Lodging Resistance In Rice Cultivars Under Rates of Nitrogen Fertilizer; Does The Main Culm Represent The General Pattern of Lodging In Primary Tiller?

Abstract Purpose Lodging resistance (LR) in rice cultivars is usually established using the main culm (MC) as a good representative of tillers on the plant. However, it remains unclear whether LR of MC represents LR of the primary tiller (PT) to guide in the selection of tillers during LR assessment in rice cultivars under rates of nitrogen fertilizer. Methods Four lodging resistant cultivars namely: NERICAs 1, 4, 6 and Moroberekan were established under three rates (0, 60, 120 kg ha-1) of nitrogen fertilizer. At 20 days after heading of each of the MC and PT, the culms were harvested for assessment of LR. Results Increasing application rates of nitrogen fertilizer increased the culm morphological traits (CMTs) such as culm wall thickness, internode and lumen diameters, bending moment and breaking strength of MC and PT with little effect on lodging index (LI). The CMTs were however, higher in the MC and with lower LI than in the PT. The higher CMTs in MC did not translate to lower LI in all the rice cultivars such as Moroberekan compared with the PT. Correlations of CMTs with LI were higher and significant in the MC than in the PT. Conclusion Main culm remains reliable for the mechanical assessment of LR in upland rice but does not represent the general pattern of lodging in the PT. There is need for consistency in selection of tiller for mechanical assessment of lodging in rice cultivars under rates of nitrogen fertilizer.