<Li> Pseudomonas spp . </Li> <Li> Pseudomonas syringae pv . tomato causes tomato plants to produce less fruit, and it "continues to adapt to the tomato by minimizing its recognition by the tomato immune system ." </Li> <P> Phytoplasma and Spiroplasma are genera of bacteria that lack cell walls and are related to the mycoplasmas, which are human pathogens . Together they are referred to as the mollicutes . They also tend to have smaller genomes than most other bacteria . They are normally transmitted by sap - sucking insects, being transferred into the plant's phloem where it reproduces . </P> <P> There are many types of plant virus, and some are even asymptomatic . Under normal circumstances, plant viruses cause only a loss of crop yield . Therefore, it is not economically viable to try to control them, the exception being when they infect perennial species, such as fruit trees . </P>

Shows some of plant diseases causative microorganisms and mode of transmission