No it should not be difficult to get the seeds from transgenic rice.

Sometimes some transgenic plants can be sterile.

Proper irrigation and growth conditions of the plant are important for obtaing proper seeds.

Thanks alot for your reply, I think they are not sterile. it still will set seeds but will be only empty!!

I was thinking reducing nitrogen just before flowering time, and increase phosphorus?

You can expect a decline in seed setting in transgenic rice sometimes, as they are under selection pressure of antibiotics or due to hardening, hence the efficiency of seed setting may be reduced to a certain extent. Other minor add on variables could be the nature of transgene introduced and its location of integration into the genome.

I'm also trying to grow rice. while with WT plants I get at least few seeds (although it's not that much), with my mutants I got hardly few seeds. For example one mutant didn't produce any panicles the first time, but the next time (the same plant) it did, so it was rather because of the conditions and not because of the genotype.

I just asked a question about conditions to grow rice in general:

https://www.researchgate.net/post/How_to_grow_rice_and_how_to_make_it_to_make_some_seeds

Thanks Tomas, I am not sure. but my colleagues plants are perfectly fine with hundreds of seeds but they are all wildtypes, also, my wildtype is perfectly setting seeds now!