Optimal media compositions were worked out for efficient callus induction and consequent plantlet regeneration using different explants (leaf, node and internode) of potato (Solanum tuberosum L.). Among seventeen media compositions used, MS medium supplemented with 3.0 mg/L 2,4-D + 0.25 mg/L BAP exhibited maximum callus induction and proliferation response. Well-proliferated calli were exposed to different treatments of physical (gamma rays 10 to 50 Gy) and chemical (EMS and NaN2; 1 to 5 mg/L) mutagens and were then screened against partially purified toxin of Alternaria solani. Plants regenerated from callus, insensitive to toxin, were supposed to be resistant and were then screened against two different isolates of A. solani under field conditions. After two year of field trials four out of 63 in vitro screened lines of gamma irradiation; four out of 52 in vitro screened lines of sodium azide treated cultures and five out of 59 screened lines of EMS treated cultures were selected according to disease rating scales. Variation was further confirmed using various biochemical and molecular markers.

Plant tissue culture provides a rapid method for producing disease free and genetically identical plant material. Plant growth regulators (PGRs), particularly cytokinins such as 6-benzylaminopurine (BAP), play an important role in in vitro morphogenesis. Besides PGRs, nanoparticles have recently emerged as promising supplements for enhancing plant growth and antioxidant defense mechanism. The present study evaluated the combined effects of BAP and zinc nanoparticles (ZnNPs) on shoot proliferation and antioxidant enzyme activity in Solanum tuberosum L. under in vitro conditions. Explants were cultured on Murashige and Skoog (MS) medium supplemented with different concentrations of BAP (1, 1.5 and 2 mg/L) and ZnNPs (10, 20 and 30ppm) either alone or in combination with each other. The highest average number of shoots per explant (6.67) was observed at 1 mg/L BAP, although shoot length was decreased as compared to control (5.87%). A low concentration of ZnNPs improved growth attributes, resulting in 5.88%, 25.00% and 36.36% enhancement in shoots per explant, shoot length and shoot fresh weight as compared to control, respectively. However, higher concentrations (30 ppm) of ZnNPs caused a decline in growth parameters. Biochemical analysis revealed that BAP (1 mg/L) enhanced antioxidant enzymes activities including peroxidase (POX), phenylalanine ammonium lyase (PAL), polyphenol oxidase (PPO) by 0.563, 0.039 and 0.317 unit/mg of protein, respectively, compared to control. ZnNPs (10ppm) further enhanced the activity of POX, PAL and PPO by 18.42%, 14.31% and 14.86% with respect to only BAP treated plants. Combined application of BAP and ZnNPs at low concentrations enhanced all the growth and biochemical parameters, while higher concentrations showed an inhibitory effect on these parameters.