Research methods used in the release of tobacco cultivars, with double resistance to PVY and TMV in Romania
The soil and climatic conditions in Romania allow for the growing of five tobacco types (Oriental, Semi-oriental, Virginia flue-cured, Burley and tobacco of large consumption). The most damaging diseases which cause important losses in quality and quantity in tobacco grown in Romania are those induced by the potato virus Y and by the tobacco mosaic virus. The release of the cultivars resistant to PVY and TMV is the best alternative for the control of the diseases induced by the viruses. The main way of creating tobacco cultivars with double resistance to PVY and TMV is to combine the classic methods of selection with up-to-date research methods (cultures in vitro). By using the classic methods, numerous tobacco cultivars resistant to TMV were obtained, and so in Romania cultivars sensitive to this virus are no longer grown. By using the in vitro method of cultures of immature embryos obtained by the hybridization of the resistant cultivars to TMV with sources of genetic resistance to PVY, tobacco cultivars with double resistance to PVY and TMV were obtained. Also, the androgenesis and the selection for the recessive gene responsible for the resistance to PVY of the haploids, allowed the obtaining of tobacco genotypes resistant to PVY and TMV. By combining the classic research methods with up-to-date research methods, it was possible to obtain many tobacco cultivars for the all five types and especially for the flue-cured tobacco and Burley, with double resistance to PVY and TMV: Virginia 232, Virginia 237, Virginia 165, Virginia 233, Virginia 235, Burley 224, Burley 190, Burley, 114, Burley 196, Burley 194 etc. In the period 1990 - 2002, these cultivars were tested in comparative cultures, in areas typical for the two tobacco types, to find out if these cultivars had a special agronomical and technological value, satisfy the increasingly high expectations of the growers and tobacco industry, as well as those of the tobacco consumers in Romania.