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Peter J. Stoffella

Sweet Spanish onion (Allium cepa L. cv. Granex 33) was transplanted in two, three, or four rows per bed at 7.6, 15.2, or 22.9 cm in-row spacings resulting in plant populations ranging from 41,000 to 246,000 plants/ha during Winter 1991. Interactions between number of rows per bed and in-row spacings were nonsignificant for onion yield and bulb size traits. As number of rows per bed increased or in-row spacings decreased, marketable onion yield linearly increased and mean bulb size (g/bulb) decreased. Percentage of small, medium, and large bulbs was unaffected by number of rows per bed, but percentage of small and medium-sized bulbs increased and percentage of large bulbs decreased as in-row spacing decreased. Onion yields linearly increased, but at the expense of smaller-sized bulbs, whether plant populations were increased by more rows per bed or narrower in-row spacings.

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Daniel I. Leskovar, Shinsuke Agehara, Kilsun Yoo and Nuria Pascual-Seva

/stem diameter) was calculated at three stages of development in both seasons. Yield and bulb sizes. Harvests were done on 6-m long plots on 27 May 2008 and 18 May 2009, a time when more than 80% of the leaves (pseudostems) were bent over. At harvest bulbs were

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Clinton C. Shock, Erik Feibert, Lynn Jensen, S. Krishna Mohan and Lamont D. Saunders

reduced yield and reduced bulb size. The virus is transmitted by onion thrips ( Thrips tabaci ) ( Kritzman et al., 2001 ; Nagata and Almeida, 1999 ). The incidence of IYSV might be increased by the inadequate control of onion thrips, which have become

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Vincent M. Russo

Exogenously applied plant growth regulators may affect development of onion, but little is know about how concentration or timing of application can affect bulb grade and quality. Two concentrations of the growth regulators abscisic acid, gibberellic acid, indole-acetic acid, jasmonic acid, kinetin, and maleic acid hydrazide, and water controls, were applied at the 7- and 20-leaf stages to the middle of the leaf whorl in greenhouse grown onion plants. Leaf and bulb weights were lighter, and bulb diameters were smaller, from plants treated with growth regulators applied at the 7-leaf stage than those from plants treated at the 20-leaf stage. Bulbs produced on plants treated with water were the same size, or larger, than those produced on plants treated with individual growth regulators.

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K.I. Theron and G. Jacobs

Large Nerine bowdenii bulbs (>14 cm in circumference) were exposed to low ligbt intensities for different periods during two successive growing seasons. The flowering percentage and number of florets in the current season's inflorescence were recorded at anthesis. Small and large bulbs were subjected to continual defoliation starting at different times during the growing season. Bulbs were dissected at planting (26 Sept. 1992) and on 12 Jan. 1993 (nondefoliated control bulbs) to determine growth and developmental stage. At anthesis, inflorescences were harvested and the florets per inflorescence were counted. After anthesis in the fall, all bulbs were dissected and the following variables recorded: 1) percentage flowering, quiescence, or abortion of the current season's inflorescence; 2) developmental stage of quiescent inflorescences; 3) number of florets in the outermost inflorescence; 4) developmental stage of the innermost inflorescence; 5) number of leaves or leaf bases in each growth unit; 6) number of daughter bulbs; and 7) dry weight of new leaf bases. There were three reasons for nonflowering of the bulbs, viz., failure to initiate an inflorescence, inflorescences remaining quiescent, and inflorescence abortion. Individual florets that had not reached stage “Late G” (gynoecium elongated, carpels fused) at the start of rapid inflorescence elongation aborted. The more florets that aborted, the greater the probability that the entire inflorescence aborted. The inflorescence was more vulnerable to stress during the first half of the growing season due to its relatively weak position in the hierarchy of sinks within the bulb.

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Clinton C. Shock, Erik Feibert and Lamont D. Saunders

Onion (Allium cepa) cultivars for commercial production in eastern Oregon and southwestern Idaho are evaluated annually in replicated yield trials conducted at the Malheur Experiment Station, Oregon State University, Ontario. Market demand has progressively called for larger bulb size and bulbs with single centers. At harvest onions were evaluated for maturity, number of bolters, and single centeredness. Cultivars showed a wide range of bulbs with only one growing point or “bullet” single centers, ranging from 1% to 57% in 2000, from 7% to 70% in 2001, and from 1% to 74% in 2002. The percentages of bulbs functionally single-centered for processing uses ranged from 18% to 88% in 2000, from 24.7% to 91.3% in 2001, and from 14.4% to 92% in 2002. Bulb yield and market grade were evaluated out of storage. Marketable yield after 4 months of storage varied significantly by cultivar from 643 to 1196 cwt/acre (72.1 to 134.1 Mg·ha–1) in 2000, from 538 to 980 cwt/acre (60.3 to 109.8 Mg·ha–1) in 2001, and from 583 to 1119 cwt/acre (65.3 to125.4 Mg·ha–1) in 2002. Averaging over cultivars, super colossal bulb size averaged 26%, 14%, and 10% in 2000, 2001, and 2002, respectively.

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Shawn D. Lyons, William B. Miller, H. Christian Wien and Neil S. Mattson

interest in the crop has increased in recent years, many commercial greenhouse growers are hesitant to produce them because of a lack of production information and other grower resources ( Carlson, 2010 ). In many geophytes, bulb size plays a major role in

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Carrie H. Wohleb and Timothy D. Waters

the farm or field. Typically, two double rows are planted ≈12 inches apart on 34, 38, 40, or 44 inches of bed width. Onion growers use different planting configurations to manipulate onion bulb size. Plant population is understood to be closely related

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Arthur D. Wall, Marisa M. Wall and Joe N. Corgan

Onions (Allium cepa L.) with ≥18% bulb dry weight are dehydrated and used for spices and food ingredients. Bulb weight characteristics and water-soluble carbohydrates (WSC) of two commercial dehydrator cultivars, GS02 and GS04, and a breeding population, NM9335, were studied before and after maturity to observe phenotypic traits that may be useful for selection during breeding programs, and to study dehydrator onion carbohydrate physiology. At maturity, NM9335, GS02, and GS04 bulbs had 11.9 ± 0.33%, 18.6 ± 0.27%, and 19.4 ± 0.40% dry weight, respectively. Mature GS04 plants had 76.5 ± 0.01% of whole plant dry weight in bulbs, which is an extraordinarily high crop harvest index. NM9335 bulbs had higher fresh (hydrated) weight than bulbs of GS04 and GS02, but bulbs in all populations accumulated similar amounts of dry weight. Bulb percent dry weight before maturity did not indicate percent dry weight at maturity in the high-solids commercial onion cultivars. Bulb percent dry weight declined slightly after maturity in all populations. Glucose, fructose, and sucrose were relatively low, and fructans with degree of polymerization ≥6 were relatively high in GS04, but the converse was observed in NM9335. Relative amounts of GSO4 bulb fructan increased sequentially, in order of rank, from DP4 to DP6, but the converse was observed for NM9335.