Tobacco flowers falling off? - Flowers fall off before setting seed (Mar/11/2010 )

Hi, I'm using N. tabacum cv. Petit Havana and I want to get seed from them. I've done this loads of times before without problems but now I'm stuck.

My problem is that the flowers keep falling off while still mature. I've even tried hand pollinating the flowers to make sure this wasn't the problem but those few that last long enough to set seed are falling off as immature capsules. Any insights as to why this might happen?

Thanks!

did you change any conditions? e.g. light, nutrient source, watering?
when i grew up maize the number of kernels was significantly different if i grew it during autumn - winter than spring - summer.

It is looking to be you are missing something big that is not in front of you...have you changed any climate condition like weather, lighting, temperature or seeds etc ? Might be there some problem with water (softens or hardens water ).
irrigation systems design

I actually discovered that my plants were stressed and that's why they were dropping their flowers. The lights were not set correctly and were much too intense. I started again with fresh plants with the correct light setting and I have had no problems since.