Effects of Infection by Belonolaimus longicaudatus on Rooting Dynamics among St. Augustinegrass and Bermudagrass Genotypes.

Understanding rooting dynamics using the minirhizotron technique is useful for cultivar selection and to quantify nematode damage to roots. A 2-yr microplot study including five bermudagrass ('Tifway', Belonolaimus longicaudatus susceptible; two commercial cultivars [TifSport and Celebration] and two genotypes ['BA132' and 'PI 291590'], which have been reported to be tolerant to B. longicaudatus) and two St. Augustinegrass ('FX 313', susceptible, and 'Floratam' that was reported as tolerant to B. longicaudatus) genotypes in a 5 x 2 and 2 x 2 factorial design with four replications, respectively, was initiated in 2012. Two treatments included were uninoculated and B. longicaudatus inoculated. In situ root images were captured each month using a minirhizotron camera system from April to September of 2013 and 2014. Mixed models analysis and comparison of least squares means indicated significant differences in root parameters studied across the genotypes and soil depths of both grass species. 'Celebration', 'TifSport' and 'PI 291590' bermudagrass, and 'Floratam' St. Augustinegrass had significantly different root parameters compared to the corresponding susceptible genotypes (P ≤ 0.05). Only 'TifSport' had no significant root loss when infested with B. longicaudatus compared to non-infested. 'Celebration' and 'PI 291590' had significant root loss but retained significantly greater root densities than 'Tifway' in B. longicaudatus-infested conditions (P ≤ 0.05). Root lengths were greater at the 0 to 5 cm depth followed by 5 to 10 and 10 to 15 cm of vertical soil depth for both grass species (P ≤ 0.05). 'Celebration', 'TifSport', and 'PI 291590' had better root vigor against B. longicaudatus compared to Tifway.

Zoysiagrass genotype responses to Sphenophorus venatus vestitus (Coleoptera: Curculionidae).

The hunting billbug, Sphenophorus venatus vestitus Chittenden, is a pest that damages stems, rhizomes, and roots of zoysiagrass through a combination of adult and larval feeding. Management of this pest is difficult because it has multiple, overlapping generations in the southern United States, and symptoms of infestations are often misdiagnosed and inappropriately treated as drought stress or disease. Experiments were conducted in a greenhouse where 18 zoysiagrass cultivars were potted and infested with S. v. vestitus adults to examine the response of zoysiagrass genotypes to S. v. vestitus feeding damage. Results showed that zoysiagrass species and cultivars differed in susceptibility to S. v. vestitus, indicating that variable tolerance may exist in these turfgrasses for improvement through breeding. In general, Zoysia japonica Steudel was more susceptible to S. v. vestitus feeding damage and supported more S. v. vestitus than Zoysia matrella (L.) Merrill. Among the Z. japonica cultivars,'Belair' and'Zenith' had less desirable agronomic traits and incurred greater feeding damage than other cultivars more tolerant to billbug damage. With Z. matrella, 'Diamond' and 'Pristine Flora' displayed superior agronomic traits and had the least feeding damage and lowest infestations of billbug immatures and were therefore considered the most tolerant or resistant Z. matrella cultivars tested. Results indicate that stem diameter may be an important factor for adult feeding and oviposition site selection, which might explain the different responses between Zoysia spp. to S. v. vestitus damage.

Field Responses of Bermudagrass and Seashore paspalum Cultivars to Sting and Spiral Nematodes.

Belonolaimus longicaudatus and Helicotylenchus spp. are damaging nematode species on bermudagrass (Cynodon spp.) and seashore paspalum (Paspalum vaginatum) in sandy soils of the southeastern United States. Eight bermudagrass and three seashore paspalum cultivars were tested for responses to both nematode species in field plots for two years in Florida. Soil samples were taken every three months and nematode population densities in soil were quantified. Turfgrass aboveground health was evaluated throughout the growing season. Results showed that all bermudagrass cultivars, except TifSport, were good hosts for B. longicaudatus, and all seashore paspalum cultivars were good hosts for H. pseudorobustus. Overall, bermudagrass was a better host for B. longicaudatus while seashore paspalum was a better host for H. pseudorobustus. TifSport bermudagrass and SeaDwarf seashore paspalum cultivars supported the lowest population densities of B. longicaudatus. Seashore paspalum had a higher percent green cover than bermudagrass in the nematode-infested field. Nematode intolerant cultivars were identified.

Sting nematodes modify metabolomic profiles of host plants.

Plant-parasitic nematodes are devastating pathogens of many important agricultural crops. They have been successful in large part due to their ability to modify host plant metabolomes to their benefit. Both root-knot and cyst nematodes are endoparasites that have co-evolved to modify host plants to create sophisticated feeding cells and suppress plant defenses. In contrast, the ability of migratory ectoparasitic nematodes to modify host plants is unknown. Based on global metabolomic profiling of sting nematodes in African bermudagrass, ectoparasites can modify the global metabolome of host plants. Specifically, sting nematodes suppress amino acids in susceptible cultivars. Upregulation of compounds linked to plant defense have negative impacts on sting nematode population densities. Pipecolic acid, linked to systemic acquired resistance induction, seems to play a large role in protecting tolerant cultivars from sting nematode feeding and could be targeted in breeding programs.