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- Author or Editor: Brent K. Harbaugh x
Caladiums, widely used in containers and landscapes as ornamental plants for their bright colorful leaves, are generally forced or grown from tubers. Commercial production of these tubers in central Florida is through dividing “seed” tubers and growing them in fields. Tuber quality is therefore of critical importance to success in container forcing, landscape use, and tuber production. Fusarium tuber rot (Fusarium solani) has been recognized as the most-destructive disease that affects caladium tuber quality. There is anecdotal evidence from growers indicating the existence of resistance in commercial caladium cultivars. To identify and confirm the source of fusarium tuber rot resistance in caladium, F. solani isolates have been collected from rotting tubers grown under different soil conditions and from different locations. The pathogenecity of these isolates has been tested through artificial inoculation of fresh harvested and/or stored tubers, and a number of highly virulent isolates have been identified. These isolates have been used to refine inoculation and disease evaluation techniques. Two techniques, spraying a conidial suspension onto fresh cut surfaces and inserting Fusarium-infested carnation leaf segments into artificial wounds, have proven to yield consistent resistance/susceptibility ratings among cultivars of known difference in resistance to fusarium tuber rot. Appropriate incubation temperatures and humidity seem to be very critical for disease development and evaluation. The two techniques have been used to evaluate 35 cultivars. Several cultivars, including `Candidum', showed a high level of resistance to fusarium tuber rot, and may be good breeding parent for developing new resistant cultivars.
Caladiums (Caladium ×hortulanum) are popular ornamental plants widely grown for their bright colorful leaves. Pythium root rot, caused by Pythium myriotylum, is one of the few soil-borne diseases in caladium that dramatically reduces plant growth, aesthetic value, and tuber yield. Information on the reaction of caladium cultivars to P. myriotylum is not available, but would be valuable for integrated control of this disease and for breeding new resistant cultivars. Three Pythium isolates obtained from decaying roots of plants collected from a field production site and two greenhouses were evaluated for pathogenicity and potential use in experiments to screen commercial caladium cultivars for resistance. All three isolates were found to be highly virulent; they were able to cause obvious root rotting within 3 to 5 days and severe root rotting and leaf losses on susceptible cultivars within 10 days after inoculation. Nineteen major commercial cultivars were evaluated for their resistance to these isolates. Fifteen of the cultivars were susceptible or highly susceptible to Pythium infection. Four widely grown cultivars, `Candidum', `Candidum Jr.', `Frieda Hemple', and `White Christmas', were found to have a moderate level of resistance (partial resistance) to pythium root rot. Pythium infection also caused leaf discoloration, epinasty, wilting, and collapse. Regression analyses revealed a linear relationship between the root rot and leaf loss severity on Pythium-inoculated plants.
Caladiums (Caladium × hortulanum) are widely grown for their bright colorful leaves. Pythium root rot, caused primarily by P. myriotylum, is one of the most important diseases in caladiums. This disease can dramatically reduce plant growth, impact plant aesthetical value, and lower tuber yield. Pythium infection in the roots may also lead to subsequent entry of Fusarium into tubers resulting in tuber rot. There has been a strong interest in the tuber production and greenhouse plant production industries to identify cultivars that are resistant or tolerant to Pythium. However, few studies have been conducted since the pathogen was identified, and little information is available regarding the existence of any possible resistance in commercial cultivars. Pythium isolates were made from diseased plants collected from different sites; their pathogenicity was confirmed using tissue culture-derived plants. Procedures were developed for oogonia spore production, inoculation, and disease severity assessment. Nineteen major commercial cultivars were inoculated at two spore densities and then maintained in greenhouses under growing conditions favorable for root rotting. Plant appearance, leaf characteristics and severity of root rotting were evaluated 2-3 times after inoculation. Observations indicated that the isolates were highly virulent. They induced visible root rot within 3-5 days, and caused a complete loss of the root system and plant death for some cultivars within 2-3 weeks after inoculation. Several cultivars, including `Candidum' and `Frieda Hemple' which are widely grown cultivars, had much less root rot, higher plant survival, and seemed to have moderate levels of resistance.
Fusarium tuber rot, incited by Fusarium solani, is the major cause of losses of tuber quality and quantity in caladium (Caladium ×hortulanum) during storage and production. To develop a reliable inoculation method for evaluating cultivar susceptibility to Fusarium tuber rot and identifying sources of resistance, the effect of temperature on the mycelial growth of F. solani in vitro and on tuber rot in vivo was examined. The optimal temperature was then used to study the aggressiveness of F. solani isolates. The effect of temperature (13, 18, 23, 28, and 33 °C) on radial mycelial growth of nine F. solani isolates in vitro was determined, and all responded similarly to temperature variables, with optimal growth predicted to be at 30.5 °C. The relationship of these temperatures to disease development was then determined for the most aggressive F. solani isolate 05-20 and it was found that disease development in inoculated tubers was greatest at low temperatures (13 and 18 °C). Cold damage to tubers was observed at 13 °C; therefore, 18 °C was chosen for all future disease screening. The aggressiveness of nine isolates was tested on two caladium cultivars. Significant differences among isolates were observed for the diameter of rotted tissue in both cultivars, indicating that choice of isolate was important for screening. Isolates 05-20 and 05-257 were highly aggressive on both cultivars. Tubers of 17 commercial caladium cultivars were inoculated with three isolates (04-03, 05-20, and 05-527) and incubated at 18 °C. The interaction between isolates and cultivars was highly significant (P < 0.0001), indicating that cultivars were not equally susceptible to different pathogenic isolates of F. solani. Lesion diameters differed significantly (P < 0.0001) among cultivars/isolates and ranged from 9.5 mm (‘Rosebud’ and ‘White Christmas’ for isolate 04-03) to 23.9 mm (‘Carolyn Whorton’ for isolate 05-20). The cultivars were ranked for susceptibility to tuber rot within each isolate and the normalized total rank for the three isolates was used to place cultivars into four categories: resistant (‘Candidum’, ‘Rosebud’, ‘White Christmas’, ‘Florida Sweetheart’, and ‘Aaron’), moderately resistant (‘White Wing’ and ‘Red Flash’), susceptible (‘Candidum Jr.’, ‘White Queen’, ‘Red Frill’, ‘Florida Cardinal’, ‘Miss Muffet’, and ‘Postman Joyner’), and highly susceptible (‘Fannie Munson’, ‘Gingerland’, ‘Frieda Hemple’, and ‘Carolyn Whorton’). The availability of these sources of host plant resistance, aggressive isolates, and resistance assessment techniques will facilitate the development of new Fusarium-resistant caladium cultivars.
Recent concerns over the environmental impact of peat harvesting have led to restrictions on the production of peat in Florida and other areas. The objectives of this study were to evaluate the use of composted dairy manure solids as a substitute for sphagnum or reed-sedge peat in container substrates on the growth of Solenostemon scutellarioides L. Codd ‘Wizard Velvet’, Tagetes patula L. ‘Safari Queen’, and Begonia ×hybrida ‘Dragon Wing Red’ and to examine the nutrient content in leachate from pots. Plants were grown for 5 weeks in a greenhouse in 15-cm plastic pots with seven substrates containing various proportions of sphagnum peat (S) or reed-sedge peat (R) and composted dairy manure solids (C), each with 20% vermiculite and 20% perlite. Substrate composition had no effect on plant quality ratings, number of flowers, or root dry mass for any of the plant species evaluated. Substrate composition did not affect the growth index (GI) or shoot dry mass of S. scutellarioides ‘Wizard Velvet’ or the GI of T. patula ‘Safari Queen’. However, growth of B. ×hybrida ‘Dragon Wing Red’ (GI and shoot dry mass) and T. patula ‘Safari Queen’ (shoot dry mass only) was highest in the 3S:0R:0C substrate. The substrates containing sphagnum peat and/or composted dairy manure solids (3S:0R:0C, 2S:0R:1C and 1S:0R:2C) had the highest NH4-N losses through the first 7 d of production. The 0S:3R:0C substrate had the highest initial leachate NO3+NO2-N losses and this trend persisted throughout most of the production cycle. Significantly more dissolved reactive phosphorus was leached from substrate mixes containing composted dairy manure solids than mixes containing only sphagnum or reed-sedge peat materials through 19 d after planting. All substrates tested as part of this study appeared to be commercially acceptable for production of container-grown bedding plant species based on plant growth and quality. However, nutrient losses from the containers differed depending on the peat or peat substitute used to formulate the substrates.
Gypsophila paniculata L. cv. Bristol Fairy flowered only under long photoperiods. Neither 5°C storage up to 8 weeks nor weekly GA3 sprays at concentration from 50 to 2,000 mg/liter induced flowering at short photoperiods. Established shoots with 12 nodes flowered after 3 weeks of 24 hours photoperiod induction, but young shoots with 5 nodes (newly pinched plants) did not flower after 3 weeks of induction. Critical photoperiod of several selections of ‘Bristol Fairy’ ranged from 12-18 hours. Inadvertent selection of clones with longer critical photoperiods appears to be responsible for poor winter flowering in Florida.
Caladiums (Caladium ×hortulanum) are widely grown as pot or landscape plants for their attractive leaves. Pythium root rot (Pythium myriotylum) is one of the most damaging diseases in caladium, severely reducing plant growth, aesthetic value, and tuber yield. Twenty-three commercial cultivars were inoculated with three aggressive isolates of P. myriotylum and evaluated for their resistance to root rot. Three cultivars, `Apple Blossom', `Blizzard', and `Etta Moore', were found to have a moderate level of resistance (partial resistance) to pythium root rot. The rest of these cultivars were susceptible or highly susceptible to Pythium infection, losing up to 94% of their root tissue to rotting within 10 days after inoculation. Data indicated a linear relationship between root rot severity and leaf loss severity on Pythium-inoculated plants and highlight the importance of controlling pythium root rot in caladium pot plant and tuber production. Comparison of some recent releases with their parents for pythium root rot resistance suggests the potential of developing new resistant caladium cultivars using the identified sources of resistance.
Evidence is presented that native populations of Rudbeckia hirta L. (Blackeyed Susan) may be adapted to regional conditions. Two Florida ecotypes, one from north Florida (NFL) and one from central Florida (CFL), were better able to withstand the low fertility sites under three AHS Heat Zones (9, 10, 11) in Florida than were plants grown from Texas (TEX) seeds. Plants from TEX seed were the largest and showiest (generally the greatest number of flowers; largest flowers) but the shortest-lived. Most of these plants did not survive beyond August (about 6 months after transplanting) regardless of site. The CFL plants were especially tolerant of flooding conditions at Ft. Lauderdale. Under garden conditions, CFL Black-eyed Susan may be a highly desirable wildflower for subtropical or tropical summers.
Growth, flowering, and survival of black-eyed susan (Rudbeckia hirta L.) from three seed sources—northern Florida (NFL), central Florida (CFL), and Texas (TEX)—were evaluated under low input conditions for one growing season at four sites in Florida. Two sites were in American Horticultural Society (AHS) Heat Zone 9 while the other two were in AHS Heat Zones 10 and 11. Growth, onset date of flowering, and number of flowers at peak flowering varied by site. With few exceptions, plants tended to reach peak flowering at about the same time. Flower diameter varied by seed source with TEX>NFL>CFL. While TEX plants were perceived as the showiest, NFL and CFL plants persisted longer under the low input conditions in Florida, and hence provided some evidence of adaptation to regional site conditions.