Modification of Growth and [6]-Gingerol Concentration In Zingiber officinale

Ginger (Zingiber officinale Roscoe) is a tropical plant grown for its fleshy rhizome of culinary importance.  Properties of ginger associated with human health are at least partly due to [6]-gingerol, a pungent vanilloid.  We are interested in understanding how to grow ginger in high tunnels in the upper Midwestern United States to diversify farm income, but also how to enhance [6]-gingerol concentration in the rhizome.  In all experiments, rhizomes were obtained in March and planted in raised beds in a 9.1×14.6-meter double-poly high tunnel in April in Minnesota.  Three separate experiments were each performed two separate years.  First, enhanced shoot proliferation and early emergence were stimulated by soaking 2 clones of ginger (blue and yellow) in ethephon (2-chloroethyl phosphonic acid; 500 or 1000 mg l^-1) prior to planting.  Second, 2 varieties of ginger (yellow and white) were planted on 4 consecutive weeks in April.  All plants were harvested on the same day in November, and rhizome yield and [6]-gingerol concentration were measured.  And third, yellow and white ginger were planted and covered with 0 to 70% shade cloth to determine optimum shading for rhizome yield and [6]-gingerol concentration.  Ethephon increased shoot growth in ‘blue’ but not ‘yellow’ ginger and did not affect [6]-gingerol concentration.  Earlier planting enhanced rhizome biomass accumulation but had little effect on [6]-gingerol yield per unit area.  Increasing shade reduced the rhizome:shoot ratio and decreased rhizome dry matter, but increased [6]-gingerol concentration per gram fresh weight.