No abstract

Study of historically important cultivars may provide information on physiological traits that have been changed during selection for yield. Traits related to grain filling and drying were studied in commercially important maize (Zea mays L.) hybrids sold over the past 50 years. Hybrid studied were of approximately the same relative maturity and adapted to central Iowa. The duration of the grain filling period increased with year of release while grain filling rate was unchanged. The increase in grain filling duration was the result of later physiological maturity (black layer formation) rather than a change in flowering date. Late season plant health was improved in newer hybrids, which may have provided more viable leaf area to support prolonged grain filling. Grain drying rates were calculated by regression of water content·kernel−1 on heat units. Slopes of water loss were the same in the 2 years despite very different environmental conditions in the two seasons. Heat unit intercepts were different in the 2 years, with grain drying earlier in the hot, dry year of 1983. Grain water content at physiological maturity was correlated with year of release in 1983, but not in 1982. Several traits previously proposed to be associated with drying rate (husk number, date of husk death, ear angle, and number of kernel rows) were correlated with year of hybrid release. Correlation with drying rates over the season was significant for date of husk death in 1983.

Distinctive strains of Pantoea are used as soil inoculants for their ability to promote plant growth. Pantoea agglomerans strain C1, previously isolated from the phyllosphere of lettuce, can produce indole-3-acetic acid (IAA), solubilize phosphate, and inhibit plant pathogens, such as Erwinia amylovora. In this paper, the complete genome sequence of strain C1 is reported. In addition, experimental evidence is provided on how the strain tolerates arsenate As (V) up to 100 mM, and on how secreted metabolites like IAA and siderophores act as biostimulants in tomato cuttings. The strain has a circular chromosome and two prophages for a total genome of 4,846,925-bp, with a DNA G+C content of 55.2%. Genes related to plant growth promotion and biocontrol activity, such as those associated with IAA and spermidine synthesis, solubilization of inorganic phosphate, acquisition of ferrous iron, and production of volatile organic compounds, siderophores and GABA, were found in the genome of strain C1. Genome analysis also provided better understanding of the mechanisms underlying strain resistance to multiple toxic heavy metals and transmission of these genes by horizontal gene transfer. Findings suggested that strain C1 exhibits high biotechnological potential as plant growth-promoting bacterium in heavy metal polluted soils.

The indiscriminate use of synthetic chemical compounds for weed control has been often responsible of damage to both the environment and the human health. To challenge these problems, in the last years research has increased its effort to find out alternative farming strategies. A feasible alternative could be the identification of natural substances with allelopathic effects for the realization of natural herbicides. Some research has already highlighted the possibility of using essential oils, extracted from aromatic plants, for weed control. The advantage in the utilization of such natural compounds is the quickly breaking down process into the environment and so the possible application in sustainable agriculture like organic farming. Objective of this research was the evaluation of the inhibition effect exerted by the essential oils of cinnamon, peppermint and lavender on seeds germination of some of the most common weeds species of the Mediterranean environment (pigweed, wild mustard and ryegrass). The results have highlighted a control in the weeds germination. Among the essential oils tested, cinnamon oil has exerted the highest inhibition effect compared with lavender and peppermint ones. The dicotyledonous species have been more susceptible compared with the monocotyledonous, even if it has been recorded only for redroot pigweed a dose able to inhibit totally the seed germination

Canola (Brassica napus L.) is the main oilseed crop grown in the northern Great Plains (Canada). This species, however, also is associated with significant seed losses before and during harvest. To determine the factors that contribute to on‐farm harvest losses in B. napus, an extensive on‐farm survey was conducted in four regions across the northern Great Plains in 2010, 2011, and 2012. In addition to measuring on‐farm harvest losses on 310 fields, a survey questionnaire was used to collect agronomic data for each field and wind data from the nearest local weather station was used to determine wind speed during the harvest season. This study showed that total on‐farm harvest losses in canola are a complex phenomenon. This study identified that managing harvest losses in B. napus begins at the time of planting. Management factors that contributed to increased yield were linked to lower proportional B. napus harvest losses. Other factors that contributed to reduced proportional harvest losses included a fungicide application at flowering, earlier windrowing and harvest dates, lower combine harvester ground speed, and reduced windrower width. Factors considered by producers as important, such as combine manufacturer or B. napus variety did not contribute significantly to total harvest losses in this crop. Nevertheless, clear management practices were identified that can be employed to minimize on‐farm harvest losses in B. napus. A better understanding of the contributions of environmental variables to harvest losses in this species is required, particularly as interest in direct‐harvesting B. napus continues to increase in western Canada.

No abstract

There have been very few studies on the effects of plant competition on the rhizosphere bacterial community. To investigate the impacts of intra-and interspecific plant competition, we analyzed the responses of rhizosphere bacterial communities to plant density as determined by 16S rRNA gene targeted sequencing. We included five weedy plant species growing in field soil in monocultures and mixed cultures at three densities in a greenhouse experiment. The rhizosphere bacterial community of each species changed more with density in a mixture of all five plant species than in monocultures, so intra-and interspecific plant competition had different effects on the bacterial community. For the dominant plant competitor, Centaurea cyanus, neither intra-nor interspecific competition had major effects on the composition of its rhizosphere bacterial communities. In contrast, the bacterial communities of the weakest competitor, Trifolium repens, were affected differently by intra-and interspecific competition. During increasing intraspecific competition T. repens maintained a highly specialized bacterial community dominated by Rhizobium; while during interspecific competition, the relative abundance of Rhizobium declined while other nitrogen fixing and potentially plant growth promoting taxa became more abundant. Contrary to previous observations made for soil microbial communities, the bacterial rhizosphere community of the weakest competitor did not become more similar to that of the dominant species. Thus, the process of competition, as well as the plant species themselves, determined the rhizosphere bacterial community. Our results emphasize the role of plant-plant interactions for rhizosphere bacterial communities. These effects may feedback to affect plant-plant interactions, and this is an important hypothesis for future research.

Current economic pressure, combined with growing public concern over nitrates in groundwater, has resulted in increased interest in managing N fertilizer in corn (Zea mays L.) production. The response of modern corn hybrids to N in a number of different field environments was investigated. Twelve elite hybrids were grown in 13 field environments and a number of other hybrids were evaluated in five additional environments. All locations were in the U.S. Corn Belt. Results indicated a statistically significant response of corn hybrid yield to N. The hybrids differed in average yield, however no consistent hybrid × N rate interaction was found in any of the experiments. This indicates that the hybrids responded to N in a similar way when averaged across the environments. While there may be differences in hybrid response in a particular type of environment, responses were not predictable across different weather patterns and soil types. Agronomic traits and leaf N were also measured and are discussed. Based on these findings, farmers should manage their N program in a similar manner for all hybrids, by efficiently applying an optimal rate of N and minimizing the possibility of nitrates leaching into groundwater.