Effect of phosphorus deficiency on allelopathic activity of lowland indica rice

Allelopathy is a phenomenon in which plants exude biochemicals that inhibit the growth of nearby plants. Allelopathic activity and biochemical production are induced by environmental stresses. This study investigated the effect of phosphorus (P) deficiency on growth and allelopathic activities in two landrace rice cultivars of southern Thailand, Nang loy and Niaw look pueng. Rice seedlings were hydroponically grown for 14 days in Yoshida Solution with normal (HP) and low (LP) P concentrations. Growth and phosphate (Pi) contents in rice seedlings were determined to evaluate the difference in internal P status between plants grown under the HP and LP conditions. Water extracts were prepared from shoots and roots of rice seedlings to test allelopathic activity against lettuce seedlings. The results showed that rice seedlings responded to P deficiency by reducing shoot and root Pi content and increasing leaf greenness. Changes in seedling growth were scarcely detected in the young rice seedlings. In a germination assay, water extracts of P-deficient seedlings from both rice cultivars lowered germination indices and inhibited lettuce seedling growth. Furthermore, shoot extracts of the same rice cultivar more strongly inhibited the development of lettuce seedlings than root extracts. The greater allelopathic activity of the shoot extracts might be a result of their higher phenolic contents, which could be induced by P deficiency. Therefore, an allelopathic trait of rice seedlings is an early response to P deficiency prior to growth inhibition under the low P condition.