Search

Context Avena sterilis subsp. ludoviciana (wild oats) is one of the major winter weeds of the Northern Grains Region of Australia. The abundance of this weed increased dramatically after the adoption of no-tillage conservation agriculture (NTCA). However, information is lacking on the germination characteristics of the two types of seed (i.e. primary and secondary) that it produces. Aims We aimed to determine the light and temperature requirements for germination and the time to germination of primary and secondary seeds of A. ludoviciana, in order to find ways to manage this weed effectively under NTCA systems. Methods Primary and secondary seeds and caryopses from two southern and two northern biotypes were exposed to a range of temperature and light regimes in the glasshouse, and germination was assessed. Key results All biotypes had ∼25% higher germination from primary than secondary seeds. Removing the hull increased caryopsis germination by ∼70%. The use of a light/dark photoperiod stimulated germination of both types of seed and caryopses compared with continuous darkness. Based on data for caryopses, 7°C and 9°C were found to be optimal germination temperatures for southern and northern biotypes, respectively. At optimum germination temperature, primary caryopses germinated 7–20 days earlier than secondary caryopses. In addition, a light/dark environment resulted in germination 2–6 days earlier than continuous darkness. Conclusions In the Northern Grains Region, seeds retained on or close to the soil surface (i.e. in NTCA systems) can undergo maximum germination during May–June (late autumn–winter), when long-term average temperatures match optimum germination temperatures. This coincides with winter crop plantings. Implications The seasonal timing of germination and the difference in germination timing between primary and secondary seeds, which help to stagger emergence of this weed, are major issues that need to be addressed in NTCA systems.

A temperature-controlled glasshouse study was conducted to evaluate the influence of elevated temperature (eT – 34/24 ± 2°C) on the growth and glyphosate susceptibility of windmill grass (Chloris t...

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. Not only is climate change having an impact on invasive plants through changes in ecosystem, atmospheric carbon may be changing the plants themselves. This analysis finds higher concentrations of parthenin at higher levels of CO2, making an invasive weed more toxic.

To elucidate the response of oxidative metabolism, triggered by elevated ammonium (NH4+) concentrations, on root growth of wheat seedlings, Yumai 49 (NH4+-tolerant) and Lumai 15 (NH4+-sensitive) cultivars were supplied with either 5.0 mmol L−1 NH4+-N (EAC) or 5.0 mmol L−1 NO3–-N (CON) under hydroponic conditions. Root growth in both cultivars was significantly reduced under EAC, and the negative effect was greater in Lumai 15. EAC enhanced the activities of monodehydroascorbate reductase and dehydroascorbate reductase in the roots of both cultivars, while it decreased ascorbic acid (ASA) content and GDP-mannose pyrophosphorylase (GMPase) activity at the 12th day after treatment in Lumai 15 by 62.0 and 71.4%; and in Yumai 49 by 38.8 and 62.2%, respectively, indicating that the regeneration of ASA was increased, but the biosynthesis of ASA was reduced under EAC treatment. Moreover, EAC increased DHA/ASA, reactive oxygen species (ROS), and malondialdehyde contents, as well as antioxidant enzyme activities in the roots of both cultivars. Relatively greater increases in ROS and soluble sugar, and lower antioxidant enzyme activities in Lumai 15 indicate severe disruption of oxidative metabolism when compared to Yumai 49. Results reveal that the reduction of ASA biosynthesis via decreased GMPase activity under the EAC condition probably acts as a trigger for accumulated ROS and imbalanced redox status, resulting in root growth inhibition during wheat seedling growth stage. Yumai 49, being an NH4+ -tolerant cultivar, had the stronger capacity to protect itself from oxidative stress, which allowed it to retain a lower DHA to ASA ratio by maintaining a better redox homeostasis than could be maintained in the NH4+ -sensitive cultivar Lumai 15.

Alien invasive aquatic macrophytes tend to displace native species and transform diverse macrophyte communities into monospecific stands. It is often thought that superior competitiveness allows alien invaders to achieve this. Cabomba caroliniana is a submersed macrophyte that is highly invasive worldwide and frequently monopolises habitats. However, field observations in Queensland, Australia, found that the native floating attached Nymphoides indica can co-exist with C. caroliniana, highlighting N. indica as a potential candidate for habitat restoration. To identify factors and processes that regulate the coexistence of these species, we conducted a field survey and two experiments in artificial mesocosms. We found that N. indica leaf areal coverage of the water surface significantly reduced C. caroliniana standing crop biomass in the field. C. caroliniana growth was also linked to water depth; N. indica was not able to grow beyond 2 m depth. There was a small reduction in N. indica root and shoot biomass when co-cultured with C. caroliniana in our experiment. Therefore, there was reciprocal competitive inhibition between the two species. However, the effect of N. indica on C. caroliniana was much larger. There was evidence that a reduction of C. caroliniana biomass below a threshold of c. 300 g dry mass/m is critical for protecting native submersed macrophyte diversity and abundance. Once C. caroliniana biomass exceeds this threshold, it dominates plant communities and forms high biomass monocultures. The experimental work identified shading as the most important factor that reduces C. caroliniana biomass, corroborating the relationship between leaf areal cover and C. caroliniana biomass found in the field. Based on these findings, N. indica could be useful for restoring the shallow lake littoral habitat, because it suppresses biomass of the invasive species to a level that allows other macrophytes to coexist and additionally increases habitat heterogeneity. Similarly, N. indica could be suitable to restore areas where C. caroliniana was previously removed to reduce the likelihood of future habitat monopolisation by C. caroliniana and realise long-term ecological benefits from invasive macrophyte management.

Using seeds to restore natural ecosystems has a greater chance of success if the seeds used are ready to germinate given appropriate environmental conditions. For Australian native Poaceae species, seed quality and dormancy can impose constraints on restoration success. In this study, germination biology of three Australian native Poaceae species, such asCymbopogon refractus,Capillipedium spicigerumandBothriochloa bladhii, was investigated. The seeds were exposed to different germination-enhancing chemicals (GECs, namely smoke water (SW), potassium nitrate (KNO3) or a combination (SW + KNO3)) and treated with three different seed enhancement technologies (SETs, namely seed priming, seed coating or seed cookies) then sown into two contrasting soil types (sodosol or black vertisol). Laboratory germination percentages achieved were C. refractusandC. spicigerum, priming and/or coating with KNO3+ SW had the highest cumulative emergence. ForB. bladhii, total seedling emergence was the highest (36% in both soils) for primed seeds with KNO3. Seedling emergence from seed cookies was low in all three species (

Amongst all biotic factors, weeds pose the most serious threat to successful cotton production. Adoption of conservation agriculture, the evolution of herbicide-resistant weed populations, and the ...

Parthenium weed is an invasive species in a growing number of countries where it infests numerous crop fields, including sorghum. Two field studies were conducted to quantify the effect of parthenium weed on the performance of grain sorghum at different weed densities (0, 5, 10, 15 and 20 plants m−2) and durations of weed-crop competition (season-long weed-free, weed-free after 2, 4, 6 or 8 weeks, and season-long weedy). Our aim was to identify the density threshold and ideal duration to control parthenium weed in sorghum fields. Both field experiments were planned in a randomised complete block design each with three replications in 2016 and were repeated in 2017. Parthenium weed biomass increased significantly with increasing density and competition duration. The increasing parthenium weed density had a linear negative effect on sorghum growth, yield and yield-contributing traits. The highest yield loss, of up to 66%, was recorded at the highest parthenium weed density of 20 plants m−2 when compared to weed-free treatment. In addition, the season-long competition of this weed with sorghum caused 81% reduction in grain yield over weed-free treatment. According to our results, parthenium weed should be managed below a density of 5 plants m−2 and throughout the crop growth duration in grain sorghum fields as it can cause serious yield losses even at low densities and through strong competition at early as well as late growth stages of the crop.

Climate change elements including elevated atmospheric carbon dioxide (CO2) concentration and soil salinity significantly impact weed biology and management. In this study, we evaluated the performance of a highly invasive plant species, parthenium weed (Parthenium hysterophorus L.) grown at various soil salinity levels (ranging from 0 to 16 dS m−1) at two CO2 concentrations (ambient: 400 ppm and elevated: 700 ppm). The CO2 concentration and soil salinity individually affected various early growth attributes of parthenium weed. The interaction between CO2 and salinity was significant for chlorophyll index, stem dry weight and phenolics content. Parthenium weed plants grew taller (13%), achieved greater leaf area (28%) and produced more dry weight (24%) when raised under elevated as compared with the ambient CO2. Soil salinity had a dose-dependent, negative effect on various growth attributes, chlorophyll index, relative water content and phenolics content. Even the modest levels of salinity (4.2 to 4.6 dS m−1) caused 50% reduction in dry weights of leaves, roots and whole plants. Sodium ion (Na+) concentration peaked at the highest salinity level (16 dS m−1) as compared with the lower salinity levels (0 to 12 dS m−1). Overall, salinity had a negative effect on different growth variables but elevated CO2 improved growth and phenolics content regardless of the salt stress regime. Hence, parthenium weed could benefit from future atmospheric CO2 concentration and may invade some salt-affected areas.

Parthenium hysterophorus is an alien invasive weed infesting grasslands in many countries around the world, including Australia. Previous studies have identified several native and introduced fodder species that can suppress biomass production of parthenium weed. In the present study, a total of 11 fodder species were tested for their ability to suppress growth of parthenium weed, of which, seven were sown at Injune and Mungallala in Queensland, Australia, with some species tested at both locations. At the Injune site, four introduced pasture species, i.e. Digitaria milanjiana, Clitoria ternatea, Cenchrus ciliaris and Chamaecrista rotundifolia significantly reduced shoot dry biomass of parthenium weed by 60 to 80%, while two native species, i.e. Bothriochloa macra and Eragrostis leptostachya had no significant effect. Cenchrus ciliaris and C. ternatea produced large amounts of dry fodder biomass, i.e. 404 and 360 g m(-2), respectively. At the Mungallala site, three introduced species, i.e. D. milanjiana, Chloris gayana and C. rotundifolia and one native species, i.e. Dichanthium sericeum significantly reduced dry biomass of parthenium weed by >80%, producing sizeable fodder biomass (260 to 400 g m(-2)). The findings support the view that certain introduced and native pasture plant species can suppress the growth of parthenium weed at two contrasting locations and therefore show promise as potential tool for improved management of parthenium weed.

Parthenium weed (Parthenium hysterophorus L.) is an internationally important invasive weed native to the tropical and sub-tropical Americas, and invasive in more than 30 countries. This weed has serious adverse influences on rangeland and agricultural crop production, on human and animal health, and on the biodiversity of natural communities. Parthenium weed leaf litter can reduce seedling emergence and affect the early growth of a wide range of pasture and crop species. Soil collected from a heavily infested parthenium weed area was shown to reduce seedling emergence of a wide range of test plants (lettuce (Lactuca sativa L.), maize (Zea mays L.), curly windmill grass (Enteropogon acicularis L.), and liverseed grass (Urochloa panicoides P.Beauv.)) by between 20 to 40%, however, the soil had no effect on the subsequent growth of the surviving test plants. Soil amended with dried parthenium weed leaf litter reduced the emergence of test species by ca. 20 to 40%, but it had no effect on the growth of the surviving test plants. One week after emergence, the growth of all test species was stimulated by 9 to 86% in the leaf litter-amended soil with the increased growth matching the increased amounts leaf litter amended. In parthenium weed-infested landscapes, the substrate (soil) is affected by the plant during the growing season by the release of allelopathic chemicals. However, the plant’s litter can affect the community outside of the growing season, first through a residual allelopathic activity, but also by a fertilizing effect as litter breakdown occurs. This study demonstrates the significant ability of parthenium weed to affect plant communities throughout the year and, when considered over several years, this may lead to the creation of a complete monoculture of the weed.

Parthenium weed (Parthenium hysterophorus L.) is a globally invasive plant with significant negative impacts on the environment, agriculture, economy, and health. This invasion problem is likely to be exacerbated by climate change. Elevated atmospheric carbon dioxide concentration ([CO2]), high ambient temperatures, heatwaves, and droughts will facilitate the establishment, range expansion, and interference potential of this invasive species while making its management more difficult. Here, for the first time, we review the potential impact of climate change elements on parthenium weed biology and management at regional and global levels. We establish that (1) parthenium weed plants morphologically and physiologically adapt to sustain or promote their growth, fecundity, competitive ability, and allelopathic effect under most climate change scenarios; (2) climate change elements can reduce the relative vigor of neighboring plants, especially C4 grasses, in competition with parthenium weed, providing this invasive species a competitive edge; (3) elevated [CO2] has the most pronounced positive effect on parthenium weed performance compared to other climate change elements; (4) the efficacy of a widely used herbicide, glyphosate, may be reduced on parthenium weed grown under elevated [CO2]; (5) mixed effects have been reported for biological control agents, with some losing ground, while others are maintaining or improving their efficacy; and (6) a greater risk of spread and range expansion under sustained climate change will pose greater challenges for management in natural and managed ecosystems. There has been a disturbing transition of this weed from noncropped landscapes to agroecosystems in response to recent climatic and land use changes. All evidence presented in this review suggests that the situation will be greatly aggravated if drastic management interventions are not implemented. Therefore, the research, policy, and outreach focus must be revisited and revamped considering the impacts of climate change to develop pragmatic solutions to combat this “superweed”.

Coconut [Cocos nucifera L.] is often called “the tree of life” because of its many uses in the food, beverage, medicinal, and cosmetic industries. Currently, more than 50% of the palms grown throughout the world are senile and need to be replanted immediately to ensure production levels meet the present and increasing demand for coconut products. Mass replanting will not be possible using traditional propagation methods from seed. Recent studies have indicated that in vitro cloning via somatic embryogenesis is the most promising alternative for the large-scale production of new coconut palms. This paper provides a review on the status and prospects for the application of somatic embryogenesis to mass clonal propagation of coconut.

Parthenium hysterophorus is a noxious invasive weed of both agricultural and natural ecosystems, spreading aggressively in Nepal. Management of this weed in Nepal has been limited, mainly because of the lack of geo-referenced data concerning the weed's distribution. We conducted a nationwide survey of P. hysterophorus and its coleopteran biological control agent Zygogramma bicolorata from 2013 to 2016 to determine their spatial distribution. Both were widespread, with the distribution of Z. bicolorata lagging behind the invasion front of P. hysterophorus. The weed was present in 21.2% of the 4838 locations examined, including several isolated satellite populations. The weed was found in the Tarai, Siwalik, Middle Mountains and High Mountains regions, reaching up to 2000 m asl. It has invaded natural and modified ecosystems including all six protected areas in the Tarai and Siwalik regions. Road access appears to be the major pathway for its long-distance dispersal. Zygogramma bicolorata had spread from the east to the west and was present in 15.4% of the weed occurrence locations, inflicting a low amount of damage. A CLIMEX modelling projection revealed the presence of additional geographic areas in Nepal which are climatically suitable for both P. hysterophorus and Z. bicolorata. Eradication of satellite populations of the weed by physical and chemical measures, and the release of Z. bicolorata into new, but climatically suitable, locations should be prioritised for P. hysterophorus management in Nepal. In conclusion, P. hysterophorus has rapidly become widespread in Nepal and the currently available biological control agent has not been able to prevent further spread of the weed.

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 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 and 2.7 t ha 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.

Parthenium hysterophorus is a prolific invasive weed species, which infests many crops in over 40 countries around the world. A 2-year field study was carried out to quantify the potential impacts of this weed on direct-seeded rice. Parthenium weed was allowed to compete for 2, 4, 6 or 8 weeks after crop emergence, while full season weedy and weed-free plots were maintained as controls. Parthenium weed plants grew taller and attained more biomass as the competition duration prolonged. The yield and yield-related attributes of rice were negatively affected with increasing competition duration. The season-long competition caused the highest reductions in panicle number (28–34%), panicle length (26–27%), grains per panicle (22–23%) and grain yield (33 and 38%) of rice in both years. Weed competition for 2–8 weeks caused 5–34% and 6–33% losses in rice grain yield during both years, respectively. Importantly, Parthenium weed control after 8 weeks of competition did not improve rice yield significantly. The results suggested that Parthenium weed should be controlled in rice fields between 4 and 8 weeks after crop emergence under direct-seeded conditions to avoid over 10% yield losses.

Parthenium hysterophorus L. (Asteraceae) utilises multiple mechanisms to facilitate its dispersal. It has been speculated that the cypsela, the propagule of this species, can be dispersed by water under varying environmental conditions. Four experiments were conducted to test this hypothesis, using simulated shaking and immersion to test floating ability and viability of the propagule in water. The influence of the acidity of the immersion medium on cypsela viability was also examined. Our results revealed that the freshly harvested cypselae could float on river water for at least 20 days, although around 80% sank within a week if moderate or severe turbulence was applied. Sinkage was observed to be more rapid in naked seeds (within a day) than in cypsela (within a week). On still water surfaces, germination occurred within a week but extended to 1.5 weeks under turbulent conditions due to sinkage. In river water, initial germination of floating cypselae was greater (70%) under illuminated conditions as compared to dark conditions (20%). The viability of immersed cypselae was found to remain high in distilled water for 45 days, when immersion was in cool conditions (10 or 15°C). However, in moderate (20 and 24°C) or warm (25 and 30°C) conditions, the rate of viability loss increased, and at 34°C, around 50% of the cypselae died after 20 days of immersion. Similar trends for cypselae longevity were observed in studies using river and pond water; viability loss was faster, especially in pond water. In summary, a proportion of cypselae will float in turbulent water and could be carried significant distances in river systems. Immersed cypselae can remain viable for weeks and can germinate on contact with soil. Water bodies or floods are therefore considered as important pathways in parthenium weed dispersal; hence, post-flood monitoring is strongly recommended to minimise its spread.

The rise in atmospheric CO has huge impacts on the biology and management of invasive weed species such as Parthenium hysterophorus. This study evaluated the effect of ambient (400 ppm) and elevated (700 ppm) CO concentrations on P. hysterophorus growth, reproductive output and response to glyphosate applied at several doses including the recommended dose (800 g a.e. ha ). The plants in control treatment (no herbicide) grew taller (41%), produced a larger number of leaves (13%) and flowers (39%), and higher dry biomass (34%) at elevated CO as compared to the ambient CO . Glyphosate caused significant reduction in chlorophyll content of P. hysterophorus plants grown at both CO concentration in a dose-dependent manner. The percentage herbicide injury was relatively less at elevated CO as compared to the ambient CO at 7 and 14 days after glyphosate application but it was almost similar at 21 days after application. This shows that elevated CO might have slowed the translocation of glyphosate initially, but most plants were killed eventually close to 21 days after application. The survival rate was higher under elevated as compared to the ambient CO at recommended and lower doses of glyphosate. There was a negligible difference between the two CO concentrations for the plant dry biomass reduction over the control treatment. P. hysterophorus growth and reproductive potential (indicated by number of flowers) improved significantly by CO enrichment but there was little effect on the overall efficacy of glyphosate applied to control this species. This article is protected by copyright. All rights reserved.

Parthenium weed is an emerging problem in direct-seeded rice due to the suitable microclimatic conditions for its establishment in this system. This two-years field study evaluated the potential of pendimethalin (pre-emergence) and bispyribac-sodium plus bensulfuron-methyl (post-emergence) herbicides to control parthenium weed when applied alone or in combination in two rice cultivars, Basmati-2000 (long duration and tall stature) and Shaheen Basmati (short duration and short stature) under direct-seeded conditions. The cultivar Basmati-2000 had a lower parthenium weed density (27 and 14%) and dry biomass (27 and 25%) but had a greater plant height (8 and 13%), produced more kernels per panicle (8 and 12%) and had a greater grain yield (7 and 9%) when compared to Shaheen Basmati in 2016 and 2017, respectively. The application of pendimethalin followed by bispyribac-sodium plus bensulfuron-methyl provided the highest reductions of 90 and 88% in parthenium weed biomass as compared to the weedy treatment in 2016 and 2017, respectively. In this treatment, rice plants were taller (8 and 10%), having greater panicle lengths (17 and 16%), branches per panicle (11 and 21%), kernels per panicle (9 and 6%), 1000-kernel weight (7 and 9%) and grain yield (33 and 37%) as compared to the weedy treatment in 2016 and 2017, respectively. The highest grain yield and net benefits were recorded in the weed-free treatment. In both years, the sole application of pendimethalin or bispyribac-sodium plus bensulfuron-methyl reduced parthenium weed biomass by 66–69% and 80–82%, respectively as compared to the weedy treatment. Overall, the herbicide treatments followed this order in terms of weed control efficiency, grain yield and economic benefits: pendimethalin followed by bispyribac-sodium plus bensulfuron-methyl > bispyribac-sodium plus bensulfuron-methyl > pendimethalin. In conclusion, rice cultivar Basmati-2000 was more suppressive to parthenium weed due to its tall stature. It also produced higher yields and economic returns than the cultivar Shaheen Basmati. The sequential application of pendimethalin and bispyribac-sodium plus bensulfuron-methyl provided an excellent way to control (ca. 90%) parthenium weed and enhanced the productivity and profitability of both rice cultivars under direct-seeded conditions.

Glyphosate-resistant (GR) weeds are the biggest concern for all cotton stakeholders worldwide. Currently, 43 weeds species are resistant to glyphosate and the number is increasing at an alarming rate. Soil residual/pre-emergence (PRE) herbicides like Pendimethalin and S-metolachlor can be effectively used for the control of GR weeds; however, their use is very limited at farmer’s side due to the adoption of herbicide-tolerant technology with complete reliance on glyphosate. The present study was conducted to evaluate the performance of PRE and post-emergence (POST) herbicides in glyphosate-tolerant (GT) cotton. The herbicide treatments were pendimethalin and S-metolachlor as PRE-residual, and glyphosate was applied as POST at 20 days after sowing (DAS) either alone or in combination with other herbicides like S-metolachlor, pendimethalin, and haloxyfop. A second application of glyphosate was made at 35 DAS. Results revealed that pendimethalin and S-metolachlor treatments gave 100% suppression of all dominant weeds and increased lint yield by 310–350% as compared to weedy control. In contrast, glyphosate applied once and twice, gave weed biomass reduction of only 10–86%, and increased lint yield by 136–185% over weedy control. This research established that PRE application of pendimethalin and S-metolachlor can be included in the weed management program of GT cotton.

Cotton is an important cash crop grown on 2.5% of the world’s arable land in over 100 countries, and has a 31% share of the world’s fibre market. In Australia, cotton is also a leading crop and contributes around AUD $3 billion to the total agricultural production. Weeds are a major biotic constraint resulting in yield losses of up to 90% and revenue losses of around AUD $100 billion globally and $4 billion to Australian agriculture. Genetically-modified (GM) crops have refashioned the weed management with more dependency on glyphosate. Such overreliance has led to the evolution of 43 glyphosate-resistant (GR) weed populations globally, with 16 species reported from Australia. Such GR weeds along with volunteer glyphosate-tolerant (GT) plants are now decreasing the value of the GM crops and forcing growers to spend more time and effort, and investment in their management. Weed management strategies need to be diversified and integrated with non-chemical methods and alternative herbicides not only to achieve efficient control, but to reduce the rate of evolution of GR weeds. In future, research is needed to improve integrated weed management through development and use of competitive and multiple herbicide-tolerant (HT) crops, organic herbicides, bio-herbicides, RNAi technology and robotics.

Chloris spp. are warm-season grasses that outcompete crops for scarce resources throughout Australia. In Queensland, mild winters and increased adoption of conservation tillage practices have led to an increase of this warm-season grass family in winter crops. The objective of this study is to understand whether droplet size (nozzle type) effects herbicide efficacy of summer perennial grasses, as previous research found no effect of droplet size (nozzle type) on herbicide efficacy of winter annual grasses. A study to compare droplet-size (nozzle type) effects on control of windmillgrass and its domesticated relative, rhodesgrass, was conducted at the University of Queensland in Gatton, QLD, Australia. Results showed little difference in dry weight reductions for windmillgrass or rhodesgrass across droplet size (nozzle type). Paraquat applications with the TTI nozzle resulted in significantly lower dry weight reductions compared with other droplet-size sprays (nozzle types) for rhodesgrass. Glyphosate, imazamox plus imazapyr, and clodinafop resulted in commercially acceptable control for both species, regardless of the droplet size (nozzle type) selected, indicating droplet size (nozzle type) has relatively little impact on the efficacy of these herbicides. Proper nozzle selection can result in control of Chloris spp., a hard to control weed species, while reducing the occurrence of spray drift to nearby sensitive areas.

An elevated atmospheric carbon dioxide (CO2) concentration and frequent droughts are two anticipated climate change scenarios in which certain invasive weeds may develop competitive advantages over crops and adversely impact productivity and herbicide efficacy. Hence, a study was conducted to explore the effect of different climatic scenarios on the growth and management of Sesbania cannabina (Retz.) Pers with glyphosate. The variables investigated were two CO2 concentrations (400 and 700 ppm), two soil moisture levels (100% and 50% of field capacity (FC)), and three glyphosate rates (0 (control), 517 (50% of recommended rate), and 1034 g ae ha−1 (recommended rate)). CO2 concentrations and soil moisture levels had different effects on the growth and management of S. cannabina. Overall, 100% FC and elevated [CO2] of 700 ppm recorded the maximum plant height (38 cm), leaves per plant (20), growth index (60), chlorophyll content (SPAD value 37), and dry biomass (3 g) in comparison with ambient [CO2] of 400 ppm and 50% FC treatment. The recommended glyphosate application gave 100% weed biomass reduction, however, efficacy was reduced (63%) when applied at 50% of the recommended rate under elevated [CO2] of 700 ppm and 50% FC conditions.

Fireweed (Senecio madagascariensis Poir), is a weed of National significance and one of the worst weeds of coastal pastures in South Eastern Australia. Chemical control has been found to be effective in killing plants but there is no information on the effect of herbicides on the seeds that may be present on plants at the time of application. Consequently, a study was undertaken to determine the effect of five selective herbicides (1) on plant mortality at different life stages and (2) on the viability (as assessed by germination) of fireweeds seeds at different stages of maturity. Potted plants of the required growth stages were obtained through several collections of different sized seedlings from a field site near Brisbane. Before herbicide application, in the mature plant cohort the inflorescences were tagged according to their maturity as being either immature (IM) or intermediate (INT). Plants were sprayed with either fluroxypyr/aminopyralid (HotShot™) (A), bromoxynil (Bromicide® 200) (B), metsulfuron-methyl (Brush-Off®) (C), triclopyr/picloram/aminopyralid (Grazon™ extra) (D), triclopyr/picloram/aminopyralid (TordonTM regrowthMaster) (E) at the recommended rates with untreated control plants of the three growth stages also included for comparison. All herbicides killed fireweed seedlings and juvenile plants, but only treatments A, D and E gave high plant mortality (>80%) of mature plants. All herbicides also caused nil germination of seeds collected 30 days after spraying, except for a small percentage (8% germination) of mature seeds from Bromoxynil treated plants. These results have identified several herbicides capable of killing mature fireweed plants and minimizing replenishment of soil seed reserves.

This chapter discusses coconut embryo culture (EC) including the morphology and physiology of the zygotic coconut embryo, culture types and growth conditions, applications such as the use of the EC technique for the collection of germplasm from isolated/distant areas, conservation (cryopreservation) and the dissemination of elite germplasm, and as a starting point for clonal propagation (via somatic embryogenesis). The technique is most commonly recognized for its application to coconut types that generally don’t germinate in vivo. As EC is the foundation tissue culture method for cloning, propagation, conservation, and transformation of coconut, the technique has been widely documented. However, the method is generally underused, and protocols have room for improvement. Key enhancements needed are method optimizations to ensure high survival rates for a wide range of genotypes, in a variety of laboratories. Losses can be high during acclimatization and transfer to field conditions.

Parthenium weed has been invading native and managed Australian grasslands for almost 40 years. This study quantified the potential of selected plant mixtures to suppress the growth of parthenium weed and followed their response to grazing and their impact upon plant community diversity. The first mixture consisted of predominantly introduced species including Rhodes grass, Bisset bluegrass, butterfly pea and green panic. This mixture produced biomass rapidly and showed tolerance to weed species other than parthenium weed. However, the mixture was unable to suppress the growth of parthenium weed. The second mixture of predominantly native pasture species (including forest bluegrass, Queensland bluegrass, Buffel grass and siratro) produced biomass relatively slowly, but eventually reached the same biomass production as the first mixture 12 weeks after planting. This mixture suppressed parthenium weed re-establishment by 78% compared to the control treatment. Its tolerance to the invasion of other weed species and the maintenance of forage species evenness was also superior. The total diversity was five times higher for the mixture communities as compared to the plant community in the control treatment. Therefore, using the suppressive pasture mixtures may provide an improved sustainable management approach for parthenium weed in grasslands.

In situ conservation of coconut germplasm refers to the maintenance of coconut genetic diversity in the agroecosystems where it has evolved. Ex situ conservation comprises all coconut germplasm currently maintained as living trees in field genebanks, screen houses, and elsewhere beyond their host agroecosystems. Ex situ conservation includes in vitro conservation, as well as cryopreservation of pollen, embryos, and embryogenic callus. This chapter presents the variety of existing approaches to conserve coconut germplasm, together with a prospective approach assessing how farmers could better benefit from the advances recently achieved in coconut biotechnology for the sustainable conservation of coconut diversity. This chapter also emphasizes biological and sociological constraints jeopardizing conservation. Ex situ coconut conservation is facing a crisis. Among the 24 registered coconut genebanks, at least 16, including 3 out of the 5 international genebanks, do not have enough capability, laboratory space, equipment, staff, and/or a budget needed to make reliable controlled pollinations for the rejuvenating or maintenance of the germplasm. The most efficient way to conserve coconut diversity should include a multifunctional approach, involving the conservation of additional appropriate crops or species by the same team, at the same site or in the same laboratory. Such multifunctional approaches that integrate “networked” and multifunctional genebanks and harness the latest developments in tissue culture and cryopreservation will help address the unique constraints facing coconut conservation and could help strengthen the networks and communications needed to ensure effective conservation.

Background: Parthenium weed (Parthenium hysterophorus L.) is an invasive weed that has invaded vast regions of Pakistan in a relatively very short period of a decade or two, threatening the crop fields of the agrarian fed country. Parthenium hysterophorus L. is native of central South America and Gulf of Mexico, has now turned out to be a weed of global significance due to its alarming invasions and profuse spread in approximately all parts of the world. Its invasion is probably due to the contamination of its seeds in the imported grains from other countries of the world. Objective: During comprehensive sampling from Pakistan and Australia, it was observed that parthenium weed accessions exhibited several distinct morphological features present at different geographical regions. Therefore this study focuses on the use of plastid DNA barcodes (psbA-trnH) to evaluate the extent of variations in nucleotide sequences between the parthenium weed sampled accessions. Methods: The variability or genetic diversity was evaluated through sequencing of the amplified products and data was subjected to phylogenetic analysis in Molecular Evolutionary Genetic Analysis (MEGA; version 6.06) software. Results: In Maximum Likelihood tree, mainly two clades with three subdivisions are evident which showed increased heterogenity. The results of sequence based markers showed 12 haplotypes of P.hysterophorus populations (having two parsimony informative sites) with 10 indels and a few SNPs (single nucleotide polymorphisms). Conclusions: The results advocate that there have been multiple introductions of parthenium weed into Pakistan.

It has been estimated that around one in ten of the human population is connected directly with coconut production and the processing, trade, and retail distribution of the diversity of its products. Industry planners, nationally and internationally, require information on the principal sources of production, and consumption, locally and through world trade, as well as awareness of the urgency for replanting and the potential means to rapidly achieve this. The production base of the coconut industry is shown to be currently stable, but the advanced age of a high proportion of the palms foreshadows an accelerating decline in productivity unless renewal begins immediately. The purpose of this book is to provide a road map for replanting by identifying up-to-date knowledge on the ecology of the coconut, its management needs, and above all the choice of genotypes possessing traits that will advance adaptation and potential productivity beyond that presently achieved by the old generation of palms needing to be replaced. Recent advances in biotechnology, offering the possibility for a new way to conserve germplasm by cryopreservation, the large-scale cloning of coconut, and the detailed understanding of coconut genetics, are shown here. Taken together, they present a great opportunity to deliver superior plantlets and seedlings in an adequate quantity to specific regions. The complexities and challenges of selecting the best possible genotype for a given location are shown to be a pressing need requiring urgent attention.

Coconut, a multipurpose palm, is facing increasing demand for its fruit as well as the pressure from industries to produce coconut-derived products. However, coconut production has been declined, and about half of the planted palms are facing senility in the producing countries. This condition will not be alleviated with the continual practice of traditional breeding methods which produces only one seedling per fruit. Hence, coconut cloning by somatic embryogenesis is the focus of the present work. Although this has been attempted for over 60 years, improvements are still needed to increase the production rate. Therefore, a cell multiplication step to increase the production of embryogenic cells through cell suspension culture is proposed because the establishment of cell suspension culture and its regeneration in oil palm and date palm have been achieved with great success. Consequently, the establishment of coconut cell suspension culture is anticipated to bring a leap in production. The initial plant material for the initiation of cell suspension culture is friable embryogenic callus. As the nature of the embryogenic callus is often compact, the effect of medium type and subculture frequency on the induction of friable embryogenic coconut callus was studied. Based on the results, their effects on the friable embryogenic callus formation were minimal, so the formation is likely to depend on other factors. There were however effects on the callus and embryogenic callus formed and it was found that those cultures in solid media require less subculture than those in liquid media.

The coconut fruit comprises the nut enclosed in a thick husk. When germination takes place, there is a delay of 20 days or more until the young shoot and roots emerge through the husk. At first the shoot produces a tiny frond followed by those of increasing size every 6 weeks, reducing to 4 weeks over time. There is a sequential increase in frond length up to a maximum around 5 years when flowering begins. The frond survives for 2 years so that the palm carries up to 30 fronds in a hemispherical array. There are two forms of palm, Tall and Dwarf. The Dwarf forms flowers earlier and remains shorter than the Tall at any age. The inflorescence comprises both male and female flowers. The Tall is normally cross-pollinating resulting in a heterozygous population, while the Dwarf is mostly self-pollinating resulting in homozygous progeny. There is no natural formation of suckers or other vegetative reproduction. The coconut fruit evolved being capable of floating for 120 days on the ocean and then establishing on the strand of tropical atolls and the coastlines of high islands with adequate rainfall. The coconut appears to have spread widely to many suitable shores between the east coast of Africa and the west coast of the Americas long before human settlement. There is evidence of evolutionary adaptation of the coconut to diverse biohazards in different tropical regions. For example, insect, virus, and mycoplasma tolerances have been described.

Sesbania [Sesbania cannabina(Retz.) Pers.] is a problematic emerging weed species in Australian cotton-farming systems. However, globally, no information is available regarding its seed germination biology, and better understanding will help in devising superior management strategies to prevent further infestations. Laboratory and glasshouse studies were conducted to evaluate the impact of various environmental factors such as light, temperature, salt, osmotic and pH stress, and burial depth on germination and emergence of two Australian biotypes ofS. cannabina. Freshly harvested seeds of both biotypes possessed physical dormancy. A boiling-water scarification treatment (100±2 C) of 5-min duration was the optimum treatment to overcome this dormancy. Once dormancy was broken, the Dalby biotype exhibited a greater germination (93%) compared with the St George biotype (87%). The nondormant seeds of both biotypes showed a neutral photoblastic response to light and dark conditions, with germination marginally improved (6%) under illumination. Maximum germination of both biotypes occurred under an alternating temperature regime of 30/20 and 35/25 C and under constant temperatures of 32 or 35 C, with no germination at 8 or 11 C. Seed germination of both biotypes decreased linearly from 87% to 14% with an increase in moisture stress from 0.0 to −0.8 MPa, with no germination possible at −1.0 MPa. There was a gradual decline in germination for both biotypes when imbibed in a range of salt solutions of 25 to 250 mM, with a 50% reduction in germination occurring at 150 mM. Both biotypes germinated well under a wide range of pH values (4.0 to 10.0), with maximum germination (94%) at pH 9.0. The greatest emergence rate of the Dalby (87%) and St George (78%) biotypes was recorded at a burial depth of 1.0 cm, with no emergence at 16.0 cm. Deep tillage seems to be the best management strategy to stopS. cannabina’s emergence and further infestation of cotton (Gossypium hirsutumL.) fields. The findings of this study will be helpful to cotton agronomists in devising effective, sustainable, and efficient integrated weed management strategies for the control ofS. cannabinain cotton cropping lands.

Parthenium weed (Parthenium hysterophorus L.) is an emerging weed species in direct-seeded aerobic systems of rice production. This two-year field study was conducted to evaluate the effect of five different densities (0, 5, 10, 15 and 20 plants m ) of parthenium weed on rice yield and yield-related attributes. Parthenium weed produced ca. 38 to 178% higher biomass at its densities of 10 to 20 plants m as compared to the lowest density of 5 plants m . The paddy yield and yield-related attributes were negatively affected with an increase in the parthenium weed density. In both years, the highest reductions in number of rice panicles (14 to 17%), panicle length (10 to 11%), number of grains per panicle (11 to 18%), 1000-grain weight (8 to 21%) and paddy yield (30 to 35%) were recorded at the highest parthenium weed density (20 plants m ) tested. However, the lower densities of 5 to 15 parthenium weed plants m also caused 11 to 24% and 12 to 26% losses in paddy yield during the years 2016 and 2017, respectively. Therefore, this weed species should be controlled below the density of 5 plants m to avoid the substantial yield losses (over 15%) in direct-seeded rice.

In Australia, winter annual grasses provide the strongest competition against wheat for resources which detrimentally affects grain yield. With increasing action from government, industry, and grower groups to reduce herbicide spray drift, adoption of drift reduction technologies (DRTs) especially DRT nozzles has increased over recent years. Some herbicides are less effective when sprays are too coarse as droplets may not be retained on target weed surfaces or not intercepted by target leaves. This is particularly an issue with winter annual grasses, whose small, narrow leaves and ability to grow within the wheat canopy makes their control more difficult. This study sought to understand the effect of droplet size on herbicide efficacy by evaluating the effect of six nozzles, five of which have DRT features across six different herbicides (amitrole, clodinafop, glyphosate, imazamox plus imazapyr, metribuzin, and paraquat) for the control of four winter annual grasses (annual ryegrass, Italian ryegrass, rescuegrass, and tame oats). Plants were grown in pots outdoors on the University of Queensland Gatton campus and were sprayed at 28 days after emergence in August and repeated in October 2015. Results from this study indicate DRT nozzles that produce sprays classified as Ultra-Coarse (>650 μm Dv0.5) can preserve efficacy for some herbicides. Differences were not observed for herbicide efficacy of clodinafop, imazamox plus imazapyr, and glyphosate across both years. Coarse sprays appear to provide the most herbicide efficacy across a wide array of modes of action, and yet reduce spray drift potential compared to finer sprays.