Some seeds are treated, it usually says that on the package. Some seeds do also list the country of origin. I haven't gotten anything from China yet, but it is actually a good idea to have the country of origin. I do have to think twice about getting seed grown out in Holland or France. Mainly because the climates are so different from my own that the plants may just not do well.
There is also the issue of seed borne diseases. Downy mildew entered the US through Florida from contaminated seed imported from France I think.
I have some seeds from China, Korea, and Thailand. They have been fine. It is just hard since except for the name everything on the package is more or less in Chinese or Korean. Sometimes there is an English label pasted on to the package. Most of the foreign seeds are also labeled for export. I suppose they have different standards to comply with for export vs local distribution.
Saving seed is a great idea, locally grown seeds are likely to do well in your area. However, it does not eliminate the risk of seed borne disease. There are a few ways seeds can be treated but there is no way I know of to tell an infected seed from a good one.
Try to get certified disease free seed if you have had a problem. They will cost more.
If you save seeds, only save them from disease free plants. Dry and store them properly.
Some seed borne diseases of crucifers like black rot will contaminate the soil for years.
Some seeds are sold pretreated and usually dyed pink or green as a warning that they are not edible. They are usually dusted with captan to reduce seed rots. It is not organic, but not a bad thing either as it does protect the seed.
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Happy gardening in Hawaii. Gardens are where people grow.