ABSTRACT
Lupinus havardii Wats., commonly known as Big Bend or Chisos bluebonnet, is a showy winter annual that can reach 1.0 to 1.5 m in height and produces blue, fragrant inflorescence (racemes). L. havardii is native to a narrow geographic range along the Mexican border in southwest Texas. The inflorescence of L. havardii has considerable potential in the cut flower industry where there is a need for high-quality, durable flowers with a blue color (1). Several crops have been produced in the greenhouse to determine production and post-harvest characteristics of the cut inflorescence. Under greenhouse growing conditions during March through June 1999, numerous plants of L. havardii cv. Texas Sapphire grown in raised beds and in containers in both Dallas and El Paso, TX, were observed with blighted flower racemes with light brown to gray lesions ranging from 1 to 5 cm in length. The racemes were attacked at varying ages and eventually assumed a hooked appearance where the terminal 15 cm of the raceme was bent downward. Isolations from symptomatic lesions removed from L. havardii flower stalks consistently yielded cultures of an Alternaria sp. on potato-dextrose agar. Typical conidia measured 27 µm length and 11 µm width with 3 to 5 transverse septa. The fungus was identified as A. alternata (Fries) Keissler consistent with the description in Ellis (2). Pathogenicity tests were conducted in the laboratory by inoculating cut inflorescences with agar disks containing the fungus. Inoculations produced light brown lesions on the racemes that were typical of disease symptoms observed on greenhouse crops. In addition to the blue-flowered Texas Sapphire cultivar, we also observed the disease symptoms on pink and white flowered breeding lines of L. havardii. This disease is important as a flower stem blighting pathogen and could severely restrict production of cut flowers during the growing season. This is the first report of Alternaria sp. attacking L. havardii. References: (1) T. D. Davis. HortScience 29:1110, 1994. (2) M. B. Ellis. 1971. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute Kew, England.
ABSTRACT
Zinnia acerosa (D.C.) Gray, is a Southwest native flowering plant frequently observed in the Trans-Pecos desert and desert grasslands of Arizona, Texas, and New Mexico. The plant is valued for producing an abundance of distinctive 2.0 cm diameter white flowers on greenish and sparsely leaved stems. Selections of Z. acerosa from West Texas are under evaluation as a water conserving plant species for use in arid landscapes of the Southwest. During April through June, Z. acerosa plants in TAMU, Dallas field plots were observed with small, brown flower spots that enlarged to include whole petals, causing conspicuous flower blighting. Microscopic examination of lesions from infected flower blossoms demonstrated the presence of short beaked, cylindrical spores near the smaller lesions on flower petals. Isolations from symptomatic flower petals consistently yielded cultures of an Alternaria sp. with long chains of conidia. Typical conidia contained 3 to 5 transverse walls and 1 to 2 longitudinal walls and measured 43 µm length by 15 µm width. The fungus was identified as A. alternata (Fries) Keissler consistent with the description in Ellis (1). Pathogenicity tests were conducted on plants maintained on a greenhouse bench by spraying spore suspensions obtained from 16-day-old A. alternata cultures on potato-dextrose agar. Inoculations produced light brown lesions on blossoms typical of field disease symptoms of the disease. This disease is important as a flower blight, however, infections on the leaves are also apparent but limited. Outbreaks of the disease are frequently observed during periods of rainfall during the summer months. This is the first report of Alternaria alternata causing a floral blight on Z. acerosa. References: (1) M. B. Ellis. 1971. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, Surrey, England.
ABSTRACT
Wilkinson and Kane (3) previously reported diseased zoysiagrass infected by Gaeumannomyces graminis (Sacc.) Arx & Olivier var. graminis in the spring in Illinois. Emerald zoysiagrass (Zoysia japonicum Steud. × Zoysia matrella (L.) Merr var. tenufolia (Willd. ex Thiele) established by sod in a home lawn for one year in Austin, TX, developed irregular, chlorotic, and, subsequently, necrotic patches 30 cm in diameter and larger in late summer of 1999. Patches were restricted to areas of the lawn receiving full sun. The lawn was fertilized, mowed at 2.5 cm, and watered daily during active growth. A thatch layer in excess of 1.9 cm was present. Tillers within diseased patches were removed easily from stolons. Crowns were rotted and colonized by dark brown septate hyphae (4.5 µm wide) and olivaceous brown lobed hyphopodia (25 × 21 µm). Diseased tillers were desiccated and newly developed leaves were chlorotic. Stolons were also chlorotic and developed water-soaked lesions adjacent to crowns. Diseased roots appeared light brown and brittle with strands of dark brown septate runner hyphae along the surface of the root axis and olivaceous brown growth cessation structures within the cortical tissue. Overall, symptoms were more severe on crowns and nodes than roots. A Gaeumannomyces fungus was isolated from root, sheath, and bud tissues. Taxonomy of the fungus was consistent with the description of G. graminis var. graminis by Walker (1,2). Diseased plants were washed free of soil and other debris and maintained in a moist chamber for 14 days. Perithecia were formed on leaf sheaths. Morphology of perithecia, asci, and ascospores was consistent with Walker's description of perithecia, asci, and ascospores of G. graminis var. graminis (2). Leaf buds and root tissue, colonized by G. graminis var. graminis, were plated directly onto potato-dextrose agar containing streptomycin sulfate and rifampicin (100 ppm, respectively). Colonies of sparse white, slightly aerial mycelium turning olive brown with age and producing lobed hyphopodia, developed from plated plant material. Hyphae at the margin of colonies curled back, characteristic of G. graminis var. graminis. Symptoms reported here are similar to those described by Wilkinson and Kane (3); however, the season and prevailing environmental conditions were different. References: (1) J. Walker. Trans. Br. Mycol. Soc. 58:427, 1972. (2) J. Walker. Mycotaxon 11:1, 1980. (3) H. T. Wilkinson and R. T. Kane. Plant Dis 77:100, 1993.
