Relationship Between Stem Characteristics And Lodging And Its Regulation Study In Wheat

Six wheat varieties with different lodging resistances were grown at Tai'an Experimental Station of Shandong Agriculture University during the 2008~2010 growing seasons. The studies were focused on stem morphological characteristics, anatomical structure feature and physicochemical properties as well as the changes of stem lodging resistance, and the result elucidated the relationship between lodging and the character of culm. This research analyzed the variety differences of stem characteristics with different lodging resistance, discussed the physiological and biochemical mechanism of planting density, nitrogen and paclobutrazol on lodging resistance of wheat. The main results were as follows:1 Difference of variety in the lodging resistance of wheatThe field experiments were carried out at Tai'an Experimental Station of Shandong Agricultural University in two growing seasons from October 2008 to June 2009 and from October 2009 to June 2010. Six wheat cultivars (Triticum aestivum L.), JM 20 and JM 22 (high lodging resistance of wheat), and Gaocheng 8901 and Yannong21 (middle lodging resistance of wheat), and Youzimai and Pingyuan 50 (low lodging resistance of wheat) were employed in this study.1.1 Stem morphological characteristics with different lodging resistance of wheatCompared with middle lodging resistance of wheat varieties (Gaocheng 8901 and Yannong 21), the plant height, ratio of gravity center height to plant height, basal internodes length and percentage of basal internode(1+2) length in the total stem length, inner diameter and dry matter transfer rate high lodging resistance of wheat varieties (Jimai 20 and Jimai 22) significantly reduced, while outer diameter, stem fresh and dry weight incresased. Correlation analysis showed that there was siginificantly negative correlation between the actal lodging percentage and the diameter thickness of basal internode and filling degree, while there was a significantly positive correlation between plant height, ratio of gravity height and length of basal. In wheat production, shorter basal internodes, lower plant height, smaller inner diameter, thicker stem diameter, higher filling degree of stem, lower the dry matter tranfer rate were significant characteristics of high lodging resistance of wheat.1.2 Anatomical structure features with different lodging resistance of wheatBy analyzing the anatomical structure of the 2nd basal internode of the six lodging resistance of different varieties, the result showed that wheat varieties with high lodging resistance (Jimai 20 and Jimai22) had wall thickness and more mechanical tissue cell layer, the large vascular bundles tended longer, wider and had more numbers. Varieties with low lodging resistance (Youzi wheat and Pinyuan 50), the mechanical tissue cell layers was less and thinner, the large vascular bundle tended shorter, narrower and lesser numbers. Correlation analysis showed that the layer and thickness of the mechanical tissue of the 2nd basal internodes and the large vascular bundle number and area had significant or very significant negative correlation with the lodging rate of wheat. The results indicated that for good quality culm, the mechanical tissue had more cell layers; the large vascular bundles tended longer, winder and had more numbers; the wall of culm was thicker.1.3 Physical and chemical characteristic with different lodging resistance of wheatThe physical and chemical characteristics of culm were closely related with its lodging resistance. The content of soluble sugar and potassium, nitrogen content, snapping resistance of the basal internodes had the greater effect on the lodging resistance of basal internodes and actual lodging percentage. The actual lodging percentage of wheat were significant negative correlation with the lodging index, snapping resistance of the basal internodes, the content of soluble sugar and potassium, and nitrogen content was significant positive correlation. The lignin content and activities of phenylalanine ammonia-lyase (PAL), tyrosine ammonia-lyase (TAL), cinnamyl alcohol dehydrogenase (CAD), and 4-coumarate:CoA ligase (4CL) were tested in the second internode of six cultivars with different lodging resistance. The snapping resistance and culm lodging index were determined at anthesis, milking, and maturity stages. The lignin content varied significantly among cultivars. Jimai 22 and Jimai 20, which showed high resistance to culm snapping and loging, had higher lignin content and the activities of PAL, TAL, CAD, and 4CL than other cultivars. The lignin content was negatively correlated with the actual lodging ratio (r =-0.83, P<0.05), and positively correlated with the snapping resistance of culm (r =0.86, P<0.05). The activities of PAL, TAL, and CAD were positively correlated with lignin content with correlation coefficients of 0.78 (P<0.05), 0.77 (P<0.05) and 0.85 (P<0.05), respectively. Based on these results, we conclude that high activities of PAL and CAD are the enzymatic basis of increased lignin content, and the lignin content in culm can be used as an important indicator to evaluate lodging resistance of wheat.2 Regulation of cultivation measures on the lodging resistance of wheat2.1 Relationship between planting density and lodging resistance of wheatWith the increase of planting density, plant height and ratio of gravity center height to plant height were incresed, basal internodes tended slender and thinner, percentage of basal internode(1+2) length were improved, weight percentage of basal internodes was significantly reduced, and lead to serious lodging of wheat. The plant height was heightened and the filling degree of internode was decreased with the increase of planting density, and this was a main cause lodging of wheat.With the increase of planting density, the mechanical tissue layer of the 2nd internodes of Yannong 21 and Gaocheng 8901 reduced, stem wall thickness decreased, the large vascular bundle number and area had different degrees of reduction. Adopting rational planting density to establish a rational structure, to promote development of the mechanical tissue of stem as well as the area and amount of the large vascular bundle were premise of realizing sound seedling and lay a good foundation to build a population structure of lodging resistance.The nitrogen and potassium element content, the souble sugar and starch content of basal internodes, the snapping resistance and lodging resistance index were redued with the increase of the planting desity. The culm lodging resistance index was positively correlated with the plant density.The lignin content of the second basal internode and PAL, TAL, 4CL and CAD activities were significantly reduced with the increase of the planting density, which led to the lowring of wheat stem.2.2 Relationship between nitrogen and paclobutrazol and lodging resistance of wheatNitrogenous significantly influenced the lodging resistance of wheat. Compared with low N (225 kg·hm-2) rate, the plant height and percentage of basal internode(1+2) length of total internode length of the plant high N (300 kg·hm-2) rate were increased, but the thickness and filling degree of basal internodes were decreased. After spraying paclobutrazol, the basal internodes of wheat shortened and percentage of basal internode(1+2) length of the plant decreased, outside diameter and wall thickness of culm increased, ratio of gravity center height to plant height were lowers, ratio weight to lenghth of stem were increased, wheat lodging resistance were enhanced. The result showed that spraying paclobutrazol had great effect on solving the lodging problems during growth later stage of high-yielding wheat.Compared with low N(225 kg·hm-2) rate, the high N(300 kg·hm-2) rate made mechanical tissue cell layers decreased and becomed thinner, the amount and area of big vascular bundles and area also decreased. Spraying paclobutrazol caused the amount and area of the second internodes increased and the mechanical tissue cell layers increased and becomed thicker. And the lodging resistance was enhanced.Compared with low nitrogen N(225 kg·hm-2) rate, the high N(300 kg·hm-2) rate made soluble sugar, starch and potassium content lower and nitrogen content increased, nitrogen potassium ratio increased, lead to the decrease of snapping resistance and lodging resistance index and increased the risk of lodging. Spraying paclobutrazol increased contents of nitrogen and potassium of basal internodes, increased starch and soluble sugar content, and improved the snapping resistance and lodging resistance index and decreased lodging area.Compared with the low N(225 kg·hm-2) rate, the high N(300 kg·hm-2) rate reduced the PAL, TAL, CAD and 4CL activities and lignin content, reduced snapping resistance and CLRI under the same cultivar condition. The application of PP333 improved the PAL, TAL and CAD activities, increased lignin content, snapping resistance and CLRI, thus reduced lodging area and lodging degree. Correlation analysis showed that the lignin content of basal stem had a significant and positive correlation with PAL, CAL and CAD activity and CLRI, respectively, yet had no significant correlation with 4CL activity. The high N(300 kg·hm-2) rate reduced the PAL, TAL,CAD enzyme activities and lodging resistance. Spaying PP333 improved the PAL, TAL, CAD enzyme activities and lignin content, and thus enhanced the lodging resistance.