Bull. Spec. CORESTA Congress, Harare 1994, p. 132, PPOST 4

Resistance of tobacco to brown spot induced by viruses and transferability of the induced resistance to the regenerated plants and their progenies via tissue culture

Shandong Agricultural University, Dept. of Plant Protection, Taian, Shandong, China
The function of viruses to induce tobacco resistance to brown spot and transfer of the induced resistance to the tissue culture-regenerated plants and their progenies were studied. Five viruses (CMV, TVBMV, PVY necrotic strain PVY-T1, satellite SV52 of CMV, and hypovirulent strain N14 of ToMV) were used as inducers in 16 combinations of 1-4 viruses. N14 and SV52 were able to induce systemic resistance of tobacco to the disease by 57% and 83% when a strong virulence strain, TBA28, of Alternaria alternata were used as challenger to inoculate cvs. NC89, NC82, and K326. The combinations containing N14 and/or SV52 gave 10-78% induced resistance; resistance was decreased by paired combinations of strains 1, 2, and 3 of PVY-T1, TVBMV, and CMV; these strains induced susceptibility of the plant to the disease when used as a single inducer. The induced resistance by both N14 and SV52 was capable of translocation from the upper to the lower parts of the tobacco plant and began to show at 7 days, peaked at 30 days and lasted at least 50 days after the induction treatment. From the heart leaves of induced plants of the three cultivars, leaf discs were cultured to produce regenerated plants. The regenerated plants had increased resistance to brown spot by 75-86% when compared with each parent. Seeds were obtained from the resistant regenerated tobacco, and named as NC89-V1 which was from the N14-induced NC89 plants, and NC89-V2 which was from the SV52-inducing NC89. The selfed progeny of NC89-V1 and NC89-V2 showed increased resistance to 81% and 74%, compared with the parent NC89.