You can try out Arabidopsis, a fast growing weed but which requires long days in order to flower. Otherwise tomato is a day neutral plant but which requires about 60 days from seed to seed. One reason I listed these two is because they are very well documented.
Another 'weed' that you can try is Ipomea, morning glory. It flowers readily indoors and produces seed.
Naz

The hybridization cycle requires growing plants from seed to full flower, pollinating, allowing the seed to ripen, sowing the new borne seeds and growing all of THEM to adulthood. 30 days? I don't think so. This person posted this question on some other forums...we think it's a science fair project started too late.

you can try hybrid of Custard Apple and Guava.

Here is a link that might be useful: http://c.1asphost.com/Sanganagouda/forum/