Departamento de Ingeniería Genética, Cinvestav-Unidad Irapuato, Apartado postal 629, Irapuato, Gto. Mexico
ILTAB Danforth Center, St. Louis, MO
R. De la
UBIPRO, ENEP-Iztacala, UNAM, Mexico
Whitefly-transmitted geminivirus diseases cause important losses in several horticultural crops in all areas in Mexico (1). Tomatillo is important in the Mexican diet since it is widely used to prepare many types of salsas and other dishes. As a result, tomatillo, also known as tomate verde (green tomato), is cultivated in 29 of 32 states in Mexico, with the main production areas located in the states of Morelos, Puebla, and Michoacán. Leaf samples of 105 tomatillo plants exhibiting yellowing, yellowing mosaic, leaf curl, bunchy top, and stunting were collected from the states of Puebla, Morelos, Estado de México, and Sinaloa. Symptomatic plants were associated with the presence of whiteflies in many fields and suggested a viral etiology. Total DNA extracted from symptomatic tomatillo plants was used as a template in a polymerase chain reaction (PCR)-based geminivirus detection procedure. MP16 and MP82 primers (2) were used to direct the amplification of a segment from the stem-loop structure in the intergenic region (IR) to a conserved region in the coat protein (CP) of begomoviruses (2). Sixty-nine percent (72/105) of the samples produced the expected PCR fragment (400 to 450 bp). Similar results were obtained with a dot-blot hybridization procedure using as a probe the component A of Pepper huasteco virus (PHV) under low stringency conditions. More than 50 PCR products were cloned and sequenced. Sequence analysis (nucleotide level for the IR; amino acid level for the CP) revealed that the tomatillo-infecting geminiviruses clustered into two main groups. The first group showed a high percent identity (average of 95.3% at the CP N terminus) to PHV, whereas the second showed a similarly high percent (average 93.8%) identity to Pepper golden mosaic virus (PepGMV, previously called Texas pepper geminivirus. Both PepGMV and PHV were found in all sampled areas. Although mixed infections (differentiated by the respective IR probes) of PHV and PepGMV were common (61%), single infections were also detected (PHV 27%; PepGMV 10%). The presence of begomoviruses in tomatillo crops has been previously reported (1); however, their identity as PHV and PepGMV was not confirmed.
References: (1) I. Torres-Pacheco et al. Phytopathology 86:1186, 1996. (2) P. Umaharan et al. Phytophatology 88:1262, 1998.