The applicability of the plant vigor and resource regulation hypotheses in explaining Epiblema gall moth–Parthenium weed interactions

A basic question in insect–plant interactions is whether the insects respond to, or regulate plant traits, or a complex mixture of the two. The relative importance of the directions of the influence in insect–plant interactions has therefore been articulated through both the plant vigor hypothesis (PVH) and the resource regulation hypothesis (RRH). This study tested the applicability of these hypotheses in explaining the interactions between Parthenium hysterophorus L. (Asteraceae) and its stem‐galling moth, Epiblema strenuana Walker (Lepidoptera: Tortricidae). Parthenium plants exposed to galling were sampled at three sites in north Queensland, Australia, over a 2‐year period, and the relationship between gall abundance and plant vigor (plant height, biomass, flowers per plant, and branches per plant) was studied. To test the predictions of PVH and RRH, the vigor of parthenium plants protected from galling using insecticides was compared to galled plants and plants that escaped from galling. The vigor of ungalled plants was less than the vigor of galled plants. The higher plant vigor in galled plants was not due to galling, as was evident from insecticide exclusion trials. The insect seemed to preferentially gall the more vigorous plants. These findings support the predictions of the PVH and are contrary to those of RRH. Since gall abundance is linked to plant vigor, galling may have only a limited impact on the vigor of parthenium. This has implications for weed biological control. If the objective of biological control is to regulate the population of a plant by a galling insect, a preference for more vigorous plants by the insect is likely to limit its ability to regulate plant populations. This may explain the paucity of successes against biocontrol of annual weeds using gall insects.     

Opposing effects of plant growth regulators via clonal integration on apical and basal performance in alligator weed

植物生长调节剂通过克隆整合对空心莲子草顶端和基部生长的不同作用 入侵植物不仅对全球生物多样性造成了巨大的威胁,同时也严重影响了农业生产与粮食安全。克隆整合使得相连植株进行资源共享,能促进入侵植物的生长从而获得优势。然而,入侵杂草 在植物调节剂(plant growth regulators, PGRs)影响下的克隆整合作用则很少有报道。PGRs被广泛应用于 农作物生产上,并能通过土壤淋溶、侵蚀和径流作用,影响分布在作物附近的农田杂草的生长。本 研究采用两种PGRs赤霉素(gibberellins, GA)和多效唑(paclobutrazol,PAC)处理恶性入侵杂草空心莲子草 (Alternanthera philoxeroides)基端,并保持或者通过剪切达到控制基端与顶端的连通,从而探究克隆整合作用在空心莲子草响应两种农业常用PGRs中的作用。研究结果表明,GA和PAC对空心莲子草生长的作用相反。GA通过克隆整合作用显著促进顶端植株的地上生长。相反地,PAC显著抑制基端和顶端的地 上生长,但是能够通过克隆整合作用显著促进基端和顶端的地下生长。这些研究结果解释了克隆整合作用能促进PGRs对空心莲子草生长的促进作用,这很可能是外来杂草能够成功入侵人为干扰较多的农业生态系统的重要原因之一。     

Biological control of Ziziphus mauritiana (Rhamnaceae): feasibility,prospective agents and research gaps

The tropical fruit tree, Ziziphus mauritiana (Rhamnaceae), a native of the Indian subcontinent, is a pasture and environmental weed in northern Australia and Fiji. In their native range, Ziziphus spp., including commercially cultivated Z. mauritiana and Z. jujuba, are subjected to a wide range of pests and diseases. The feasibility of classical biological control of this weed has not been explored to date. Effective biological control could reduce plant vigour and seed output, thereby limiting the spread of Z. mauritiana in Australia. Two Ziziphus species are native to Australia, hence, any prospective biological control agent should be specific to Z. mauritiana. Opportunistic field surveys and literature searches identified 133 species of phytophagous insects, 9 species of phytophagous mites and 12 plant pathogens on Ziziphus spp. Host records suggest the following are possibly specific to Z. mauritiana and hence are prospective biological control agents in Australia: the seed‐feeding weevil Aubeus himalayanus; the leaf‐feeding gracillariid moth Phyllonorycter iochrysis; the leaf‐mining chrysomelid beetle Platypria erinaceus; the leaf‐folding crambid moth Synclera univocalis; the leaf‐galling midge Phyllodiplosis jujubae; and the gall‐mites Aceria cernuus and Larvacarus transitans. Host range of the rust Phakopsora zizyphi‐vulgaris includes many Ziziphus species, including the native Z. oenoplia and hence would not be a suitable biological control agent in Australia. The powdery mildew Pseudoidium ziziphi, with a host range restricted to Ziziphus species, has not been reported on Z. oenoplia. All available information on the pests and diseases of Z. mauritiana are from cultivated varieties. Hence, future surveys should focus on wild Z. mauritiana in the Indian subcontinent in areas that are climatically similar to the regions of northern Australia, where it is currently most abundant.     

Assessment of endangered synanthropic plants of Hungary with special attention to arable weeds

Abstract

In the present study, species were selected from the new Red List of the vascular flora of Hungary which can be regarded as a weed. For each species, current conservation status and the most important traits were assessed. Altogether 149 weed species were found to be at risk according to the International Union for Conservation of Nature (IUCN) categories: 11 species are extinct, 11 are critically endangered, 27 are endangered, 26 are vulnerable, 62 are near threatened and 12 are data deficient. These species belong to 37 plant families, from which the most important are Caryophyllaceae, Brassicaceae, Asteraceae, Scrophulariaceae, Chenopodiaceae, Poaceae and Fabaceae. The most significant chorological elements are Mediterranean (28%) and Eurasian (27%); endemic (Pannonian) taxa constitute only 5.4%. Over 90% of these species are of native or archaeophyte origin, according to their residence time. Considering the main habitat types, 46% of the species are originated from dry habitats, 23% from arable lands, 17.5% from wet habitats and 13.5% from ruderal habitats. In the life form spectra, a pronounced dominance of therophytes (81%) is represented. The factor that currently offers the greatest conflict to the conservation of endangered weed species in Hungary are side effects of strong eradication campaigns against the invasive Ambrosia artemisiifolia.     

Changes in size and composition of weed communities during planted and natural fallows

The use of trees and herbaceous cover crops for weed management in smallholder farms is a promising alternative to the unsustainable traditional shifting cultivation system. The reported experiment was conducted from 1993 to 1996 in fallow plots established in 1989 to rehabilitate a degraded Alfisol after 10 years of continuous cultivation of maize/cassava. Treatments consisted of four plots each of woody legume species (Acacia auriculiformis, A. leptocarpa, Leucaena leucocephala, and Senna siamea), and a herbaceous legume cover crop (Pueraria phaseoloides). Two controls (natural bush fallow and continuous maize/cassava) were included. Each treatment was cleared and cultivated in 1993 and 1995 (after 4 and 6 year fallow). Cultivation was repeated in 1994 for plots cleared in 1993 and in 1996 for subplots cleared in 1995. In all the years, weed density and dry weight was lower in planted fallows than in the controls. Per capita weed population growth rate decreased in all the fallow treatments most notably in A. auriculiformis and S. siamea fallow. All fallow species except A. auriculiformis would require more than 6 years of fallow to prevent growth of the weed population over the long term. The weed seed bank was 75% lower in A. auriculiformis and P. phaseoloides fallow than the control plots. Canonical correspondence and redundancy analysis indicated differences in species composition between treatments in the aboveground weed flora and in the weed seed bank. Cynodon dactylon and Digitaria horizontalis dominated continuously cultivated maize/cassava plots. Chromolaena odorata occurred more in natural bush fallow. In contrast, annual broadleaf weeds dominated the planted fallow treatments.Die Einsatz von stickstoffbindenden Bäumen und Bodenbedeckungspflanzen zur Unkrautbekämpfung in kleinbäuerlichen Anbausystemen ist eine vielversprechende Alternative zum traditionellen Wanderfeldbau. Zwischen 1993 und 1996 wurde auf einem degradierten Alfisol ein Feldversuch durchgeführt, mit dem Ziel, den Einfluss von verschiedenen Brachesystemen auf den Unkrautbefall zu ermitteln. Die Versuchsfläche hatte seit 1989 brachgelegen, zwischen 1979 und 1989 wurde die Fläche alljährlich zum Anbau von Mais und Maniok genutzt. Der Versuch beinhaltete fünf Behandlungen mit verbesserter Brache: Acacia auriculiformis, A. leptocarpa, Leucaena leucocephala und Senna siamea als Baumleguminosen and Pueraria phaseoloides als stickstoffbinden Bodenbedecker. Als Kontrollbehandlungen dienten Naturbrache und jährlicher Anbau von Mais/Maniok. Alle Parzellen wurden nach 4- und 6-jähriger Brache in 1993 and 1995 kultiviert, die Bodenbearbeitung auf diesen Parzellen wurde jeweils im folgenden Jahr wiederholt. In allen Jahren waren die Unkrautdichte und Unkrauttrockenmasseerträge in den Baum- und P. phaseoloides Parzellen geringer als in den Kontrollparzellen. Die Abnahme war deutlich niedriger in A. auriculiformis und in S. siamea. Mit Ausnahme von A. auriculiformis, würden alle verbesserten Brachesysteme mehr als 6 Jahre benötigen, um die Wachstumrate der Unkrautpopulation zu hemmen. Die Unkrautsaatgutdichte im Boden war 75% niedriger in A. auriculiformis und in P. phaseoloides Parzellen als in der Kontrolle. Canonical Korrespondenz- und Redundanzanalysen zeigten, dass die Behandlungen die Zusammensetzung der Unkrautarten sowie die Unkrautsaatgutdichte beeinflussten. Cynodon dactylon und Digitaria horizontalis waren die dominanten Arten in den Parzellen, auf denen jährlich Mais/Maniok angebaut wurde. Chromolaena odorata war die dominante Art in Parzellen mit Naturbrache während einjährige, zweikeimblättrige Unkrautarten in den verbesserten Bracheparzellen vorherrschend waren.     

Prior hydration of Brassica tournefortii seeds reduces the stimulatory effect of karrikinolide on germination and increases seed sensitivity to abscisic acid

Background and Aims

The smoke-derived compound karrikinolide (KAR₁) shows significant potential as a trigger for the synchronous germination of seeds in a variety of plant-management contexts, from weed seeds in paddocks, to native seeds when restoring degraded lands. Understanding how KAR₁ interacts with seed physiology is a necessary precursor to the development of the compound as an efficient and effective management tool. This study tested the ability of KAR₁ to stimulate germination of seeds of the global agronomic weed Brassica tournefortii, at different hydration states, to gain insight into how the timing of KAR₁ applications in the field should be managed relative to rain events.

Methods

Seeds of B. tournefortii were brought to five different hydration states [equilibrated at 15 % relative humidity (RH), 47 % RH, 96 % RH, fully imbibed, or re-dried to 15 % RH following maximum imbibition] then exposed to 1 nm or 1 µm KAR₁ for one of five durations (3 min, 1 h, 24 h, 14 d or no exposure).

Key Results

Dry seeds with no history of imbibition were the most sensitive to KAR₁; sensitivity was lower in seeds that were fully imbibed or fully imbibed then re-dried. In addition, reduced sensitivity to KAR₁ was associated with an increased sensitivity to exogenously applied abscisic acid (ABA).

Conclusions

Seed water content and history of imbibition were found to significantly influence whether seeds germinate in response to KAR₁. To optimize the germination response of seeds, KAR₁ should be applied to dry seeds, when sensitivity to ABA is minimized.     

Distribution of Nothanguina phyllobia and Its Potential as a Biological Control Agent for Silver-leaf Nightshade

The nematode Nothanguina phyllobia Thorne was found within large foliar galls on the perennial weed Solanum elaeagnifolium Cav. in west Texas. A two-year survey of a 6400 sq-km area in west Texas showed extensive distribution of the nematode. No hosts other than S. elaeagnifolium were observed. Densities of juvenile nematodes in the soil were high. N. phyllobia spread rapidly after small numbers of infective juveniles were applied in a foliar spray to an S. elaeagnifolium population. The host plant declined in vigor and frequently died. Artificial inoculation of an S. elaeagnifolium population with large numbers of the nematodes by broadcasting infected plant tissue resulted in high infection incidence.