seed. The infection can persists for years inside the seed. Environment Unlike many viruses, there are no known insect vectors to spread the disease. Rather, BSMV relies on parent to offspring transmission. Temperature at which the infected plant is grown is critical to spreading and developing the disease. At higher temperatures, the symptoms are more severe. According to one study, when infected host plants were held at 7 °C, they took approximately 30 days to develop symptoms, and never were able to infect other potential hosts. However, at higher temperatures of 12-18 °C symptoms developed in 7–8 days and the virus was transmissible. However, it is still important to note that severity of symptoms don't always correlate with the amount of the virus present. Another found that the levels of virus present remained relatively constant over a range of 13 °C-25 °C and that the amount of virus present was related only to the age of the hosts and length of time that they were infected. Light intensity may also have an effect on the development of the disease symptoms. A study showed that heavily shaded infected plants showed little to no symptoms after 11 days when compared to non-shaded infected plants. A factor that affects the spread and severity of the virus is the species and variety of host, as some are more susceptible than others. For example, the barley variety CM67 is very susceptible. It has a much higher transmission rate than other varieties, and if symptoms are severe enough due to weather conditions, this variety can even be sterile. Another factor that affects the spread of the disease is the gametes bred to produce the offspring. One study found that about 10% of seeds produced from an infected harvest also contain the virus. One belief was that the virus could be spread to offspring by infected pollen grains, and because of this it was believed that it could potentially spread over long distances. However, an infected ovule is a more important factor for the spread of this disease. The disease is more likely to spread when an infected ovule produces progeny with infected pollen, with a 70% transmission rate. When an infected ovule is pollinated by an uninfected pollen there is only about a 66% transmission rate. In an uninfected ovule that is pollinated by infected pollen there is only about a 3% transmission rate to the