Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/1997
Publication Date: N/A
Interpretive Summary: Yellow vine of cucurbits has caused millions of dollars losses to cantaloupe and watermelon growers in Texas and Oklahoma. The disease was first observed in 1991 and is most severe on early planted melons. Recently, the cause of yellow vine was determined to be caused by a bacteriumlike organism and suspected of being transmitted by an insect. Because the phloem-limited bacteriumlike organism cannot be cultured, othe means of characterization and detection was persued. A primer pair, based on nucleotide sequences, was designed to amplify the DNA of the bacterium. Using polymerase chain reaction (PCR), the designed yellow vine primers amplfied DNA from symptomatic plants but not asymptomatic plants. This provides a tool to identify the insect vector, determine time of infection, and identify the alternate host which is necessary to develop a disease control strategy.
Technical Abstract: Diagnosis of yellow vine in cucurbits, an important disease in the south central United States, relies on external symptom appearance, phloem discoloration, and the presence of bacteriumlike organisms (BLOs) in phloem. Polymerase chain reaction (PCR) amplification of BLO nucleotide sequences was explored as a means to improve diagnostic techniques. A primer pair based on sequences of the citrus-greening BLO amplified a 0.15 kbp fragment from the DNA of symptomatic plants, but not from that of asymptomatic plants. Its nucleotide sequence suggested that the DNA amplified was of prokaryotic origin. A primer pair designed to amplify non-specific procaryotic 16S rDNA amplified a 1.5 kbp DNA fragment in both the symptomatic and asymptomatic plants. The 1.5 kbp fragment from the asymptomatic plants corresponded to chloroplast 16S rDNA and the band from the symptomatic plants was composed of 16S rDNAs from both chloroplasts and da prokaryote. The nucleotide sequence of th prokaryotic DNA was determine and used to design three primers (YV1, YV2 and YV3). Fragments of 0.64 and 1.43 kbp were amplified with YV1/YV2, and primers YV1/YV3, respectively, from symptomatic plants. Neither primer set yielded fragments from asymptomatic plants, bacteria, or selected soil-borne fungal pathogens of cucurbits. Phylogenetc analysis indicated that the prokaryote is a gamm-3 proteobacterium. The consistent association of the 0.64 and 1.43 kbp fragment with symptomatic plants suggests that the gamma-3 proteobacterium may be the causal agent of yellow vine of cantaloupe, squash, and watermelon.