梨树衰退病主要分布在北美太平洋沿岸和西欧部分国家和地区。该病是由类菌质体引起的一种毁灭性病害。1934年在意大利以梨树滞育病的名称最早报道,以后在美国的华盛顿州和加拿大的不列颠哥伦比亚省发现,并沿太平洋沿岸扩展、蔓延,大面积危害梨树,使其果实变小、产量降低,最终导致梨树枯死。此病的外部症状:罹病梨树的新梢生长不良,叶小、叶缘向上卷缩,叶量减少,叶脉变褐,叶片变灰呈革质;着花、着果不良,果实变小;整个树势生长衰弱乃至枯死。 Pear tree recession is mainly distributed in the North American Pacific Coast and some Western European countries and regions. The disease is a devastating disease caused by the mycoplasma. Originally reported as a diapause disease in pear in 1934 in Italy, it was later discovered in Washington State, USA and in British Columbia, Canada and spreads and spreads along the Pacific Rim, damaging pear trees over large areas, Reduce, eventually leading to withered pear. The external symptoms of the disease: the lesser growth of disease pear disease, small leaves, curling up the leaf margin, reduce the amount of leaves, brown veins, gray leaves turn leathery; with flowers, poor fruit, the fruit becomes smaller; The entire tree growing weak and even dead.