Fruits of the revolution

Queensland researchers are developing GM cultivars of three tropical crops - pineapple, papaw and banana, to solve disease and quality problems.

Assoc Prof Jimmy Botella, of the School of Integrative Biology at the University of Queensland, said pineapple growers spray their crops with an ethylene-producing chemical to stimulate flowering, so that they can time their harvest to avoid competition with Filipino and Malaysian imports.

But Botella said up to 30 per cent of the crop flowers spontaneously before the spray is applied; growers in Central and South America have the same problem.

His research team has developed and patented an externally inducible co-suppression "silencer" gene that suppresses flowering until the fruit is sprayed. In the first contained field trial of the GM pineapple, fewer than 7 per cent of the plants flowered prematurely, compared with 30 per cent of controls. In the second generation, the incidence of premature flowering was zero.

Botella said that his team will complete its proof-of-concept work this year, but the GM varieties will probably not be released for five years, while other commercially desirable traits are added, such as resistance to blackheart, and nematodes.

Blackheart results from chilling injury in early-season pineapples grown in subtropical environments that experience low winter temperatures. The problem causes major losses to processors because it manifests only when apparently normal pineapples are cut.

Dr Mike Smith, of the Queensland Department of Primary Industries and Fisheries, is using CSIRO's RNA-interference gene-silencing technology to switch off the gene for polyphenol oxidase, an enzyme that catalyses the conversion of phenolic compounds present in the tissues of many fruits and vegetables to quinones, causing them to turn black or brown.

Smith is engineering 'Smooth Cayenne', the world's leading processing pineapple. Conventional breeding has been unable to produce blackheart-resistant Smooth Cayenne varieties.

QDPI&F researchers at Maroochy Research Station have developed an efficient transformation system for pineapple.

QDPI&F researcher Dr Dennis Persley has developed a papaw variety that is resistant to papaya ringspot virus, which had all but wiped out the Hawaiian papaw industry in the early 1990s. US molecular geneticist Dr Dennis Gonsalves developed a GM papaw containing a co-suppression gene that prevents the virus replicating - the industry is now flourishing again.

Persley said ringspot virus was found in south-east Queensland in 1993. It's not a Hawaiian import, but almost certainly an opportunistic, local mutant of cucurbit ringspot virus, which has been infecting watermelons in Queensland for many decades.

Routine quarantine measures contained the outbreak, and Persley said that, given continuing community concerns with GM crops, and anti-GM activism, ringspot-resistant GM cultivars will only be deployed if ringspot becomes a serious problem.

QDPI&F is involved in a hybridisation project in the Philippines, to transfer the ringspot resistance into local varieties - ringspot is a serious problem in the Philippines.

Smith said QDPI&F and Queensland University of Technology scientists are working to introduce genes for resistance to Fusarium wilt into Australia's - and the world's - top banana, Cavendish.

In the absence of effective chemical controls for Fusarium wilt, farmers must either grow some other crop, or replant with resistant varieties.

Cavendish and other commercial bananas are seedless, making hybridisation extremely difficult, so GM may be the best way to create Fusarium-resistant varieties.

QDPI&F maintains an extensive banana germplasm bank at Maroochy Research Station, and QUT researchers have identified resistance genes in wild bananas from Malaysia and Indonesia.

Smith said researchers have also been experimenting with gamma irradiation to create taller, more productive varieties from an extra-dwarf cultivar of Cavendish that is resistant to Fusarium wilt.

Queensland already grows one GM crop - cotton growers in the south-west of the state, around St George, and around Emerald, already grow Australia's new Bollgard 2 pest-resistant cultivars. The industry is now eying the tropics, and the well-watered Burdekin Delta, south of Townsville.