The present study was carried out at ICAR -Central Potato Research Station, Gwalior during 2012-13 to assess the effect of dormancy breaking chemicals, their dip duration and microtuber size on growth and yield parameters. The three different size >4-6mm, >6-8mm and >8mm of variety Kufri Sindhuri were given dip treatment with six types of growth regulators/ dormancy breaking chemicals viz 1ppm gibberelic acid, 0.5 ppm gibberllic acid, 1% thiourea, 0.5 % thiourea, 1ppm gibberllic acid + 1%

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... ea and 0.5 ppm gibberllic acid + 0.5 % thiourea along with water control for 30 min, 45 min and 60 min. All the treatments exhibited better growth and yield parameters over water control but significantly best at 5% was 0.5 ppm gibberllic acid treatment for growth parameters and 0.5 ppm gibberllic acid + 0.5 % thiourea treatment for yield parameters. All the dip duration 30 min, 45 min and 60 min had not significant at 5% level effect for both growth and yield parameters. The larger sized micro-tuber (>8 mm) showed significantly superior plant emergence, plant height, number of compound leaves per plant, number of stems per plant both at 50 and 75 days after planting followed by 4-8 mm grade and <4 mm grade micro-tubers. Similar trend was observed for all the yield parameters. The overall mean finding indicates that micro-tubers treated with 0.5 ppm gibberllic acid in combination with 0.5 % thiourea gave highest yield (226.0 q/ha tuber), among micro-tuber size of >8mm (295.0 q/ha tuber) and among dip duration 30 min (206.67q/ha) and 45 min (210 q/ha) resulted in significantly higher yield parameters under nucleus seed production in in vivo conditions of central India.