South Johnstone field trials are rating the growing performance of new varieties, including two that were developed for TR4 resistance. Story by Jeff Daniells

Two Cavendish varieties sourced from a Taiwanese research program developing TR4-resistant plants are among new varieties that have had their plant crop assessed at a South Johnstone field trial.

The trial has rated a range of Cavendish, Gros Michel and Plantain selections on agronomic measures including bunch weight, crop cycle, fruit length and plant height. The new varieties were compared with a plant crop of the industry’s standard variety, the Williams Cavendish.

Field work comparing the varieties has taken on additional significance following the confirmation of TR4 in the Tully Valley.

One of the Taiwanese TR4 selections showed promise in terms of bunch weight – being much the same weight as Williams – however it took longer from planting to achieve this.

The selection, called GCTCV 217, was obtained a few years ago by Queensland Department of Agriculture and Fisheries and comes from the Taiwan Banana Research Institute (TBRI). The institute researches tissue culture selections and
GCTCV stands for Giant Cavendish Tissue Culture Variant.

A comparison of the GCTCV 217 plant crop showed it had much the same bunch size as Williams, at 32kg compared with 30kg, but took just over two months longer to produce its bunch. It also had a lower percentage of fruit in the premium size range.

The second Taiwanese variety included in the trial – GCTCV 105 – had a much lower bunch weight than Williams, and a slower crop cycle than both the Williams and its Taiwanese stable mate. Its bunches also contained a higher percentage of smaller, non-premium-sized fruit.

The South Johnstone trial is part of the Banana Plant Protection Program’s continuing research into new varieties. Planted in August 2012, the trial’s plant crop has been followed with a first ratoon harvest. The data from the ratoon crop harvest is now been analysed and will soon be reported on.

Comparing plant crops

North Queensland growers who attended a June 2013 field walk saw the varieties nearing harvest of the plant crop.

The results of that first crop are presented here. More background information on the varieties can be found in Australian Bananas vol 41, p 20; vol 38, p 15 and vol 28, pp 44-45.

Interestingly, many of the varieties had as heavy or heavier bunches than Williams but Williams took the least time from planting till harvest.

When this extra growing time was taken into consideration, no varieties yielded significantly higher than Williams. The Cavendish selection Fa’i Palagi produced much the same yield as Williams. Those yielding more than 80 per cent of the Williams’ bunch weight were the Gros Michel selections Highgate and IBP 5-61, the Cavendish GCTCV 217 and the Plantain SH-3748.

Both Taiwanese selections GCTCV  217 and GCTCV 105 were much slower (by two to three months) in development than Williams, as is typical of the TBRI TR4-tolerant Cavendish selections.

The Cuban Gros Michel selections IBP 5-61 and IBP 5-B had the bulk of their fruit in the 22-26 cm size category, a category receiving a price premium for Cavendish fruit. Then followed Williams, IBP 12, Highgate, Gros Michel and GCTCV 217.

In terms of plant height, Williams and Fa’i Palagi were the shortest, followed by GCTCV 217 and GCTCV 105. Gros Michel and the Cuban selections were very tall (more than 4 metres to the plant throat) whilst the remainder were intermediate in height.

Wind damage

Wind damage is typically the most important cause of bunch losses in banana production.

The tall varieties of Gros Michel from Cuba had losses of 20 to 30 per cent. The intermediate-height Highgate also lost 20 per cent. These losses mostly
resulted from strong winds over a twoday period in early September 2013 with gusts up to 59 km/hr damaging bunched plants.

At this time, most of the other quicker cycling varieties had already been harvested and did not experience the winds at their most vulnerable stage during bunch filling. Notably, Gros Michel was marginally earlier than the Cuban selections to complete its harvest, and as a result had no losses.

Best on taste

Consumer taste testing will play an important part in future assessments of new varieties.

At South Johnstone, we conducted some preliminary tasting panels and also measured fruit brix (sugar content).

Hom Thong Mokho was found to have outstanding eating quality with South Johnstone staff specially requesting fruit of this variety to eat! Its appeal is partly related to its higher brix (18.3 compared to 15.6 for Williams). GCTCV 105 also had high brix similar to Hom Thong Mokho. More detailed measurements need to be made at a later date when any varieties are moved forward for further evaluation.

TR4 screening

The freckle disease eradication program in the Northern Territory has delayed the Banana Plant Protection Program’s screening of the Taiwanese selections against TR4 at the Coastal Plains trial site.

Of the two Taiwanese selections being developed for TR4 resistance, GCTCV217 has performed the better agronomically, but it’s important to consider that any variety that shows TR4 resistance may have promise in some way.

For example the variety DPM25, which has been trialled in the subtropics as well as on-farm in Tully, has shown tolerance to Subtropical Race 4. It resembles Williams closely in appearance and was developed by the then Queensland Department of Primary Industries in the early 1990s. The process involved selecting clones from a race 4-resistant Dwarf Parfitt (an extra Dwarf Cavendish only one-metre tall) until one with favourable agronomic characteristics was found.

What next?

Following on from the plant crop assessment, the results from the first ratoon crop from the South Johnstone field trial are being assessed. These results will soon be reported on and will give more information on the agronomic performance of the plants in North Queensland conditions.

Following the ratoon harvest, the trial block was nurse suckered to prepare it for yellow Sigatoka screening during the 2014-2015 wet season.