RESUMO
Different strains of Xylella fastidiosa cause a variety of significant disease problems in agricultural and ornamental plants, including Pierce's disease in grapes, oleander leaf scorch, pecan bacterial leaf scorch, and alfalfa dwarf disease. X. fastidiosa has never been reported in New Mexico but is known to exist in surrounding states (California, Arizona, and Texas). During the summer of 2006, several chitalpa (Chitalpa tashkinensis) hybrid trees with leaf scorch symptoms and branch die back were observed in Las Cruces, NM and they tested positive for X. fastidiosa by ELISA. Additional samples from these plants and others were analyzed by ELISA, PCR (2), and cultured on XfD2 medium (1). Known positive and negative oleander samples from Arizona were included as controls. Fifteen of thirty tested chitalpa were PCR and ELISA positive, indicating that they were infected with X. fastidiosa. Bacterial colonies that were PCR positive were also recovered from 10 of the XF positive samples that were plated. DNA sequences of PCR products amplified from chitalpa and isolated bacterial colonies (GenBank Accession Nos. EF109936 and EF109937) were identical to each other, 97% similar to X. fastidiosa strain JB-USNA, and 96% similar to the Temecula 1 strain. Independent ELISA testing (Barry Hill, California Department Food and Agriculture, Sacramento, CA) confirmed our ELISA and PCR results. On the basis of these results, we conclude that X. fastidiosa is present in New Mexico and that the common landscape ornamental chitalpa is a host for X. fastidiosa. Additional work is required to determine if X. fastidiosa is pathogenic to chitalpa and to examine the relevance of this potential X. fastidiosa reservoir to agricultural production in New Mexico and other areas where chitalpa is grown. References: (1) R. P. P. Almeida et al. Curr. Microbiol. 48:368, 2004. (2) M. R. Pooler et al. Lett. Appl. Microbiol. 25:123, 1997.
RESUMO
In 1998 to 1999, geminivirus-like symptoms were observed in whitefly-infested pumpkin, honeydew melon, and muskmelon in Arizona and Texas and in Coahuilla, Mexico (MX), respectively. Plants exhibited leaf curl and/or mottling, reminiscent of symptoms caused by Squash leaf curl virus (SLCV-WAZ) described from Arizona in 1981 (2). The isolate from Arizona pumpkin fields was experimentally transmitted to pumpkin seedlings by the "B type" of Bemisia tabaci (Genn.), and symptoms were indistinguishable from those observed in infected fields. Samples from AZ, MX, and TX were assessed for begomovirus presence by polymerase chain reaction (PCR) using degenerate primers that amplify a contiguous fragment containing the viral coat protein (Cp) gene and common region (CR) of the A component (CR-A) (~2,100 bp) and a fragment containing the CR of the B component (CR-B) (~1,100 bp). One to four isolates from each location were examined by PCR using both primer pairs, and at least three amplicons per isolate were cloned and their sequences determined. Alignment of viral Cp nucleotide (nt) sequences revealed that AZ [AF256199], MX, and TX field isolates shared 98.7 to 100% sequence identity, but were only 84.5 to 85.6% identical to the Cp gene of SLCV-extended (SLCV-E) [M38183] and SLCV-restricted (SLCV-R) (S. G. Lazarowitz, unpublished), respectively, suggesting a new, previously undescribed begomoviral species (3). Further, the Cp nt sequence of the three field isolates was 6 nt shorter than SLCV-E, SLCV-WAZ [AF256203], and SLCV-R Cp sequences. The CR-A [AF256200] and CR-B [AF256201] sequences (179 nt, each) of field isolates, including the theoretical Rep binding element, GGTGT, were 100% identical. Although the Rep binding site is identical among field isolates, SLCV-E, SLCV-R, and SLCV-WAZ, the field isolate CR sequence shared only 64.2, 67.5, and 66.9% overall identity with CR-A SLCV-E, SLCV-R [M63155], and SLCV-WAZ [AF256202], respectively. Prior to 1998 to 1999, SLCV-WAZ was the only New World begomovirus of cucurbits known to infect both melon (Cucumis) and pumpkin (Cucurbita) (1). Therefore, SLCV was initially suspected as the causal agent. However, here we provide evidence for a new, previously undescribed bipartite begomovirus of cucurbits in AZ, MX, and TX that is herein provisionally designated Cucurbit leaf curl virus (CuLCV). Prediction of its closest begomovirus relatives by Cp nt sequence and Rep binding site comparisons suggest that CuLCV is a new member of the SLCV lineage, also containing Bean calico mosaic virus, Cabbage leaf curl virus, SLCV-E, and Texas pepper virus-TAM. References: (1) J. K. Brown and M. R. Nelson. Phytopathology 74:1136, 1984. (2) J. K. Brown and M. R. Nelson. Ann. Appl. Biol. 115:243, 1986. (3) M. A. Mayo and C. R. Pringle. J. Gen. Virol. 97:649, 1998.