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  • Author or Editor: Russell T. Nagata x
  • Journal of the American Society for Horticultural Science x
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Abstract

Dry seeds of common bean, Phaseolus vulgaris L., were treated with 10 and 20 kilo roentgen (kR) of gamma rays to induce plant mutations suitable for use as genetic markers in mapping studies. The 10 and 20 kR treatments produced a total of 9 marker mutations from a total of 412 separate M2 progenies. The mutations changed leaf shape and texture, and produced dwarfism and various chlorophyll deficiencies. Inheritance characteristics were determined and the mutant markers are described. The round leaf (rnd), dark green savoy leaf (dgs), diamond leaf (dia), chlorotic cup leaf (cc), and stipelless lanceolate leaf (sl) mutants are adequately described by their names. Dwarf out-crossing (do) has small leaves, short internodes and pods, and a natural out-crossing frequency of 10%–56%. Chlorotic stem (cs) has a milky white stems, while silver leaf (sil) has its leaf color modified by a silvery reflectance. Progressive chlorosis (pc) has leaves which emerge normal green in color, but become chlorotic with age. The relationship of these mutants to previously reported mutants is discussed.

Open Access

Abstract

Nine recessive gamma ray induced bean, Phaseolus vulgaris L., mutants were selected for linkage testing in diallel crosses. All mutants had a common genetic background, Florida dry bean breeding line 7-1404. Linkage was calculated using F2 data, employing Fisher and Balmukand's product ratio method for crosses in repulsion and coupling phases. Repulsion phase linkage tests revealed 2 linkage groups involving 5 genes. Round leaf (rnd), stipelless lanceolate leaf (sl), and dark green savoy leaf (dgs) formed one linkage group, while diamond leaf (dia) and progressive chlorosis (pc) formed the 2nd linkage group. Recombination values from combined repulsion and coupling phase data were: rnd with sl, p = 11.51 ± 0.95; sl with dgs, p = 20.50 ± 1.34; and rnd with dgs, p = 30.07 ± 1.38. Dgs was found to be linked to the yellow wax locus, y, thereby tying the dgs - sl - rnd linkage group into linkage group VII defined by Lamprecht. Also, the y locus was found to be independent of rnd. Preliminary data suggest that the dwarf seed (ds) character may be controlled by the same locus as Lamprecht's tenuis (te), also of linkage group VII, and ds was found to be linked to rnd. If te and ds are identical, then the orientation of the dgs - sl - rnd linkage group with respect to y and te is determined.

Open Access

Lettuce (Lactuca sativa L.) seeds can fail to germinate at temperatures above 24 °C. The degree of thermotolerance is thought to be at least partly related to the environment under which the seed developed. In order to study the effects of temperature during seed development on subsequent germination, various lettuce genotypes were screened for their ability to germinate at temperatures ranging from 20 to 38 °C. Seeds of the selected genotypes `Dark Green Boston' and `Valmaine' (thermosensitive), `Floricos 83', `Everglades', and PI 251245 (thermotolerant) were produced at 20/10, 25/15, 30/20, and 35/25 °C day/night temperature regimes in plant growth chambers. Seeds were germinated on a thermogradient bar from 24 to 36 °C under 12 h light/dark cycles. As germination temperature increased, the number of seeds that failed to germinate increased. Above 27 °C, seeds matured at 20/10 or 25/15 °C exhibited a lower percent germination than seeds that matured at 30/20 or 35/25 °C. Seeds of `Dark Green Boston' and `Everglades' that matured at 30/20 °C exhibited improved thermotolerance over those that matured at lower temperatures. Seeds of `Valmaine' produced at 20/10 °C exhibited 40% germination at 30 °C, but seeds that matured at higher temperatures exhibited over 95% germination. Germination of `Valmaine' at temperatures above 30 °C was not affected by seed maturation temperature. The upper temperature limit for germination of lettuce seed could thus be modified by manipulating the temperature during seed production. The potential thermotolerance of seed thereby increased, wherein thermosensitive genotypes became thermotolerant and thermotolerant genotypes (e.g., PI251245) germinated fully at 36 °C. This information is useful for improving lettuce seed germination during periods of high soil temperature, and can be used to study the biology of thermotolerance in lettuce.

Free access

Glyphosate-resistant plants of `South Bay' lettuce (Lactuca sativa L.) were produced by using Agrobacterium tumefaciens containing a plasmid carrying glyphosate oxidase and EPSPS gene. An in vitro assay was performed to determine the sensitivity of `South Bay' leaf discs and seedling explants to varying glyphosate concentrations. The I50 for glyphosate leaf discs was 53.8 μm and for glyphosate seedlings 7.6 μm. There was a high correlation between the response of leaf discs and seedlings to glyphosate based on dry weight. These findings will allow identification of glyphosate-resistant transformants in an early stage of plant development, saving time and reducing the cost in generating an improved cultivar with the glyphosate resistance trait.

Free access

Six transgenic `South Bay' lettuce lines (Lactuca sativa L.) with elevated levels of 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS) were evaluated for tolerance to the herbicide glyphosate. The six lines were selected from ≈150 independent transformation events using an Agrobacterium tumefaciens system. Three assay methods were used to identify gene expression with regard to glyphosate resistance. Leaf disks of the transgenic lines were cultured on media containing 0 to 1280 μm glyphosate. Leaf disks of the control had lower dry weight (DW) at 40 μm and greater glyphosate than all the transgenic lines. The transgenic lines continued to grow even at 1280 μm. Plants 21 days old were sprayed in the greenhouse with rates of glyphosate at 0 to 35.84 kg·ha-1. DW of all the lines were similar to the control, with a few exceptions, at glyphosate concentrations from 0 to 0.56 kg·ha-1. At 2.24 to 8.96 kg·ha-1 all of the transgenic lines had DW greater than the control, while at 17.92 and 35.84 kg·ha-1 only B-32, B-33, C-3, and C-14 had DW greater than the control. The resistant line from the greenhouse experiment, B-32, grew normally in field trials at the highest glyphosate rate, 17.92 kg·ha-1, while control plants died at 0.56 kg·ha-1 glyphosate. Lines A-11 and C-3 had lower DW than B-32 at 2.24 kg·ha-1 glyphosate and greater. While leaf disk assays can identify potential transformed lines expressing the EPSPS and glyphosate oxidase (GOX) gene, and greenhouse screening can evaluate seedling vigor after glyphosate application, field trials are necessary to evaluate plant growth and yield through the growing season. Chemical name used: N-(phosphono-methyl) glycine (glyphosate).

Free access

Ethylene synthesis and sensitivity, and their relation to germination at supraoptimal temperatures, were investigated in lettuce (Lactuca sativa L.) seeds matured at 30/20 °C [12-h day/night, high temperature matured (HTM)] or 20/10 °C [12-h day/night, low temperature matured (LTM)]. HTM seeds of both thermosensitive `Dark Green Boston' (DGB) and thermotolerant `Everglades' (EVE) had greater germination at a supraoptimal temperature (36 °C), in both light or dark, than LTM seeds of DGB and EVE. HTM seeds of DGB and EVE produced more ethylene during germination than LTM seeds, regardless of imbibition conditions. The ethylene action inhibitor, silver thiosulfate, led to reduced germination in both cultivars. The ethylene precursor, 1-aminocyclopropane-1-carboxylic acid at 10 mm increased germination of both cultivars at supraoptimal temperatures, whereas germination of HTM seeds was greater than that of LTM seeds. No differences in ethylene perception were detected between HTM and LTM germinating seeds using a triple response bioassay. This study demonstrated that at least one method through which seed maturation temperature influences lettuce germination is by affecting ethylene production.

Free access

Abstract

‘Champion’, ‘Georgia’, ‘Heavicrop’, and ‘Vates’ collards (Brassica oleracea L. var acephala) were planted in Fletcher and Lewiston, N.C.; Charleston, Clemson, and Florence, S.C.; and Attapulgus and Plains, Ga. to determine the most reliable method to predict harvest maturity based on temperature. Although cultivar differences existed within some of the planting dates, when pooled over all planting dates, cultivars yielded similarly within locations. Eight methods of calculating heat units from planting to harvest were applied to daily maximum and minimum air temperatures supplied from local weather bureaus for the spring and fall growing seasons from 1985 through 1987 in the three-state area. Coefficients of variation were used to determine which method was most reliable in predicting day of first harvest. The method with the lowest cv was to sum, over days for planting to harvest, the difference between the daily maximum and a base temperature of 13.4C; however, if the maximum was >23.9C, the base temperature was subtracted from an adjusted maximum equal to 23.9C minus the difference between the maximum and 23.9C. This method produced a cv of 9.1% compared to 11.4% for the standard method of summing the mean temperature minus the base of 4.4C over the entire growing season, or compared to 13.4% for counting days to harvest from planting.

Open Access