Disscussion

Disscussion Transgenic papaya resistant to papaya ringspot virus (PRSV) line B/123 that showed high PRSV resistant level was test for biosafety assessment under screenhouse condition in Kasetsart university, Kamphaeng Saen Campus during march 2006-december 2007. Morphological characteristics were measured in order to test the effect of transgene on plant morphology including plant character, fruit characters and reproductive characters. Moreover, the influence of transgenic papaya on environment under screenhouse along with horizontal gene transferred to soil microbe and following rotation crops were performed. From our experiments showed that plant morphology of PRSV resistant transgenic papaya had so much similarity to non-transgenic. The day at first flowering and the first fruit set was also the same. Comparing to nontransgenic papaya, fruit quality of transgenic papaya included fruit number, fresh weight, flesh thickness seed number especially length and diameter was the same which made shape of fruit becoming in cylindrical shape which may mean achieving the commercial need. From our results there was no significant difference between transgenic and non-transgenic morphology and quality of papaya fruits. We could be assume that insertion of foreign gene did not affect on plant morphology and fruit quality the same as reported by Popenoe, 1974. Furthermore, we can conclude that transgenic and non-transgenic papaya was substantially equivalent. In this study, we also investigated papaya reproductive characteristic especially in pollen. Because of pollen is plant reproductive which is the most important vector of gene flow, biosafety assessment regarding pollen-mediated gene flow is become extremely important issue for future release of transgenic plant. Pollen viability, germinability and longevity are the most critical factors to be considered in biosafety assessment (Shivanna et al,1991). The result obtained indicated that there is no significant difference in reproductive characteristics including pollen size, pollen grain number which had been confirmed by Fitch et al. (1992); Paull et al. (1999) and Yasar and Donald (2003). Therefore, introduced gene had no effect on reproductive characters along with there is no evidence of harmful critical fitness of pollen viability comparing to non-transgenic papaya pollen . Through the biosafety assessment, influences of growing transgenic papaya on the environment were tested comparing to non-transgenic papaya planting. Although the effects of transgenic plants and their products on soil microbial populations and following rotation crop have become a biosafety concern, investigated whether transgenic papaya cause negative effect on the rhizospheric microbial populations and rotation crop must be evaluated. The results obtained showed that there

is no significant difference in soil microbial populations and cucumber characteristic which is rotation crop grown following transgenic papaya as well as reported by Donegan et al. (1997); Siciliano and Germida (1999); Griffiths et al. (2000) and Wu et al. (2004). It is clear that transgenic papaya and their products do not affect the microbial communities and the morphology of following cucumber plants. Horizontal gene is also important problem because the most public concern is transgenes could be transfer from transgenic plants to soil microorganisms and resulting in genotypic changes and interfering natural processes and displacing natural populations (Bertolla and Simonet 1999; Callaghan and Glare 2001; de Vries et al. 2001) which could be harmful to human health or cause undesirable environmental effects. From our results, horizontal gene transfer through soil microbes are not detected as reported by Schluter et al. 1995; Nielsen et al. 1997; Gebhard and Smalla 1999; Tepfer et al. 2003; adosa et al. 2004 and Heineman and Traavik 2004. It could be indicate that introduced gene including 35S promoter, PRSV-CP and antibiotic resistance genes especially nptII in our construct were not transferred from transgenic papaya to microorganisms as well as reported by Smalla et al. 1994 and Badosa et al. 2004. Moreover, horizontal gene transfer from transgenic papaya to rotation crop in this case is cucumber plants were also evaluated. From the result, horizontal gene transfer could not detect in any part of cucumber (leaf, flower, fruit and root). It could be conclude that rotation crops followed the growing of transgenic papaya are unaffected on gene transfer. Honey bee (Apis mellifera) is important insect pollinators in papaya plants. The major protein source for honey is come from pollen. In order to investigate the effect of transgenic papaya pollen, pollen source from transgenic papaya was fed to honey bee larvae comparing to nontransgenic pollen. The results showed no negative effect from transgenic papaya pollen could be detected on biological life table and size of honey bee since egg stage till fully adult the same as reported by Stokstad E. (2007); Latsch G. (2007) and McDonald J. (2007). From the results could be indicated that the insertion of PRSV-CP, nptII along with 35S promoter gene has no influence on honey bee. Although transgenic papaya we are investigated displayed no significant difference from those of non-transgenic, the further study must be investigated especially in the field trial level to confirm the result. For our experiment, the number of the replications was quite small because we did the experiment in screenhouse condition. Thus, that limited, the next experiment should be used more replications or performed in more than one screenhouse. The information obtained from our experiment could be answered the public concern about the biosafety of transgenic papaya along with could be useful for other transgenic plants that must be evaluated in the closed containment level.