Background In studies of plant stress signaling, a major challenge is the lack of non-invasive methods to detect physiological plant responses and to characterize plant–plant communication over time and space. ResultsWe acquired time series of phytocompound and hyperspectral imaging data from maize plants from the following treatments: (1) individual non-infested plants, (2) individual plants experimentally subjected to herbivory by green belly stink bug (no visible symptoms of insect herbivory), (3) one plant subjected to insect herbivory and one control plant in a separate pot but inside the same cage, and (4) one plant subjected to insect herbivory and one control plant together in the same pot. Individual phytocompounds (except indole-3acetic acid) or spectral bands were not reliable indicators of neither insect herbivory nor plant–plant communication. However, using a linear discrimination classification method based on combinations of either phytocompounds or spectral bands, we found clear evidence of maize plant responses.ConclusionsWe have provided initial evidence of how hyperspectral imaging may be considered a powerful non-invasive method to increase our current understanding of both direct plant responses to biotic stressors but also to the multiple ways plant communities are able to communicate. We are unaware of any published studies, in which comprehensive phytocompound data have been shown to correlate with leaf reflectance. In addition, we are unaware of published studies, in which plant–plant communication was studied based on leaf reflectance.
This study compared the development of fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), on forage species of different genera (Arachis, Axonopus, and Cynodon) in relation to maize (preferred host) as well as its adaptability on these forage species, which are the main cultivated forages in southern Brazil. The biological performance of S. frugiperda fed on host plants studied showed the highest adaptation index (AI) in maize (26.89), followed by bermudagrass (22.02), suggesting that bermudagrass is the most suitable alternative host for the development of S. frugiperda. In contrast, the giant missionary grass (18.80) and Pinto peanut (13.81) showed lower adequacy, with a relative adaptation index (RAI) 69.93 and 51.35%, respectively, using maize as standard. The cluster analysis based on similarity of the chemical-bromatological parameters showed that maize has a richer composition than the other plant species studied. The multivariate correlation analysis between AI and chemicalbromatological composition showed a positive correlation between AI and contents of ashes, ethereal extract, potassium, phosphorus, and magnesium and, to a lesser extent, with contents of nitrogen, crude protein, and copper. In this context, complexity of host composition and balance between components could explain the biological fitness of S. frugiperda on host plant species. Pasture diversification with giant missionary grass, or especially with Pinto peanut, may be an interesting strategy for integrated pest management of fall armyworm in pasturelands in a regional context.
The indiscriminate use without criteria of nitrogen fertilization can lead to an accumulation of nitrate in pastures, animal poisoning and potential increase in residual content of this compound in milk. The objective of this study was to determine the residual levels of nitrate throughout the year in pastures and milk from small farms in western Santa Catarina (SC) that use high levels of nitrogen fertilization. The experiment was carried out from April/2018 to March/2019 on 10 dairy farms in the municipality of Riqueza (SC). Two annual collections of water samples and monthly collections of pastures and milk were carried out, in addition to obtaining information on the property and management of pasture fertilization through a structured questionnaire. Nitrate was also evaluated in pastures using the diphenylamine test. Temperature and rainfall data were obtained daily by a weather station. The average amount of nitrogen fertilizer used in the properties was 654 ± 176 kg/ha/year. The average nitrate content in the drinking water of the animals was 1.5 ± 1.4 mg/L, in the pasture it was 270 ± 76 mg/kg DM, while in milk it was 2.0 ± 0.3 mg/L. There was seasonal variation with an increase in nitrate content in pastures and milk in autumn, a period of the experiment in which low rainfall was observed. It was concluded that despite being dairy properties with high use of nitrogen fertilization, safe milk is produced in terms of nitrate levels, even in times of the year with adverse climatic conditions. The diphenylamine test has a good ability to discriminate the nitrate content in pastures and can be indicated as a quick test to verify the presence of high levels of nitrate in the pasture.
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