Increasing Rice Allelopathy by Induction of Barnyard Grass (Echinochloa crus-galli) Root Exudates

An allelopathic rice PI312777 and a non-allelopathic rice Lemont were hydroponically cultured and treated with extracts of seeds and tissues and root exudates of barnyard grass ( Echinochloa crus-galli , BYG) to induce an allelopathic response. The results of bioassays showed that the % inhibition of two rice leaf extracts was significantly ( p  < 0.05) increased by treatment with BYG root exudates. This induced trait was dosage- and time-dependent. The highest % inhibition for both PI312777 and Lemont was obtained following treatment with 15 mL of BYG root exudates for 2 days. Under these conditions, total allelopathy (TA) values of PI312777 on root length, plant height, and plant dry weight of BYG were 73.39, 68.01, and 70.42%, respectively, and induced allelopathy (IA) values were 21.53, 17.04, and 16.62%, respectively, accounting for 24–29% of TA. Correspondingly, TA values of Lemont were 28.38, 21.38, and 23.38%, respectively, and IA values were 14.49, 11.37, and 12.11%, respectively, accounting for 51–53% of TA. The % inhibition of two rice culture solutions was in agreement with the results of their leaf extracts. The total contents of 7 phenolic acids in the culture solutions of PI312777 and Lemont were 2.18 and 1.47 times, respectively, as much as those in the control solutions. The phenylalanine ammonia-lyase ( PAL ) gene in PI312777 leaves was significantly up-regulated after induction treatments. The results indicated that rice allelopathy is a chemical induction mechanism, and confirmed that chemical induction to raise rice allelopathy is a practical and feasible method.