consistently isolated from diseased petioles, rhizomes, and roots on a selective medium (4). Two single zoospore isolates (2), each from a different nursery, were used for morphological and pathogenicity tests. The isolates were grown on vegetable juice agar (10% V8 juice, 0.02% CaCO3, and 2% agar [VJA]) at 28°C with 12-h irradiation for 10 days. Sporangia were nondeciduous, terminal or intercalary, and attached to irregularly or sympodially branched sporangiophores. Papillate sporangia were spherical to broadly ovoid or obpyriform, averaged 37.3 × 30.2 μm, and ranged from 23 to 55 μm in length by 17 to 46 μm in diameter, with a length/breadth ratio of 1.24 and a range of 1.1 to 1.4. Chlamydospores with walls 1 to 4 μm thick were terminal or intercalary, spherical, averaged 30.6 μm in diameter, and ranged from 18 to 46 μm. On the basis of the morphological characteristics above, Phytophthora nicotianae Breda de Haar. (synonym P. parasitica Dastur) was identified (1). Paired with known A1 and A2 mating types of P. cinnamomi on VJA, both P. nicotianae cultures were A2, forming oospores after 14 days in darkness at 28°C. Disease-free ZZ plants were propagated by rhizomes in 242-cm3 round pots with 500 g of sterilized potting medium (vermiculite/peat moss/perlite = 1:2:1). Plants with 30 cm long petiole were used for inoculation. For the pathogenicity test, both isolates were grown on VJA plates sealed with Parafilm at 28°C in darkness. After 10 days, aerial mycelia with sporangia were scraped off the plates, placed in 10 ml of sterile distilled water at 8°C for 15 min to release zoospores. A zoospore suspension was adjusted to 104 zoospores/ml following enumeration with a microliter pipette (3) and 200 ml of the suspension was added to each pot, or rhizomes and roots were dipped in 400 ml of the suspension for 60 min and planted immediately. Ten plants were inoculated with either method and water was added to inoculated control plants. Water soaking of the petiole bases developed in 7 days and mortality occurred in 10 days in a screenhouse after plants were inoculated with either method. Control plants remained healthy and no petiole, root, or rhizome rots developed. P. nicotianae was isolated from the advancing lesions of the inoculated plants and both experiments were repeated. To our knowledge, this is the first report of basal petiole rot and plant kill of Zamioculcas zamiifolia caused by P. nicotianae.
References: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (2) W. C. Ho and W. H. Ko. Bot. Bull. Acad. Sin. 38:41, 1997. (3) W. H. Ko et al. Phytopathology 63:1206, 1973. (4) W. H. Ko et al. Trans. Br. Mycol. Soc. 71:496, 1978.
