Tracy M. Sterling

Physiological Response to Salt (NaCl) Stress in Selected Cultivated Tetraploid Cottons

In the southwestern and western Cotton Belt of the U.S. soil salinity can reduce cotton productivity and quality. This study was conducted to determine the physiological responses of six genotypes including five Upland cotton (Gossypium hirsutum L.) cultivars and one Pima cotton line (G. barbadense L.) to NaCl under greenhouse conditions. Seeds were germinated and grown for 14 days prior to salt treatment (daily 100 ml of 200 mM NaCl) for 21 days. Compared with the control (daily 100 ml tap water), the NaCl treatment significantly reduced plant height, leaf area, fresh weight, and dry weight. The NaCl stress also significantly increased leaf chlorophyll content, but did not affect leaf fluorescence. Of the six genotypes, Pima 57-4 and SG 747 had the most growth reduction, and were most sensitive to NaCl; DP 33B, JinR 422 and Acala Phy 72 had the least growth reduction and were most NaCl tolerant. Although all the six genotypes under the salt treatment had significantly higher Na and Cl accumulation in leaves, SG 747 and Pima 57-4 accumulated more Na and Cl than DP 33B. Increases in leaf N, Zn, and Mn concentrations were also observed in the NaCl-treated plants. While leaf P, Ca, and S concentrations remained unchanged overall in the genotypes tested, leaf K, Mg, Fe, and Cu concentrations significantly decreased during salt stress. Reduction in plant height is a simple, easy, sensitive, non-destructive measurement to evaluate salt tolerance in cotton.

Weed science research and funding: A call to action

Abstract Weed science has contributed much to agriculture, forestry and natural resource management during its history. However, if it is to remain relevant as a scientific discipline, it is long past time for weed scientists to move beyond a dominating focus on herbicide efficacy testing and address the basic science underlying complex issues in vegetation management at many levels of biological organization currently being solved by others, such as invasion ecologists and molecular biologists. Weed science must not be circumscribed by a narrowly-defined set of tools but rather be seen as an integrating discipline. As a means of assessing current and future research interests and funding trends among weed scientists, the Weed Science Society of America conducted an online survey of its members in summer of 2007. There were 304 respondents out of a membership of 1330 at the time of the survey, a response rate of 23%. The largest group of respondents (41%) reported working on research problems primarily focused on herbicide efficacy and maintenance, funded mainly by private industry sources. Another smaller group of respondents (22%) reported focusing on research topics with a complex systems focus (such as invasion biology, ecosystem restoration, ecological weed management, and the genetics, molecular biology, and physiology of weedy traits), funded primarily by public sources. Increased cooperation between these complementary groups of scientists will be an essential step in making weed science increasingly relevant to the complex vegetation management issues of the 21st century.

Implications of Invasive Plant Variation for Weed Management1

Abstract Genetic variability of invasive plant populations may create significant challenges to weed management through (1) selection for resistant genotypes and (2) differential efficacy of control methods resulting from genotypic variation. Effects of variation on management success may be particularly problematic for native invasive plants because they possess more genetic variation than bottlenecked exotic invasive species. We review the influence of genetic variation among populations and species on efficacy of chemical and biological control of select invasive rangeland plants. Population or genotype variation was more important for successful management when using biological agents than when using herbicides. Long-term success in weed control requires integrating multiple management strategies with attention to specificity of biological control agents to avoid selection for resistant genotypes. Additional index words: Biological control, common garden, genetic variation, metsulfuron, native plants, picloram, rangeland plants.

Locoweed dose responses to nitrogen: Positive for biomass and primary physiology, but inconsistent for an alkaloid

PREMISE OF THE STUDY Plant communities may be influenced by toxic secondary metabolites or enhanced plant growth from plant-symbiont interactions. The C:N hypothesis predicts that carbon or nitrogen constrains plant secondary metabolite production, but it does not consider compounds produced by plant symbionts. Locoweeds are legumes that can have fungal endophyte alkaloid (swainsonine [SWA]) production, which causes livestock poisoning. We studied four locoweed taxa to test whether average SWA concentrations influenced SWA positive dose responses to N fertilizer. METHODS We measured locoweed leaf SWA, pigment concentrations and photosynthetic activity, and plant biomass dose responses to N supplementation for 3 mo in two greenhouse experiments. KEY RESULTS Leaf photosynthesis, leaf pigment concentrations, and plant biomass had positive, unsaturated dose responses across tested N doses. Although N enhanced primary growth, two moderate-SWA taxa (Astragalus mollissimus var. bigelovii and Oxytropis sericea) had negative SWA dose responses to increasing N, the high-SWA taxon (A. moll. var. mollissimus) had no SWA change, and the very low-SWA taxon (A. moll. var. matthewsii) had a transient positive dose response. CONCLUSIONS Supplemented N led to positive dose responses for plant biomass and leaf photosynthesis and pigments, but SWA dose responses differed across locoweed taxa and time. At N levels that enhanced plant growth and reduced antioxidant protective systems, fungal endophyte alkaloid production was not strongly influenced. Production of SWA may be more strongly influenced by factors other than C:N supply (e.g., seasonality, plant age) in the locoweed-endophyte-Rhizobium complex.

Physiological and ultrastructural effects of lead on tobacco

The effects of lead toxicity on leaf gas exchange, chlorophyll content, chlorophyll fluorescence, chloroplast ultrastructure, and opening of stomata were examined in tobacco (Nicotiana tabacum L.) plants. Plants were grown in a growth chamber for 7 d in Hoagland nutrient solution supplemented with 0.0 (control), 5, 10, 25, 50, 100, 300 and 500 μM Pb(NO3)2. Plants treated with 5, 10, and 25 μM Pb(NO3)2 exhibited no abnormalities. Root and shoot growth, net photosynthetic rate and stomatal conductance were significantly reduced in plants treated with 100, 300 and 500 μM Pb(NO3)2. In plants treated with 500 μM Pb(NO3)2, the majority of stomata were closed. The effect of Pb(NO3)2 on chlorophyll content and chlorophyll fluorescence parameters was negligible. However, in plants exposed to 100, 300, and 500 μM Pb(NO3)2, the mesophyll cells showed altered chloroplasts with disrupted thylakoid membranes.

Picloram-resistant and -susceptible yellow starthistle accessions have similar competitive ability

Abstract The relative competitive abilities of yellow starthistle accessions that are resistant (R) and susceptible (S) to picloram were compared using a replacement series experiment. With no herbicide treatment, total shoot dry weights at vegetative and early reproductive stages of plant growth were similar for the two accessions, although S plants accumulated more total shoot dry weight by the late reproductive stage, mainly as a result of a greater contribution of vegetative growth. Without herbicide, relative yield of total biomass or reproductive structures did not differ from theoretical competitive equivalence at any accession ratio, thereby indicating that interaccession interference was similar. For picloram-treated plants, R plants accumulated more total, vegetative, and reproductive dry weight than did S plants at the early and late reproductive stages, and there was no difference between S and R plants at the vegetative growth stage. Seed production by R plants was 10-fold greater than that observed in S plants, but seed size remained unchanged, regardless of accession ratio. With herbicide present, the relative yield of S plants differed from theoretical competitive equivalence as S:R accession ratios decreased, but relative yield of R plants did not. Therefore, only in the presence of picloram will R plants have a competitive advantage over S plants. Some of the progeny from mixed populations of S and R plants that were cross-pollinated, even at low R frequency (25%), expressed resistance to picloram. Nomenclature: Picloram; yellow starthistle, Centaurea solstitialis L. CENSO.

Phylogenetic relationships among New Mexico Astragalus mollissimus varieties and Oxytropis species by restriction fragment analysis

Abstract The phylogenetic relationships within two major locoweed genera, Astragalus and Oxytropis, and among varieties of woolly loco found in New Mexico were analyzed by comparing their chloroplast rpoC1 and rpoC2 gene sequences. Nucleic acids from locoweed species and varieties collected from different geographical locations in New Mexico were amplified using specific primer sets and subjected to restriction fragment analyses. Identity of the amplicons was confirmed by determining the 5′-end sequences from pea and woolly loco var. matthewsii. The amplified sequences from all samples were digested with 16 different restriction enzymes. Presence or absence of individual restriction fragments was scored as binary characters and used to develop a similarity coefficient matrix for cladistic analyses to determine the phylogenetic relationships. The target sequence was conserved, yielding 7% polymorphic data. Oxytropis species were monophyletic and, as expected, formed a clade distinct from Astragalus. The average similarity coefficient among woolly loco varieties was very high (0.9733), but the varieties still separated into three different clades. The phylogenetic relationship among woolly loco varieties coincided with their geographic distribution but was unrelated to insect feeding preference. Nomenclature: Woolly loco, Astragalus mollissimus Torr. ASAML; pea, Pisum sativum L. ‘Alaska’.

Ethylene is not involved in clopyralid action in yellow starthistle (Centaurea solstitialis L.)

Abstract Auxinic herbicides often increase ethylene production in susceptible but not resistant plants. Thus, a role for ethylene biosynthesis in the resistance to, and mode of action of, auxinic herbicides has been suggested. Experiments were conducted to determine the role of ethylene production induced by clopyralid (3,6-dichloro-2-pyridine carboxylic acid) in the mode of action of, and cross-resistance to, this herbicide in picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid)-susceptible (S) and -resistant (R) yellow starthistle ( Centaurea solstitialis L.) plants. Foliar-applied clopyralid induced ethylene production, epinasty, and necrosis in S but had no effect on R. Wounding induced ethylene production in both S and R, so R possesses a functional ethylene biosynthesis pathway. Aminoethoxyvinylglycine (AVG), an ethylene synthesis inhibitor, inhibited ethylene production in S; however, clopyralid-induced epinasty, necrosis, and shoot weight reduction were not prevented. Therefore, herbicide damage was not attributable to induced ethylene. In addition, silver thiosulfate (STS), an ethylene action inhibitor, did not alter herbicide damage. Foliar-applied ethephon, an ethylene-releasing compound, increased ethylene released from S and R, but did not visibly affect plants. Exogenous-applied ethylene in a flow-through system for 48 h did not induce morphological symptoms in plants at 0 or 250 μL L −1 ; at 500 μL L −1 and greater ethylene induced slight leaf rolling and wilting in both accessions although there was no effect on plant weight 3 weeks after treatment. The low sensitivity to exogenously applied ethylene and the inability of AVG and STS to block any symptoms induced by clopyralid suggest that ethylene is a symptom, not a mediator, of auxinic herbicide action and resistance in yellow starthistle.

Spurred anoda (Anoda cristata) interference in wide row and ultra narrow row cotton

Abstract A field experiment was conducted in 2000, 2001, and 2002 at Stoneville, MS, to determine the effect of spurred anoda interference on yield loss of two cotton cultivars, ‘Delta Pine 5415’ and ‘Pima S-6’, grown under wide (1 m) (WR) and ultra narrow (0.25 m) row (UNR) spacings. The relationship between spurred anoda density and dry weight per plot was linear each year. At a spurred anoda density of 8 m−2, spurred anoda dry weight per plot was 507, 322, and 777 g m−2 in 2000, 2001, and 2002, respectively. However, spurred anoda did not interfere with seed cotton yield in 2001, which was probably attributable to the low branch development in that year. Yield losses exceeded 55% at a spurred anoda density of 8 m−2 compared with controls in both WR and UNR. The effect of spurred anoda density on boll numbers was nearly identical in 2000 and 2002, regardless of cotton cultivar and row spacing. Boll weights decreased in response to spurred anoda interference. Spurred anoda interference resulted in a decrease in cotton branch dry weight in WR but not in UNR. The yield decrease as a result of spurred anoda interference in WR was due to reduction in boll retention or fruiting sites (predicated on a decrease in branch weight). However, in UNR, the yield decrease was due to plant mortality; the plant density of both cotton cultivars decreased by one plant for each additional spurred anoda, but the yield per plant for surviving plants remained constant. Neither WR nor UNR cotton had significant advantage in response to spurred anoda interference. The decreased boll weight observed in UNR, and the failure to increase boll numbers m−2 to compensate for decreased boll weight in UNR compared with WR, may limit its appeal to cotton producers. Nomenclature: Spurred anoda, Anoda cristata (L.) Schlecht. ANVCR; cotton, Gossypium hirsutum L. ‘DP 5415’; Gossypium barbadense L. ‘Pima S-6’.

Morphological variation among Gutierrezia sarothrae populations.

Abstract To evaluate relationships among populations, phenotypic variation of morphological characters in one Gutierrezia microcephala and eight Gutierrezia sarothrae populations from New Mexico was quantified and compared with variation expressed when these same populations were grown in a common garden. During flowering, plants were randomly collected from each population across New Mexico during two growing seasons. A common garden of stem cuttings from these same populations was established in Las Cruces. Vegetative and reproductive characters were measured for each population at original and common sites. Vegetative characters did not differ between G. sarothrae and G. microcephala collected from the same location; however, reproductive characters were dissimilar between these two species. Vegetative and reproductive characters differed among G. sarothrae populations at original and common sites between years, although certain populations clustered. Based on morphological characters, more populations clustered when collected from original sites compared to when grown at the common site. Genetics and environment both played a role in the expression of G. sarothrae phenotype when measuring morphological characters; however, G. sarothrae genotypes maintained their general population phenotype expressed at original sites when grown in the common site. Apparently, vegetative and reproductive characters are fairly stable, and the Gutierrezia genotype has more influence on resulting phenotype than the environment in which it grows. Nomenclature: Gutierrezia sarothrae (Pursh) Britt. & Rusby GUESA, broom snakeweed; Gutierrezia microcephala (DC.) Gray GUEMI, threadleaf snakeweed.