McRITCHIE & MILLER: CORYNESPORA SPOT OF ZEBRA 389

CORYNESPORA SPOT OF ZEBRA PLANT

J. J. MCRITCHIE AND J. W. MlLLER To investigate the cross-pathogenicity of several isolates of C. cassiicola, non-variegated and varie FDACS, Division of Plant Industry gated hydrangea, Aphelandra, and variegated Li- Gainesville gustrum sinense Lour, were cross-inoculated with isolates from non-variegated hydrangea, non- Abstract Corynespora cassiicola was isolated variegated L. sinense, and Aphelandra. The zebra from necrotic leaf spots on . plants were wounded in the manner described, Pathogenicity was demonstrated only on wounded while the other plants were not wounded. Inoculum . The Aphelandra isolate was not cross was prepared and applied as described above. pathogenic to Hydrangea macrophylla and Li- gustrum sinense, but isolates from those hosts Results and Discussion caused leaf spots on wounded leaves of A. squar Two days after inoculation, the puncture points rosa. on the Aphelandra controls appeared as dry,black, non-spreading areas. On the leaves inoculated with Introduction the Aphelandra isolate of C. cassiicola, however, Aphelandra squarrosa Nees, commonly called a black area of necrosis spread from the points of zebra plant, is a popular ornamental plant because inoculation to form a circular leaf spot. of its showy yellow spikes and attractive After 6 additional days in the mist chamber, no dark green foliage with white veins. change was noted in the wounded, non-inoculated Few diseases have been reported on this host. leaves (Fig. 1A). The inoculated leaves showed Our records, however, show that a fungus, circular, brown to black necrotic spots, 10-20 mm Corynespora cassiicola (Berk. & Curt.) Wei, is as in diameter, expanding from the wounded area sociated consistently with leaf spots. The path (Fig. IB). Under conditions of high humidity in ogenicity of the fungus and resultsof cross-path- the mistchamber, the fungus sporulated heavily ogenicity trials are reported here. in the necrotic area. A narrow margin of water- soaking surrounding the lesions was also evident, Materials and Methods but this disappeared soon after the plants were removed from the mist chamber. Isolates of C. cassiicola were grown on potato Host-specificity of C. cassiicola was demon dextrose agar in petri plates for 10 to 13 days. strated with isolates from cucumber and hydrangea The inoculum was prepared by removing the by Miller and Alfieri (3). They also found that conidia with sterile distilled water, fragmenting isolates from variegated and non-variegated Li- the mycelium in water in a blender, and combining gustrum sinense were cross-pathogenic, but neither the 2 suspensions. The inoculum, filtered through attacked cucumber or hydrangea. All the isolates cheesecloth, was applied with an atomizer to the that we tested were pathogenic to wounded zebra top and bottom leaf surfaces of 2 healthy Aphe plants. Hydrangea and Ligustrum were attacked landra plants. The plants were covered with plastic only by their respective isolates. bags, and placed in a mist chamber. The bags Corynespora cassiicola is reported as a primary were removed after 2 days, and theplants re pathogen on many hosts, including cucumber (1), mained in the chamber an additional6 days. No tomato (2), soybeans (4), and hydrangea (5). On evidence of disease was observed. zebra plant, it is a wound-invading pathogen which In a second experiment, 5 half-leaves on each exhibits a high degree of virulence when estab of8 plants were wounded in 2 areas per leaf with lished, as demonstrated by the continuing expan a multiple needle inoculator (a ring of fine insect sionof lesions. pins). Four of these plants were inoculated in the Since C. cassiicola is exclusively a wound manner described above, and 4 were sprayed with pathogen of Aphelandra, avoid improper handling sterile distilled water as controls. After 2 days, which causes injuries. If disease occurs, removal of the plastic bags were removed and the plants were diseased leaves should provide control. Benlate, incubated as above. Daconil, Dithane M-45, and Thiabendazole are ef fective as protective sprays against Corynespora leaf spot of Ligustrum sinense (3). Contribution No. 357. Bureau of Plant Pathology, 390 FLORIDA STATE HORTICULTURAL SOCIETY, 1973

Fig. 1. Corynespora cassiicola on Aphelandra squarrosa, A) wounded, non-inoculated leaf, B) wounded, inoculated leaf showing enlarging black necrotic spots.

Literature Cited Ligustrum sinense caused by Corynespora cassiicola and its control. Phytopathology 63:(in press). 1. Blazquez, C. H. 1967. Corynespora spot of cucumber. 4. Olive, L. S. 1949. Target spot of cowpea and soybean. Proc. Fla. State Hort. Soc. 80:177-182. Mycologia 41:355. 2. . 1972. Target spot of tomato. Plant Dis. 5. Sobers, E. K. 1966. A leaf spot disease of azalea and Keptr. 56:243-245. hydrangea caused by Corynespora cassiicola. Phytopathology 3. Miller, J. W., and S. A. Alfieri, Jr. 1973. Leaf spot of 56:455-457.