M.A. Martínez-Ghersa

The Role of Fluctuating Temperatures in Germination and Establishment of Sorghum halepense. Regulation of Germination at Increasing Depths

Field and laboratory tests explored the response of Sorghum halepense seeds to fluctuations in soil temperature, and whether that response serves as a mechanism for sensing depth and regulating seed germination. Seedling production in the field was severely curtailed when seeds were planted at increasing soil depths. Soil-temperature fluctuations were strongly dependent on depth. When soil columns containing seeds were incubated at alternating temperatures of 20 and 30°C, however, seed germination did not diminish with increasing depth, and an evaluation of how soil-surface shading affects the perception of depth by the seeds indicated that soil cover reduced germination of only those seeds in the upper strata of the profile (...)

Ecological correlates of weed seed size and persistence in the soil under different tilling systems: implications for weed management

Abstract In the pursuit of more sustainable approaches to agricultural management, there is an obvious need to integrate knowledge of the agricultural sciences and ecology. We used recent findings on ecological correlates of seed characteristics as a framework to discuss the impact of shifting from soil ploughing to farming with reduced or zero tillage on weed communities. In the future, knowledge about seed bank ecology may become increasingly applicable towards improving the way we manage weeds. It is also possible that the effects of cultural activities on moulding weed characteristics will become more apparent.

Advances in weed management strategies

Abstract Weed problems are currently solved by using inputs such as herbicides and soil tilling and by improving our knowledge of the ecophysiological process governing weed infestations and their competitive outcome on crop yield. In this paper, we review three different approaches for studying weed population dynamics (demographic, mechanistic and long-term studies) and discuss some of the advances in weed management strategies deriving from them. We present encouraging examples of successful strategies designed from population studies in annual and perennial weeds, as well as some ideas of how we should expand our knowledge base to achieve sustainable weed management strategies.

Coevolution of agricultural systems and their weed companions: implications for research

Abstract Weed management opportunities can be found in responses such as seed germination, development of canopy architecture, flowering, and seed production and dispersal. However, there are still research challenges to be addressed before prediction of crop and weed phenology can be reliably used in weed management strategies. In this paper we will focus on those ecological processes where we believe research efforts hold the greatest promise for the use of phenology prediction: succession , evolution , and interference . Research challenges for new management strategies are finding ways to forecast future weed populations in response to environmental changes, and to engineer crop cultivars capable of producing the desired environmental changes and responses to biotic and abiotic interactions.

Farm and landscape level variables as indicators of sustainable land-use in the Argentine Inland-Pampa

Sustainable land-use evaluation in agricultural systems needs to accommodate the landscape mosaic. Landscape characteristics, together with data gathered by farmers, were used to classify farms according to a scale related to sustainable land-use. The value of this scale as a tool enabling land managers to use information recorded by farmers and to diagnose land-use sustainability as a means of improving their land-management strategies was evaluated. Sustainability values were not related to any landscape in particular; farms with high sustainability could be found adjacent to farms with low sustainability. This indicates two important facts. First, differing management alternatives were mainly controlled by human decisions that in some way disregarded the ecological systems where the farms were located. Second, the observed variability demonstrates that there is room for improvement, especially by reducing inputs, without harming stability or productivity. An examination of the effect of incoming technologies on sustainability suggests other variables that could be considered in the calculation of farm sustainability indexes, such as those reflecting crop water-use efficiency, soil physical and biological characteristics, biological indicators of wildlife status, and intensification of grazing or harvesting of biomass for human and animal use.

Mutualism effectiveness and vertical transmission of symbiotic fungal endophytes in response to host genetic background.

Certain species of the Pooideae subfamily develop stress tolerance and herbivory resistance through symbiosis with vertically transmitted, asexual fungi. This symbiosis is specific, and genetic factors modulate the compatibility between partners. Although gene flow is clearly a fitness trait in allogamous grasses, because it injects hybrid vigor and raw material for evolution, it could reduce compatibility and thus mutualism effectiveness. To explore the importance of host genetic background in modulating the performance of symbiosis, Lolium multiflorum plants, infected and noninfected with Neotyphodium occultans, were crossed with genetically distant plants of isolines (susceptible and resistant to diclofop‐methyl herbicide) bred from two cultivars and exposed to stress. The endophyte improved seedling survival in genotypes susceptible to herbicide, while it had a negative effect on one of the genetically resistant crosses. Mutualism provided resistance to herbivory independently of the host genotype, but this effect vanished under stress. While no endophyte effect was observed on host reproductive success, it was increased by interpopulation plant crosses. Neither gene flow nor herbicide had an important impact on endophyte transmission. Host fitness improvements attributable to gene flow do not appear to result in direct conflict with mutualism while this seems to be an important mechanism for the ecological and contemporary evolution of the symbiotum.

Evolution of resistance to diclofop-methyl in ryegrass (Lolium multiflorum): investigation of the role of introgression with related species†

Populations of Lolium multiflorum (ryegrass) exposed to increasing levels of herbicide selection have variability in the rate of evolution of herbicide resistance. We tested the hypothesis that herbicide dose and gene flow with related species are important factors regulating the rate of evolution of herbicide resistance in L. multiflorum. Seeds of the latter were planted in pure stands and in mixture with Festuca rubra and subjected to four herbicide rates. The level of herbicide resistance attained by the offspring after two years of selection was evaluated. Evolution of resistance observed in the field was compared to that calculated by Gressel and Segels rotational model.

The use of hedges to reduce winter wheat losses caused by Italian ryegrass (Lolium multiflorum)

Abstract We hypothesized that short duration plant interference aiming to change mainly light intensity and red:far red ratio during crop establishment in Italian ryegrass-infested winter wheat fields, could hinder the development of Italian ryegrass and thus reduce its effect on wheat yield. To test this hypothesis, wheat was planted between previously established live (low red:far red ratio) or dead (high red:far red ratio), barnyardgrass or maize, plant hedges. Experimental results demonstrated that the presence of live or dead plant hedges during the first 30 days of crop establishment and also hedge orientation were important factors regulating weed and crop biomass production and competitive relationships. In barnyardgrass hedge treatments wheat yield was improved up to 67% and Italian ryegrass production was reduced by more than 20%. In plots with maize live hedges oriented N–S the biomass production of wheat was independent of production of Italian ryegrass. Data presented here suggests that there is room for developing weed control technologies on the basis of understanding photosensory processes of weed and crop species.