Transfer of tolerance to different Potato virus Y (PVY) isolates from Nicotiana africana Merxm. to Nicotiana tabacum L.

The wild species Nicotiana africana is a source of Potato virus Y (PVY) resistance. Tolerance to PVY was transferred from N. africana to Nicotiana tabacum by two backcrosses with variety 'BP-210'. Successive generations were obtained by selfing. Cytological investigations covered counts of mitotic chromosomes, study of meiotic configurations and pollen viability. The number of mitotic chromosomes varied according to generations. In pollen mother cells, the number of univalents decreased with advancing generations. Stable 48-chromosome lines were found in the BC(2)F(5). There was an increase of the percentage of PVY tolerant plants with each of the advancing generations. Challenged with two PVY isolates, the breeding lines showed higher levels of tolerance than conventional N. tabacum cultivars. There was a conspicuous absence of necrotic responses in the N. africana-derived materials. These stable breeding lines carrying N. africana-derived tolerance factors to different strains and isolates of PVY are the source of a very valuable germplasm to be used for breeding.