Lyn A. Gettys

Genetic Control of Floral Morph in Tristylous Pickerelweed (Pontederia cordata L.)

Pickerelweed (Pontederia cordata L.) is a diploid (2n = 2x = 16) tristylous aquatic perennial. Populations usually contain 3 floral morphs that differ reciprocally in style length and anther height (referred to as the long-, mid-, and short-styled morphs, hereafter L-, M-, and S-morphs). The floral polymorphism promotes disassortative mating among the 3 floral morphs and is maintained in populations by negative frequency-dependent selection. The objective of this study was to determine the number of loci, number of alleles, and gene action controlling floral morph in pickerelweed. Three parental lines (one each of the L-, M-, and S-morph) were used to create S1 and F1 populations. F2 populations were produced through self-pollination of F1 plants. Progeny ratios of S1, F1, and F2 generations revealed that tristyly is controlled by 2 diallelic loci (S and M) with dominant gene action. The S locus is epistatic to the M locus, with the S-morph produced by plants with the dominant S allele (genotype S _ _ _). Plants with recessive alleles at the S locus were either L-morph (ssmm) or M-morph (ssM_). The results of this experiment demonstrate that the inheritance of tristyly in pickerelweed is the same as previously reported for several tristylous species in the Lythraceae and Oxalidaceae.

Palmer Amaranth (Amaranthus palmeri) Identification and Documentation of ALS-Resistance in Argentina

Abstract Palmer amaranth has greatly disrupted agricultural practices in the United States with its rapid growth and rapid evolution of herbicide resistance. This weed species is now suspected in Argentina. To document whether the suspected plant populations are indeed Palmer amaranth, molecular comparisons to known standards were conducted. Additionally, these same plant populations were screened for possible herbicide resistance to several acetolactate synthase (ALS)-inhibiting herbicides. Sequencing data confirmed that suspected populations (A2, A3, A4) were indeed Palmer amaranth. Another population (A1) was tested to determine whether hybridization had occurred between Palmer amaranth and mucronate amaranth the native amaranth species of the region. Tests confirmed that no hybridization had occurred and that A1 was simply a unique phenotype of mucronate amaranth. Each population was screened for resistance to imazapic, nicosulfuron, and diclosulam. All Palmer amaranth populations from Argentina were shown to be resistant to at least one ALS-inhibiting herbicide. The populations were then subjected to further testing to identify the mutation responsible for the observed ALS resistance. All mucronate amaranth populations exhibited a mutation previously documented to confer ALS resistance (S653N). No known resistance-conferring mutations were found in Palmer amaranth. Nomenclature: Diclosulam; glyphosate; imazapic; nicosulfuron; mucronate amaranth; Amaranthus quitensis L; Palmer amaranth; Amaranthus palmeri S. Wats.

Optimum Storage and Germination Conditions for Seeds of Pickerelweed (Pontederia cordata L.) from Florida

Clean seeds of pickerelweed (Pontederia cordata L. [Pontederiaceae]) germinated best (84 to 94%) under water, even after being stored dry up to 6 mo at about 25 °C (77 °F), but germination of clean seeds under water was reduced to 43% when seeds were stored at 4 °C (39 °F) for 6 mo. Underwater germination of seeds enclosed in fruits was less effective; germination of fresh fruits or fruits stored for 3 mo ranged from 70 to 90% and was reduced to 38 to 42% when seeds were stored for 6 mo. The least effective method was burial, which significantly reduced germination in seeds or fruits stored for 3 or 6 mo. Understanding seed cleaning and germination requirements will make it even easier to propagate this attractive native perennial freshwater shoreline species.

Herbivory by Biological Control Agents Improves Herbicidal Control of Waterhyacinth (Eichhornia crassipes)

Classical biological control of waterhyacinth is difficult to evaluate against the backdrop of active herbicide programs. Two experiments evaluated the additive impact of herbivory by two biological control agents with three different rates of 2,4-D on waterhyacinth growth and development in outdoor concrete mesocosms. The herbicide 2,4-D was applied at three rates: (1) control (no herbicide), (2) reduced (2.1 kg ai ha-1), and (3) operational (4.3 kg ai ha-1). Biomass of waterhyacinth populations was reduced by 16.9% by biological control only, 10.5% by the reduced rate of herbicide alone, 44.6% by the operational rate, and 97.3% and 99.9% by the combination of biological control and the reduced and operational rates of herbicides, respectively. These results quantified the relative contributions of both tactics to waterhyacinth management and posit the question of whether further reductions in 2,4-D rates are possible without sacrificing efficacy. Nomenclature: 2,4-D; waterhyacinth, Eichhornia crassipes (Mart.) Solms.

Response of Two Chemotypes of Melaleuca quinquenervia (Myrtales: Myrtaceae) Saplings to Colonization by Specialist Herbivores

Abstract Two chemotypes of Melaleuca quinquenervia (Cav.) S. T. Blake (Myrtales: Myrtaceae) saplings were planted in a common garden under 2 water treatments and exposed to either restricted or unrestricted herbivory from 2 insect herbivores. Chemotypes consisted of either a predominately E-nerolidol terpenoid complex or one that consisted primarily of viridiflorol; both types had influenced the performance or preference of both insect herbivores in laboratory studies. The densities of the 2 specialist herbivores Boreioglycaspis melaleucae Moore (Hemiptera: Psyllidae) and Oxyops vitiosa Pascoe (Coleoptera: Curculionidae) were monitored regularly as they colonized the plantings, as were plant responses like leaf abscission and tree height. Neither the chemotype nor the water treatments influenced the densities of B. melaleucae and O. vitiosa. Trees subjected to unrestricted herbivory shed more leaf biomass than those protected by insecticides from herbivory. There was no relationship between the amount of biomass shed via abscission and the density of either herbivore despite a significant correlation with a damage rating developed for O. vitiosa. There was a chemotype response to herbivory whereby more leaf biomass was shed by the E-nerolidol chemotype than by the viridiflorol chemotype when subjected to unrestricted herbivory. Tree height was influenced by herbivory but not chemotype or water, although there were separate 2-way interactions between all factors. Thus, despite equal herbivore pressure, the response of young M. quinquenervia trees to abiotic and biotic forces diverged at the plant variant level.

A gall-forming biological control agent suppresses vegetative growth of an invasive tree

ABSTRACT Attack by the gall-forming biological control agent Lophodiplosis trifida Gagné (Diptera: Cecidomyiidae), reduced Melaleuca quinquenervia sapling height by 10.1%, leaf biomass by 42%, woody biomass by 42.7%, and root biomass by 30.3%. This provided the first quantitative evidence of the potential of L. trifida to suppress pre-reproductive M. quinquenervia.

THE RELATION BETWEEN ROAD CRACK VEGETATION AND PLANT BIODIVERSITY IN URBAN LANDSCAPE

The objective of this study is to collect basic information on vegetation in road crack, especially in curbside crack of road, for evaluating plant biodiversity in urban landscape. A curbside crack in this study was defined as a linear space (under 20 mm in width) between the asphalt pavement and curbstone. The species composition of plants invading curbside cracks was surveyed in 38 plots along the serial National Route, over a total length of 36.5 km, in Fukuoka City in southern Japan. In total, 113 species including native plants (83 species, 73.5%), perennial herbs (57 species, 50.4%) and woody plants (13 species, 11.5%) were recorded in curbside cracks. Buried seeds were also obtained from soil in curbside cracks, which means the cracks would possess a potential as seed bank. Incidentally, no significant differences were found in the vegetation characteristics of curbside cracks among land-use types (Kolmogorov-Smirnov Test, P > 0.05). From these results, curbside cracks would be likely to play an important role in offering habitat for plants in urban area.

Growth of the Aquatic Plant Southern Naiad in Varying Percentages of Sand and Controlled-release Fertilizer

Native aquatic plants are important tomaintaining a balanced ecosystem, but they often are displaced by exotic invasive plant species. The research on the control and growth of the invasive aquatic species hydrilla (Hydrilla verticillata) using sand substrates and controlled-release fertilizers (CRF) provides a potential production technique for other aquatic plants. We questioned if we could use hydrilla production techniques to grow southern naiad (Najas guadalupensis), a Florida-native aquatic plant that is often mistaken for hydrilla. We grew southern naiad cuttings in containers filled with 100:0, 75:25, 50:50, 25:75, or 0:100 coarse builder’s sand and sphagnum moss (by volume). Before planting, containers were fertilized with 0, 1, 2, or 4 g kg CRF (15N–4P–10K). Containers were submerged in large storage tubs filled with rainwater and grown for 8 weeks. Southern naiad shoot dry weight was greater in the 100% sand substrate than that in the 0% sand substrate. Substrate electrical conductivity (EC) levels were greater in the 0% sand with no difference among the other substrates. Shoot and root dry weight of plants fertilized with 1–2 g kg CRF were greater than 0 or 4 g kg CRF. Substrate EC also increased as fertilizer rate increased, with the highest EC observed at 4 g kg CRF. Based on our results, we would suggest growing southern naiad in substrates with 100% sand and fertilized with 1–2 g kg CRF.

Assessing the risk of Eccritotarsus eichhorniae to pickerelweed, Pontederia cordata in North America

ABSTRACT The mirid Eccritotarsus eichhorniae is a newly described species with potential as a biological control agent for water hyacinth, Eichhornia crassipes, in North America. A series of quarantine-based studies quantified E. eichhorniae usage of Pontederia cordata with no-choice, adult choice, nymph choice, multi-generation, and impact tests. Although greater numbers of E. eichhorniae adults developed on E. crassipes in two separate no-choice trials, some E. eichhorniae were able to complete development on P. cordata in both trials. Adults showed a clear oviposition preference for E. crassipes and F1 progeny reduced the mean relative growth rate of E. crassipes but not P. cordata. Naïve nymphs were more likely to leave P. cordata for E. crassipes but not all nymphs left P. cordata when given a choice. Both multi-generation trials showed a rapid increase in the density of adults and nymphs on E. crassipes over four to five generations while population densities on P. cordata did not change, indicating that this insect can maintain populations on this plant. The modest damage inflicted by a sibling species on E. crassipes, coupled with the ability of E. eichhorniae to persist on P. cordata, may pose an interpretation challenge to U.S. regulatory agencies concerned with non-target impacts by biological control agents. Another option for the continuing efforts to increase the biological control of E. crassipes is to prioritise the evaluation of other potential agents like Taosa longula Remes Lenicov (Homoptera: Dictopharidae) or Thrypticus truncatus Bickel and Hernández (Diptera: Dolichopodidae) over E. eichhorniae.

Biological control increases the susceptibility of melaleuca quinquenervia to fire

ABSTRACT A field experiment evaluating herbivory from biological control agents on Melaleuca quinquenervia saplings experienced a wildfire, which resulted in post-fire tree mortality of 64.6% and 28.1% in the unrestricted and restricted herbivory treatments, respectively. The fire did not negatively impact populations of the biological control agent Oxyops vitiosa.