Environment
Aphids are the main vector by which CTV is transmitted. Initially the United States only had the melon (cotton aphid) Aphis gossypii, spirea aphid Aphis spiraecola, and black citrus aphid Toxoptera aurantii. These aphids transmit the virus much less efficiently than the brown citrus aphid Toxoptera citricida. Toxoptera citricida had been found in East Asia and South America, and had slowly made its way up through Central America and the Caribbean Islands. By 1993 it had reached Cuba, and in 1995 it was found in Florida. The aphids require at least 30 to 60 minutes of feeding to acquire the virus, and remain viruliferous for at least 24 hours after. T. citricida is much more efficient than the other aphids, and it can transmit CTV strains causing severe stem pitting or decline that the other aphids cannot vector. Even though A. spiraecola is less efficient, it tends to have higher populations and thus can still transfer the virus fairly well. T. aurantii has been shown to only transmit certain strains of CTV. Of the three lesser efficient aphids, A. gossypii has a 78% transmission efficiency, while A. spiraecola and T. aurantii are between 0-6%. The main cultural practice that increases the severity of the CTV is when the citrus trees are grafted onto the sour orange rootstock. Using CTV infected budwood for grafting can transfer the CTV from the original tree to the new one.
Read more about this topic: Citrus Tristeza Virus
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