Chino del tomate virus: Relationships to other begomoviruses and identification of A-component variants that affect symptom expression

Phylogenetic and distance analyses place Chino del tomate vines (CdTV) in t he New World clade of begomoviruses and indicate that CdTV and Tomato leaf crumple virus (TLCrV) are closely related strains of the same virus. One cl oned CdTV A component (pCdTV-H6), when inoculated to tomato with the B comp onent (pCdTV-B52), produced mild symptoms and low DNA titers. Another clone d CdTV A component (pCdTV-H8), when coinoculated to tomato with the B compo nent, produced moderate leaf curling and veinal chlorosis similar to that o f TLCrV. Coinoculation of both CdTV A components and the B component to tom ato produced wild-type chino del tomate (CdT) disease symptoms consisting o f severe leaf curling, veinal and interveinal chlorosis, and stunting. The two CdTV A components were nearly identical, except at nucleotide positions 1,722 and 2,324. The polymorphism at nucleotide 1,722 resulted in a change at Rep amino acid 261. The second polymorphism at nucleotide 2,324 resulte d in changes at Rep amino acid 60 and AC4 amino acid 10. Two chimeric A com ponents constructed by reciprocal exchange of a fragment bearing the polymo rphic site at nucleotide 1,722 were evaluated for symptom phenotype. One ch imeric A component (pCdTV-H86) produced wild-type CdT symptoms when coinocu lated to tomato with the B component. The reciprocal chimeric A component ( pCdTV-H68), when coinoculated to tomato with the B component, also produced severe leaf curling, veinal chlorosis, and stunting. However, pCdTV-H68 in duced less obvious interveinal chlorosis than wild-type or pCdTV-H86. Exami nation of A component genotypes recovered from tomato coinoculated with pCd TV-H6 and pCdTV-H8 indicated that recombination occurred to produce a genot ype identical to pCdTV-H86. These results indicate that subtle genotypic va riation has significant effects on symptom expression and may explain pheno typic differences observed among isolates and cloned DNAs of CdTV and TLCrV .