Biological Characterization of Different Citrus Tristeza Virus Isolates in Spain

Abstract

Sixty citrus tristeza virus (CTV) isolates representative of most Spanish citrus areas were collected and initially inoculated on Mexican lime and Duncan grapefruit. Ten of them were selected on the basis of origin, host and symptoms on those indicator plants. Selected isolates were separated from other virus and virus-like pathogens by transmission with Aphis gossypii from graft-inoculated sweet orange to Mexican lime seedlings. Purified isolates were inoculated into ten seedlings each of Duncan grapefruit and sour orange, 20 seedlings of sweet orange cvs. Pineapple and Comuna and 20 budlings of Washington navel orange grafted on sour orange. Inoculated Duncan grapefruit and sour orange seedlings were incubated in a temperature-controlled greenhouse maintained at 18º-26ºC. Sweet orange seedlings and navel orange budlings were split in two groups of ten plants each after inoculation. One of them was incubated under greenhouse conditions (18º-26ºC) and the other was kept in an insect-proof screenhouse. Vein clearing in young flushes and stem pitting intensity inoculation were evaluated one year after by three observers and their scores averaged. The following conclusions were drawn: 1) different pathotypes were found among the Spanish CTV isolates characterized; 2) none of the 60 CTV isolates initially inoculated on grapefruit gave a seedling yellows reaction; 3) none of the isolates studied induced stem pitting on Duncan grapefruit or sweet orange cvs. Pineapple or Comuna; 4) some differences in symptom expression were observed between plants incubated under greenhouse and screenhouse conditions.