Abstract

Host resistance would be a valuable defense against the sting nematode, Belonolaimus longicaudatus Rau, a pathogen of many crops including turfgrass.  Sting nematode damage and host suitability were compared among diploid and polyploid Stenotaphrum genotypes.  A time-course experiment compared diploid (2n = 18) 'FX-313' and polyploid (2n = 30) 'FX-10' St. Augustinegrasses [Stenotaphrum secundatum (Walter) Kuntze] genotypes, planted in pots with 250 mL Margate fine sand (siliceous, hyperthermic Mollic Psammaquent).  Nematode numbers were determined 42, 84, 126, 168, and 210 d after inoculating with 50 sting nematodes per pot.  Root and shoot dry weights and transpiration rate were compared with uninoculated pots of each grass.   Sting nematode numbers increased more rapidly on FX-313 than on FX-10, reaching a maximum 2580 nematodes (adults plus juveniles) per pot on FX- 313, 84 d after inoculation, compared with 380 nematodes per pot of FX-10.  Root damage by sting nematodes was severe in FX-313 but was minor in FX-10.  Sting nematode numbers and root dry weight of inoculated FX-313 were essentially unchanging from 84 to 210 d after inoculation, which suggested possible nematode suppression due to nematode injury of roots.   Transpiration rate, a nondestructive indicator of nematode effect, was reduced in inoculated FX-313, compared with uninoculated controls, throughout 84 to 168 d after inoculation, while FX-10 transpiration rate was not affected. While FX-313 was susceptible to the sting nematode, FX-10 was resistant through a mechanism of antibiosis.  We subjected four polyploid and four diploid Stenotaphrum genotypes to the same procedure, but harvested 128 or 129 d after inoculation.  Nematode numbers differed (P < 0.001) among genotypes, ranging from 980 per pot of FX-313 to 140 per pot of FX-10.  Root dry weight of diploids was reduced 33% due to nematodes but polyploids showed no effect.  Some good hosts such as pembagrass [S. dimidiatum (L.) Brongn.] 'FL-2195' showed little or no damage, thus may represent resistance through a tolerance mechanism.