[Music] hi and welcome back to three science lessons cold okay by the end of this video you should be able to describe the causes and symptoms of infectious diseases in plants these are the viral disease tobacco mosaic virus and the fungal disease rolls black spot now we've already looked at a number of infectious diseases in humans but plants can also contract infectious diseases it's really important that you learn the specific details of these diseases as they could be asked in your exam we're going to start with tobacco mosaic virus which is also called tmv now DMVs a very widespread plant infection and it in fact a number of different plant species including tomatoes tmv causes the leaves to discolor in a mosaic pattern like this because of this discoloration the rate of photosynthesis is reduced and this means that the growth of the plant is also reduced okay the second plant disease we're going to look at is called rose black spot and this is caused by a fungus rose black spot causes the leaves to develop purple or black spots the leaves then often turn yellow and fall off now just like tmv rose black spot causes the rate of photosynthesis to fall and this reduces the rate of growth as we said rose black spots caused by a fungus and this can be spurred by water or by wind there were two ways to treat rose black spot firstly we can spray the plants with chemicals which kill fungi these are called fungicides the other way is to remove the infected leaves and then destroy them remember you'll find plenty of questions on infectious plant diseases in my vision workbook and you can get up I click on the link above okay so hopefully now you should be able to describe the causes and symptoms of infectious diseases in plants these are the viral disease tobacco mosaic virus and the fungal disease rose black spot [Music]