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Moderated conference on GMOs in the pipeline, hosted by the FAO Biotechnology Forum in 2012

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Wed, 21 Nov 2012 17:51:51 +0100
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This is from C Kameswara Rao again, responding to Message 44 from Neha Saigal with a request for references on sexual incompatibility among varieties of brinjal. Besides published literature, my familiarity with pollination and reproductive behavior of species of Solanum comes from three of my co-researchers who worked on inter-specific hybridization in the genus at the Andhra University a long time ago.

The anthers (pollen sacs) in potato, tomato and brinjal are tubes with a terminal pore (characteristic of the genus Solanum) through which the rather sticky pollen cannot easily come out and also cannot be easily air borne. In tomato, the pollinators (bumble bees) hang on to the anther column and 'sonicate' by a very rapid vibratory movement of the wings to force out a small quantity of pollen. In potato, tomato and brinjal, insects can take the nectar without touching the anther tips or the stigmas and so insect visitation is not an evidence of pollination and mere pollination is not an evidence for hybridization. This fact would certainly be appreciated by those who know the floral structure of brinjal and its pollination behavior and not those who simply circulate popular misconceptions.  

On experimental hybridization among species of Solanum supposedly related to brinjal, Rao and Rao (1984) found the chances for fertile F1 progeny were extremely low and fertile F2 progeny was not obtained. When experimental hybridization was difficult, the chances for natural hybridization are far less. There is no evidence to show that transgenes enhance sexual promiscuity among related varieties and species.

A small quantum of cross-pollination may occur even in the most rampantly self-pollinated crops. Cross-pollination can be of concern only when its incidence results in hybrid seed (F1) and then only if fertile F2 population results from the F1 seed. Even this is of no consequence if there was no selection pressure for the new gene(s) to be fixed in the population, which would require at least five or six generations. It is only the scientists who know the species and those who work with the crop understand its reproductive behavior but not even those in other areas of biology. Pollen flow data generated during Bt brinjal evaluation and most literature that is available indicate that brinjal is over 90 per cent self-pollinated, outcrossing was less than 2.7 per cent and pollen migration distance is about 20 meters (see Chaudhary and Gaur, 2009 for details). 

Cultivated brinjal does not run wild and no appreciable volunteer or feral populations are known. Farmers are quick to detect changes in crop features and qualities and have grown for decades different varieties of brinjal in neighbouring fields without ever complaining that the varieties were not breeding true. The fact that there is a large number of cultivars of brinjal is in itself an evidence that the quantum of cross-breeding in brinjal need not be a matter of concern.  

No crop variety is successful outside the cultivated field where it is heavily pampered, with irrigation, fertilizers and crop protection chemicals. Without such protection, non-Bt brinjal plants and hybrids would rapidly succumb to pests and diseases. What would happen if the Bt gene in Bt brinjal gets into a non-Bt brinjal variety? A new Bt brinjal variety without effort or expense.  

Professor C Kameswara Rao, 
Executive Secretary, 
Foundation for Biotechnology Awareness and Education, 
No 1, Gupta's Layout, 
Southend Road, 
Bangalore 560004, 
India  
Mobile 91-9845145777.
e-mail: pbtkrao (at) gmail.com 

References:
- Choudhary, B. and Gaur, K. 2009. The development and regulation of Bt brinjal in India. ISAAA Brief No. 38. ISAAA, Ithaca, NY.
- Rao, S.V. and B.G.S.  Rao. 1984. Studies on the crossability relationships of some spinous Solanums.  Theoretical and Applied Genetics, 67:419-426.

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