First Report of Phytoplasmas Infecting Watercress in Hawaii

Abstract

Symptoms of leaf yellowing, reduced leaf size, and witches'-brooms have recently been observed affecting watercress (Nasturtium microphyllum Boen. × Rcbh.) in Hawaii. These symptoms are followed by the collapse of affected plants. This condition has led to 80 to 90% losses for one of the largest watercress farms on Oahu and is now affecting other watercress farms in the area. Nutritional deficiencies or toxicities, water salinity, and insect or mite feeding damage were investigated but could not be implicated in the etiology of this syndrome. Eighteen watercress plants with early yellowing or advanced symptoms and nine symptomless plants were analyzed for phytoplasma infection using polymerase chain reaction (PCR) assays with primer pairs P1/Tint or P1/P7 (4). Amplicons of the expected sizes were produced from all symptomatic plants, whereas no products were amplified from symptomless plants. Sequence analysis of the cloned PCR products confirmed their phytoplasma origin and indicated that the watercress was infected with a phytoplasma most similar to SAY (2), a severe strain of western aster yellows phytoplasma previously classified as a 16SrI-B group member (3). Leafhoppers collected from an affected watercress planting have been identified as the aster leafhopper (Macrosteles quadrilineatus Fbs.) This species is the most efficient vector of the aster yellows phytoplasma and had not been previously recorded in Hawaii. The only other phytoplasma disease known in Hawaii prior to this report is Dodonaea yellows (1), which affects one of the most common native plants (Dodonaea viscosa (L.) Jacq.) in dry upland forests on all the islands. Dodonaea yellows, however, has been attributed to an X-disease (16SrIII) group phytoplasma. The occurrence of an aster yellows group phytoplasma in watercress, a previously unrecorded host, and the presence of a very efficient vector, M. quadrilineatus, poses a serious threat to the production of other vegetable and floral crops in Hawaii. References: (1) W. Borth et al. Plant Dis. 79:1094, 1995. (2) C. Kuske and B. Kirkpatrick. Int. J. Syst. Bacteriol. 42:226, 1992. (3) I.-M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998. (4) C. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996.

Molecular data reveals California as the potential source of an invasive leafhopper species, Macrosteles sp. nr. severini, transmitting the aster yellows phytoplasma in Hawaii

“…The genus Macrosteles has a holarctic distribution and contains over 100 species, several of which cause severe agricultural damage, primarily through the transmission of the aster yellows phytoplasma. In 2001, Macrosteles leafhoppers were recorded on Oahu, Hawaii, where they have severely impacted the watercress (Nasturtium officinale L.) industry (Borth et al, 2002). These leafhoppers act as vectors for an asters yellows phytoplasma that causes necrosis, yellowing and occasionally witches' brooms in their agricultural hosts (Borth et al, 2002).…”

“…In 2001, Macrosteles leafhoppers were recorded on Oahu, Hawaii, where they have severely impacted the watercress (Nasturtium officinale L.) industry (Borth et al, 2002). These leafhoppers act as vectors for an asters yellows phytoplasma that causes necrosis, yellowing and occasionally witches' brooms in their agricultural hosts (Borth et al, 2002). The invasive species was initially identified as the aster leafhopper, Macrosteles quadrilineatus Forbes (formerly Macrosteles fascifrons Stå l) complex (Borth et al, 2002).…”

“…These leafhoppers act as vectors for an asters yellows phytoplasma that causes necrosis, yellowing and occasionally witches' brooms in their agricultural hosts (Borth et al, 2002). The invasive species was initially identified as the aster leafhopper, Macrosteles quadrilineatus Forbes (formerly Macrosteles fascifrons Stå l) complex (Borth et al, 2002). However, a revision identified it as Macrosteles sp.…”

Detection, characterisation and transmission by Macrosteles leafhoppers of watercress yellows phytoplasma in Hawaii

“…There are few diseases associated with this crop in Hawaii; the primary limitation on production has been the diamondback moth ( Plutella xylostella , Lepidoptera), whose larvae can consume large amounts of the leafy canopy if not controlled. Recently, watercress in Hawaii has been afflicted with a yellows disease with symptoms of leaf yellowing and crinkling, reduced leaf size and occasionally witches’ brooms (Borth et al , 2002). This disease is present in all the watercress farms on the island of Oahu but has not yet been found on any of the other Hawaiian Islands.…”

“…We used molecular approaches to test if phytoplasmas were associated with this watercress disease and also conducted transmission experiments to determine if this leafhopper found in large numbers on afflicted farms could be a vector of this possible aetiological agent. A preliminary report has been previously published (Borth et al , 2002).…”