POSSIBILITIES FOR REGULATION STEM GROWTH OF TOBACCO SEEDLINGS BY TREATMENT WITH SOME GROWTH-RETARDANTS

Some growth retardants, structural analogues of Alar, such as the monomethyl ester of itaconic acid (MEIA), the monoethyl esters of adipinic (MEEAdA) and of succinic acids (MEESA) were tested as possible regulators of stem growth of tobacco seedlings. The compounds, in concentrations of 500, 1000, 1500 and 2000 mg/l, were sprayed on the leaves of oriental tobacco cv. Plovdiv 5 at the fourth true leaf stage and produced an obvious retarding effect. This effect was well expressed on the tenth day after treatment, when the compounds ranked as follows: Alar, MEIA, MEESA, MEEAdA, according to their retarding effect. The stems of treated plants were shorter, their fresh and dry weights were reduced and they were characterized by higher amounts of lignin and phenols. Two weeks after transplanting, the differences observed in height, weights and amounts of lignin and phenols decreased. The conclusion is reached that treatment of tobacco seedlings with Alar, MEIA, MEEAdA and MEESA can temporarily inhibit growth through transplanting period, but has no influence on subsequent growth rates. The use of these retardants may be suitable for protecting tobacco seedlings from overgrowth in cases when the climatic conditions do not permit their planting in the fields in time.