A tospovirus-like virus recovered from netted melon was transmitted by Thrips palmi in a persistent manner but had different cytopathological features from tospoviruses previously reported. Viral nucleocapsid (N) was purified with two protective reagents, 2-mercaptoethanol and L-ascorbic acid, and RNA extracted from the viral nucleocapsid was used for genomic analysis. The virus had a genome consisting of three single-stranded RNA molecules. The open reading frame on the viral complementary strand, located at the 3' end of the viral S RNA, encoded the N protein. The 3' terminus of this RNA also contained an eight-nucleotide sequence similar to the conserved sequence at the 3' end of genomic RNA molecules of tospoviruses. These features of the viral genome are identical to those of tospoviruses; therefore, this virus is considered to belong to the genus Tospovirus. Its N protein comprised 279 amino acids and had a molecular mass of 31.0 kDa. Comparisons of its amino acid sequence with those of known tospoviruses revealed less than 60% identity. This melon virus is concluded to be a distinct species in the genus Tospovirus, and the name Melon yellow spot virus is proposed.

A new virus disease occurred in tomato in Shizuoka and Aichi prefectures. The virus from Shizuoka was transmitted by Bemisia tabaci of B biotype, but not by sap. Its narrow host range was restricted to five species from two families. Geminate particles were observed in partially purified virus preparation from infected leaves of Datura stramonium. Specific DNA bands were detected from infected plants by polymerase chain reaction using two sets of primers designed for DNA A component of geminiviruses. The viruses from Shizuoka and Aichi had extremely high degrees of nucleotide sequence similarities (98%) with a mild isolate of tomato yellow leaf curl virus from Israel (TYLCV-Is-M). Their genomic organization of DNA A was the same as that of TYLCV. The amino acid sequence similarity between six ORFs of TYLCV-Is-M and the equivalent ORFs of the virus isolates from Shizuoka and Aichi was over 95%. From these results, the two virus isolates were identified as TYLCV and were closely related to TYLCV-Is-M from Israel. This report is the first on the occurrence of TYLCV in tomato in Japan.

Ultraweak luminescence generated by sweet potato and nonpathogenic Fusarium oxysporum interactions associated with a defense response was detected by a photoncounting method using ultrahigh-sensitive photodetectors. The time-dependent intensity variation, the spectrum and the two-dimensional imaging of the ultraweak luminescence are indicative of the defense response of the sweet potato to F. oxysporum. The production of ipomeamarone as a phytoalexin means that F. oxysporum induced the defense response in the sweet potato.

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