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Abstract
Cymbidium mosaic virus (CyMV) is a serious disease of Dendrobium orchids in Hawaii. Symptoms of the disease include foliar pitting or streaking and floral necrosis. Some plants do not express floral necrosis even though they are infected with the virus. These necrosis-free plants were defined as resistant for this study. Crosses were made between resistant and susceptible plants, and seedlings were inoculated with the virus. Susceptible × susceptible crosses produced susceptible offspring, resistant × resistant crosses produced resistant offspring, and susceptible × resistant crosses produced susceptible offspring, with the exception of one cross that segregated for susceptible and resistant. Expression of floral necrosis is genetically controlled and expression of necrosis is dominant to nonexpression.
Use of wild species for in vitro sweetpotato improvement has been limited, in part, by the lack of suitable regeneration systems for these species. Shoot regeneration in 4 closely related species, I. batatas, I. cordatotriloba, I. trifida and I. triloba, were evaluated. Callus was initiated using methods described by Otani and Shimada (1988). Calli were transferred to regeneration media containing 17.75 uM BAP and 0, 1, 10 and 100 uM PCIB. Organogenesis was enhanced by the presence of PCIB. With I. cordatotriloba calli grown on media with 10 uM PCIB, a 2-fold increase in the percentage of calli exhibiting shoot regeneration was observed as compared to calli grown on media with BAP alone. A significant increase in the average number of shoots per callus was also observed. The other species examined appeared to be less sensitive than I. cordatotriloba to the PCIB treatments.
Leaf callus of Ipomoea cordatotriloba was initiated by culturing explants on Linsmaier and Skoog medium containing 3 g yeast extract/liter, 18.9 μm ABA, 2.3 μm 2,4-D, and 0.15 m sucrose. Calluses were transferred to Murashige and Skoog media containing 17.8 μm BA and 0, 1, 10, or 100 μm PCIB. The number of shoots from calluses grown on medium containing 10 μm PCIB increased significantly, and the percentage of calluses exhibiting shoot regeneration almost doubled compared to calluses grown on regeneration medium without PCIB. Protoplasts isolated from stem and petiole tissues of in vitro-grown plants were cultured in Kao and Michayluk 8p medium to the callus stage. Calluses (4-6 mm) were transferred to the callus induction and regeneration media used to regenerate leaf-explant callus. Of the protoplast-derived calluses cultured on media containing 10 or 100 μm PCIB, ≈13% and 18%, respectively, regenerated shoots after 2 months; none regenerated on the medium without PCIB. Chemical names used: abscisic acid (ABA); 2,4-dichlorophenoxyacetic acid (2,4-D); N6-benzyladenine (BA); α -p-chlorophenoxyisobutyric acid (PCIB).
The use of wild Ipomoea species in sweetpotato improvement may be facilitated by the use of in vitro techniques such as somatic hybridization. Plant regeneration from callus cultures is essential to the successful application of these in vitro techniques. This is the first report of plant regeneration of I. cordatotriloba from protoplast derived calli. Protoplasts isolated from petiole and stem tissues of in vitro grown I. cordatotriloba were initially cultured on KM8p media. All calli cultured regenerated roots after 1 month on regeneration media. Approximately 13% and 19%, respectively, of the calli cultured regenerated shoots after 2 months on media containing 10 and 100 uM parachlorophenoxy isobutyric acid (PCIB). Regenerated shoots developed into whole plants when transferred to MS media without hormones. The regenerated plants closely resembled the parent's morphology.
Solanum ochranthum, a woody non-tuber bearing species, may possess genes for insect and disease resistance which could be useful in solanaceous crop improvement. Methods for tissue and protoplast culture of S. ochranthum were developed as part of an ongoing project to improve tomato and potato using wild relatives and in vitro techniques such as somatic hybridization. For protoplast experiments, axenic shoot tip cuttings were propagated on medium containing MS salts, Staba vitamins, 100 mg·l-1 casein, 3% sucrose and 0.6% activated charcoal (OM) or medium containing MS salts and vitamins, 100 mg·l-1 casein and 2% sucrose (TPM). Plants grown on OM were significantly taller, had higher root dry weight and gave protoplasts with higher average plating efficiency than plants grown on TPM. Leaf protoplasts from 5 week old plants cultured in medium with high Ca2+ and myoinositol generally had higher percent viability and plating efficiency than protoplasts grown in a modified Kao and Michayluk 8p medium.
Incorporation of genes from wild species has been a major contributor to tomato improvement in recent years. Solanum ochranthum, a woody non-tuber bearing species, is a potential source of resistance against tomato diseases and insect pests but is genetically isolated from tomato. Somatic hybridization methods were developed to facilitate the use of S. ochranthum for tomato germplasm improvement. Leaf mesophyll protoplasts of S. ochranthum and a Lycopersicon esculentum hybrid were chemically fused with polyethylene glycol. The protoplasts were initially cultured in Shepard's CL, a MS based medium, containing 1 mg·1-1 NAA, 0.5 mg·1-1 BAP and 0.5 mg·1-1 2,4-D. Hybrid regenerants and regenerants of the L. esculentum parent were recovered; S. ochranthum did not regenerate. Hybridity was established by morphological characters, peroxidase isozyme and RAPD markers. Use of these somatic hybrids for tomato improvement was evaluated.
The objective of this study was to identify the specific weeks and night lengths when poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) flowering is most sensitive to high temperatures. One experiment was conducted in greenhouses under natural daylength (ND) conditions at lat. 34.7°N starting on 4 Sep, and a second experiment was conducted in growth chambers with an initial night length (NL) of 11 hours 01 minutes that was increased by 2 min/d to simulate ND conditions through September and October. Each week, one group of plants was moved from a moderate-temperature environment [22 °C average daily temperature (ADT)] to a high-temperature environment 28 °C ADT. Each group of plants spent 1 week in the high-temperature environment before returning to the moderate-temperature environment. The temperature treatments lasted for 7 or 8 weeks for the growth chamber and greenhouse studies, respectively. Additional groups of plants were kept in either the moderate- or high-temperature environment for the entire treatment period as controls. Four cultivars were used in the greenhouse study: Advent Red, Freedom Red, Prestige Red, and Tikal Red; only Prestige Red was used in the growth chamber study. Advent Red was identified as the most heat-tolerant cultivar followed by Tikal Red, Freedom Red, and Prestige Red. ‘Advent Red’s’ period of sensitivity to high temperatures ranged from 4 Sep to 1 Oct. ‘Tikal Red’s’ period of sensitivity to high temperature ranged from 11 Sep to 8 Oct. ‘Freedom Red’ had a longer period of high-temperature sensitivity: from 11 Sep to 22 Oct. ‘Prestige Red’ had the longest period of sensitivity to high temperatures encompassing 4 Sep to 29 Oct, and 11 hours 01 minute to 12 hours 37 minutes NL for the greenhouse and growth chamber studies, respectively. Within periods of sensitivity to high temperatures, time to visible bud and anthesis were most affected by high temperatures in earlier weeks, and final bract color development and time to first bract color were more affected by high temperatures during the latter weeks. As cultivars varied in their duration of sensitivity to high temperatures, duration, as well as magnitude of response to high temperature, should be considered in future breeding projects.