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  • Author or Editor: Kent E. Cushman x
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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.

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Evaluations of 21 entries (commercial cultivars and breeders' experimental hybrids) of triploid watermelon (Citrullus lanatus) were conducted in northern and central Mississippi during 2000 and 2001. The purpose of this research was to identify high-yielding, medium-sized triploid cultivars with good horticultural characteristics and consumer qualities for commercial production in Mississippi. Most entries were similar to `Tri-X 313' and had red flesh, oval shape, and a mottle stripe rind pattern. SXW 5052, `Triple Crown,' `Crimson Trio,' `SeedWay 4502,' and `Millionaire' produced the highest total marketable yields; however, SXW 5052 is no longer available. `Crimson Trio' produced slightly smaller-sized melons compared to other entries and `SeedWay 4502' produced melons with relatively low soluble solids concentration. Based on total marketable yield, average size of melons, soluble solids concentration, and lack of undesirable characteristics such as hollowheart, black and colored seed, and rind necrosis, `Triple Crown,' `Millionaire,' `Cooperstown,' `Summer Sweet 5244,' and `Crimson Trio' can be recommended as mid- to late-maturing cultivars for commercial production in Mississippi. Based on early marketable yield, and using the same criteria listed above, `Tri-X 313' and `Tri-X Carousel' can be recommended as early-maturing cultivars for commercial production in Mississippi. `Tri-X 313' exhibited only one undesirable trait, producing a relatively high number of black and colored seeds. `Diamond' had high early and total yields, as well as high soluble solids concentration, but it should be recommended only on a trial basis to determine its potential susceptibility to hollowheart.

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Expanding leaflets of young `Kennebec' potato plants (Solanum tuberosum L.) develop visible necrotic spotting after 8 to 9 days of constant light and constant temperature, but little is known about this disorder before the appearance of injury. Whole-leaf autoradiography and iodine staining of terminal leaflets (5 to 10 mm long at the beginning of the constant-light period) showed a normal pattern of CO2 assimilation and starch content over the entire leaflet surface after 5 days of constant light. However, small areas of tissue devoid of CO2 assimilation and starch content became apparent on day 6, and these areas expanded to encompass much of the leaflet's medial and basal regions by day 7. At this stage of leaf development, on day 7, leaflets had attained 50% of their final leaflet length and ceased importing photosynthates from other leaves. Electron micrographs of chloroplasts from the medial and basal regions of leaflets on day 7 revealed a loss of membrane integrity and a senescence-like appearance. At this time, and within these affected regions, scattered groups of necrotic palisade cells began to appear. These scattered groups soon expanded in size and distribution and became apparent as visible necrotic spots on the upper leaflet surface by day 8 or 9. Leaflets on plants grown under constant light hut alternating temperatures, an environment known to be noninjurious, did not exhibit visible spotting or tissue devoid of starch content. In addition, none of these injury symptoms developed in `Denali', a potato cultivar tolerant of constant light. Despite its occurrence in expanding leaf tissue, constant-light injury appears to be a senescence-like event that leads to the catastrophic loss of photosynthetic competence, starch content, and chloroplast membrane integrity, producing chlorosis and necrosis of leaves and eventually stunting the plant.

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Small- and large-scale farmers must often decide when to begin application of fungicides, either before the onset of disease as a preventative treatment or after disease becomes evident in the field. Growers also must decide about products that claim to enhance fungicide efficacy when added to the spray mixture. A study was conducted during the summer of 2002 to investigate control of foliar diseases of vine crops (Cucurbita spp.) with low-input (LI) or high-input (HI) management approaches and six fungicide/spray combinations at four locations in southeastern United States. Fungicide applications began for LI when leaf disease first became evident and for HI about 20 days after seeding. Both approaches continued applications at 7- to 10-day intervals until harvest. Spray treatments consisted of a water-only control or one of six combinations of azoxystrobin/chlorothalonil alone or in combination with potassium bicarbonate, foliar phosphite (0N–12.2P–21.6K), or foliar nitrogen (25N–0P–0K). Azoxystrobin was applied in rotation with chlorothalonil for all treatments except the control. Seeds of ‘Lil’ Goblin’ pumpkin (Cucurbita pepo) were planted July to August and fruit harvested October to November, depending on location. Plants were rated twice for powdery mildew (Sphaerotheca fuliginea and Erysiphe cichoracearum) and downy mildew (Pseudoperonospora cubensis). HI did not significantly increase yield compared with LI. All fungicide treatments significantly increased yield and reduced foliar diseases compared with the water-only control. The simplest of treatments, the azoxystrobin/chlorothalonil rotation without any other chemicals, can be recommended for general use where strobilurin resistance has not been documented.

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Leaves of American mayapple (Podophyllum peltatum) are being investigated as an alternative and renewable source of podophyllotoxin, a pharmaceutical compound used in the manufacture of several drugs. This study examined long-term performance of mayapple populations subjected to different harvest strategies. A naturally occurring population in shade was subjected to leaf removal treatments of frequency (every year, every 2nd or 3rd year) or timing (early or late season). Plots were 1.0 m2, established during Spring 2001, and treatments were applied from 2001 to 2004. Control plots not previously harvested were also included each year. Plants did not tolerate the severest of leaf removal treatments: early harvest time in combination with annual harvest frequency. Early annual harvests reduced total leaf dry mass and total leaf area in a quadratic manner. Late harvest conducted annually, and early harvest conducted every other year, also reduced leaf dry mass and area but not as much as early annual harvest. Plants harvested every year, early, or early every year produced fewer sexual shoots than other treatment combinations. Contents of α-peltatin, β-peltatin, and total lignans were higher for leaves harvested early than those harvested late during each year of the study, demonstrating that lignan contents were affected by leaf age and not treatment. In conclusion, our results for plants grown in shade show that leaves can be removed late in the growing season every 2nd or 3rd year or early every 3rd year without reducing long-term performance of the population. This is more restrictive than that reported for populations in full sun where plants tolerated late harvests every year.

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Watermelon (Citrullus lanatus) production is concentrated in southern Florida where growers often use seepage irrigation. According to a recent survey, growers believe that nitrogen (N), phosphorus (P), and potassium (K) rates recommended by the University of Florida Institute of Food and Agricultural Sciences (UF-IFAS) are low. A study was conducted during Spring 2004 and 2005 at a UF-IFAS research farm to compare three nutrient and water management systems: high rate [HR (265, 74, and 381 lb/acre N, P, and K, respectively)], recommended rate [RR (150, 44, and 125 lb/acre N, P, and K, respectively)], and recommended rate with subsurface irrigation (RR-S). Irrigation was managed to keep soil moisture content at 16% to 20% for HR and 8% to 12% for RR and RR-S. The experimental design was a randomized complete block design with two replications and three subsample areas within each 0.25-acre plot. The HR management approach produced ≈60% to 80% higher yields (cwt/acre) during 2005 than RR or RR-S. The HR treatment produced larger watermelons than RR or RR-S in 2005. Triploid watermelon prices had to be at least $3.74/cwt to cover all costs associated with HR. The HR approach increased the grower net returns by $590/acre and $1764/acre under conservative and higher yield and price expectations, respectively. Soluble solids content and hollowheart ratings were unaffected by treatment. Total biomass, recorded during 2005, followed a similar trend as yield, with HR producing 105% and 125% greater total dry weight than RR and RR-S, respectively. Total N content of HR biomass was 56% higher than that of RR and RR-S. Total P content was 29% and 50% higher than that of RR and RR-S, respectively. Leaf and petiole tissue from the HR treatment exhibited consistently higher N and K leaf tissue values during 2005 than RR and RR-S. In conclusion, trends in the data consistently showed greater plant performance with higher rates of fertilizer and soil moisture content. Our ability to detect differences in 2005 was probably enhanced by higher rainfall during 2005 compared with 2004.

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