Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Secrets of Wild Ginger Revealed

In previous issues we have detailed how CABI – Europe UK are searching for potential biocontrol agents for wild ginger (Hedychium spp.) in India, and some of the interesting beasts they have found.

We also explained that Landcare Research was assisting the project by undertaking molecular studies of Hedychium to develop diagnostic tools for the various species, which can be hard to tell apart in the field. We also hoped to be able to pinpoint the geographic origins of the weedy populations so CABI could further concentrate their searches for biocontrol agents. However, as so often happens when you study plants in finer detail, we have come up with some interesting and unexpected results!

The two problematic species in New Zealand are known as kahili ginger (Hedychium gardnerianum) and yellow ginger (H. fl avescens). The molecular studies showed that New Zealand, Hawaiian and Indian yellow ginger have a similar genetic sequence throughout their various ranges, which makes surveying for potential biocontrol agents in India quite straightforward – any part of the range would be fi ne in terms of agent–host compatibility. However, the same cannot be said for kahili ginger. While New Zealand and Hawaiian material were again uniform, and similar to each other, they were quite different to any material from India collected to date. “Our results indicate that the specimens from New Zealand and Hawai’i appear to be hybrids,” explained plant population geneticist Gary Houliston. Chromosome counts of New Zealand material show that it is tetraploid, meaning it has four sets of chromosomes. “We think that one parent is H. gardnerianum and the other is probably white ginger H. coronarium,” said Gary. Although white ginger is present in New Zealand, it is not currently a problem here, but it is weedy in Hawai’i. Hedychium has been widely hybridised by the nursery trade over the last 70 years so in that context this result is really not that surprising. Most of the hybrids tend to resemble one of the parents, so their true identity can easily be overlooked without using molecular tools. Two samples from the Manawatu-Wanganui Region suggest that another hybrid may also be present in New Zealand and we will be following up on that further. We are also hoping to get further samples from the invaded range, including the Azores, Hawai’i and South Africa, to complete the picture.

So what does this finding mean for attempts to find suitable biocontrol agents? If our kahili ginger is likely to be an artificially bred hybrid it is quite likely that none of the ginger growing in the wild in India will be a match. Instead it will be crucial at an early stage to test whether potential agents are capable of attacking this hybrid material, and it is possible that any species that are very highly host specific may well be ruled out. One of the most promising species found to date, the large red and black weevil (Tetratopus sp.), was found attacking kahili, white, and yellow ginger in India, which augers well. This striking weevil is thought to damage all parts of the plant. However, a frit fly (Merochlorops dimorphus), commonly associated with shoot death, stunting, and flower abortion in India, and the gregarious leaf-feeding moth (Artona flavipuncta) have only been found on kahili ginger, so fingers crossed they can attack the hybrid material. CABI recently made new collections of the most promising potential control agents from India and are working to establish breeding populations to allow host-range testing to be undertaken. Fortunately ginger appears to have many natural enemies in its native range and the chances that some will prove to be useful biocontrol agents remain high.

This project is funded by the National Weed Biocontrol Collective and the Nature Conservancy of Hawai’i.