Production of Edible Ginger Clean Seed by Sub-Irrigation Methods In Hawaii

Edible ginger (Zingiber officinale) is a spice and vegetable crop produced on the Island of Hawaii.  It is asexually propagated from rhizomes, called seed pieces, which are saved from a previous crop.  Bacterial wilt (Ralstonia solanacearum race 4) causes severe yield losses of edible ginger. Many ginger fields are infested with Ralstonia and there is a high risk that ginger seed pieces collected from these fields will be infected with the pathogen.  Two growing methods were developed to produce rhizomes that are free from Ralstonia.  Clean ginger seed pieces that originated from tissue cultured plants were grown using hydroponic methods for 8 successive crop cycles.  First, ginger pieces were grown in 26L pots. To conserve growing medium and increase aeration, an upside-down 3L pot was placed on the bottom of the larger pot. Three 50g seed pieces were planted in a 26L pot that was filled with peat mix: medium perlite: coir (1:1:1, v:v:v).  Pots were placed in elevated polyethylene-lined tanks (0.6 x 2.4 m x 14 cm high) which were protected by open-sided, plastic-covered rain shelters.  Pots were continuously sub-irrigated with 5 cm of a complete nutrient solution (1.5 -2.0 mS).  Plants were topped after 8 months, allowed to dry for 3 weeks, and then pots were emptied and rhizomes washed and roots removed.  Average yield per pot was 4.9 kg of rhizomes which were cut into seed pieces to plant the next crop.  In the second method, ginger was grown in heavy duty, perforated plastic slings (23 cm x 2.4 m x 15 cm high) filled with growing medium.  Slings rested on 5 cm upside-down nursery trays in channel-type tanks made by rolling out heavy duty plastic sheets over a level greenhouse bed.  Fertilizer stock solutions were injected into drip irrigation lines and a float valve maintained a 5-cm level nutrient solution in the tank.  Plants were top-irrigated as well as sub-irrigated for 8 months.  After the foliage dried and was removed, the entire sling was taken to a washing table where the sling was tipped over and the growing medium washed from the rhizomes.  The average rhizome yield from each sling was 14.5 kg.