GENETIC BEHAVIOR FOR MOMILACTONE B IN SOME LINES AND THEIR HYBRIDS OF RICE

The allelopathy-competition separation (ACS) based approach was used to explore the biointerferance relationship between rice accessions and barnyardgrass exposed to different nitrogen (N) supplies in hydroponics. Some crosses had higher percentage for allelopathic activity as follow; IR69625A × Rikuto Norin 22, IR69625A × IR65617-52-2-3-3-2-3, IR69625A × Vener1A and IR69625A × Giza182 and their values were 87, 85, 85 and 85%, respectively. The varieties Rikuto Norin22, IR67413-71-4-2-2, Giza182, IR65617-52-2-3-3-2-3 and Vener1A exhibited the highest activity against E. crus-galli during 2009 season. These results referred to highly genetic effect which controlled these traits since the environmental effect is not significant. The additive and dominance genetic variances might be important in the inheritance of weed control, although the dominance genetic variance played more important role in this case. Rice accession Rikuto Norin22 exhibited high allelopathic potential to suppress the growth of accompanying weeds, especially when the culture solution had low N content. Although rice accession Giza182 has restoring fertility but it also exhibited high allelopathic activity under field conditions. Allelopathic activity of rice seedlings (Rikuto Norin22) exhibited 5.3–6.3-fold increase when rice and barnyardgrass seedlings were grown together, where there may be the competitive interference between rice and barnyardgrass for nutrients. Barnyardgrass is one of the most noxious weeds in rice cultivation. The momilactone B concentration in rice seedlings incubated with barnyardgrass seedlings was 6.9-fold greater than that in rice seedlings incubated independently. Low nutrient growth conditions also increased allelopathic activity and momilactone B concentrations in rice seedlings. However, the increase in the low nutrient-induced allelopathic activity and momilactone B concentration were much lower than those in barnyardgrass-induced allelopathic activity and momilactone B concentration. Root exudates of barnyardgrass seedlings increased allelopathic activity and momilactone B concentration in rice seedlings at concentrations greater than 30 mg/L of the root exudates, and increasing the exudate concentration increased the activity and momilactone B concentration. Therefore, barnyardgrass-induced allelopathic activity of rice seedlings may be caused not only by nutrient competition between two species, but also by components in barnyardgrass root exudates. As momilactone B shows strong allelopathic activities, barnyardgrass-induced allelopathic activity of rice may be due to the increased concentration of momilactone B in rice seedlings.