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Russell T. Nagata and Gregg Nuessly

Damage due to leaf mining by Liriomyza trifolii (Burgess) is a major problem in many leafy vegetables, especially lettuce. A hierarchy of feeding preference of leafminer on lettuce, Lactuca sativa L. cultivars 'Valmaine', `Parris Island Cos', `Floricos 83', and `Tall Guzmaine' was determined. Leafminers were given a choice of two plants. Observations on the number of times that leafminers probed the leaf surface to feed or oviposit in each plant was counted. `Tall Guzmaine' was significantly preferred in all combinations. Probe ratio of `Tall Guzmaine' verses the other cos lines ranged from 4:1 to 90:1. There were no significant difference between the other three lines, although `Valmaine' had the lowest count in most cases. Based on the pedigrees of the cultivars tested, the observed preferences appears to be under genetic control.

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Laurie E. Trenholm and Russell T. Nagata

The objectives of this research were to rank the relative shade tolerance of some new st. augustinegrass (Stenotaphrum secundatum) cultivars and to determine what levels of shade the various cultivars can tolerate. Two consecutive studies were conducted in a glasshouse at the University of Florida Turfgrass Research Envirotron. Cultivars tested were `Bitter Blue', `Floratam', `Palmetto', `Seville', and `1997-6'. Grasses were grown in full sun or under shade structures that provided 30%, 50%, or 70% shade. In trial 1, `Seville' and `1997-6' generally provided best performance under increasing shade, with worst responses seen in `Floratam'. `Seville' and `1997-6' were predicted to maintain an acceptable quality rating of 6 at all shade levels. In trial 2, `Floratam' again had lowest visual quality scores. At 30% shade, `Seville', `Palmetto', and `Bitter Blue' ranked in the highest category, while only `Seville' and `Bitter Blue' had highest rankings at 50% shade. Reduced density was a major factor in turf decline as shade increased. Most of the cultivars performed best under some degree of shade. With the exception of `Floratam', acceptable visual scores were maintained at shade levels exceeding 60% in trial 1 and up to 61% in trial 2.

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Jennifer A. Gargiulo, Russell T. Nagata, and Thomas A. Bewick

An-assay was developed to determine the level of resistance to the herbicide glyphosate in trangenic seedlings of lettuce. Results of the seedling assay were correlated to results of a similar assay using callus lines of the identical transgenic plants. Transgenic plants were found to be a 32-fold increase in tolerance to glyphosate when compared to wild type plants. This was similar to the response of these transgenic lines in the callus line assay.

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Yu Sung, Daniel J. Cantliffe, and Russell T. Nagata

Thermotolerance in lettuce seed at high temperature was investigated using primed and nonprimed seed or seeds matured at 20/10°C and 30/20°C. During seed germination at 36°C, the structural changes of the seed coverings in front of the radicle tip were observed in an anatomical study. In all seeds during imbibition, regardless of seed maturation temperature or priming, a crack appeared on one side of the cap tissue and the endosperm separated from the integument in front of the radicle tip. Additional changes took place during imbibition: the protein bodies in the vacuoles enlarged and were gradually depleted, large empty vacuoles formed, the cytoplasm condensed, the endosperm shrank, the endosperm cell wall dissolved and ruptured, then the radicle elongated toward this ruptured area. The findings suggested that the papery endosperm layer presented mechanical resistance to lettuce seed germination and the weakening of this layer was a prerequisite to radicle protrusion at high temperature. Seeds of `Dark Green Boston', `Everglades', and PI 251245 matured at 30/20°C had greater thermotolerance than those matured at 20/10°C. Results of the anatomical study indicated that the endosperm cell walls in front of the radicle of seeds matured at 30/20°C were more easily disrupted and ruptured during early imbibition than seeds matured at 20/10°C, suggesting that these seeds could germinate quickly at supra-optimal temperatures. From anatomical studies conducted to identify and characterize thermotolerance in lettuce seed germination, it was observed that genotype thermotolerance had the ability to reduce physical resistance of the endosperm by weakening the cell wall and by depleting stored reserves.

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Laurie E. Trenholm, Lawrence E. Datnoff, and Russell T. Nagata

The objectives of these studies were to evaluate the effects of silicon on drought and shade tolerance of st. augustinegrass (Stenotaphrum secundatum). Studies were conducted during 2001 in a glasshouse at the University of Florida Turfgrass Research Envirotron in Gainesville. For both drought and shade evaluations, calcium silicate slag (CaSiO3) was pre-incorporated into pots with commercial potting soil at the rate of 3.36 kg·ha-1 (0.069 lb/1000 ft2). `FX-10' and `FHSA-115' st. augustinegrass were planted into 15.2-cm-diameter × 30.5-cm-deep (6 × 12 inches) plastic pots for the drought study and subjected to minimal irrigation. Under severe drought stress, silicon-amended plants had better responses than non-amended plants. Little improvement was seen under moderate drought stress. `Floratam' and genotype 1997-6 were placed under full sunlight or 50% to 70% shade. There was no benefit from use of silicon under shaded conditions. These findings suggest that silicon might provide improved tolerance to st. augustinegrass under severe drought stress.

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Yu Sung, Daniel J. Cantliffe, and Russell T. Nagata

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.

Open access

Russell T. Nagata and Mark J. Bassett

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

Russell T. Nagata and Mark J. Bassett

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.

Free access

Russell T. Nagata, Kenneth L. Pernezny, Darrin M. Parmenter, Eugene McAvoy, and Kent E. Cushman

Twenty-five varieties of bell peppers (Capsicum annuum) were transplanted in commercial pepper fields in Immokalee and Delray Beach, Fla., to evaluate horticultural characteristics and resistance to race 3 bacterial spot of peppers caused by Xanthomonascampestris pv. vesicatoria. All cultural and management procedures were based on commercial best management practices. Eighty to 90% of marketable fruits had three or four lobes. Total marketable fruit yield from three harvests ranged from 4596 to 7089 kg·ha-1 and marketable fruit number ranged from 20,571 to 31,224 fruit/ha. Most fruit were slightly elongated with length to diameter ratios between 1.1 and 1.2. Seminis 7602 had a ratio of one, while lines ACR 252, PRO2R-3, and PR99R-16 had ratios of 1.40, 1.36, and 1.28, respectively. Significant differences were observed for fruit wall thickness, with those grown in Delray Beach having thicker fruit walls that averaged 7.5 mm vs. 5.3 mm for the Immokalee site. Bacterial spot infection at both sites did not affect yield, due to late natural infection of the field. Susceptible control `Jupiter' had a mean foliage disease incident rating of 26% after the final harvest and was surpassed only by 7682 and 8328 from Enza. The most resistant lines with disease ratings of <3% were 5776, 7141, and 8302 from Seminis, and Telstar from Hazera.

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Russell T. Nagata, Joan A. Dusky, Robert J. Ferl, Antonio C. Torres, and Daniel J. Cantliffe

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).