Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 11, 2011
Publication Date: November 1, 2011
Citation: Burelle, N.K., Rosskopf, E.N., Holzinger, J. 2011. First report of the root-knot nematode Meloidogyne arenaria on cheeseweed mallow (Malva parviflora) in the United States. Plant Disease. 96:2-3. Interpretive Summary: Weed samples were collected from field trials conducted in Florida to evaluate chemical alternatives to methyl bromide for cut flower production. The root-knot nematode Meloidogyne arenaria was isolated from cheeseweed mallow (Malva parviflora L.), which not previously reported as a host for this species of nematode. The nematodes were isolated and cultured on in the greenhouse and reinoculated onto mallow plants to complete Koch's postulates. Two methods of nematode identification were then performed. The first method identified the isolate as Meloidogyne arenaria based on its esterase phenotype using the PhastSystem,™ (GE Healthcare). The second method involved DNA extraction from mature female nematodes collected from mallow roots. DNA was isolated using the PowerSoil®DNA Isolation Kit (MO BIO Laboratories, Inc.). Identification of M. arenaria was confirmed using species specific primers. The importance of weeds as hosts for plant parasitic nematodes cannot be over emphasized. As growers, particularly in Florida and California, continue to lose the use of broad-spectrum fumigants, the ability of nematodes to reproduce on weed that survive in and around production fields will become increasingly problematic.
Technical Abstract: During a 2010 field trial examining alternatives to methyl bromide soil fumigation for the production of field-grown cut flowers, weeds were collected for identification and evaluated for their potential as hosts for plant pathogenic nematodes. In one cut flower field, located in Martin County, FL, six cheeseweed mallow (Malva parviflora L.) plants were collected which had root-galling typical of infection by root-knot nematode. Field collected plants were used for species identification of the weed and maintained in the greenhouse for seed production. Several gravid female nematodes were extracted from field collected mallow roots and individually identified as Meloidogyne arenaria based on their esterase phenotype (PhastSystem,™ GE Healthcare). A single egg mass was then extracted from the field collected mallow roots and inoculated onto a tomato plant (Solanum lycopersicum, ‘Rutgers’) grown in steamed builders sand in the greenhouse. The single egg mass culture was amplified for 8 weeks, until galling was sufficient to produce adequate nematode inoculum to complete Koch’s postulates on the original mallow host. Ten mallow plants were inoculated with single egg masses originally isolated from mallow and increased on tomato. Ten additional plants were maintained in the greenhouse as uninoculated controls. Inoculated and control mallow plants were grown in the greenhouse for 8 weeks, after which roots were evaluated for galling, and root-knot nematode J2 were extracted from roots and soil and counted. All inoculated plants produced galled roots and control plants did not. Gravid females were extracted from mallow roots and identified as M. arenaria based on esterase phenotype as previously described. Ten gravid females for each DNA extraction were collected from mallow roots and DNA was isolated using the PowerSoil®DNA Isolation Kit (MO BIO Laboratories, Inc.). Identification of M. arenaria was confirmed using species specific primers F5’-TCGAGGGCATCTAATAAAGG-3’ and R5’-GGGCTGAATAATCAAAGGAA-3’ and F5’-TCGGCGATAGAGGTAAATGAC-3’ AND R5’-TCGGCGATAGACACTACAACT-3’, which produced single amplicon bands of the expected size of 420 and 950 bp respectively. This weed species has been reported as a host for M. javanica in Algeria and as an experimental host in Egypt, but this report, to the best of our knowledge, constitutes the first documentation of M. parviflora as a natural host of M. arenaria. The importance of weeds as hosts for plant parasitic nematodes cannot be over emphasized. As growers, particularly in Florida and California, continue to lose tools for broad-spectrum pest control, the ability of nematodes to reproduce on weed escapes will become increasingly problematic.