EFFECT OF LEAF MALEIC HYDRAZIDE CONCENTRATION ON YIELD AND DRY-MATTERPARTITIONING IN BURLEY TOBACCO (NICOTIANA-TABACUM-L)

Maleic hydrazide (MH) is commonly used to prevent axillary bud (sucker ) development in tobacco (Nicotiana tabacum L.) after inflorescences h ave been removed by topping. Although MH provides an inexpensive and e ffective method to control sucker development, high concentrations (> 80 mug g-1) of MH residue in cured leaves are undesirable. The objecti ve of this study was to determine the effect of a wide range of MH rat es on leaf MH residue, yield, and dry matter partitioning among plant parts of burley tobacco. The feasibility of using near infrared spectr oscopy as a method to rapidly screen tobacco samples for MH residue al so was tested. MH was applied at rates of 0 (suckers manually removed) , 1.68, 3.36, 5.04, 6.72, 10.08, and 13.44 kg ha-1, where 3.36 kg ha-1 corresponds to the usual commercial rate. Adequate sucker control was provided for up to 3 weeks by 1.68 kg ha-1 MH. Concentrations in the leaves (midribs removed) increased progressively with increasing rate of MH. Concentration of MH decreased over time but plants treated with rates above 3.36 kg ha-1 had MH concentrations at or above 80 mug g-1 in air-cured leaves of the upper third of the canopy. Leaf MH concent ration decreased from the top to the bottom of the plant, and at MH ra tes above 6.72 kg ha-1, the MH concentration was above 80 mug g-1 in l eaves at the bottom of the canopy. Air-cured leaf yield was slightly i ncreased for the 1.68 kg ha-1 MH rate compared with hand-suckered cont rols, but higher MH rates did not further affect yield. A large portio n of the yield increase was due to increased cured-leaf moisture conte nt of MH-treated plants. Additionally, MH-treatment decreased partitio ning of dry matter in stalks. On a whole-plant basis, dry matter accum ulation was similar for all treatments. The results indicated that MH rates above 3.36 kg ha-1 did not alter plant development, yield, or su cker control, but did lead to excessive undesirable leaf MH concentrat ions. For cured-leaf and especially midrib tissue, there was a signifi cant relationship between MH concentration determined by the chemical method and estimated by NIR spectroscopy. These results indicated that the potential exists to use NIR spectroscopy to rapidly estimate MH r esidue levels of tobacco leaf tissue.