PEST MANAGEMENT: WEEDS Nitrogen Stress Response in Red Rice and Wells Rice Grown in Hydroponics

Red rice (Oryza sativa L.) is a prevalent weed in rice production, competing with cultivated rice for nutrients and other resources. We hypothesize that red rice has a more efficient nitrogen (N) assimilation due to adaptive molecular mechanisms that are absent in rice. Our greenhouse experiments comparing the growth and physiological responses between red rice and ‘Wells’ rice, one of the commonly grown rice cultivars, at N stress demonstrated these differences in N assimilation. The experimental design was a split plot: main plot was a randomized complete block with rice type (Wells cultivar and Stuttgart strawhull red rice) as factor; split plot factor was the N treatment [T1 (Full N); T2 (N starvation); T3 (early N supplementation after N starvation); and T4 (late N supplementation)]. Plants were hydroponically grown in Yoshida solution until panicle initiation (PI) when the N stress treatments were implemented. Nitrogen stress was defined as an N-sufficiency index (NSI) <95% calculated from chlorophyll meter readings. Starvation and supplementation were the removal and addition, respectively, of NH4NO3 in the nutrient solution. Growth responses including plant height, tiller number, biomass, root length, and number of root tips were determined from days of emergence to PI. Shoot tissue concentrations of N, other essential elements, and total sugars were analyzed to determine physiological response. Data were subjected to ANOVA in SAS and means were separated by Fisher’s protected LSD (α=0.05). Red rice had significantly higher growth measurements: 90 cm tall, 10-m roots, 59 x 103 root tips, 7 tillers, and 5-g biomass. Red rice sucrose was highest (23.0 mg/g; LSD=4.09) when N was at its lowest (2.78%; LSD=0.27). Wells rice did not show significant differences in sucrose at all treatments (9.61 to 11.63 mg/g). Plant tissues were collected for genomic analysis to explain the physiological differences between these two rice types. AAES Research Series 550