Lowland rice (Oryza sativa L.) encounters flooded soils that are anaerobic and chemically reduced. Exposure of the roots to high soil Fe2+ concentrations can result in toxicity. Internal aeration delivering O2 to submerged roots via the aerenchyma is well understood, but the effect of Fe2+ on O2 transport in roots is less studied. We aimed to evaluate the effects of Fe2+ on growth and root aeration. O. sativa var. Amaroo was grown in aerobic and deoxygenated solutions with 0 mM, 0.18 mM, 0.36 mM, 0.54 mM or 0.72 mM Fe2+ using FeSO4.7H2O and a control with 0.05 mM Fe-EDTA. The treatments were imposed on 14-day-old plants (28–30 days old when harvested). Dry mass, shoot Fe concentration, root porosity and patterns of radial O2 loss (ROL) along roots were determined. In the aerobic solution, where Fe2+ was oxidised in the bulk medium, root dry mass increased with higher Fe2+; this was not the case in stagnant solutions, which had no significant root growth response, although Fe oxidation near the root surface was visible as a precipitate. In the highest Fe2+ treatment, shoot Fe concentrations in aerobic (667 mg kg–1) and stagnant (433 mg kg–1) solutions were below the level for toxicity (700 mg kg–1). Rice responded to high Fe2+ in aerobic conditions by increasing root porosity and inducing strong barriers to ROL. In stagnant conditions, root porosity was already high and the ROL barrier induced, so these root aeration traits were not further influenced by the Fe2+ concentrations applied.

Abstract:Rice is the main staple crop for one-third of the world population. To maximize yields, large quantities and constant input of fertilizers containing essential nutrients such as phosphorus (P) and iron (Fe) are added. Rice can germinate in both aerobic and anaerobic conditions, but the crosstalk between oxygen (O 2 ) and nutrients such as P and Fe on plant growth remains obscure. The aim of this work was to test whether such interactions exist, and, if so, if they are conserved between up-and lowland rice varieties. To do so, we assessed shoot and root biomass as well as inorganic phosphate (Pi) accumulation in four rice varieties, including two lowland rice varieties Nipponbare and Suphanburi 1 (SPR1) (adapted to non-aerated condition) and two upland rice varieties CMU122 and Sew Mae Jun (SMJ) (adapted to aerated condition) under various conditions of Pi and/or Fe deficiencies, in aerated and non-areated solution. Under these different experimental conditions, our results revealed that the altered shoot biomass in Nipponbare and SPR1 was O 2 -dependent but to a lesser extent in CMU122 and SMJ cultivars. In this perspective, discovering the biological significance and molecular basis of these mineral elements and O 2 signal interaction is needed to fully appreciate the performance of plants to multiple environmental changes.

Pathogens associated with Chinese kale leaf spot disease were recovered from necrotic lesions on the Chinese kale leaves and identified as Alternaria brassicicola (Schw.) Wiltshire. This disease is one of the most significant destructive pathogens to vegetable crops in Thailand and Southeast Asia. Disease management of these pathogens is done by using synthetic fungicides which are expensive and harmful to the environment. This study aimed to investigate the efficacy of the extracts from five plants, Hydnocarpus anthelminthicus Pierre ex Laness., Crateva magna (Lour.) DC., Caesalpinia sappan L.,Xanthophyllum lanceatum J. J. Sm., and Carallia brachiata (Lour.) Merr. to control the Chinese kale leaf spots caused by A. brassicicola in in vivo condition. In an in vivo test, we found that the plant extracts of C. brachiata, H. anthelminthicus, X. lanceatum and C. magna showed a potential in control efficacy against brassica dark leaf spots caused by A. brassicicola. The four plant extracts effectively suppressed the development of leaf spots at a concentration of 10,000 ppm and 50,000 ppm at 30 DAT. However, at 40 DAT the C. magna and H. anthelminthicus extracts strongly inhibited A. brassicicola at concentrations of 10,000 ppm and 50,000 ppm respectively when compared with the water control. This is the first report demonstrating that the plant extracts collected from riparian forest can provide control against brassica dark leaf spots disease. Based on our study, we demonstrated that the ability of plant crude extracts can be used as natural fungicides to control Chinese kale leaf spots and replace synthetic fungicide.