Search Results (5)

When colonizing new ranges, plant populations may benefit from the absence of the checks imposed by the enemies, herbivores, and pathogens that regulated their numbers in their original range. Therefore, rates of plant damage or infestation by natural enemies are expected to be lower in the new range. Exposing both non-native and native plant populations in the native range, where native herbivores are present, can be used to test whether resistance mechanisms have diverged between populations. Datura stramonium is native to the Americas but widely distributed in Spain, where populations show lower herbivore damage than populations in the native range. We established experiments in two localities in the native range (Mexico), exposing two native and two non-native D. stramonium populations to natural herbivores. Plant performance differed between the localities, as did the abundance of the main specialist herbivore, Lema daturaphila. In Teotihuacán, where L. daturaphila is common, native plants had significantly more adult beetles and herbivore damage than non-native plants. The degree of infestation by the specialist seed predator Trichobaris soror differed among populations and between sites, but the native Ticumán population always had the lowest level of infestation. The Ticumán population also had the highest concentration of the alkaloid scopolamine. Scopolamine was negatively related to the number of eggs deposited by L. daturaphila in Teotihuacán. There was among-family variation in herbivore damage (resistance), alkaloid content (scopolamine), and infestation by L. daturaphila and T. soror, indicating genetic variation and potential for further evolution. Although native and non-native D. stramonium populations have not yet diverged in plant resistance/constitutive defense, the differences between ranges (and the two experimental sites) in the type and abundance of herbivores suggest that further research is needed on the role of resource availability and adaptive plasticity, specialized metabolites (induced, constitutive), and the relationship between genealogical origin and plant defense in both ranges. Full article

Weeds can be one of the most severe threats to crop production, especially when they are widespread and highly adaptable. Part of the adaptive strategy of plants is the ability to germinate in different conditions. Germination is the first developmental phase of plant life and is fundamental for its establishment. In this work, the germination of two populations of Datura stramonium L. at two different sites in Croatia (one cropped, the other non-agricultural) was tested under a wide range of salinity stress, 4, 8, 12, and 16 dS/m, and pH stress, values 1–9, at two temperature ranges of 15–25 °C and 18–30 °C. The results show that this species can tolerate high salinity, with a high number of seeds germinating, even under the highest level of saline stress and especially at higher temperatures: 21.7% of seeds germinated at 15–25 °C and 51.2% at 18–30 °C. D. stramonium also appears to be quite acid tolerant, with a significant reduction in germination only at pH 2, and no germination only at pH 1. Germination was always higher at higher temperatures, independently of abiotic stress. Although there were some differences between the two populations in the final germination percentages, they were similar in their responses to the abiotic stresses. Full article

The objective of this study was to explore the physical properties of maize seeds in competition with weeds. The basic and complex geometric characteristics of seeds from maize plants, competing with Datura stramonium L. (DS) or Xanthium strumarium (XS) at different weed densities, were studied. It was found that the basic and complex geometric characteristics of maize seeds, such as dimension, aspect ratio, equivalent diameter, sphericity, surface area and volume, were significantly affected by weed competition. The increase in weed density from 0 to 8 plants m² resulted in an increase in the angle of repose from 27° to 29°, while increasing weed density from 8 to 16 plants m² caused a diminution of the angle of repose down to 28°. Increasing the density of XS and DS to 16 plants m² caused a reduction in the maximum 1000 seed weight of maize by 40.3% and 37.4%, respectively. These weed side effects must be considered in the design of industrial equipment for seed cleaning, grading and separation. To our knowledge, this is the first study to consider the effects of weed competition on maize traits, which are important in industrial processing such as seed aeration, sifting and drying. Full article

Some herbivores suppress plant defenses, which may be viewed as a result of the coevolutionary arms race between plants and herbivores. However, this ability is usually studied in a one-herbivore-one-plant system, which hampers comparative studies that could corroborate this hypothesis. Here, we extend this paradigm and ask whether the herbivorous spider-mite Tetranychus evansi, which suppresses the jasmonic-acid pathway in tomato plants, is also able to suppress defenses in other host plants at different phylogenetic distances from tomatoes. We test this using different plants from the Solanales order, namely tomato, jimsonweed, tobacco, and morning glory (three Solanaceae and one Convolvulaceae), and bean plants (Fabales). First, we compare the performance of T. evansi to that of the other two most-commonly found species of the same genus, T. urticae and T. ludeni, on several plants. We found that the performance of T. evansi is higher than that of the other species only on tomato plants. We then showed, by measuring trypsin inhibitor activity and life history traits of conspecific mites on either clean or pre-infested plants, that T. evansi can suppress plant defenses on all plants except tobacco. This study suggests that the suppression of plant defenses may occur on host plants other than those to which herbivores are adapted. Full article