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Open access

S. K. O’Hair

Abstract

Cassava (Manihot esculenta L. Crantz) plants of ‘CMC-40’ and ‘CMC-92’ were grown over a 3-year period with annual harvests at the end of each growing season. Root tissues were divided into peel (secondary phloem with the thin cork tissue layer removed) and up to three parenchymatous tissue age groups. Up to 40% of the starch concentration can be deposited in root parenchymatous tissue. Root starch is permanently removed from parenchymatous tissue of older roots, probably in association with new foliage growth at the start of a new growing season. As a result of periods of little or no growth, visible annual growth rings develop in the root, separating each season’s major root enlargement periods. Genetic differences in starch content were noted among the tissues between ‘CMC-40’ and ‘CMC-92’. However, both demonstrated similar loss of starch from older tissue.

Open access

M. P. Asokan, S. K. O’Hair, and R. E. Litz

Abstract

Leaf disks of Hausa potato (Coleus parviflorus Benth.) were cultured on Murashige and Skoog (MS) medium. Optimum adventitious shoot development on the explant was obtained using 6.0 to 8.0 mg/liter 6-benzylamino purine (BA) in combination with 2.5 to 4.0 mg/liter naphthaleneacetic acid (NAA). Shoot regeneration was obtained from callus following callus subculture on media with 4.0 to 8.0 mg/liter BA in combinations with 1.5 to 4.0 mg/liter NAA. Rooting was induced on shoots by transfer to a growth regulator-free medium.

Open access

S. K. O’Hair and J. C. Miller Jr.

Abstract

The effects of the cowpea strains of southern bean mosaic (SBMV-CS), cucumber mosaic (CMV-CS), and tobacco mosaic (TMV-CS) viruses on cowpea [Vigna unguiculata (L.) Walp] plant growth and N fixation parameters were evaluated in greenhouse and field experiments. TMV-CS infection resulted in the most severe symptoms and was associated with significant reductions in nitrogenase activity, total nodule weight, nodule number, and plant dry weight, in susceptible cultivars. Infection with CMV-CS was associated with significant reductions in nitrogenase activity, nodule number, and plant dry weight in field-grown ‘Mississippi Silver’. SBMV-CS infection was least severe and was associated with a significant reduction in nitrogenase activity and nodule weight in only 1 susceptible cultivar under field conditions.

Open access

M. P. Asokan, S. K. O’Hair, and R. E. Litz

Abstract

Shoot tips of Xanthosoma caracu were cultured and rooted successfully in 5 to 6 weeks in an agitated liquid Murashige and Skoog (MS) basal medium with 100 mg/liter ascorbic acid and multiplied in MS basal medium with (per liter) 250 mg NaH2PO4 · H2O, 0.4 mg thiamine-HCl, 30 mg adenine sulphate, 8 g Difco Bacto agar and supplemented with 2 mg benzylaminopurine (BA), and 0.5 mg indoleacetic acid (IAA). Multiplication rate was 45 to 70 plants per culture flask within 9 to 10 weeks after subculture.

Open access

M. P. Asokan, S. K. O’Hair, and R. E. Litz

Abstract

Bulbil explants of one Dioscorea bulbifera L. and two D. alata L. genotypes were cultured on Murashige and Skoog (MS) medium which was modified to contain 500 mg/liter NH4NO3 as the only N source. Factorials involving kinetin, 2,4-dichloro-phenoxyacetic acid (2,4-D), benzylamino purine (BA), and naphthaleneacetic acid (NAA) were tested. Plant development was obtained from one D. alata genotype using 10.0 to 14.0 mg/liter kinetin in combination with 0.01 to 0.02 mg/liter 2,4-D.

Open access

S. K. O’Hair, R. B. Forbes, S. J. Locascio, J. R. Rich, and R. L. Stanley

Abstract

Four cultivars of cassava (Manihot esculenta Crantz), grown at 4 locations, were analyzed for root starch distribution. Starch and glucose variation among cultivars and locations indicated that both genetic and environmental factors were involved. Glucose content of all tissues sampled was less than 2%. The correlation between glucose and starch was negative in the parenchymatous and pith tissues for all cultivars except ‘HMC-2’. Location seemed to have little effect on starch concentration, which ranged from 23-33% in the central pith, 19-26% in the peel, and 34-44% in the parenchymatous tissue between the peel and the pith. The portion of the root closest (proximal) to the plant had a higher starch concentration than did the distal portion.

Free access

C.M. Tankou, B. Schaffer, S.K. O'Hair, and C.A. Sanchez

The effects of applied N and shading duration on net gas exchange and growth of two southern Florida cassava (Manihot esculenta Crantz.) cultivars grown in containers were determined. Both cultivars responded similarly to shading and N with respect to the measured variables. There were no interactions between shading duration and N application rate for any of the variables measured. Tissue dry weights, total leaf N and chlorophyll concentrations, net CO2 assimilation (A), transpiration (E), water-use efficiency (WUE), and stomatal conductance (gs) were quadratically related to the concentration of N applied to the soil. The optimum N application rate for maximum growth of both cultivars was 60 mg/plant per day. Increased shading duration reduced A, E, gs, WUE, storage root number, and weight and increased the shoot : root ratio.

Free access

R. Nuñez-Elisea, B. Schaffer, M. Zekri, S.K. O'Hair, and J.H. Crane

Tropical fruit trees in southern Florida are grown in porous, oolitic limestone soil that has very low organic matter content and water-holding capacity. Thus, trees require frequent irrigation during dry periods. In these soils, a quantitative basis for monitoring soil water content to determine when and how much to irrigate has been lacking. Multi-sensor capacitance probes (EnviroSCAN™, Sentek, Australia) were installed in commercial carambola, lime, and avocado orchards to continuously monitor changes in soil water content at depths of 10, 20, 30, and 50 cm. Eight probes were installed per orchard. Volumetric soil water content was recorded at 15-min intervals with a solar-powered datalogger. Results were downloaded to a laptop computer twice a week. Monitoring the rate of soil water depletion (evapotranspiration) allowed irrigation before the onset of water stress. The time at which soil reached field capacity could be determined after each irrigation (or rain) event. Soil water tension was recorded periodically using low-tension (0–40 cbars) tensiometers placed adjacent to selected capacitance probes at 10- and 30-cm depths. Soil water tension was better correlated with volumetric soil water content at a 10-cm depth than at 30-cm depth. Using multi-sensor capacitance probes is a highly accurate, although relatively expensive, method of monitoring soil water content for scheduling irrigation in tropical fruit orchards. Whereas tensiometers require periodic maintenance, the multi-sensor capacitance probe system has been virtually maintenance free. The correlation between soil water content and soil water tension obtained in situ indicates that tensiometers are a less precise, but considerably cheaper, alternative for scheduling irrigation in tropical fruit orchards in southern Florida.