First Report of Xylella fastidiosa in Peach in New Mexico.

Abstract

Xylella fastidiosa is a gram-negative bacterium that causes disease in a wide variety of plants such as grapes, citrus trees, oleanders, and elm and coffee trees. This bacterium is xylem limited and causes disease symptoms such as leaf scorch, stunting of plant growth, branch dieback, and fruit loss. The presence of X. fastidiosa was previously reported in New Mexico where it was found to be infecting chitalpa plants and grapevines (3). In the summer of 2010, peach (Prunus persica (L.) Batsch) trees from two locations in northern New Mexico exhibited leaf deformity and stunting, dark green venation, slight mottling, and branch dieback. Preliminary viral diagnostic screening was performed by Agdia (Elkhart, IN) on one symptomatic tree and it was negative for all viruses tested. Three trees from two different orchards tested positive for X. fastidiosa by ELISA and PCR analysis using X. fastidiosa-specific primer sets HL (1) and RST (2). Bacterial colonies were also cultured from these samples onto periwinkle wilt media. Eight colonies obtained from these three plants tested PCR positive using the X. fastidiosa-specific primers. The 16S ribosomal and 16S-23S rRNA internal transcribed spacer (ITS) region (557 nucleotides) (GenBank Accession No. HQ292776) along with the gyrase region (400 nucleotides) (GenBank Accession No. HQ292777) was amplified from the peach total DNA samples and the bacterial colonies. Sequencing analysis of these regions indicate that the X. fastidiosa found in peach is 100% similar to other X. fastidiosa multiplex isolates including isolates from peach, pecan, sycamore, and plum trees and 99% similar to the X. fastidiosa isolates previously found in New Mexico. Further analysis of the 16S ribosomal and 16S-23S rRNA ITS sequences with maximum likelihood phylogenetic analysis using Paup also groups the peach isolates into the X. fastidiosa multiplex subspecies. The gyrase sequence could not be used to differentiate the peach isolates into a subspecies grouping because of the lack of variability within the sequence. This X. fastidiosa multiplex subspecies could possibly be a threat to the New Mexico pecan industry since pecan infecting X. fastidiosa isolates belong to the same bacterial subspecies. It is not known if X. fastidiosa subspecies multiplex isolates from peach are capable of infecting pecans but they are closely genetically related. It is interesting to note that the isolates from peach are different than previously described X. fastidiosa isolates in New Mexico that were infecting chitalpa and grapes (3). X. fastidiosa has previously been described in peach; the disease is called "phony peach". The peach trees exhibited stunting and shortened internodes as reported for "phony peach". They also exhibited slight mottling and branch dieback that may be due to the environment in New Mexico or perhaps they are also exhibiting mineral deficiency symptoms in association with the X. fastidiosa disease. To our knowledge, this is the first report of X. fastidiosa in peach in New Mexico.