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  • Author or Editor: Thomas A. Evans x
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One-year-old crowns of `Jersey Giant' asparagus (Asparagus officinalis L.) were forced into spear production at 28C in darkness. Total spear fresh weight and number per square meter responded quadratically to the percentage of sand incorporated in Pro-Mix BX (PMX) peat-lite medium, with maximum yields at 25% to 75% (by volume) PMX. In a second study conducted at 22 and 28C, total spear fresh weight and number per square meter for 96 days of harvest were similar when grown in weathered, spent mushroom compost (SMC) or 1 PMX: 1 sand (v/v), but were lower than those grown in PMX. The lower temperature caused heavier individual spears, while the higher temperature stimulated earlier spear production. During the first month of harvest at 22C, the total number and fresh weight of spears in SMC were 11% and 17% less, respectively, than in PMX. SMC may be a low-cost forcing substrate for white asparagus.

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Switchgrass (Panicum virgatum L.) is one of the perennial, native, warm-season grasses recommended as a component of wildflower meadows. Seed treatments to alleviate low seed vigor and seed dormancy of switchgrass would enhance establishment of either plug transplants or seedlings after direct sowing into the meadow. “Heavy” seeds (45.5 mg/50 seeds) of open-pollinated switchgrass stored under cool and dry conditions (average 13 °C, 30% relative humidity) for 24 months had higher germination percentage than “light” seeds (26.0 mg per 50 seeds). In factorial combination, the heavy seeds were subjected to acid scarification (8 M H2SO4 for 5 min), sodium hypochlorite treatment (5.25% NaOCl for 15 min), and moist chilling (prechilling in 0.2% KNO3, for 14 days). Acid scarification followed by NaOCl treatment additively increased germination, a response that was associated with marked corrosion of the lemma margin in the distal region of the caryopsis, as observed by scanning electron microscopy. Prechilling the seeds following acid scarification and NaOCl further increased germination. All three treatments combined (acid scarification, NaOCl, and prechilling) almost doubled the final emergence and greatly increased seedling shoot dry mass in both a warm and cool postsowing environment. However, the effectiveness of these seed treatments was lost after 32 months of dry storage.

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The percentage of normal grain amaranth seedlings decreased and that of abnormal seedlings increased as threshing cylinder speed increased from 8.1 to 30.7 m·s-1. At the highest threshing speed, seed deterioration (loss of germination and increase in the percentage of abnormal seedlings) was exacerbated by increasing seed storage from 7 to 47 months. Threshing cylinder speeds of 8.1 to 12.8 m·s-1 resulted in similar percentages of normal seedlings as those achieved with hand-harvesting and threshing. Although injury to hand-harvested seeds or seeds threshed at 8.1 m·s-1 was not apparent, scanning electron micrographs of seeds threshed at 12.8 or 22.4 m·s-1 revealed damage to the seedcoat and the endosperm. Damage extended to the embryo when threshing cylinder speed was increased to 30.7 m·s-1.

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Hand-harvested and threshed grain amaranth seeds stored for 6.5 years and combine-harvested and threshed seeds (cylinder speed 26.4 m·s-1) stored for 9.5 years were subjected to several osmotic priming treatment. The selected priming treatment (–1.25 MPa polyethylene glycol at 15C for 10 days) increased percent radicle emergence of hand-harvested seeds and mechanically damaged, combine-harvested seeds and resulted in germination rates that were at least as high as those achieved with other priming treatments. In an incubator test, priming increased percent radicle emergence of hand-harvested seeds only at 15C; however, it increased percent radicle emergence of combine-harvested seeds at 15 and 35C. Priming also increased radicle emergence rate, but this response was more pronounced and exerted over a wider temperature range for the older, lower-vigor, combine-harvested seeds than for the younger, higher-vigor, hand-harvested seeds. In a greenhouse test, hand-harvested seeds had a higher percentage of normal seedlings and a lower percentage of abnormal seedlings than combine-harvested seeds. Priming had no effect on these variables. As a result of priming, normal seedling emergence rate and shoot fresh weight were higher from combine-harvested seeds than from hand-harvested seeds, such that values of these variables for primed, combine-harvested seeds were at least equal to those for nonprimed, hand-harvested seeds. Thus, the invigorating effect of priming was more pronounced for the lower-vigor, mechanically damaged, combine-harvested seeds than for the higher-vigor, hand-harvested seeds.

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The oomycete Phytophthora phaseoli is one of the most threatening pathogens of lima bean (Phaseolus lunatus) in the humid Mid-Atlantic United States. In the last 60 years, P. phaseoli has evolved to overcome genetic resistance in the host and several physiological races have been identified during the last 6 decades. Six physiological races A, B, C, D, E, and F have been identified over the years. Only race F has been detected in the field over the past decade. Identifying and characterizing sources of resistance to this pathogen and determining the nature of resistance were the main objectives. Eight commercial cultivars and 35 germplasm accessions of P. lunatus were evaluated for their reaction to races E and F. Four commercial cultivars and four accessions with resistance to race E, and two cultivars and four accessions with resistance to race F were identified. None of the germplasm evaluated were resistant to both races. Five populations of F2 plants and a recombinant inbred line (RIL) population were produced and inoculated to investigate the inheritance of resistance to races E and F. Resistance to races E and F was determined to be conferred by single, independent, dominant genes.

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'Maffei 15' baby lima bean seeds were sown every 6 cm in rows 76 cm apart to yield a nominal stand of 215,000 plants/ha at two locations in Delaware over 2 years. Seedlings were thinned within 2 weeks of planting to provide 0%, 16.7%, 33.3%, and 50.0% stand reduction at two in-row spacing patterns to determine subsequent effects on vegetative and reproductive growth. Shoot fresh weight per square meter was decreased only in 2003 by 21% and bean fresh weight per square meter was decreased only in 2004 by 13.8% when plant stand decreased to 50%. This disproportional vegetative and reproductive growth response to stand reduction resulted from a compensatory linear increase in shoot fresh weight, usable pod number, and bean fresh weight of individual plants. Thus, 'Maffei 15' lima bean tolerates a considerable loss of plant stand with little or no effect on yield.

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A mechanical planter was developed to sow seed of baby lima beans (Phaseolus lunatus) in small plots. The mechanical seeder allowed small plots to be quickly and consistently seeded at a fixed spacing. Seeds were manually spread along a 10-ft (3.0 m) base plate containing 50 holes of slightly larger diameter than the seed length and at the desired seed spacing [2.4 inches (6 cm)]. Once all the holes were filled, a slider plate below the base plate containing holes of the same diameter and spacing, but which were slightly offset, was slid horizontally so that the holes of the base and slider plates aligned and the seeds dropped to the bottom of the furrow. Compared to manual planting, the mechanical planter increased the precision of seed placement and reduced the time needed to plant 50 seeds. The planter was easy to use and transport, and was inexpensive.

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Prohexadione-Ca (BAS 12511W or Apogee™ Plant Growth Regulator) acts within a plant by blocking the biosynthesis of growth-active gibberellin. The result is decreased cell and shoot elongation; thus, vegetative growth in apple trees can be reduced. Air blast applications of prohexadione calcium were made in the Spring 1998 in commercial orchards. Application rate was 125 ppm a.i. applied twice beginning at 5 to 12 cm of new shoot growth. Reduction of shoot growth averaged 45% across locations. As a result of reduced vegetative growth, dormant pruning was reduced. In total, significant benefits to the grower included reduced pruning costs in addition to other positive effects such as improved light penetration and enhanced resistance to some pathogens. Research will continue with the effect of prohexadione-Ca on pruning in multiple year studies.

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