During 2002-03, field-infected onion ( Allium cepa ) plants, exhibiting characteristic symptoms of chlorotic spindle-or diamond-shaped lesions on the leaves and scapes with twisting or bending flower-bearing stalks, were observed in the Jalna and Nasik regions of Maharashtra, India. In the advanced stages, single spindle-shaped chlorotic lesions coalesced, leading to withering of leaves and flower-bearing stalks. The disease was transmitted to a number of virus-indicator plants by mechanical inoculation using phosphate buffer (0·01 m sodium sulfate, pH 7·0, containing 0·1% sodium sulfite). Inoculated Nicotiana benthamiana plants produced systemic necrotic lesions, eventually resulting in dieback and wilting of the plants, while Nicotiana tabacum (varieties Xanthi NC, White Burley, Samsun and GT-4) and Nicotiana clevelandii produced local chlorotic ring spots 3-6 days after inoculation. In Vigna unguiculata , necrotic local lesions developed 3-4 days postinoculation, while Nicotiana rustica failed to produce any symptoms and did not become infected.Field-infected onion samples and glasshouse-inoculated plants were tested by ELISA using the following antisera: Tobacco streak virus (DSMZ AS-0615); Watermelon silver mottle virus (DSMZ AS-0118); Iris yellow spot virus (DSMZ AS-0528); Tomato spotted wilt virus (DSMZ AS-0105); Impatiens necrotic spot virus (DSMZ AS-0115); Chrysanthemum stem necrosis virus (DSMZ AS-0529); Peanut bud necrosis virus (ICRISAT); and Potato virus Y (DSMZ AS-0573), utilizing the respective positive control samples. Field-infected onion samples and the respective mechanically inoculated tobacco plants reacted strongly with Iris yellow spot virus (IYSV) antisera, but failed to react with any of the other antisera tested. RT-PCR using primers designed to the capsid gene and flanking sequences of IYSV (GenBank accession number AF001387) produced the expected 925-bp amplicon from infected but not healthy onions. The results of symptomatology, host range, ELISA and RT-PCR indicate that the causal agent is a strain of IYSV, which is a new report from an important oniongrowing region of Maharashtra State, India. This virus has been reported as a potentially devastating pathogen of onion in Europe (Cortes et al ., 1998), Israel (Gera et al ., 1998 and the USA (Gent et al ., 2004).

A serious disease of sunflower (Helianthus annuus) with putative virus aetiology was found occurring in all major sunflower-growing regions of India. Symptoms of this sunflower necrosis disease (SND) comprised chlorotic and necrotic ringspots and leaf distortion. A general leaf and stem necrosis extending to midveins, petioles and flower bracts eventually results in stunting and dieback, especially when plants become infected in the early stages of development.Ilarvirus-like particles were detected by electron microscopy in crude sap of SND-affected sunflower, and in Chenopodium quinoa plants inoculated with leaf extracts prepared from SND-affected sunflower plants. In addition to several other herbaceous virus indicator plants, groundnut, cowpea and cotton, significant crops in India, also became infected. Back-transmission to healthy sunflower seedlings with leaf extracts of systemically infected indicator plants resulted in identical symptoms of SND, confirming the ilarvirus-like component as the causative agent of sunflower necrosis disease.An antiserum (DSMZ AS-0615, Braunschweig, Germany) raised against purified virus preparations reacted well in DAS±ELISA and proved reliable for field diagnosis of Sunflower necrosis virus (SNV). In a comparative serological study using plants infected with other ilarviruses, a reaction was demonstrated only with Tobacco streak virus (TSV). This serological relationship was confirmed by Western blot analysis and by immunosorbent electron microscopy decoration assays using SNV and TSV antisera in reciprocal tests.In RT±PCR, using oligonucleotide primers deduced from conserved sequences within TSV RNA3 and flanking the entire coat protein region, an approximately 1000 bp dsDNA fragment was amplified from SNV-infected sunflowers. Sequence analysis of cloned SNV PCR fragments revealed nucleotide identities of approximately 90% with TSV RNA3 (EMBL accession number X00435) and a coat protein amino acid homology between SNV and TSV of more than 90%.

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