The Hindu Business Line : `India must focus on delayed ripening tech'

INDIA must aggressively adopt `delayed ripening' and `enhanced shelf-life' technologies if it wishes to consolidate its position as the world's No. 2 producer of fruits and vegetables after China, according to Dr Autar K. Mattoo, Research Leader of the US Department of Agriculture's Beltsville Agricultural Research Centre at Maryland.

Currently, the country loses roughly a third of its annual produce on account of wastage and deterioration taking place during the journey from farm to plate.

Dr Mattoo, whose field of specialisation is in regulation of ethylene biosynthesis and fruit ripening, said that advances in genetically engineered shelf-enhancing technologies had particular relevance for India, with both producers and consumers standing to gain from reduced post-harvest losses.

The key agents behind ripening are the genes that code two proteins, ACC synthase and ACC oxidase, which are responsible for producing a volatile gaseous hormone called ethylene.

It is this compound produced by the fruit that causes ripening. And since ethylene is a gas released into the air, a single ripe fruit can speed up the ripening of others as well if they are stored in the same bag.

Delayed ripening technologies basically involve `silencing' the two genes, so that the fruit does not synthesise ethylene, which triggers ripening.

"What I do is to silence the ACC synthase and ACC oxidase genes for a particular period, say from the point where the fruit is harvested in a green stage to its being transported to a warehouse. Once the fruit is close to the supermarket, it is sprayed with an ethylene-releasing compound to induce ripening," Dr Mattoo said.

There are many such ethylene-releasing substances, including ethaphon.

"You can even burn kerosene, which releases volatile gases, one of which constitutes ethylene."

As for the methods of gene silencing, the most established one is `antisense RNA technology', which involves genetically engineering a mirror image copy (antisense) of the ACC synthase or ACC oxidase gene into the fruit.

In the normal gene sequence, the ACC gene produces the enzyme through a

`messenger' RNA. In the antisense technology, a gene in reverse orientation is inserted in the plant.

"When the gene is in reverse orientation and is expressed so in the plant, it produces the messenger RNA also in a reverse orientation. The attraction of the two mirror image RNAs creates a complex, which gets degraded by ribonuclease enzymes. As a result, the plant ends up producing neither the reverse ACC enzyme nor the normal, forward version already present in it."

According to him, while knowledge regarding the two ACC genes and the ethylene signalling pathway was mainly a product of the 1980s, it took about 10 years to genetically manipulate and produce the first slow-ripening genetically engineered tomatoes such as `Flavor Savor' and `Endless Summer'.

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