Effect of Agrobacterium Infection Time, Co-Cultivation and Cell Density on in vitro Response in Hypocotyl of Eggplant ( Solanum melongena L.)

The present study purports to assess the effect of Agrobacterium infection time, co-cultivation and cell density on in vitro response in hypocotyl explants of eggplant (brinjal) cv. Manjarigota. Agrobacterium (OD₆₀₀ 0.3-0.5) infection for 10-15 minutes (24.44±2.34%) was found to be optimum, while, higher or lower infection-time resulted in reduced callus initiation, shoot regeneration and explant survival. Explants with no (only Agrobacterium infection) or short (1 day) co-cultivation, showed reduced callus-initiation response and turned yellow, with no regeneration. Callus-initiation response increased from Day 1 (96.66±03.33%), and reached a maximum on Day 2 and Day 3 (100±00.00%). It decreased on further increase in co-cultivation time. Explants co-cultivated for three days showed highest regeneration response (30.00±02.96%) which thereafter reduced with further increase in co-cultivation time. Explants infected with Agrobacterium culture at 0.05 OD₆₀₀ showed hardly any regeneration, and turned yellow and necrotic on the selection medium. Highest regeneration response (28.33±02.33%) was obtained in explants infected with 0.1 OD₆₀₀ culture, and this gradually reduced as celldensity increased (upto 1.0 OD₆₀₀), becoming zero in explants treated with cultures at 1.5 OD₆₀₀ or above. Agrobacterium overgrowth was noticed on explants infected with cultures of 0.5 OD₆₀₀ and above. Exposure of hypocotyl explants to higher cell-density, longer infection-time and prolonged co-cultivation regime resulted in severe necrosis of explants; time taken for development of Agrobacterium overgrowth was less with increase in the level of these factors. Regenerated shoots were healthy, green, elongated and showed ischolar_main induction on culture medium containing Kanamycin.