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Raymond P. Chée and Daniel J. Cantliffe

Embryogenic callus of sweetpotato [Ipomoea batatas (L.) Lam.] disassociates in liquid medium to form a heterogeneous population of embryogenic and nonembryogenic cell aggregates of varying sizes. To improve embryo production, such cell aggregate populations were obtained by manually fragmenting calli 5 to 10 mm in size into liquid medium. The resulting suspensions were analyzed and the embryogenic fraction identified. The percentage of embryogenic aggregates and the percentage of aggregates forming embryos decreased with decreasing aggregate size. Thus, 76% of the 710- to 1000-μm-diameter aggregates but only 14% of the 180- to 250-μm aggregates had embryogenic potential. However, only 20% of the 710- to 1000-μm aggregates and only 2% of the 180- to 250-μm aggregates actually formed embryos. Conversely, embryogenic callus and embryo production per milligram of cultured embryogenic callus increased quadratically with decreasing aggregate size. Individual torpedo-stage embryos were produced from cell aggregates 180 to 250 μm in size.

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Raymond P. Chée, Daniel I. Leskovar and Daniel J. Cantliffe

Embryogenic callus growth of sweetpotato [Ipomoea batatas (L.) Lam.] was selectively enhanced by subculture on basal callus proliferation medium modified to contain 15 mm NH4NO3. Embryogenic callus production was doubled on basal callus proliferation medium modified to contain 60 mm K+, while nonembryogenic callus production was reduced 40%. Additions of up to 40 mm NaCl to basal callus proliferation medium did not affect callus proliferation. The development of embryos from calli subculture to embryo production basal medium was unaffected by the KCl or NaCl treatments of the callus proliferation phase. However, embryo production was increased by subculturing callus from callus proliferation medium containing 20 mm NH4 + to embryo production medium containing 10 mm NH4 + Our results demonstrate that changes in mineral nutrition, in addition to growth regulator differences between callus proliferation and embryo production media, are important factors in sweetpotato somatic embryogenesis.

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Zachary N. Hoppenstedt, Jason J. Griffin, Eleni D. Pliakoni and Cary L. Rivard

Sweetpotatoes (Ipomoea batatas) are nutritious, easily stored, and well adapted to a variety of organic farming operations. This widely consumed root crop is propagated through the use of cuttings, known as slips. Slips are commercially grown primarily in the southeastern United States, and growers in the central United States still have limited access to sweetpotato planting material. Production of organic slips in high tunnels (HTs) could be a profitable enterprise for growers in the central United States given the season extension afforded by controlled-environment agriculture, which could allow growers to diversify their operations and facilitate crop rotation. In trials conducted in 2016 and 2017 at two research stations in northeast and south central Kansas, a systems comparison was used to evaluate the yield and performance of organic sweetpotato slips grown in HT as compared with the open field (OF), with four to six replications at each location. Propagation beds planted with ‘Beauregard’ seed roots in 2016 and ‘Orleans’ in 2017 were established in HT and OF under similar cultural methods and planting schedules. Slips were harvested from both treatment groups and transplanted to field plots to investigate the impact of production system on transplant establishment and storage root production. Slip yield from HT was greater than OF at both locations in 2016 (P ≤ 0.001), but this trend was inconsistent in 2017. Slips grown in HT were on average 12% less compact (slip dry weight per centimeter length) with fewer nodes than their OF counterparts in 2016. Nonetheless, mean comparisons for vine length, stem diameter, and total marketable storage root yield were not significant between HT and OF treatments (1.7 and 2.1 lb/plant, respectively). Similarly, the number of marketable storage roots for HT and OF groups was comparable (3.4 and 3.8 storage roots/plant, respectively). Although more research is needed to evaluate the feasibility of slips grown in HT and to determine recommendations for seed root planting densities, results from this study suggest that HT organic sweetpotato slip production could be a viable alternative to OF production as it relates to slip performance. According to this study, HT production could be a useful mechanism for growing sweetpotato slips, which could provide regional growers more control over planting material. Furthermore, HT slip production could promote the adoption of an underused vegetable crop that can be grown throughout many parts of the United States.

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A.G. Taylor, D.H. Paine and C.A. Paine

marked advertisement solely to indicate this fact. 2 Research Technician. 3 Former Research Techinician. This research was partially supported by a grant from Seed Systems, Gilory, Calif. We acknowledge technical assistance from G.G. Mass and P

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A.G. Taylor, D.B. Churchill, S.S. Lee, D.M. Bilsland and T.M. Cooper

a grant from Seed Systems, Gilroy, Calif. We acknowledge statistical advice from K.S. Yourstone. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby

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J. Cavero, R. Gil Ortega and C. Zaragoza

Pepper (Capsicum annuum L. `Piquillo de Lodosa') was seeded and then covered with clear plastic mulch, and various cultural practices to improve seedling emergence were compared. Planting dates (8, 12, and 25 Apr. 1991), seeding systems (raised bed vs. flat, 1991), and one or two rows per bed (1991 and 1992, respectively) were evaluated for their effects on stand establishment and yield. Plant stand was 60% when seed was under plastic mulch, compared to 0% when no mulch was used. Maximum plant stand was obtained 4 weeks after seeding in mulched soil. With plastic mulch, earlier (on or before 12 Apr.) season plantings were best because soil temperatures were so high (≥35C) later as to reduce plant stands. The risk of excessive high temperatures was greater when seeding was on a raised bed rather than flat ground; however, using plastic mulch, temperatures were higher, often resulting in acceptable plant stands regardless of bed arrangement. Higher yields were realized with raised beds compared to flat ground sowing. When two rows per bed were used, higher temperatures on the south side reduced emergence compared to the north side of the east–west-oriented beds. Direct seeding of pepper appears to be commercially acceptable in our Mediterranean conditions, provided seed is under plastic mulch and seeding is completed on or before 12 Apr.

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A. G. Taylor, D. H. Paine and D. F. Grabe

The purpose of this study was to develop a procedure to determine seed moisture content from intact pelleted seeds. Samples of `Sentinel' onion and `Salinas' lettuce were pelleted by the following companies; Asgrow, Germains (Seed Systems), Harris Moran, Incotec, Peto and Seed Dynamics. Physical characteristics of the various pellets were quantified including weight, volume and density. Measurements were made on intact pellets and densities ranged from 0.84 to 1.67 g/cc. Seed drying curves were obtained on the different pellets under controlled environmental conditions. Pellets were first equilibrated at 85% RH, and then dried at 25C and 18% RH. In general drying rates were similar among pellet types within crops. With regards to seed moisture content determination, neither the electronic moisture meter, based on measuring capacitance, nor oven methods were able to accurately measure seed moisture from intact pellets. Measurement of the head space RH from pre-equilibrated intact pellets (water activity) resulted in an accurate method to assess seed water status for all samples. The actual seed moisture content could be determined by using the moisture isotherms for each seed lot at a given temperature.

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Scovia Adikini, Settumba B. Mukasa, Robert O.M. Mwanga and Richard W. Gibson

in Uganda Ann. Appl. Biol. 130 481 490 Gibson, R.W. Mwanga, R.O.M. Namanda, S. Jeremiah, S.C. Barker, I. 2009 Review of sweetpotato seed systems in East and Southern Africa. Integrated Crop Management Working Paper 2009-1/ International Potato Center

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Bielinski M. Santos and Persio R. Rodriguez

July 2001 < http://www.infoagro.go.cr/tecnologia/papa > Bryan, J. Meléndez, N. 1985 Manejo de plántulas in vitro , esquejes y tubérculos pequeños en cobertizos 28 Oct. 2001 < http://www.cipotato.org/potato/seed_systems > Evans, E.A. 2005 Marginal

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Addenda

105th Annual Conference of the American Society for Horticultural Science, Orlando, FL, 21–24 July 2008: The following changes were made to the conference schedule after the Program and Abstracts issue [HortScience 43(4)] went to press.

under various stress conditions. Knowledge generated from these studies will serve as a base for collaborative research and development projects with AVRDC's regional and international partners. Developing a Sustainable Seed System in Malawi —*Carol