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use preformed crown buds as part of the perennating structure. For use as an ornamental plant, floral productivity of gentians is associated with the growth and development of these crown buds ( Samarakoon et al., 2010 , 2012 ), and the timely

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nonfreezing cold acclimation conditions, and sucrose content in crown tissues was associated with freezing tolerance ( Dionne et al. 2001 ). Perennial ryegrass ( Lolium perenne ) crown tissue water-soluble carbohydrates (WSC) increased during cold acclimation

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Cold acclimation (CA) of `Midiron' and `Tifgreen' turf bermudagrasses (Cynodon dactylon L. Pers. × C. transvaalensis Burtt-Davy) induced tolerance to lower freezing temperatures and altered protein synthesis in crowns. LT50 (lethal temperature for 50% of plants) values were lowered ≈5C after 4 weeks in controlled-environment chambers under CA [8/2C (day/night) cycles with a 10-hour photoperiod] vs. non-CA (28/24C) conditions. LT50 values for `Midiron' plants decreased from -6.5 to -11.3C after CA and from -3.6 to -8.5C for `Tifgreen'. Proteins synthesized by isolated crowns were radiolabeled in vivo for 16 hours with 35 S-methionine and 35 S-cysteine. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography revealed increased synthesis of several cold-regulated (COR) proteins in CA crowns of both cultivars. Synthesis of intermediate molecular weight (MW) (32 to 37 kDa) and low-MW (20 to 26 kDa) COR proteins was greater in `Midiron' than `Tifgreen' crowns.

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Abstract

Seed of asparagus (Asparagus officinalis L.) germinated normally after 2 months of constant freezing (-10°C) or chilling (4°) under water-saturated conditions in laboratory germination studies. However, temperatures cycling weekly from chilling to freezing for 2 months reduced germination to less than 50%, and temperatures cycling weekly from warm (21°/16°, day/night) to chilling to freezing for 2 months reduced germination to 0. The stands of asparagus, field-seeded in November and December, were reduced 85% by winterkill in comparison to spring seeding in March and April. Seeding densities from 10 to 40 seed/m did not compensate for stand loss. The greatest contributor to winterkill apparently was seed rot. March seeding increased plant height, but not crown quality or the number of shoots initiated in comparison to conventional April seeding. High seeding densities did not reduce plant growth or crown yields in the spring plantings. Stand establishment was not different between the spring planting dates. Early March seeding at high densities is recommended.

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Abstract

Growth studies of field-seeded hybrid and open-pollinated asparagus (Asparagus officinalis L.) were conducted to determine the differences in shoot, bud, and crown growth during the first season after seeding and to determine growth relationships between shoot and crown variables that indicate critical periods of bud and crown production. F1 hybrid (UC 157) and UC800 open-pollinated (OP) asparagus seedlings emerged 4 to 6 weeks after seeding. A lag phase of shoot and root growth lasted 4 to 5 weeks after emergence in both cultivars. UC157 initiated more roots and accumulated more fern and crown fresh weight than UC800 early in the season, but by harvest crowns were not different in root and bud number, fresh weight, or fructose content (crown quality). Root/shoot ratios increased from a 2:1 ratio 6 weeks after emergence to 8:1 (UC157) and 6:1 (UC800) 23 weeks after emergence. Shoot/bud ratios stabilized from an approximate 2:1 ratio initially to an approximate 1:2 ratio 18 weeks after emergence. Bud production in the F1 and OP cultivars increased 6 and 10 weeks after emergence, respectively, and continued unabated up to crown harvest 23 weeks after emergence. Shoot number and fresh weight were not correlated highly with bud number. The number of roots vs. buds and the crown vs. fern fresh weights were correlated highly and were the best indicators of quality crown production. Vigorous fern development throughout the growing season increased the potential to produce higher-quality large crowns.

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`Earliglow' strawberry (Fragaria xananassa Duchesne) plants were frozen to -5 or -50C to examine the distribution of ice in the crowns. Anatomical studies were also performed to characterize tissue growth in a greenhouse at 4, 8, and 15 weeks after freezing to -5C. Ice masses observed in fresh crown tissue corresponded to the presence of extracellular tissue voids in specimens fixed for scanning electron microscopy (SEM). Voids were present near the peduncle and adjacent to the vascular system in crown tissue. After plants were grown in the greenhouse, cell division and enlargement were observed near the voids in crowns subjected to -5C. By 15 weeks after freezing, a few small extracellular voids remained in the crowns. Tissue voids were also present in crowns of plants frozen rapidly to -50C and subsequently thawed. Cells in the crown of these plants were intact and did not appear collapsed after exposure to -50C, a lethal temperature.

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Asparagus officinalis L. cv. Centennial established with transplants in 1983 was maintained with tillage or a no-till (NT) system to evaluate effects of tillage on yield and plant growth in a mature asparagus planting. Metribuzin or metribuzin + napropamide at 1.12 and 1.68 kg a.i./ha, respectively, were used for weed control in both tillage regimes. Marketable yields were assessed for 5 years. In 1989, in addition to yield data, destructive harvests of entire plants were made every 3 weeks from March to November to evaluate the effect of tillage on fern, crown, and bud growth, and carbohydrate status. Yields were reduced by tillage from 12% to 50% from 1985 to 1989. There were no herbicide effects nor was there an effect on yield due to an interaction between herbicides and tillage. All indices of growth measured for NT exceeded those in tilled plots, although seasonal patterns of growth were similar in both. Crown and fern weight, bud cluster, and bud and fern counts were higher by 178%, 175%, 152%, 161%, and 195%, respectively, in NT than in tilled plots. The metribuzin + napropamide combination did not reduce fern fresh weight or yield, but significantly reduced the number of bud clusters, buds, and ferns when compared to metribuzin alone. Chemical names used: 4-amino-(1,1-dimethylethyl)-3-(methylthio)-l (metribuzin); 2,4-triazin-5(4H) -one, N,N-diethyl-2-(naphthalenyloxy)-propanamide (napropamide).

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Asparagus (Asparagus officinalis L. Cv. Cal. 711) grown both from seed and 1-year old crowns was maintained in a zero-tillage cultural system for 4 years and compared with that grown in a conventional tillage system. In the first 3 harvest seasons, yields of asparagus produced from crowns were increased 27% in the zero-tillage system. Asparagus from seed yielded as much as that from crowns after the third year, but spear size was appreciably smaller. Paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) in combination with either simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), monuron (3-(P-chlorophenyl)-1,1-dimethylurea), or terbacil (3-tert-butyl-5-chloro-6-methyluracil) provided excellent weed control during each growing season without injuring asparagus. Rotary chopping was a satisfactory method for returning mature brush to the soil. Additional advantages of zero-tillage were a reduction in volunteer asparagus seedlings, improved late season weed control, and less mechanical injury to crowns and buds. This cultural system provided excellent weed control in fields produced by direct seeding where crown depth was shallow and tillage impractical.

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The viability of freeze-stressed Fragaria × ananassa Duch. cv. Catskill strawberry crown tissues was evaluated using triphenyl tetrazolium chloride (TTC) reduction and oxidative browning. Both tests showed the medulla tissue to be the most susceptible to low-temperature injury, while vascular tissue was least susceptible. TTC reduction appears to be negatively related to tissue browning, and both provide similar results pertaining to tissue viability.

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Plants of four apple (Malus ×domestica Borkh.) rootstock clones, M.7, M.26, MM.111, and Ottawa (O.) 3, were grown in unamended potting medium or in the same medium infested with Phytophthora cactorum (Leb. & Cohn) Schroet., P. cambivora (Petri) Buisman, P. cryptogea Pethyb. & Laff., or P. megasperma Drechsler, causal agents of crown and root rots. Plants were flooded for either 0, 24, 48, or 72 h every 7 days for 4 months, then assessed for disease incidence and severity. Averaged across all pathogens and rootstocks, mean crown rot incidences were 2.5%, 6.3%, 19%, and 50% following weekly flooding periods of 0, 24, 48, and 72 h, respectively; when averaged across all rootstocks and flooding treatments, mean incidences of crown rot caused by P. cryptogea, P. cactorum, P. cambivora, and P. megasperma were 36%, 26%, 15%, and 8.8%, respectively; when averaged across all four pathogens, mean crown rot incidences after 72 h of flooding were 40%, 45%, 50%, and 75% for M.26, 0.3, M.7, and MM.111, respectively. In contrast, 72-h flooding periods in the absence of a pathogen were least detrimental to growth of MM.111 clones and most detrimental to shoot growth of M-26. Exceptions to general trends were reflected by statistical interactions among pathogens, rootstocks, and flooding durations, e.g., after 72-h floodings, 0.3 was the rootstock with the greatest amount of root rot caused by P. cryptogea but the least amount caused by P. megasperma. Differential disease susceptibility among rootstocks appeared greatest with respect to P. cactorum and least with respect to P. cryptogea.

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