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Robert W. Goth, Ernest W. Goins, and Kathleen G. Haynes

Potato leafroll virus (PLRV) is a serious aphid transmitted virus disease of potato (Solanum tuberosum L.). Field observations suggest that the cv. BelRus is tolerant to PLRV. Greenhouse grown BelRus and PLRV susceptible potato cvs. Green Mountain and Katahdin were tested for PLRV with enzyme linked immunosorbant assay (ELISA) and subsequently infested with PLRV infected green peach aphids (Myzus persicae). ELISA was used to test leaves from the top, middle and bottom portion of the plants at 7 day intervals beginning 7 days after aphid infestation. PLRV was detected in all tested locations of the Green Mountain and Katahdin plants 21 days after inoculation. In BelRus, throughout the 11 week test, PLRV was detected predominantly in the top portion of the plants and at low titres. These results suggest that tolerance to PLRV infection in the cv. BelRus may be due to suppression of virus replication.

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H.Z. Zaiter

Iron-deficiency symptoms are observed on some genotypes of potato (Solanum tuberosum L.) grown on high-pH and calcareous soils. seven potato cultivars differing in response to iron deficiency chlorosis (FeDC) were grown on high-pH (8.1), calcareous (38% calcium carbonate equivalent in surface 20 cm) and silty clay soil in the field (Beka'a Valley, Lebanon), to determine the effects of FeDC on tuber yield of cultivars sprayed with Fe. A significant interactions between cultivars and Fe spray treatment were noted for visual FeDC ratings and tuber yield. Even though only slight FeDC was noted on some cultivars receiving no Fe spray, tuber yields were significantly increased when sprayed with Fe. Some cultivars with moderate FeDC ratings did not show a significant increase in yield when sprayed with Fe while other cultivars did. Sprayed cultivars generally produced higher tube; yields than unsprayed ones. Indicating that Fe-deficiency chlorosis in the Mediterranean region may be a serious limitation to potato tuber yield.

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Qin Chen and Hai Y. Li

An improved method is described for the isolation of potato metaphase chromosomes for karyotypic and cytogenetic studies. Root tips from diploid Mexican species, Solanum pinnatisectum (2n = 2x = 24) and tetraploid cultivated S. tuberosum (2n = 4x = 48) were given four different pretreatments. The synthetic pyrethroid, Ambush, was the most stable and effective pretreatment reagent, providing the highest percentage of mitotic chromosomes at metaphase and the best spread of countable chromosomes for cytogenetic studies. Compared with an Ambush pretreatment at concentrations of 100-400 ppm, 1 to 10 ppm Ambush produced more easily distinguished chromosomes, which can be useful for comprehensive observation and karyotype analysis in both 2x and 4x potato species. This improved technique for examining mitotic chromosomes will be helpful in describing karyotypes, characterization of new hybrids, and identifying chromosome structural changes that are important in breeding schemes.

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Gary W. Stutte

NASA has investigated the use of recirculating nutrient film technique (NFT) systems to grow higher plants on long-duration space missions for many years and has demonstrated the feasibility of using recirculating systems on numerous crop species. A long duration (418-day) experiment was conducted at Kennedy Space Center, Fla., to evaluate the feasibility of using recirculating hydroponics for the continuous production of Solanum tuberosum L. `Norland'. The productivity of four sequential batch plantings was compared to staggered harvest and plantings. The accumulation of bioactive organic compounds in the nutrient solution resulted in reduced plant height, induced early tuber formation, and increased harvest index of the crops in both production systems. The changes in crop development were managed by increasing planting density and reducing cycle time to sustain production efficiency.

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Chieri Kubota and Toyoki Kozai

Growth and net photosynthetic rate of potato (Solanum tuberosum L.) `Benimaru' plantlet in vitro were studied under a conventional photomixotrophic condition [with 20 g sucrose/liter in the medium and under 70 μmol·m-2·s-1 photosynthetic photon flux (PPF)] with minimal ventilation (MV) and under photoautotrophic conditions (without sugar in the medium and under 190 μmol·m-2·s-l PPF) with enhanced natural ventilation using an air diffusive filter (DV) or with forced ventilation (FV). Fresh weight of the plantlets cultured in the FV and DV treatments was 2.4 times that of the plantlets cultured in the MV treatment. Net photosynthetic rate and dry weight per plantlet were the highest in FV followed by DV. For photoautotrophic micropropagation, FV was superior to DV.

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A. Golmirzaie and F. Serquen

A field experiment was conducted at two locations to determine the correlation between seedling and mature plant characters in a large potato (Solanum tuberosum) population developed for production from true potato seed. There was no significant correlation between seedling and reproductive characters, including earliness, at the two locations. Number of internodes and yield per plant were significantly correlated at Huancayo, and at San Ramon, root length and hypocotyl length had a significant correlation with the number of tubers per plant and yield per plant. Although significant, the latter correlations are not high enough to be used to predict the final behavior of genotypes by their seedling traits. Thus, it may be assumed that a certain independence between seedling and mature plant growth characters exists.

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Y. Desjardins and J. Abdulnour

Microtubers (Solanum tuberosum cv Snowden) were produced in 1-L jar fermentors using a two-step method consisting of a shoot multiplication phase (21 days) followed by a tuberization phase (25 days). The plantlets were immersed in Murashige and Skoog (MS) liquid medium for 3.5 min every 4 h. Low concentrations of ancymidol (anti-gibberellic substance), particularly during the shoot multiplication phase, were essential for tuber initiation and development. A continuous supply of 2 μMol ancymidol during the two phases of culture decreased plant height, but produced >100 microtubers per jar. Although the tuber development phase was short (25 d), 25% of the microtubers produced were >0.5 g with 17.5% to 18.0% of dry-matter content.

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George Hochmuth, Pete Weingartner, Chad Hutchinson, Austin Tilton, and Dwight Jesseman

Phosphorus (P) fertilization studies were conducted on four commercial farms and at the University of Florida Institute of Food and Agricultural Sciences Hastings Research and Education Center in Hastings. All sites were in the potato (Solanum tuberosum) production area of northeastern Florida. Preplant Mehlich-1 soil test P was very low at one commercial site and very high at the other four sites. The yield of marketable size A tubers, the desired tuber category, did not respond to P fertilization from 0 to 66 lb/acre (74.0 kg·ha-1) of P at any site. The average yield across all sites was 324 cwt/acre [16.2 ton/acre (36.3 t·ha-1)]. Leaf-P concentration at midseason did not respond to P fertilization. Leaf-P concentration averaged 0.38%, which was sufficient for potato. Potato tuber specific gravity averaged 1.075 and responded slightly to P fertilization only at one site.

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Chen-Yi Hung, John R. Murray, Sarah M. Ohmann, and Cindy B.S. Tong

The color of red potato tubers is due to an accumulation of anthocyanins in periderm and peripheral cortex tissues. The objective of this study was to characterize changes in anthocyanin content and tuber surface color during tuber development. Using the red tuber-producing potato (Solanum tuberosum L.) cultivar Norland, we observed that chroma (intensity of redness) and anthocyanin content per unit of surface area of greenhouse-grown tubers decreased as tuber weight increased. There was no increase in hue (tint) during the same developmental periods. Using high-performance liquid chromatography (HPLC), we determined that pelargonidin and peonidin are the major anthocyanidins (aglycones of anthocyanins) in the tuber periderm. Northern blot analyses indicated that steady-state mRNA levels of dihydroflavonol reductase (DFR), an anthocyanin biosynthetic enzyme, continued throughout tuber development. These results suggest that anthocyanins are synthesized throughout tuber development, and that cell division and/or enlargement contribute to a decline in chroma and anthocyanin concentration.

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Aref A. Abdul-Baki and Theophanes Solomos

The diffusion coefficient of CO2 in `Russet Burbank' potato (Solanum tuberosum L.) tubers was determined under steady-state conditions at 10 and 27C. The data showed that the skin is the main barrier to gas diffusion, with an average diffusion coefficient of 6.57 × 10-7 and 7.61 × 10-7 cm·s-1 at 10 and 27C, respectively. The flesh also presents an appreciable barrier to gas diffusion. The average diffusion coefficient of CO2 in the flesh was 2.00 × 10-4 and 2.24 × 10-4 cm·s-1 at 10 and 27C, respectively. Under regular storage conditions, the tuber is well aerated and the concentration of O2 at the center of the tuber is sufficient to maintain aerobic respiration.