Allelopathic Effects of Different Organs of Redroot Pigweed （Amaranthus retroflexus L.） on Cucumber and Wheat Plants

Allelopathy is one of the most important interactions between plants. Weeds are famous plants from this viewpoint, which can decrease crop production in farms by their allelopathic effects. Research has shown that different plant organs have different allelopathic effects. Redroot pigweed （Amaranthus retroflexus L.） is one of the most common weeds with well-known allelopathic potential. This experiment aimed to study the allelopathic effects of different organs＇ leachate of redroot pigweed on germination and growth of cucumber （Cucumis sativus L.） and wheat （Triticum aestivum L.） as two important crop species. The effect of different organs＇ leachate on seed germination and seedlings growth parameters of tested plants was significantly different. In addition, the effects on cucumber were not the same as wheat. According to the results, wheat plant was more resistant at both seed germination and seedling growth stages in comparison to cucumber. Cucumber only showed normal growth potential when treated with the stem leachate, while wheat showed measurable growth potential in all treatments and leaf leachate showed the highest negative effect on wheat. Accordingly, allelopathic effects of redroot pigweed are dependent not only on leachate concentration and plant species, but also on plant organ from which the leachate was released. Therefore, understanding the altelochemical source （organ） of a donor plant is essential for accurate evaluation ofallelopathic interactions between plants.

Using Vegetation Indices as Input into Random Forest for Soybean and Weed Classification

Weed management is a major component of a soybean (Glycine max L.) production system;thus, managers need tools to help them distinguish soybean from weeds. Vegetation indices derived from light reflectance properties of plants have shown promise as tools to enhance differences among plants. The objective of this study was to evaluate normalized difference vegetation indices derived from multispectral leaf reflectance data as input into random forest machine learner to differentiate soybean and three broad leaf weeds: Palmer amaranth (Amaranthus palmeri L.), redroot pigweed (A. retroflexus L.), and velvetleaf (Abutilon theophrasti Medik). Leaf reflectance measurements were acquired from plants grown in two separate greenhouse experiments conducted in 2014. Twelve normalized difference vegetation indices were derived from the reflectance measurements, including advanced, green, greenred, green-blue, and normalized difference vegetation indices, shortwave infrared water stress indices, normalized difference pigment and red edge indices, and structure insensitive pigment index. Using the twelve vegetation indices as input variables, the conditional inference version of random forest (cforest) readily distinguished soybean and velvetleaf from the two pigweeds (Palmer amaranth and redroot pigweed) and from each other with classification accuracies ranging from 93.3% to 100%. The greatest errors were observed between the two pigweed classes, with classification accuracies ranging from 70% to 93.3%. Results suggest combining them into one class to increase classification accuracy. Vegetation indices results were equivalent to or slightly better than results obtained with sixteen multispectral bands used as input data into cforest. This research further supports using vegetation indices and machine learning algorithms such as cforest as decision support tools for weed identification.

Isolation and Characterization of a Phytotoxin from Xanthomonas campestris pv. retroflexus

A phytotoxin from Xanthomonas campestris pv. retroflexus was isolated using a chromatographer and HPLC, and the components were identified to be a mixture of minor molecular compounds including organic acids and cyclo-（proline-phenylalanine）. The greenhouse cultivation test was used to determine the influence of the isolated fractions on the growth of target weed redroot pigweed （Amaranthus retroflexus L）. The experimental results demonstrated that the cyclo-（Pro-Phe） had the weed inhibit activity obviously on dicotyledonous weed and the mixture with six organic acids showed stronger bioactivity. Further, greenhouse and field test were processed, and the test showed that the use of the toxin appeared to have the potential to be developed further as a bioherbicide system to control weedy grasses.