A LEAFSPOT OF SENECBO CONFUSUS CAUSED BY

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1 490 FLORIDA STATE HORTICULTURAL SOCIETY, 1964 A LEAFSPOT OF SENECBO CONFUSUS CAUSED BY ALTERNARIA SENECIONIS E. K. Sobers Plant Pathologist Division of Plant Industry Florida Department of Agriculture Gainesville Introduction Senecio confusus Britten (Mexican flame vine) is a subtropical plant used in parts of the South as an ornamental vine. During November 1962, four collections of leaves exhibiting circu lar to subcircular lesions, with light gray to tan centers, wide reddish purple margins, and measuring 1-5 mm in diam were received from different locations in central Florida. Additional specimens, consisting of several severely dis eased plants, were submitted for examination and diagnosis early in Occasional stem lesions and die-back of stem tips were apparent, as were numerous leaf lesions similar to those observed on previous specimens. A species of Altemaria, resembling A. senedonis Neerg., was consistently associated with leaf lesions, and after several days in a moist chamber, the same fungus developed from affected stem tissue. Preliminary morphological and pathogenicity studies were initiated when it was found that no species of Altemaria had been previously re ported on S. confusus. The results of these studies prompted an investigation of the effect of temperature on symptomatology and disease development and a more detailed morphological study of the pathogen. Disease Occurrence In 1943, Neergaard (6) reported a species of Altemaria as the cause of leaf spotting and damping-off of Senecio cruentus DC. (cineraria) seed lings grown from seed lots originating in Den mark, France, and Germany. The causal fungus was subsequently described as a new species (7) and found to be strongly pathogenic to cineraria and lettuce; slightly pathogenic to cucumber, godetia, and tomato; and capable of damping-off cineraria seedlings. Green and Hewlett (4, 5) reported occur rences of A. senedonis on leaves of cineraria plants grown in Great Britain during 1949 and They substantiated pathogenicity of their isolate to cineraria leaves but were unable to induce damping-off among seedlings. The only known report of A. senedonis in the United States is one by Baker and Davis (2) who cite three occurrences in California. Leafspotting and damping-off were observed among cineraria seedlings growing in a flat of steam sterilized soil during November 1942, and in January 1943 and 1947, leafspotting of mature cineraria leaves was attributed to A. senedonis. Brief notes (1, 2) indicate that the pathogen has been identified on leaf lesions of S. cruentus plants grown in North Ireland and New Zealand. Materials and Methods Fungus inocula for pathogenicity tests were prepared by homogenizing 14-day-old, singlespored cultures growing on 10 ml potato-dextrose agar (PDA) in 10-ml portions of demineralized water to which had been added 1 drop of emulsifier. Mixtures consisting of 10-ml portions of sterile PDA in 10 ml demineralized water and 1 drop of emulsifier were prepared to spray on those plants serving as controls. All preparations were filtered through four thicknesses of cheese cloth before use. Inocula for damping-off experi ments were prepared in the same manner, but without filtering and without addition of the emulsifier. Plants for both experiments were placed in a mist chamber 24 hr before applying inocula, and then maintained in a greenhouse at C for the duration of the experiment. Each plant species was checked twice for sus ceptibility, with a maximum of ten control and ten test plants used on each occasion. Plants used in studying the effect of tempera ture on symptomatology and disease development were spray-inoculated with a suspension of the pathogen prepared in the same way as that used in pathogenicity studies. Plants were maintained in a mist chamber for 24 hr at 20 C, and then placed in an appropriate temperature chamber for further observation. Studies to determine the optimum temperature range for growth of the fungus were carried out at 2 C intervals from C on standard nu-

2 SOBERS: SENECIO CONFUSUS LEAFSPOT 491 trient agar (SA), as reported by Neergaard (7), and on phytone-dextrose agar (PhDA) described by Sobers and Seymour (8). The average colony diameter of four replicates at each temperature was recorded after seven days growth. Conidia produced by the fungus on leaves under field conditions were compared with those developing on leaves maintained in a moist cham ber for seven days at 20 C, and with those formed in culture on SA and PhDA after 14 days at 20 C. The average size of spore bodies and beaks is based on a minimum of 500 measure ments. Experimental Results Pathogenicity Studies. Lesions were ap parent on S. confusus, S. cruentus, and lettuce (Lactuca sativa DC.) leaves 6-8 days after the plants were inoculated. All of approximately 100 cineraria and lettuce seedlings damped-off 4-8 days after the tests were initiated. Occasional tip die-back and stem lesions were noted on S. confusus plants 2-4 weeks after in oculation. Stem lesions were elongate, reddish brown, and measured 0.5 X 3-5 mm. The lesions were found only at points where infected, and subsequently, withered leaves were attached to the stem. All cases of stem tip die-back were similarly preceded by leaf infection and wither ing. Damping-off and leafspotting were not ob served among the following species: Cabbage (Brassica oleracea var. capitata L.), carnation (Dicmthus cwryophyllus L.), carrot (Daucus carota L. var. sativa DC), castor bean (Ricinus communis L.), godetia (Godetia hybrida), onion (Allium cepa L.), pepper (Capsicum frutescens L.), radish (Raphanus sativa L.), shasta daisy (Chrysanthemum maximum Ramond), stocks (Matthiola incana R. Br.), tobacco (Nicotiana tabacum L.), tomato (Lycopersicon esculentum Mill.), and zinnia (Zinnia elegans Jacq.). Results of pathogenicity tests agree generally with those reported by Neergaard (7) for A. senecionis. Infection of cineraria and lettuce leaves, and damping-off of cineraria seedlings was substantiated. Cucumber, godetia, and tomato were listed by Neergaard as slightly susceptible hosts, but several attempts to obtain leaf in fection were without success. Effect of Temperature on Symptomatology and Disease Development. Lesions developed on spray inoculated leaves in 5, 6, 8, and 10 days at 16, 20, 24, and 28 C respectively. Infection was obtained at 32 C only by wounding the leaves before applying inoculum. Disease development was assessed on the basis of the number of days after inoculation required for 50 percent of the infected leaves to wither. Ten days were required at 16 C, 12 days at 20 C, and 23 days at 24 C. After 30 days, less than 15 percent of the diseased leaves at 28 C were withered. Lesions at 16 C and 20 C first appeared as irregularly circular, dark brown to black watersoaked spots with depressed centers. An area of water-soaked tissue, darker in color than the green of healthy leaf tissue, surrounded these spots. Similarly shaped and colored lesions oc curred on leaves at 24 C. Water-soaked areas surrounding these lesions, however, were not as large, and there was a distinct reddish-brown color associated with the tissue (Fig. 1-A). The first indication of infection at 28 C was the appearance of irregular reddish purple spots. These spots developed slowly, becoming circular to subcircular, with light gray to tan centers, and wide reddish purple margins (Fig. 1-B). Even though more time was required for dis ease symptoms to become apparent at 24 C and 28 C, the number of lesions which eventually developed did not vary significantly from the number developing at the two lower tempera tures. Leaf lesions described for the higher temperatures were typical of those most fre quently observed under field conditions. Figure 1. Typical lesions on Senecio confusus leave; caused by Alternaria senecionis at A) 24 C, B) 28 C.

3 492 FLORIDA STATE HORTICULTURAL SOCIETY, 1964 Stem tip die-back and stem lesions were more prevalent among those plants infected at 16 C and 20 C, suggesting a direct relationship to increased leaf withering at these temperatures. Isolations from leaf petioles and infected stem tissue suggested that the fungus entered the stem through the leaf petioles from infected leaves. It appeared that the age of the stem tissue de termined whether or not die-back or stem lesions would result after the stem became infected. This is based on the fact that die-back failed to develop after approximately mm of the stem was affected. Morphology of the Pathogen. 1) On naturally infected host tissue. Conidiophores were pale olivaceous to olivaceous brown, erect, septate, oc curring singly or in fascicles of 2-5, occasionally branched at or near enlarged basal cells, meas ured X jlt, and averaged 90 X 6.8 p. Conidiophore apicies were bluntly rounded, slight ly swollen, and exhibited a single prominent spore scar. Geniculations or lateral spore scars were not observed (Fig. 2, G-I). Conidia are usually borne singly, but chains of 2, and rarely 3 were observed. They were smooth, muriform, pale to medium olivaceous brown, dis tinctly ellipsoid to obclavate, with a prominent spore scar at the tip of a conically shaped basal cell, and at times exhibiting a slight longitudinal curvature. Transverse septa numbered 3-11, mostly 6-9; longitudinal septa 0-9, mostly 4-7 (Fig. 2, A-B, F). Spore bodies measured X p, and averaged 104 X 34 ^ (Table 1). The beaks of these conidia were usually the same color as the spore body, attenuate, 0-3 septate, rounded at the tips, measured X ju,, and averaged 36 X 6.7 p. Approxi mately 94 percent of the spores measured were beaked, and about 17 percent of the beaks had spore scars. 2) In the moist chamber. After seven days in the moist chamber at 20 C, conidiophores were olivaceous, non-fasciculate, erect, unbranched, measured X p, and averaged 96 X 6.2 p. Other characteristics were the same as conidiophores developing from naturally infected host tissue. Conidia were produced terminally in chains of 3-4, and rarely as many as 6 in a chain. They were pale to medium olivaceous, muriform, smooth, ellipsoid to obclavate, slightly curved along the longitudinal axis, and with a prominent spore scar at the tip of a rounded or sometimes conically shaped basal cell. Transverse septa 3-11, mostly 5-9; longitudinal septa 0-8, mostly 2-5 (Fig. 2, C-E). Spore bodies measured X (jl, and averaged 80 X 25 p, (Table 1). Beaks were usually the same color as the spore body, 0-2 septate, and much less attenuate than beaks on those conidia from naturally in fected host tissue. They measured X jj, and averaged 49 X 5.6 p. Eighty-six per cent of the spores were beaked, and 73 percent of these exhibited spore scars. 3) In culture. Aerial growth of the fungus ranged from light gray to medium olive-gray on SA, and medium to dark olive-gray on PhDA. Submerged growth was dark olive to almost black on both media. The optimum temperature range for growth of the fungus after seven days on these media was C. Growth maxima of 48 mm and 59 mm occurred at 20 C on SA and PhDA respectively (Fig. 3). No appreciable pig mentation of either medium was observed at any temperature. Conidiophores arise from procumbent mycelia, are pale to medium olivaceous, measure X ju,, and average 57 X 5.6 p. Other characteristics were essentially the same as those exhibited by conidiophores developing in the moist chamber. Conidia occurred mostly in chains of 3-4, were pale olivaceous, smooth, muriform, frequently misshapen and beakless, measured X fx (averaged 78 X 25 jx) on PhDA, and X [x (averaged 74 X 23 p) on SA (Table 1). The length to width ratio for spore bodies was slightly greater than 3:1. The beaks were pale olivaceous, 0-1 septate, slightly attenuate, measured X ^ on PhDA, and X ^ on SA. Fiftynine percent of the conidia produced in culture were beaked, and 62 percent of this number had spore scars. 4) Comparison with A. senecionis. Morpho logical characteristics exhibited by the Florida fungus in culture on SA differed only slightly from those reported by Neergaard (7) for A. senecionis on the same medium. An average spore body length and width of 74 X 23 ^ is noted for the Florida fungus as compared with 70 X 24 jx for A. senecionis; the average spore length including beaks was 97 ll and 102 p re spectively; and the optimum growth temperature was 20 C for both organisms. Neergaard's report (7) does not indicate that A. senecionis was studied under moist chamber

4 SOBERS: SENECIO CONFUSUS LEAFSPOT 493 Figure 2. Conidia and conidiophores of Alternaria senecionis: A, B, F) Typical conidia from naturally infected Senecio confusus leaves. C-E) Conidia from host tissue maintained in a moist chamber at 20 C for seven days. G-I) Conidiophores from naturally infected host tissue. conditions. A comparison of A. senecionis from gus from 5. confusus leaves measured 80 X 25 S. cruentus seedlings, with the Florida fungus as compared with 74 X 23 ^ for A. senecionis, and on S. confusus leaves maintained in a moist the average beak length was 49 ^ and 42 ^ re chamber for seven days at 20 C, however, showed spectively. the two organisms to be morphologically indis When observed on fresh material from the tinguishable. The average spore body of the fun field, the fungus associated with S. confusus

5 494 FLORIDA STATE HORTICULTURAL SOCIETY, 1964 TABLE 1. Physical dimensions of Alternaria senecionis Neerg. conidia developing on Senecio confusus leaves after natural infection (HOST), on leaf tissue maintained in a moist chamber for seven days at 20 C (MC), in culture after 14 days at 20 C on phytone-dextrose agar (PhDA), and on standard nutrient agar (SA). Spore body length \i Spore body width n Beak length [i Range Ave Range Ave Range Ave HOST MC * PhDA SA leaves exhibited important morphological char acteristics not apparent in the description of A. senecionis. Conidiophores on such material were frequently found in fascicles of 2-5, rather than singly as noted in the description; branching was observed occasionally at or near the base of the conidiophores, and the basal cells were noticeably enlarged. Conidia were usually borne singly on the conidiophores, rather than in chains of 3-4, and although the spore body length fell within the range described for A. senecionis, their aver age length was 30-34^ greater than that reported by Neergaard (7) B o TEMPERATURE *C Figure 3. Average colony diameter of Alternaria senec ionis after 10-day growth at various temperatures on A) phytone-dextrose agar, B) standard nutrient agar. Identity op the Pathogen Based on pathogenicity studies, and detailed morphological studies of the Alternaria from S. confusus, it is concluded that the fungus is A. senecionis. The following is offered as an amended description of A. senecionis: Conidiophores single or in fascicles of 2-5, pale olivaceous to olivaceous brown, erect, septate, with a single prominent terminal spore scar, branched at or near enlarged basal cells, and measuring X p Conidia pale olivaceous to medium olivaceous brown, 0-6 catenulate, smooth, muriform, trans verse septa 3-11, longitudinal septa 0-9, ellips-

6 SMITH AND BREWSTER: TURF MARKETING 495 oid to obclavate, measure X ^ and exhibit a prominent basal spore scar. Beaks pale olivaceous to olivaceous brown, 0.3 septate, attenuate, occasionally exhibiting a prominent terminal spore scar, and measuring X /x. LITERATURE CITED 1. Plant pathology division. Res. & exp. Rec. Minist. Agric. Nth. Ireland 6(1956), p Baker, K. F., and L. H. Davis Some diseases of ornamental plants in California caused by species of Alternaria and Stemphylium. Plant Disease Reptr. 34; Brien, R. H., and J. H. Dingley Second sup plement to a revised list of plant diseases recorded in New Zealand New Zealand J. Sci. Tech. 37: Green, D. E., and A. M. Hewlett A cineraria disease new to Great Britain. Gdner's. Chron. 126: Green, D. E., and A. M. Hewlett A leaf spot disease of cineraria (Senecio cruentus) new to Great Britain. J. Roy. Hort. Soc. 75: Neergaard, P Annual Reports from the Phytopathological Laboratory of J. E. Ohlsen's Widow p Neergaard, P Danish species of Alternaria and Stemphylium. Oxford Univ. Press, London, p Sobers, E. K., and C. P. Seymour Stemphyl ium leafspot of Echeveria, Kalanchoe, and Sedum. Phyto pathology 53: MARKETING CHANNELS FOR FLORIDA COMMERCIAL TURF GRASSES Cecil N. Smith and Robert H. Brewster1 University of Florida Gainesville The rise in Florida's population has resulted in a concomitant demand for houses, home yards, golf courses and parks. In turn, a derived de mand developed for many products needed in the construction of living and recreation areas. One of these requirements was for a source of grass which would result in a finished lawn without the necessity of waiting for seeded or sprigged grasses to spread and cover a lawn or golf course surface. Following World War II, the development and general acceptance of an improved strain of St. Augustine grass, the Bitter Blue variety, and its growth in popularity brought a demand for increased supplies of this product. Thus was born the commercial turf producing industry which has had a rapid rate of growth over the past 15 years. A sizable sod producing industry sprung up in Southern Florida to meet the rising de mand. Specialized sod farms, however, could not meet the growing demand for their product. An immediate and additional source of sod was the pastures in the Everglades and elsewhere in South Florida. Owners of such land found it more profitable to market sod than to sell their grass in the form of beef or milk. Operators known as "converters" moved in to ready the Florida Agricultural Experiment Stations Journal Series No lappreciation is expressed by the authors to Dr. Edwin W. Cake, Economist, University of Florida Agricultural Extension Service, for the helpful comments made in re viewing an earlier draft of this paper. pastures for marketing the sod. They fertilized and mowed the grass and followed other ap propriate maintenance practices to groom it into salable turf within 60 to 90 days. They were then followed by cutters who harvested the sod and next by truckers who hauled it to various points in the distribution channels. Procedure At the request of the commercial sod industry a research study was begun with the initial ob jective of developing data on the scope and marketing practices of the turfgrass or sod in dustry. Later phases of the research will be con cerned with the generation of data on the marketing and scope of allied components of the sod industry. Two steps, which were carried out concur rently, preceded all others in the conduct of the research reported in this paper. One step in volved the development of a list of all sod growers in Florida. The second was concerned with designing a questionnaire in which informa tion regarding growers' acreage, sales volume and other aspects of their business could be recorded. No complete list of sod growers was avail able. Extension workers, the Florida Turf-Grass Association, the Division of Plant Industry, co operating sod growers, allied tradesmen and other sources were contacted for the purpose of acquiring growers' names and their approximate acreages. The names of a limited number of these growers were not known until visits were made to cooperating growers in their localities. A list of 46 growers, later expanded to 62, was developed. The primary information requested in the