Root Distribution and Growth of Maize As Affected By Wheat Root Exudates in Wheat/Maize Intercropping.

Plants have the ability to recognize and respond to neighbors, root exudates may have been involved in mediating interspecific recognition. In maize / wheat intercropping system, roots of wheat (Triticum aestivum L.) can spread under maize (Zea mays L.) plants, while roots of intercropped maize were limited laterally in previous field experiment. We conducted four experiments to examine the effect of different neighbors and wheat root exudates on root distribution and root morphology of maize. Experiment 1, maize was grown with another maize seedling or wheat seedling in a root box filled with sterile quartz sand, and was supplied with full-strength nutrient solution. Experiment 2, maize seedlings grew in a PVC box filled with quartz sand  and the box was added with root exudates of wheat grown in nutrient solution with or without sodium othovanadate (3μM). Experiment 3, maize grown with wheat and wheat root exudates. Experiment 4, maize plants were grown in quartz sand with nutrient solution (CK), wheat root exudates, MBOA compounds or 0.3 μg / LMBOA standard substance. Our results showed that roots of intercropped maize distributed preferentially to the fractions away from wheat, but equally distributed when grew with another maize seedling. Root length of maize seedlings grown with wheat root exudates or maize grown alone but treated with wheat root exudates were both decreased compared to control. The inhibition effect caused by wheat root exudates was reversed by addition of sodium orthovanadate. In addition to root length, 6-methoxy-2-benzoxazolinone (MBOA) compounds and MBOA standard substance reduced root surface area and root volume as well. The results support the hypotheses that roots of maize can discriminate roots of different species (maize and wheat), and root exudates are vital for interspecific root recognition between maize and wheat.