Recent CO2 levels promote increased production of the toxin parthenin in an invasive Parthenium hysterophorus biotype.

Recent carbon dioxide (CO2) concentrations promoted higher parthenin concentrations in an invasive Parthenium hysterophorus biotype. Mean concentrations of parthenin, an allelopathic and defensive sesquiterpene lactone, were 49% higher at recent (~400 ppm) than at mid-twentieth-century (~300 ppm) CO2 concentrations, but did not vary in a non-invasive biotype, suggesting that recent increases in atmospheric CO2 may have already altered the chemistry of this destructive weed, potentially contributing to its invasive success.

Suppresive plants as weed management tool: Managing Parthenium hysterophorus under simulated grazing in Australian grasslands.

Parthenium hysterophorus L. is among one of the most problematic invasive grassland weeds in Australia, and in many other countries around the world. It can reduce pasture and livestock production, natural community biodiversity, and negatively affect human and animal health. Sowing of selected suppressive pasture plants in parthenium weed infested grasslands has shown potential to improve efficacy of management. However, such species need to be tested for their ability to suppress weed growth under grazing conditions. The parthenium weed suppressive and fodder production capacity of six selected pasture species [purple pigeon grass (Setaria incrassata), buffel grass (Cenchrus ciliaris), butterfly pea (Clitoria ternatea), Kangaroo grass (Themeda triandra), bull Mitchell grass (Astrebla squarrosa) and Indian bluegrass (Bothriochloa pertusa)] was tested under no (0%), low (25%), moderate (50%) and heavy (75%) simulated grazing pressures in a grassland area of south-central Queensland, Australia. Purple pigeon grass, buffel grass and butterfly pea legume suppressed the growth of parthenium weed by >50% under low and moderate simulated grazing pressures, as well as generating moderate to high amounts of fodder biomass (up to 5.07 t ha-1 per year). Native species, Kangaroo grass and bull Mitchell grass both suppressed the parthenium weed's growth by >50% under low simulated grazing pressure, however, they generated low to moderate amounts of biomass, 1.83 t ha-1 and 2.7 t ha-1 per year, respectively. The sowing of selected suppressive pasture species in parthenium weed infested grasslands with low-to-moderate grazing pressure, assuming this corresponds closely with the simulated treatment, would provide an additional tool to the best practice weed management strategy as well as sustaining fodder production.

Mimicking a semi-arid tropical environment achieves dormancy alleviation for seeds of Australian native Goodeniaceae and Asteraceae.

BACKGROUND AND AIMS: Seed physiological dormancy (PD) limits the use and conservation of some of Queensland's (Qld) native forb species. It was hypothesised that optimum dormancy-alleviating treatments would reflect environmental conditions that seeds experience in situ, and this premise was tested for PD seeds of four species native to south-west Qld. METHODS: High temperatures and increased rainfall during summer are characteristic of this semi-arid tropical environment. Ex situ treatments were designed to mimic conditions that seeds dispersed in spring experience during the summer months before germinating in cooler autumn temperatures. Seeds received between 4 and 20 weeks of a dry after-ripening (DAR), warm stratification or dry/wet cycling treatment (DAR interspersed with short periods of warm stratification), in darkness, before being transferred to germination test conditions. In addition, natural dormancy alleviation of one of the Goodeniaceae species was investigated in situ. KEY RESULTS: Dry/wet cycling resulted in higher levels of germination of Actinobole uliginosum (Asteraceae), Goodenia cycloptera and Velleia glabrata (Goodeniaceae) when compared with constant DAR or stratification, while Goodenia fascicularis (Goodeniaceae) responded better to short durations of warm stratification. Long durations of DAR partially alleviated PD of A. uliginosum; however, stratification induced and maintained dormancy of this species. Modifications to the dry/wet cycling treatment and germination test conditions based on data collected in situ enabled germination of G. cycloptera and V. glabrata to be further improved. CONCLUSIONS: Treatments designed using temperature, relative humidity and rainfall data for the period between natural seed dispersal and germination can successfully alleviate PD. Differences between the four species in conditions that resulted in maximum germination indicate that, in addition to responding to broad-scale climate patterns, species may be adapted to particular microsites and/or seasonal conditions.

RAPD polymorphisms among variant and phenotypically normal rice (Oryza sativa var.indica) somaclonal progenies.

RAPD analysis was performed among eight rice somaclonal families known to vary for specific characters and four somaclonal families which were phenotypically normal. The parental cultivar,indica rice cv. FR13A, was found to be homogeneous and homozygous at all but one of the 45 RAPD loci. Polymorphisms were found at 28 of the 45 bands among the somaclonal families, including both loss of parental bands, and the appearance of novel non-parental bands. Segregation data revealed both heterozygous and homozygous mutation events, with recessive mutations more prevalent than dominant. All somaclonal families differed significantly from the parental material, indicating that genomic alterations occurred in all families regardless of phenotype. None of the variant families could be regarded as isogenic lines of FR13A at the DNA level. However, some of the DNA level variation may be in highly repeated sequences with no phenotypic effects. The implications for somaclonal breeding and genetic engineering programs are discussed.

Random amplified polymorphic DNA (RAPD) detection of dwarf off-types in micropropagated Cavendish (Musa spp. AAA) bananas.

A RAPD marker specific to the dwarf off-type (hereafter known as dwarf) from micropropagation of Cavendish banana (Musa spp. AAA) cultivars New Guinea Cavendish and Williams was identified following an analysis of 57 normal (true-to-type) and 59 dwarf plants generated from several different micropropagation events. Sixty-six random decamer primers were used in the initial screen, of which 19 (28.8%) revealed polymorphisms between normal and dwarf plants. Primer OPJ-04 (5'-CCGAACACGG-3') was found to amplify an approx. 1.5 kb band which was consistently present in all normal but absent in all dwarf plants of both cultivars. Reliable detection of dwarf plants was achieved using this marker, providing the only available means ofin vitro detection of dwarfs. The use of this marker could facilitate early detection and elimination of dwarfs from batches of micropropagated bananas, and may be a useful tool in determining what factors in the tissue culture process lead to this off type production.Other micropropagation-induced RAPD polymorphisms were observed but were not associated with the dwarf trait.

Studies in Wild Oat Seed Dormancy: II. ACTIVITIES OF PENTOSE PHOSPHATE PATHWAY DEHYDROGENASES.

A selected strain of wild oat (Avena fatua L.) seed has been shown to lose dormancy rapidly during moist soil incubation at 25 C, whereas seed kept similarly at 5 C maintained a high level of dormancy.The activities of cytosolic dehydrogenase enzymes of the pentose phosphate pathway were assayed throughout a period of moist soil incubation at these two temperatures. A distinction was made between extractable dehydrogenases from the embryo and the endosperm regions of the caryopsis.Dehydrogenase activities monitored in seeds incubated at 25 C gradually increased over the course of the investigation. The largest increases in activity occurred during incubation at 5 C, the situation in which dormancy is maintained. No obvious connection could be found between dormancy breakage and increased activity of the pentose phosphate pathway dehydrogenases.

Studies in Wild Oat Seed Dormancy: I. THE ROLE OF ETHYLENE IN DORMANCY BREAKAGE AND GERMINATION OF WILD OAT SEEDS (AVENA FATUA L.).

Seed of Avena fatua were shown to exhibit a characteristic loss of dormancy during dry storage at 25 C, whereas similar seed stored at 5 C maintained dormancy. 2-Chloroethylphosphonic acid was shown to increase germination of partly dormant seed imbibed under certain temperature regimes; a similar effect could not be established for fully dormant or fully nondormant seed. Using gas-liquid chromatography, natural ethylene levels were followed during imbibition of fully dormant and nondormant seed. A large peak in production was observed in the period prior to radicle emergence in the case of the nondormant seed. Measurements of ethylene production taken at 15 C, following periods of after-ripening in moist soil at either 5 or 25 C, indicated that endogenous production was unlikely to be a main cause of dormancy breakage in this species. The possibility that endogenous ethylene could play a role in natural dormancy breakage in aged seeds is discussed. The practical possibilities of 2-chloroethylphosphonic acid as a dormancy breaking agent in a field situation are outlined.