Norman K. Lownds

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.

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.

Factors affecting the absorption of gibberellin A3 by sour cherry leaves

Abstract The effects of leaf surface, light, temperature, time, concentration, and pH on absorption of [14C]gibberellin A3 (GA3) into newly expanded sour cherry (Prunus cerasus L., cv. Montmorency) leaves were investigated. GA3 penetration was sevenfold greater into the abaxial (7.8%) than adaxial (1.1%) surface. Light markedly enhanced penetration into the abaxial but not the adaxial surface. Penetration was greater at 25°C than at 15° or 35°C. GA3 absorption by the adaxial surface was rapid initially (0–1 h), followed by a slower, almost constant rate of uptake after the droplets dried (1–24 h). Rate of GA3 uptake by the abaxial surface approached zero after 3h. Uptake by the tissue fraction of the adaxial surface was linearly related ( r 2 = 0.99 ∗∗ ) with GA3 concentration from 0.05 to 5 m m , whereas uptake by the abaxial surface was saturated between 1 and 5 m m GA3. Decreasing pH from 5.0 to 3.0 resulted in increased GA3 uptake.

The Garden Wonder Wall: Fostering Wonder and Curiosity on Multi-Day Garden Field Trips

Field trips to the Michigan 4-H Childrens Garden must provide rich science learning experiences for students and teachers. A key to this is getting students to ask questions. To facilitate student question asking we developed the Wonder Wall, a “wall” where students could write their questions. Student questions were answered as part of the field trip and written answers were provided following the field trip. Nearly 75% of the 455 2nd and 3rd grade students in this study posted questions. Questions were both basic information (50%) and wonderment (50%). Basic information questions were simple questions that focused on the garden, plants, staff, and field trip activities. Wonderment questions were more complex questions that focused on field trip learning activities. The 50% wonderment questions was greater than expected, suggesting that students posted these questions after carefully thinking about what they had learned. Student questions provided a real-time assessment of student understanding and interests. Wonderment questions could easily be extended into an experiment, giving students the opportunity to direct their own learning. The Wonder Wall is a simple, easily integrated tool that engaged students in asking questions. It provided educators with valuable insights into student understanding and interests. The Wonder Wall was a powerful part of our field trips and we recommend incorporating it into field trips where ever possible.

Environmental effects on picloram uptake and ethylene production by broom snakeweed.

Broom snakeweed [Gutierrezia sarothrae (Pursh) Britt. R therefore, it appears that changes in uptake and physiological sensitivity as measured by picloram-induced ethylene production are not the only factors controlling differential sensitivity to picloram.

Studies on octylphenoxy surfactants: X. Effect of oxyethylene chain length on ethylene production by cowpea and mung bean and comparison with linear alcohol hydrophobes

The effects of ethoxy (EO) chain length on surfactant-induced ethylene production for selected octylphenoxy (OP) and linear alcohol (LA) surfactants were established using primary leaves of cowpea (Vigna unguiculata (L.) Walp. subsp. unguiculata ‘Dixielee’) seedlings. OP surfactant-induced ethylene production was concentration dependent and decreased log linearly with increasing EO content. C12–15 LA-induced ethylene production decreased log linearly with increasing EO content at 0.1%; however, at 1.0% the relationship was curvilinear with maximum response at 7 EO. Relationships for the C9–11 and C9 LA series were nonlinear with greatest biological activity at intermediate (8–12) EO content. Short EO chain length OP surfactants were only slightly water soluble, and induced low levels of ethylene production and phytotoxicity. Addition of OP+1EO to a long chain, water soluble, non-ethylene inducing surfactant (OP+40EO) solution significantly increased ethylene production by OP+1EO in cowpea. A similar response was found for surfactant-induced phytotoxicity and EO chain length as between ethylene production and EO content. Similar EO chain length and ethylene production relationships were found for germinating mung bean (Vigna radiata (L.) R. Wilcz) seeds as for ethylene production and phytotoxicity in cowpea. Radicle growth was markedly inhibited by OP surfactants with an EO chain length of 10 or less and, in some cases, radicles were irreversibly damaged by ethylene inducing surfactants.