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接种试验表明，霜霉病对苜蓿幼苗生长发育影响显著，感病植株幼苗高度减低４２．６％～５２．０％，生长速度明显减慢，健苗的平均增长率为４５．７％，而病苗仅为２２．７％；地下部主根入土深度（根长）减少２７％，根的直径（根颈部）减少４４．３％，根鲜重减少７５％，根瘤的数量减少５４．１％，而且病苗的根瘤均为白色无效根瘤，健苗的根瘤约半数为粉红色的有效根病。根的长度与根瘤数量呈明显正相关，健苗的相关系数ｒ＝０．８６８６，病苗的相关系数ｒ＝０．５６７９，说明幼苗感病后根瘤数量明显减少并很快失效，根瘤对病苗生长所起的作用明显减弱
Inoculation tests showed that downy mildew had significant effects on the growth and development of alfalfa seedlings. The height of seedlings of susceptible plants was reduced by 42.6% -52.0%, the growth rate was obviously slowed down, and the average growth rate of Jian-Miao was 45.7% Only 22.7% of the seedlings were inoculated, the root depth (root length) of underground roots was decreased by 27%, the root diameter (root and neck) decreased by 44.3%, the root fresh weight decreased by 75% and the number of nodules decreased by 54.1 %, And the nodules of the disease are white nodules are invalid, healthy seedling nodules about half of effective root cause of pink. Root length and nodule number was positively correlated, the correlation coefficient of Jianmiao r = 0.8686, the correlation coefficient of the disease seedlings r = 0.5679, indicating that the number of nodules decreased significantly and soon after the onset of disease failure, nodules on the disease The role of seedling growth significantly weakened