What is the fine-grained topic of the following text: Five types of transgenic flax that were generated to improve fiber quality and resistance to pathogens, through increased levels of either phenylpropanoids W92.40, glycosyltransferase GT4, GT5, or PR2 beta-1,3-glucanase B14 or produce polyhydroxybutyrate M50, were used. Only return the topic.
Improvement of flax fiber quality and pathogen resistance through transgenic modification.