柠檬苗期一种新病害的病原鉴定及防治药剂的室内筛选

近年,在云南省瑞丽市柠檬上发生一种严重的苗期新病害,该病害主要危害柠檬苗的嫩叶、嫩梢和茎,症状表现为褐色叶斑,枝梢枯,严重时植株叶片全部脱落,甚至整株干枯而死。本研究从柠檬苗的病叶和茎上分离得到23株菌株。对病原菌的培养性状、形态特征的观察表明,这些菌株都属于疫霉属棕榈疫霉。致病性测定证明,该菌为柠檬苗疫病的病原菌。采用生长速率抑制法测定了7种杀菌剂对该病菌的菌丝生长抑制作用,并测定其中4种杀菌剂对该病菌的毒力。结果表明:68%精甲霜.锰锌水分散粒剂、50%烯酰吗啉可湿性粉剂和68.75%氟吡菌胺.霜霉威悬浮剂3种杀菌剂对病菌菌丝生长的抑制效果较好,抑菌率在90%左右。毒力测定结果表明,68%精甲霜.锰锌水分散粒剂、68.75%氟吡菌胺.霜霉威悬浮剂、50%烯酰吗啉可湿性粉剂和64%噁霜.锰锌可湿性粉剂的有效中浓度(EC50)分别为121.372、133.392、133.833mg/L和814.071mg/L,其中68%精甲霜.锰锌水分散粒剂有效中浓度最低,相对抑制效果最好。4种药剂的相关系数均在0.92以上,表明药剂浓度与抑制作用呈现较高的相关性。

Identification of the pathogen of a new seedling disease on lemon and screening of fungicides

In recent years,a new seedling disease on lemon Citrus limon(Linn.)Burm.f.] has been observed in Ruili City of Yunnan Province.The disease mainly occurred on leaves,shoots and stems with typical symptoms of leaf brownish spots and dieback.All leaves dropped and eventually the whole plant dried up to die when seriously infected.The 23 isolates of the pathogen were collected from diseased lesions on the leaves and stems of lemon.The pathogen of the disease was identified as Phytophthora palmivora,based on symptoms,morphological features,cultural characteristics and pathogenicity.In vitro,7 fungicides were used to test the inhibition of mycelium growth by means of mycelium growth rate method.The results indicated that 68% metalaxyl-M mancozeb WG,50%dimethomorph WP and 68.75% fluopicolide·propamocarb hydrochloride SC could significantly inhibit mycelium growth,with an inhibition rate of about 90%.The results of toxicity test showed that the EC50 values of 68% metalaxyl-M mancozeb WG,68.75% fluopicolide·propamocarb hydrochloride SC,50% dimethomorph WP and 64% oxadixyl-mancozeb WP were 121.372,133.392,133.833 mg/L and 814.071 mg/L,respectively,suggesting that 68% metalaxyl-M mancozeb WG was the best with the lowest EC50 and better relative inhibition.The correlation coefficients of the four fungicides were all above 0.92,indicating that concentration had high correlation with inhibition.