EVALUATION OF TOBACCO ACCESSIONS FOR RESISTANCE TO TOBACCO CYST-NEMATODE AND WILDFIRE

Control of tobacco cyst nematode (Globodera tabacum solanacearum Mille r and Gray) is of major concern to growers of due-cured tobacco (Nicot iana tabacum L.) in Virginia. A diverse geographic array of accessions including cultivars of several classes of tobacco, flue-cured type to bacco introductions, and Nicotiana species were evaluated during 1993 and 1994 in the greenhouse to identify new sources of resistance to to bacco cyst nematode (TCN). Six-week-old transplants were inoculated wi th 6000 TCN eggs from crushed cysts. An average of eight weeks after i noculation, a 1-g sample of root was stained and vermiform, swollen, p yriform, and adult nematodes were counted. Accessions were also evalua ted for response to wildfire (Pseudomonas syringae pv. tabaci Wolf and Foster) to determine if resistance to these two pathogens was correla ted. The underside of a single 10- to 15-cm leaf from 6-wk-old transpl ants was inoculated with a suspension of wildfire bacteria by means of a CO2 air brush. Leaves were rated for disease severity 5 d after ino culation. Several accessions had significantly reduced nematode reprod uction including TI 1597, TI 1625, 'Burley 64', 'MD 40', 'Pennbell 69' , and 'Kutsaga Mammoth 10'. Although wildfire resistance was highly co rrelated with TCN resistance, some accessions had no resistance relati onship to the two pathogens, Nicotiana miersii Ramy was susceptible to wildfire while supporting very low nematode populations and both TI 5 51 and 'KY 190' were resistant to wildfire but were susceptible to TCN . Evaluation of accessions for wildfire resistance may not be a reliab le method of screening for TCN resistance and would result in alternat e sources of TCN resistance being overlooked.