Lodging Resistance Characteristics Of Super-hybrid Indica Rice And Response To Nitrogen

Lodging is one of the primary factors to limit the rice productions.There were many factors involved in lodging,and the mechanism is complex.Although there were a lot of studies had been done on rice lodging in the past,but few studies were taken on mechanism of the lodging resistance capacity of super hybrid indica response to nitrogen.The main objective of this study was to reveal the mechanisms of the divergence oflodging resistance and effects of nitrogen on rice lodging resistance between super-hybrid rice.Results of the study will provide a theoretical basis for breeding and nitrogen management for high yield.Experiments were conducted with super-hybrid rice Yliangyou2 which was strong in lodging resistance and II you084 which was weak in lodging resistance to compare the difference of lodging resistance between the two varieties and study the effects of nitrogen on rice morphological,mechanical,physiological and anatomical traits.135,270,405 kg N ha-1 were arranged.(1)The yield of Yliangyou2 reached 11.3t/ha,4.6%higher than IIyou084.This was mainly attributed to the higher number of spikelets per panicle and spikelets per hectare,which were 29.7%,28.4%higher than Ⅱyou084,relatively.Yliangyou2 which was stronger than IIyou084 had higher yield.As raised the input of nitrogen rates,the spikelets per square meter,the panicles per square meter increased.Excessive nitrogen reduced seed-setting rate and 1000-grain weight and the yield had the tendency to decrease accordingly.(2)From the mechanic point,in 2013 and 2014,Yliangyou2 had no large-scale lodging while lodging occurred in a large area for IIyou084 in nitrogen application area.The lodging index of Yliangyou2 reduced significantly at mature stage,19.0%higher than IIyou084.The main reason was that breaking moment of Yliangyou2 was significantly greater than IIyou084(32.7%higher than IIyou084),and Yliangyou2 had a higher breaking moment was because of its higher bending stress(48.4%higher than IIyou084),it indicated that Yliangyou 2 has a higher lodging resistance mainly because its larger stalk material strength.With the nitrogen increasing,the lodging index of Yliangyou2 and Ⅱyou084 showed an overall upward trend,but the responses of them to nitrogen were quite different.The lodging index of Yliangyou2 showed an increasing trend,and that of Ⅱyou084 raised rapidly at low nitrogen fertilizer level,the excess nitrogen fertilizer failed to significantly increase its lodging index,which indicated thatⅡyou084 was more sensitive to nitrogen.(3)From the morphology point,the height of panicle-neck,relative height of gravity center,height of gravity center and dry weight of panicle were significantly lower than Ⅱyou084,dry weight of single stem was higher than Ⅱyou084,but the difference was not significant.Compared with Ⅱyou084,although the dry weight of basal stem was just a little heavier,but the dry weight of basal leaf sheath was significantly higher,which added support and protection to culm.The disadvantage of the culm diameter of Yliangyou2 was compensated by the deascreasing length of the basal internode,thickening stem wall and significant increasing dry weight per unit length of leaf sheath,which provided morphological basis to increase stem mechanical strength.With increased the nitrogen rates,fresh weight from broken point to panicle top had a significant increase which increased the risk of lodging to a certain extent.Height of gravity center did not change significantly while the length of the 1st and 2nd internode had a increasing trend.(4)From the physiology point,compared with IIyou084,the non-structural carbohydrate content of Yliangyou2 in basal internode was lower,but structural carbohydrates(cellulose and lignin)content reached a higher level,leading to bending moment at breaking and bending stress significantly increased which add to lodging resistance.Dry weight of basal culm and leaf sheath at heading stage and dry weight per unit length of basal leaf sheath at late filling stage were significantly reduced with a substantial increase in nitrogen levels,which caused stem quality deterioration,the protection and support capabilities of leaf sheath reduced.In addition,with the nitrogen increasing,cellulose and lignin content of the basal stem and leaf sheath decreased,bending moment at breaking and bending stress thereupon fall which leaded to the risk of lodging increase.(5)From the anatomy point,compared with IIyou084,although Yliangyou2 had a smaller number of secondary vascular bundle(SVB),it had thicker bundle sheath cells and larger SVB area which would increase the mechanical strength of the outer side of the stem,significantly improved lodging resistance.With the nitrogen increasing,the SVB area of the two super hybrid indica decreased and the primarily vascular bundle(PVB)area and the thickness of epidermal thick-walled cells did not change significantly.Lignin content reduced with nitrogen increasing,mainly occurred in the thick-walled cells and SVB bundle sheath cells.For the purpose of increasing the lodging resistance of super-hybrid indica rice varieties,it would be favorable to compensate the decrease in culm diameter with increasing wall thickness,SVB area and shortening the length of basal internode,enhance the protection and support to the culm with increasing the filling degree of leaf sheath.Nitrogen reduced the lodging resistance of super-hybrid indica rice mainly through decreasing the dry weight per unit length of leaf sheath,the SVB area and the content of the structural carbohydrates,especially the content of lignin,in the basal internode.