For Kauai farmers, recovering from a major flood event is more complicated that just removing silt. As communities continue the process of recovery, growers are looking at the long process of bringing their impacted fields back into production. This is a significant challenge for farmers of perennial crops that are not propagated from seeds, including important local crops like taro, sweet potato, and banana. It can be difficult to obtain sufficient cuttings to plant a new crop.
In the case of taro, farmers usually save huli (cuttings) during harvest to plant for the subsequent crop. The options for obtaining huli from off-farm are very limited; finding clean planting stock that is free from insects and diseases is even more difficult. In a situation like this, where flooding impacted most growers across the island, the challenge is even greater.
Bringing huli in from neighbor islands poses its own set of problems. For example, taro from the Big Island is quarantined by the Hawaii Department of Agriculture to prevent the spread of taro root aphid, a serious pest that can cause total crop loss at times, especially in dryland plantings.
Huli from other islands may be infected with taro vein chlorosis virus, dasheen mosaic virus, or several fungal diseases. While importing huli from other islands may offer short-term solutions to the lack of planting material, the longer-term implications of moving insects and diseases around (or into) the state are sure to be detrimental to the industry.
Pests not only reduce crop production, they may also impact the ability to export crops to out-of-state markets
Growers should use extreme caution when transporting any taro plants or plant parts between islands. To help reduce risk of transporting pests and diseases, even local huli should be thoroughly cleaned and all soil, roots, and petioles should be removed. Rotten or decayed spots should be cut out, leaving a generous margin of healthy plant tissue.
Submerging cuttings for 6-10 minutes in 120°F water and then placing them into a cool water bath will help minimize pests without damaging the plant tissue. Dunking the huli in 10 percent bleach solution (regular, unscented bleach) will help reduce fungal pathogens.
However, there is currently no home treatment that will remove viruses from taro plant tissues. The Big Island quarantine remains in effect, and home treatments, while helpful, are not 100 percent effective. One effective long-term solution for taro farmers is to take advantage of plant tissue culture techniques to ensure clean planting material.
Tissue culture is a method used to grow plant cells under sterile conditions on a nutrient culture medium such as agar. Taro plant cells can be heat-treated to eliminate pathogens without harming the cells, and then grown out in a laboratory under sterile controlled conditions in a medium containing nutrients, vitamins, and plant hormones.
There is no modification of genes or DNA. It is a slow process, taking more than a year until the newly formed huli are big enough to plant in the field _ but it is the best way to ensure disease-free planting material.
When most commercial growers need 10,000 – 20,000 huli per acre, tissue culture is an efficient way to generate the large quantities needed to replace widespread losses. A team at the University of Hawaii College of Tropical Agriculture and Human Resources (CTAHR) has already begun to increase tissue culture production of several important commercial taro varieties to help the taro industry recover from flood damage and get fields back into production.
As a reminder, whether you are a backyard gardener looking for a handful of huli or a commercial grower needing more than 10,000 huli per acre, the concerns around phytosanitation – clean plants _ are the same.
Take the extra time to double check the source of your plants, clean huli for insects, rots, and bacteria, and avoid any planting material carrying a virus.
Emilie Kirk is with University of Hawaii College of Tropical Agriculture and Human Resources Cooperative Extension Service.