|January 2006. A betel nut disorder in Papua New Guinea. Palms of any age are affected and the symptoms can appear anywhere on the stem. There is a characteristic narrowing of the stem associated with the symptoms (see picture advanced stage, middle right). Secondary insect damage usually leads to the death of the palm, with the stem breaking at the weakened areas. The disorder is said to be spreading at an alarming rate in the Markham Valley. Betel nut is an important cash crop in the country.
A member from PNG reported the sugarcane weevil, Rhabdoscelus obscurus, present in affected palms. The weevils were making tunnels around the softer part of the stem just beneath the crowns. But whether they were the primary cause of the decline or just exploiting already weakened palms was not verified. The problem started from Water Rise (upper Markham) and spread through the Mutzing area, near the vicinity of Ramu Sugar. However, the tapering of the palms and the fact that many had symptoms without weevil damage suggested that the weevils were indeed not the primary cause of the decline.
There was also a suggestion to check for Red ring disease, cause by a nematode.
Addtional photos were sent in November 2007 (middle, right – late stage; lower row – early stage and internal).
In February 2008, as there had been little advance in knowledge about the cause of the condition, further emails were sent to PestNet. There was also a suggestion that coconuts in the Bogia area, Madang Province showed similar symptoms.
To date: a) examination for phytoplasma has proved negative; b) viroids have not been investigated and c) there is a suggestion that the planthopper Zophiuma lobulata is involved. This planthopper was implicated in the Finschhafen disorder of coconuts some years’ ago. There is currently an ACIAR project investigating this insect and its potential to cause disease.
In an email from NARI, the following summarised recent observations and research:
1) Symptoms of the betel disorder differs from those reported in Kerala, India.
2) Bud rot caused by Phytophthora palmivora has been excluded as have other fungi and bacteria, except that one bacterial cultured, Xanthomonas campestris, is of interest.
3) The Central Science Laboratory, UK, mentioned that they have shown recently that Xanthomonas campestris pv. arecae from betel nut is very closely related to the Xanthomonas wilt bacterium (Xanthomonas vasicola pv. musacearum) that is causing severe problems on banana in East Africa and is almost certainly a member of X vasicola. There is no current information on pathogenicity and host range. The reference strain for pv. arecae comes from India. The CSL would be very pleased to receive a culture from PNG or even infected material and would identify it based on their gene sequencing method.
4) During surveys, no insects were found consistently associated with the stems, but mites were observed inside the lesions that develop on the stem at advanced stages. It may be that the stem symptoms develop long after any insects (perhaps associated with the symptoms) have left the palms.
5) The symptoms can appear on any part of the stem where there is still young green tissue; no symptoms have been observed on the foliage or crown that are consistently associated with those on the stems. In fact, the crown and foliage continue to look quite healthy even in palms with advanced stem symptoms. In very advanced stages, the stem will break wherever the symptoms developed, not only at the top of the palm. However, in many older palms, the symptoms develop very close to the crown – most likely because that is were young tissue remains.
6) The few photos seen of the coconut problem at Bogia suggest that it is not the same problem as that on betel nut, but it requires further investigation.