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Kent E. Cushman and Muhammad Maqbool

Leaves of american mayapple (Podophyllum peltatum L.) contain podophyllotoxin, a compound of interest to the pharmaceutical industry. Cultural practices for establishment of mayapple in field plantings for commercial harvest have not been investigated. A factorial arrangement of three planting dates (Fall 2000, Spring 2001, or Summer 2001) and three propagule types (Nt+N1, Nt, or Nx; as described by Maqbool et al., 2004) were used to investigate strategies for establishing mayapple plantings. Rhizome segments were harvested from the wild and transplanted into plant beds in full sun in northern Mississippi. Plant emergence was recorded during March and April of each year from 2001 to 2004. Leaves within each plot were harvested as soon as they began to yellow, from the third week of April to the first week of June each year. Propagule type and planting time interacted to affect subsequent plant growth when measured on an area basis (per square meter of growing area). In 2004, spring-planted Nt+N1 produced more shoots with greater total leaf area and dry mass than spring-planted Nx or Nt. In contrast, Nt+N1 transplanted during fall or summer was equal in performance to that of Nx or Nt. Performance of summer-planted Nt was poor, producing far less leaf area and dry mass than any of the other treatment combinations. On a per plant basis, fall-planted propagules produced greater leaf area and dry mass in 2004 than spring- or summer-planted propagules, and Nt+N1 produced greater leaf area than Nx or Nt. The effect of year was not analyzed in this study due to complications of the experimental design. In conclusion, overall plant growth and performance of spring-planted Nt+N1 can be recommended as excellent and that of fall-planted Nt as poor. All other treatment combinations can be recommended as good. These results will assist growers of specialty crops in establishing mayapple plantings under field conditions in full sun.

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Kent E. Cushman and Thomas E. Horgan

Mississippi growers produce southernpea for the fresh market on raised beds using 20 to 30 lb/acre nitrogen. This study compared conventional production practices to alternative approaches in a 3 × 2 × 2 factorial arrangement in a randomized complete-block design with four replications. Three cultivars of southernpea, `Quickpick' (QP), `Texas Pinkeye' (T × PE), and `Mississippi Pinkeye' (MsPE), were planted into either raised or flat beds using either 30 lb/acre ammonium nitrate without seed inoculation or no ammonium nitrate with Rhizobium seed inoculation. QP and T × PE were harvested with a one-row Pixall harvester and MsPE was hand harvested. All plots were harvested at the mature-green stage. Yields were reduced due to drought conditions during pod fill. MsPE was hand harvested only once due to dry conditions and less-than-ideal yields. QP produced significantly greater yield (1208 lb/acre) than T × PE (962 lb/acre) or MsPE (981 lb/acre). The two nitrogen treatments were not significantly different. QP and T × PE were not affected by bed architecture, but MsPE on raised beds yielded significantly more than on flat beds. As with a similar study in 1998, also under nonirrigated conditions, MsPE had a significantly greater shellout than QP or T × PE. There were no significant interactions for yield or percent shellout.

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Kent E. Cushman and Theodore W. Tibbitts

Chlorosis and necrotic spotting develop on the foliage of particular cultivars of potato (Solanum tuberosum L.) when grown under constant light. `Kennebec', a cultivar severely injured by constant light when propagated from tissue-cultured plantlets, also was injured when plants were propagated from small tuber pieces (≈1 g). However, plants did not develop injury when propagated from large tuber pieces (≈100 g). Plants from large tuber pieces grew more rapidly than plants from small tuber pieces. The role of plant vigor and carbohydrate translocation in controlling injury development is discussed.

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H. Brent Pembcrton and Kent E. Cushman

Basal sucker shoots between 15 and 30 cm tall on multi-branched, tree-form crape myrtles (Lagerstroemia indica) were sprayed to run-off with NAA solutions of 0, 0.5, 1.0, and 1.5% in June. Five weeks later, sucker growth was assigned a visual rating from 0 to 4 denoting 0 to 100% control. Heights of three basal shoots were measured for each plant as another indicator of control. Visual ratings increased linearly from 1 to 3.6 as NAA increased from 0 to 1.5%. Basal shoot height decreased quadratically with increasing NAA concentration with the 1.0 and 1.5% NAA treatments resulting in a 53% reduction when compared to the control. Further work is needed to assess the effect of NAA on flowering and to determine if spring applications will result in season long control.

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Kent E. Cushman, Muhammad Maqbool and Patrick D. Gerard

American mayapple (Podophyllum peltatum L.) is a rhizomatous herbaceous perennial found in wooded areas of eastern North America and is a source of the pharmaceutical compound podophyllotoxin. To explore the possible domestication of this species, this research examined strategies for establishing mayapple in field plantings using organic mulches. Mayapple rhizome segments were harvested from the wild and transplanted to raised beds in northern Mississippi in Fall 2001. Two types of mulch (pine bark or wheat straw), two depths of mulch (7.5 or 15 cm), and two planting depths (0 or 5 cm) of rhizome segments were examined in a factorial arrangement and randomized complete block design. Data were recorded during spring of 2002 and 2003. Shoot number was not affected by mulch depth, but there was a significant interaction between mulch type and rhizome planting depth. Rhizome segments planted 0 cm deep and covered with straw mulch produced about 30% fewer shoots compared to any of the other treatment combinations. Number of emerging shoots was also affected by year, with a 33% increase in shoots from 2002 to 2003. Total leaf area and total leaf dry weight were not affected by mulch depth, but there was a significant three-way interaction between mulch type, rhizome planting depth, and year. During 2002, treatment combinations were not different, but during 2003 rhizome segments planted 0 cm deep and covered with straw mulch produced less leaf area and leaf dry weight than any of the other treatment combinations. The ratio of sexual shoots to total shoots was affected by year, with a higher ratio of sexual shoots occurring in 2002 than 2003. Grasses established in bark mulch to a greater extent than in straw mulch in 2002, but weed control was excellent for all treatments in 2003. These results indicate that rhizome segments planted 0 cm deep and covered with straw mulch consistently produced fewer shoots with less leaf area and dry mass compared to any other treatment combination. We preferred bark mulch, but we can recommend either bark or straw mulch for the purpose of establishing field plantings of american mayapple in full sun as long as rhizome planting depth is 5 cm. There was no difference between the two mulching depths used in this study; therefore, a mulch depth of 7.5 cm can be recommended because of its lower cost.

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Kelly T. Morgan, Kent E. Cushman and Shinjiro Sato

Fertilizer material costs, particularly nitrogen (N), have increased substantially over the past 5 years. Increased costs, along with increased awareness of the impact of fertilizer leaching on the environment in humid regions, have increased interest in use of slow-release fertilizer (SRF) or controlled-release fertilizer (CRF) materials. The goals of SRF and CRF use are that no nutrient should be limiting for crop uptake, there should be improved nutrient uptake efficiency, and nutrient-leaching potential should be reduced. These considerations are particularly important for crops grown on sandy soils with relatively low nutrient and water holding capacities. Release rates of biodegradable, or slow-release materials, such urea formaldehyde, isobutylidene diurea, and methylene urea are proportional to soil microbial activity and are therefore soil temperature dependent. These materials are N sources and depend on soil biological activity, thus, soil temperature during specific crop growth phenology must be considered and release may be delayed by soil fumigation. Whereas CRFs depend on diffusion through coatings and not biodegradation, both are soil moisture and temperature dependent. Examples of coated materials are sulfur-coated urea, polymer-coated urea, and polymer/sulfur-coated urea. The advantage of these materials is that leachable fertilizer elements other than N can be incorporated within the coating. However, this comes at an increased cost. The use of any single or combination of these materials depends on time of year, the length of crop cycle and crop nutrient demand patterns, and the use of soil fumigants.

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William B. Evans, Christine E. Coker, Kent E. Cushman, Thomas E. Horgan and Keri L. Paridon

Three years of trials in Mississippi have led to the naming of a Mississippi Medallion vegetable award winner for 2007, the fourth vegetable winner in the program's history. The Medallion program looks for garden crops that will perform throughout the state of Mississippi and help improve sales of plant materials to gardeners at retail. The Medallion selection process illustrates how growers and marketers, not just gardeners, can select specialty vegetables and cultivars for production and sale. Between 2003 and 2005, the Mississippi Medallion trials evaluated 11 sweet peppers with no green fruit stage for ornamental and yield value. Each site had three or four replications of all cultivars under evaluation annually with four plants per plot set out on raised beds with drip irrigation. Objective evaluation included total yield, marketable yield, fruit size, and days to harvest. Subjective evaluation included crop uniformity, pest tolerance, and appearance of the fruit based on color, uniformity, and shape. After nine trials, four cultivars were among the highest-yielding group in most trials: Mavras, Tequilla, Blushing Beauty, and Gypsy. The Medallion winner, to be announced in Fall 2006, was selected in part because it was within or near the top-yielding group, by least significant difference, in most trials. The perceived attractiveness of the mature fruit to the evaluating team and the perceived potential marketability of the cultivar moved it above the others under consideration. The reasons for not selecting other cultivars as the winner are as important as the reasons for selecting the winning cultivar. In the Medallion pepper case, these were mostly marketability concerns with the other cultivars, not yield issues, relative to that of the winner.

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Kent E. Cushman, Thomas E. Horgan, David H. Nagel and Patrick D. Gerard

Pumpkins (Cucurbita pepo, C. moshata) were grown in northern Mississippi during 2000 and 2001 for the purpose of more narrowly defining plant population recommendations for commercial production in the humid southeastern United States. Four plant populations were examined for `Aspen': 908, 1361, 2045, and 3068 plants/acre (2244, 3363, 5053, and 7581 plants/ha, respectively) and for `Howden Biggie': 605, 908, 1361, and 2045 plants/acre (1495, 2244, 3363, 5053 plants/ha, respectively). Plant populations were adjusted by varying in-row spacing while holding between-row spacing constant at 8 ft (2.4 m). Plant population significantly affected yield of `Aspen' and `Howden Biggie'. Linear and quadratic terms were significant for `Aspen', with maximum yield (ton/acre and fruit/acre) for the quadratic relationship occurring at about 2045 plants/acre. In contrast, yield of `Howden Biggie' decreased significantly (ton/acre) and nonsignificantly (fruit/acre) in a linear relationship as plant population increased from 605 to 2045 plants/acre. Plant population significantly affected fruit weight and size. As plant population increased, weight and size decreased slightly but significantly in a linear relationship for `Aspen' (lb/fruit and inch3/fruit) and `Howden Biggie' (lb/fruit). The quadratic relationship for `Howden Biggie' (inch3/fruit) was significant and the minimum value occurred at about 1361 plants/acre. Plant population significantly affected pumpkin yield components associated with plant productivity. As plant population increased, number and weight of fruit per plant decreased sharply in a quadratic relationship for `Aspen' (lb/ plant and fruit/plant) and `Howden Biggie' (lb/plant). The linear relationship for `Howden Biggie' (fruit/ plant) also decreased significantly. At the highest plant populations for `Howden Biggie', 40% of the plants did not produce marketable pumpkins. In conclusion, recommendations of optimum plant populations for a semi-vining cultivar such as `Aspen' should be centered on about 2045 plants/acre. Published recommendations from Kentucky appear sound, advocating plant populations within the range of 1360 to 2720 plants/acre (3361 to 6721 plants/ha). For a vining cultivar such as `Howden Biggie', recommendations can be as low as 605 plants/acre. Published recommendations from Kentucky and Georgia, along with those published in the Vegetable Crop Guidelines for the Southeastern U.S., advocate plant populations for vining cultivars of approximately 725 to 1465 plants/acre (1790–3620 plants/ha). Our results with `Howden Biggie', a cultivar that produces larger pumpkins than most other vining cultivars grown for the wholesale market, indicate that producers of vining cultivars should use plant populations from the lowest values of these recommendations or use even lower values. Our results also indicate that growers can control size and weight of pumpkins by varying plant population, with increasing populations resulting in a slight decrease of size and weight.

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Kent E. Cushman, Muhammad Maqbool, Hemant Lata, Ebru Bedir, Ikhlas A. Khan and Rita M. Moraes

Four levels of shade (0%, 30%, 55%, and 80%) were used to determine their effect on growth and lignan content of american mayapple (Podophyllum peltatum L.). Mayapple rhizomes were harvested from the wild and transplanted into plant beds on 20 Dec. 2001 using a randomized complete block design with four blocks. Growth and lignan content were recorded during spring of 2002 and 2003. Leaf samples were analyzed for the following lignans: podophyllotoxin, alpha-peltatin, and beta-peltatin. Increasing levels of shade increased shoot longevity, leaf area per plant (cm2/plant), and shoot height. Shade did not affect shoot emergence, total leaf area (cm2·m-2), or leaf dry mass (g·m-2 or g/plant). Regardless of year, podophyllotoxin and total lignan contents at 0% shade were significantly greater than those at 80% shade, and the overall trend was for decreasing contents with increasing shade. Shade did not affect alpha-peltatin content. Content of beta-peltatin was greatest at 0% shade compared to the other three shade treatments. Year affected alpha-peltatin and beta-peltatin contents, with less content of each in 2003 than in 2002. There were large numerical decreases in podophyllotoxin yield (podophyllotoxin content per unit area, mg·m-2) as shade increased from 0% to 80%, but these differences were only marginally significant (P = 0.0897). In contrast, podophyllotoxin yield was significantly greater in 2003 than in 2002 as total leaf area and dry mass significantly increased. Increasing levels of shade slightly decreased air and soil temperatures. Our results indicate that american mayapple is not a shade-requiring species. Under full sun (0% shade) shoots did not persist as long as under shade and leaves were smaller and thicker, but total lignan content was significantly greater than under shade. It appears that growers of specialty crops serving the pharmaceutical industry can establish and cultivate american mayapple under full sun, thus providing leaf biomass with high podophyllotoxin content while avoiding the cost of expensive shade structures.

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Muhammad Maqbool, Kent E. Cushman, Rita M. Moraes and Patrick D. Gerard

American mayapple (Podophyllum peltatum L.) is a rhizomatous, herbaceous perennial found in wooded areas of eastern North America and is a source of the pharmaceutical compound podophyllotoxin. This research was conducted to determine the optimum duration of low temperature exposure in overcoming dormancy of fall-harvested rhizome segments for subsequent use as propagules in greenhouse plantings. Two types of rhizome segments were harvested from the wild and used in this study: two-node rhizome segments consisting of a terminal node and its adjacent one-year-old node and one-node rhizome segments consisting of a single node, other than a terminal node, of unknown age or rhizome position. For growth cycle I, rhizome segments were exposed to low temperature (≈4 °C) for 30, 45, 60, 75, or 90 days, planted in pots, and grown in a greenhouse set at 21 °C. Shoot emergence, shoots per pot, and plant height were recorded. Leaves were removed from plants when senescence first became evident, and leaf area was recorded. For growth cycle II, rhizome segments remained undisturbed in the original pots and were exposed to low temperatures (≈4 °C) for 90 days. Pots were again placed in the greenhouse and shoot emergence, shoots per pot, plant height, and leaf area were recorded. Increasing duration of low temperature exposure of rhizome segments up to 75 days appeared to increase percent emergence and plant height and decrease days to emergence, though changes in greenhouse conditions over the study period may have also influenced shoot emergence and plant growth. Two-node rhizome segments exhibited higher percent shoot emergence, shoot longevity, leaf area, and plant height than single-node segments during each growth cycle. Two-node rhizome segments also exhibited fewer days to emergence during growth cycle I. Rhizome segments produced no more than a single shoot in growth cycle I, whereas more than one shoot was produced in growth cycle II. Most of the effects of low temperature exposure during growth cycle I persisted throughout growth cycle II. These results indicate that dormancy of mayapple rhizomes can be overcome with low temperature exposure and shoots can be induced to grow at any time of year.