Abstract
Three strains of melon necrotic spot virus, NH strain (MSNV-NH), NK strain (MSNV-NK) and S strain (MNSV-S), were detected by direct double antibody sandwich ELISA (DAS-ELISA), nonprecoated indirect ELISA (Np-I-ELISA) and precoated indirect double antibody sandwich ELISA (P-I-ELISA) using the respective antiserum. The three methods of ELISA using these homologous antisera proved to be applicable for discriminating between healthy and infected melon (Cucumis melo L.), with detection end points ranging from 10-4-10-5 dilution of leaf extracts and 0.01μg/ml of purified preparations. On the other hand, in heterologous reactants, the absorbance values on MNSV-NH and MNSV-NK, both were serologically identical, were almost the same as those in homologous reactants by the three methods of ELISA, and the two strains could be detected reciprocally with each heterologous antiserum. The two strains of serotype N and the strain of serotype S (MNSV-S) could be reciprocally detected by Np-I-ELISA, therefore Np-I-ELISA seemed to be the most useful for the diagnosis of field samples. However, the absorbance values on the serotype N strains and the serotype S strain in heterologous reactants by DAS-ELISA and P-I-ELISA were considerably lower than those in homologous reactants. Thus, two types of antisera to serotype N and serotype S were indispensable for the diagnosis of field samples by these two methods. Nevertheless, the two methods could distinguish the two serotypes of MNSV. All isolates of MNSV collected from various melon-cultivating areas in Japan were serotype N, MNSV-NH or MNSV-NK.
