CHEMICAL TOPPING BURLEY TOBACCO

The act of topping tobacco (Nicotiana tabacum L.) involves the removal of the terminal bud or inflorescence of the tobacco plant. This practice ordinarily is accomplished by manually removing the top of each tobacco plant in an entire field which is labor intensive and costly. Chemical topping utilizes sucker control products to inhibit the terminal bud and axillary bud growth without manually removing the top of the tobacco plant. There were several research objectives in order to determine the utility of a chemical topping system: 1) determine if burley tobacco could be chemically topped with currently registered suckercide products while maintaining control of subsequent sucker growth; 2) compare chemical topping to manual topping for yield and leaf quality; 3) identify burley tobacco varieties that are better suited for chemical topping systems; 4) determine the optimum plant growth stage at which chemical topping treatments should be applied; and 5) identify genes that are differentially expressed following suckercide applications. To pursue our objectives, studies were initiated investigating the optimum timing of application, ideal variety maturity, and efficacy of suckercide applications using combinations of maleic hydrazide (MH), butralin, and fatty alcohols (FA). The terminal bud was not well controlled with FA or butralin alone nor was acceptable sucker control or total yield achieved. Our data suggest that chemically topping burley tobacco with a tank mixture of MH and a local systemic may be a suitable alternative to manual topping, as total yield and leaf quality grade index were not significantly different and total TSNA and MH residues were not significantly higher compared to manual topping. The 10% button and 50% button application timings were best suited for chemical topping practices. Treatments that targeted the 10% bloom stage did not completely halt flower development, but all application timings resulted in excellent sucker control. Medium and late maturity burley varieties were found to be suitable for chemical topping methods; however, timing the suckercide application may be less difficult in later maturing varieties. Chemically topping burley tobacco at 10 to 50% button stages with a tank mixture of MH and a local systemic suckercide was found to be a suitable alternative to manual topping, and would potentially result in labor savings for burley tobacco growers. Expression of genes related to phytohormones, meristem development, cell division, DNA repair and recombination were affected following MH treatment, which likely leads to the inhibition of apical and axillary meristem development