广州地区十字花科蔬菜花叶病的传染途径及流行规律的初步研究

广州地区十字花科蔬菜花叶病(主要病毒是芜菁花叶病毒的油菜毒系和芜菁毒系)的越夏寄主,根据11年来的观察特别是1956—1958年间的实地调查结果,主要是小白菜、菜心和西洋菜。在野生植物中曾发现过2株蔊菜和1株荠菜自然感病,说明野生植物不是本病的重要毒源。室内试验结果证明,此病的自然传染媒介为萝卜蚜、桃蚜和普通红蜘蛛。黄条跳(虫甲)、斜纹夜盗蛾和菜粉蝶都不是本病的虫媒,病株的种子不会传病,中国菟丝子也不会传递本病。在带有未腐熟的病菜残体的土里进行直播,长出来的菜苗没有发病的;但是把菜苗移植在这样的土里,会有极小量的植株感病。根据1956年7月至1958年6月,每十日田间调查一次结果:萝卜蚜是广州地区最重要的传病媒介,桃蚜每年只在3—4月间略有发生,作用不大。根据这24个月的田间发病率,萝卜蚜(有翅蚜及无翅蚜)的虫口密度和气候情况,我们认为本地区本病的发生及流行程度主要受降水量和降水天数所影响,并认为可以从降水情况来预测约30日后的病害流行程度。

ON THE TRANSMISSIONS AND EPIPHYTOTICS OF A MOSAIC DISEASE OF CRUCIFEROUS VEGETABLES IN CANTON

It was reported earlier by the authors that the mosaic disease of the cruciferous vegetables was mostly caused by two strains of turnip mosaic virus(TrMV),i.e."turnip strain"(commonly called turnip mosaic virus)and "rape strain"(commonly called rape mosaic virus).Field surveys made in the past 11 years(especially those made in 1956-1958)revealed that the virus oversummered mainly in the summer grown cruciferous vegetables,including Pak-Tsai(Brassica chinensis Linn.),Tsai-Shen(B.spp.)and water-cress(Nasturtium officinarium Wall.).The cruciferous weeds including Nasturtium montanum Wall.(only 2 plants found naturally infected in 11 years)and Capsella bursa-pastoris Medic.(only 1 plant found naturally infected in 11 years)were not important as over-summering hosts.The results of the transmission tests showed that the two strains of TrMV were readily transmitted by false cabbage aphid(Rhopalosiphum pseudobrassicae Day.)and peach aphid(Myzus persicae Sulz.),less so by red mite(Tetranychus telaxius Linn.),and not transmitted by the adults of striped flea-beetle(Phyllotrata vittata Fab.)and the larvae of army-worm(Prodenia litura Fab.)and white-fly(Pierie rapae Linn.). They were not transmitted by seeds of the host and by the dodder plant(Cuscutus chinensis Linn.).Soil mixed with fresh residue of diseased plant might cause occasional infection of replanted plants,but did not cause any infection of plants that were grown up from seeds sown in the infested soil.According to the field surveys made in July 1956 to June 1958(once in every10 days),the false brassica aphid was the most important vector in Canton,infesting the cruciferous vegetables all the year round,while the peach aphidappeared only occasionally in March and April.On ground of the field infectionpercentages,the aphid''s populations,and the climatic conditions in every 10 days'' period in these 24 months,it was found that the epiphytotic of the disease inCanton was closely related to the aphid population that occurred about 10-20days earlier,and the aphid population was again closely related to the amount of rain fall and the number of rainy days in the past 10-20 days.It was there for econsidered possible that on ground of the prevailing condition of rainfall,one was able to forecast the epiphytotic of the disease about 30 days ahead.