After a delayed start due to an outbreak of Freckle Disease, a disease screening trial of Fusarium wilt Tropical Race 4 (TR4) in the Northern Territory (NT) is gaining ground, in the ongoing search to find varieties resistant to Panama TR4.
A varietal screening trial was planted at Coastal Plains Research Station in early June 2016 to assess resistance to Fusarium wilt TR4 (Panama disease). This was part of the Hort Innovation [GS1] (HIA) and Australian banana industry funded Banana Plant Protection Program project — BA10020.
Replicated plots of 27 varieties (see table) were established from tissue culture plantlets in a plot known to be infested with TR4, and were assessed over a plant and ratoon crop. Bunch harvest of early maturing varieties commenced at the beginning of March this year — a mere nine months after planting.
Emphasis in this trial has been on determining the reaction of several Cavendish selections, as well as many hybrids from the Honduran breeding program to TR4.
The trial site was artificially inoculated with TR4 because an earlier sentinel planting of Williams in the previously inoculated site produced disease in just one or two plants, indicating the pathogen was only present at extremely low levels.
To artificially inoculate, 200 ml ofmillet grain pre-colonised by the TR4 pathogen was added to the planting hole in the field. Once external disease symptoms were evident, ratings of severity were taken on a monthly basis.
The date of first disease symptoms, type of symptom and date of death were recorded. Upon death of the plant, the pseudostem was examined for the presence of internal symptoms and infected vascular tissue of each variety was collected for laboratory confirmation of TR4.
All remaining plants which reached bunch harvest stage, with or without any external symptoms, were then examined internally and any infected vascular tissue collected as required.
There are four control (check/reference) varieties in the trial:
– The industry standard and very susceptible Williams
– GCTCV 218 (Formosana), previously shown to be less susceptible than Williams, and probably represents the minimum level of genetic resistance which would be necessary to build an integrated crop management system around to continue production in the presence of TR4
– FHIA-01 (Goldfinger) resistant
– FHIA-25 highly resistant.
These controls are essential to help put the disease reaction of new varieties into context.
Despite the relaxation of TR4 quarantine restrictions by the NT government in the NT in 2012, safeguards are firmly in place to ensure that TR4 trial sites, including this one, do not present a risk to the remainder of the industry.
Safeguards include the use of dedicated footwear for the NT locations and decontamination of footwear of NT government staff and their government vehicles.
Where to from here?
The following valuable outcomes are expected from the trial.
· Determine the level of resistance in new Cavendish selections for possible deployment in the NT and in Queensland (should TR4 become widespread).
· Identify additional varieties for the mutagenesis work. Currently Dwarf Nathan is shaping as a likely candidate.
· Provide information on the disease reaction of hybrids and parental lines to the Honduran breeding program to promote the development of more TR4 resistant varieties for evaluation and potential commercial deployment.
· Determine the disease reaction of niche varieties like Senorita and others that may be developed alternative markets.
A second trial is scheduled to commence in 2018 as part of the new HIA/Banana industry project ‘Improved plant protection for the banana industry’ — BA16001, which will include more new Cavendish selections from Taiwan and hybrids from the French research centre CIRAD[GS2] , Guadeloupe.