Evaluation location: South Carolina, United States
All accessions of
Citrullus colocynthis and
Citrullus lanatus var.
citroides, and about 10% of
C. lanatus var.
lanatus (156) accessions from the U.S. Plant Introduction (PI) Citrullus germplasm collection were evaluated for resistance to root-knot nematode (
Meloidogyne arenaria race 1) in greenhouse tests.
Meloidogyne arenaria race 1 was cultured on 'Rutgers' tomato and 'Kentucky Wonder 191' pole bean in isolated soil benches in the greenhouse. Seeds of each accession were sown in the greenhouse in plastic growing trays and ten days later an aliquot containing approximately 2,500 eggs of
M. arenaria race 1 was pipetted into the soil surrounding each root system. Eight weeks after inoculation, the plants were severed at the crown and the roots were washed and immersed in a 15% solution of red food color to stain the egg masses. After rinsing gently under running tap water, they were evaluated for galling severity and egg mass production using a 1 to 9 scale.
View the disease assessment scale in an Excel Spreadsheet or as an HTML webpage.
The primary criterion for designating resistance and susceptibility of the accessions was the root gall severity index. Egg mass data was also presented because it provides additional information about the reaction of the accessions to Meloidogyne arenaria race 1. However, accessions were considered resistant only if both the root gall index and the egg mass index were <= 4.9. 'Charleston Gray', 'Crimson Sweet', and 'Dixie Lee' were included as susceptible check cultivars in all tests. Only one C. lanatus var. lanatus accession, PI 459074, could be classified as low resistance [root gall index (GI) = 4.9 and egg mass index (EMI) = 3.10]. All C. colocynthis accessions were highly susceptible (GI range = 8.5 to 9.0 and EMI range = 5.00 to 9.00). Twenty C. lanatus var. citroides accessions appeared moderately resistant with a GI = 3.1 to 4.0, but none were highly resistant.