MIRCETICH. 1976. The ultrastructure of the bacterium in grape xylem tissue. J. Bacteriol. LOWE. 1973. Association of a rickettsia-like 119:612-618. organism with Pierce's disease of grapevines and almond leaf scorch bacterium with special wall. 13. NYLAND, G., A. C. GOHEEN, S. K. LOWE, alfalfa dwarf and heat therapy of the disease in reference to topography of the cell Phytopathology 66:147-151. and H. C. KIRKPATRICK. 1973. The grapevines. Phytopathology 63:341-345. organism from 11. MIRCETICH, S. M., S. K. LOWE, W. J. ultrastructure of a rickettsia-like 9. HOPKINS, D. L., H. H. MOLLENHAUER, disease. MOLLER, and G. NYLAND. 1976. Etiology of a peach tree affected with phony and W. J. FRENCH. 1973. Occurrence of a 63:1275-1278. almond leaf scorch disease and transmission of Phytopathology rickettsia-like bacterium in the xylem of peach 1969. A low-viscosity epoxy resin the causal agent. Phytopathology 66:17-24. 14. SPURR, A. R. trees with phony disease. Phytopathology embedding medium for electron microscopy. J. 63:1422-1423. 12. MOLLENHAUER, H. H., and D. L. HOPKINS. study of Pierce's disease Ultrastruct. Res. 26:31-43. 10. LOWE, S. K., G. NYLAND, and S. M. 1974. Ultrastructural Crown and Root Rot of Gloxinia and Other Gesneriads Caused by Phytophthora parasitica RANDY C. PLOETZ, Assistant in Plant Pathology, and ARTHUR W. ENGELHARD, Plant Pathologist, IFAS, University of Florida, Agricultural Research & Education Center, Bradenton, FL 33508 new hosts Columnea spp. and E. cupreata ABSTRACT was shown. A preliminary report was PLOETZ, R. C., and A. W. ENGELHARD. 1980. Crown and root rot of gloxinia and other published in 1979 (16). gesneriads caused by Phytophthoraparasitica. Plant Disease 64:487-490. MATERIALS AND METHODS Phytophthora parasitica incited a root and crown rot of the florist gloxinia. Subdue 5W was Experiment 1. Gloxinia seedlings (1 in controlling the disease on the superior to Banrot 40W, Truban 30W, or Ortho 20615 50W mo old) were planted one per 10-cm Red Velvet and Improved Pink Velvet cultivars of gloxinia. Host range studies showed Improved plastic pot in a soil mix containing 5:3:3:1 pathogenic variation among isolates of P. parasitica on gloxinia, African violet, and new hosts Florida peat, sand, vermiculite, Episcia cupreata, Columnea gloriosa, and an unidentified species of Columnea. (v/v) of and perlite, respectively. The mix was amended with dolomitic limestone, hydrated lime, superphosphate, and a Gesneriaceae contains a the warmer months of the year. Fungal The family trace element mix, resulting in a final mix variety of floriculturally important organisms isolated from diseased plants wide with a pH of 6.5. Two pathogenic isolates (Sinningia included P. parasiticaDastur. plants. The florist gloxinia of P. parasitica (No. 3967, isolated from [Lodd.] Hiern. of the Fyfiana A black discoloration of gloxinia speciosa gloxinia, AREC-Bradenton, FL, and an immensely popular leaves was attributed to P. cactorum or P. group) has been FTCC No. 560, isolated from gloxinia, a century (5). The parasitica in Holland in 1925 (21). P. potted flower for over Division of Plant Industry, Gainesville, violet (Saintpaulia ionantha H. parasitica was observed in 1935 on African FL) were used to infest the soil. Each Wendl.) has been known and appreciated gloxinia in England and Wales (3), and a isolate was grown separately on 200 cc of about half as long but is stem and leaf rot of gloxinia was for only oat seed plus 200 ml of deionized water the most important and reportedly caused by P. parasiticaand P. considered autoclaved on consecutive days in l-qt the family today cryptogea in Austria in 1956 (23). More popular member of Mason jars. The two isolates were because of its adaptiveness as a house recently, Busch and Smith reported a incubated at 28 C under constant cool, plant and the variety of flower colors root and crown rot of African violet and white fluorescent light. After a 3-wk available. Other members of the family gloxinia caused by P. nicotianae var. incubation period, the isolates were include Achimenes (Achimenes spp. nicotianae (P. parasiticavar. nicotianae combined (1:1, v/v) and added to the soil Pers.), Columnea (Columnea spp. L.), Tucker) in Canada (4). P. cryptogea on mix at the rate of 5,200 cc of inoculum Episcia (Episcia cupreata Hook. and E. gloxinia has been reported in Florida per cubic meter of soil mix. Seedlings of Mart.), lipstick plant (Aeschy- (1,18), California (13,14), and New reptans the gloxinia cultivars Improved Red spp. Jack), Nematanthus York (14). nanthus Velvet and Improved Pink Velvet were spp. Schrad.), and Strepto- The magnitude of African violet (Nematanthus watered in with 50 ml of a solution carpus (Streptocarpus spp. Lindl.). production in Florida exceeds that of the containing 7.5 ml of soluble fertilizer (20- of gloxinia seedlings are florist gloxinia by several times (A. John, Millions 20-20 plus trace elements) per 4 L of in Florida as transplants for personal communication). Of the disease produced water. The soil was then drenched with 50 in and out of the problems confronting the growers of this potted plant production ml of one of the following fungicide state. Tuberous rhizomes are of minor plant, none is more serious than the root suspensions (Table 1): Banrot 40W, importance as a means of propagation. A and crown rot incited by P. parasitica. 5-etho xy-3-(trichlo ro methyl)- 1,2,4- disease with symptoms resembling those The disease has been reported in thiadiazole (Truban 15%) plus dimethyl incited by Phytophthora cryptogea Germany (12), California (17), North 4,4-0-phenylenebis (3-thioallophanate) Pethyb. and Laff. was first observed in Carolina (19), and Florida (11) and (25%); Truban 30W; Ortho 20615 5OW, the state in 1970 (W. H. Ridings,personal constitutes a threat to all stages of 2-chloro-N-(2,6-dimethylphenyl)-N- communication). Seedlings as well as growth. (tetrahydro-2-oxo-3-furanyl) acetamide; mature plants are affected, usually during Research reported here established the pathogenicity of P. parasiticaon gloxinia and Subdue 5W, metalaxyl, N-(2,6- dimethylphenyl)-N-(methoxyacetyl)-D Journal in Florida and demonstrated pathogenic Florida Agricultural Experiment Stations methyl ester. Treatments were Series No. 2027. variation among different P. parasitica L-alanine isolates on gloxinia, African violet, replicated four times and arranged in a Columnea spp., and Episcia cupreata. completely randomized design on a 00191-2917/80/05048704/$03.00/0 shaded (about 35%) greenhouse bench. 1980 American Phytopathological Society Also, pathogenicity of P. parasitica on Plant Disease/May 1980 487 Plants were observed for phytotoxicity Velvet, 6-wk-old rooted leaf cuttings of brown rot originating at the root collar beginning 3 days after treatment, and the African violet cultivars Erica and and progressing basipetally to the roots disease ratings were made after 10 days. Lisa, rooted stolons of the Episcia (E. and acropetally to the stem, leaf petioles, Experiment 2. Each of seven isolates of cupreata) cultivar Frosty, and rooted leaves, and peduncles (Fig. 1). Diseased P. parasiticafrom various hosts (Table 2) stems of the Columnea sp. cultivar Rose roots were brown and water-soaked and was grown on 200 cc of millet seed plus and Columnea gloriosa cultivar unknown. usually sloughed off when washed. 150 ml of deionized water autoclaved on Treatments were completely random- Infected seedlings invariably died. consecutive days. The infested millet seed ized and replicated five times on a shaded Although initially soft, diseased tissue was incubated for 3 wk at 28 C under greenhouse bench. All pots were placed usually maintained its original form when constant cool, white fluorescent light. on plastic trays to elevate them above the dried (Fig. 2). Diseased mature gloxinia Seven batches of infested soil were then bench surface and fertilized as described plants frequently lost their foliage to prepared by individually incorporating for experiment 1 the day after planting. decay but some subsequently resprouted the resultant inoculum for each isolate in Night temperatures in the greenhouse from the rhizome. Given favorable the soil mix described for experiment 1 were consistently above 21 C for the moisture and temperature (the cardinal (3,000 ml of inoculum per cubic meter of duration of the experiment, whereas day temperatures of P. parasitica are 10 C, soil mix). The same soil mix amended temperatures frequently rose to 35 C. All 30-32 C, and 37 C), however, these plants with a comparable rate of sterilized millet plants were rated for disease 14 and 23 and rhizomes also eventually decayed seed was used for a control treatment. days after planting. and died. Planted into each of the above soils in Experiment 1. Both cultivars of 10-cm plastic pots were 2-mo-old RESULTS gloxinia were highly susceptible to both seedlings of the gloxinia cultivars Symptoms on gloxinia, African violet, P. parasitica isolates (Table 1). Disease Improved Red Velvet and Improved Pink Episcia, and Columnea included a soft development was severe but uniform within treatments. The 4X rate (four times the label rate) of Truban 30W Table 1. Control of crown and root rot of gloxinia incited by Phytophthoraparasitica with soil provided only moderate disease control drenches of fungicides relative to the water control plants. The three rates of Subdue 5W (one, two, and Treatment Disease index" four times the suggested rate) provided (a.i./L) Cv. Improved Red Velvet Cv. Improved Pink Velvet disease control superior to that provided by corresponding rates of Truban 30W, Control (H2 0) 5.0 e 5.0 d Banrot 40W0.13 g-(0.5X) 4.8 de 4.8 cd Banrot 40W, and Ortho 20615 50W. All Banrot 40W 0.27 g (IX) 4.0 bcde 4.8 cd other treatments gave poor disease Banrot 40W 0.54 g (2X) 4.8 de 4.5 cd control.