Citrus cultivars and relatives, even within the
same group, tend to exhibit variable reactions to CTV
infection. Limes, grapefruit, and Alemow (Citrus
macrophylla) are highly susceptible to CTV-SP.
Sweet oranges and rough lemon are tolerant to many
CTV isolates, but show strong stem pitting when
infected by CTV-SP. Mandarins are considered
tolerant, but may show stem pitting under some
conditions. Trifoliate orange and trifoliate hybrids
carrying the CTV-resistance gene are resistant to
CTV infection and CTV-SP, but hybrids without this
gene may show strong pitting. Some pummelos show
selective resistance specific to some severe CTV-SP
isolates, but are highly susceptible to others. It
appears that several independent virus factors cause
stem pitting in different hosts. Tristeza-induced stem
pitting and decline are also apparently under separate
genetic control. Decline isolates often do not cause
stem pitting and some CTV-SP isolates do not cause
decline or seedling yellows (another symptom
associated with decline isolates of CTV).