Secondary metabolites are major constituents of plant defense against herbivore attack. Relatively little is known about the cell type-specific formation and antiherbivore activities of secondary compounds in roots despite the substantial impact of root herbivory on plant performance and fitness. Here, we describe the constitutive formation of semivolatile diterpenes called rhizathalenes by the class I terpene synthase (TPS) 08 in roots of Arabidopsis thaliana. The primary enzymatic product of TPS08, rhizathalene A, which is produced from the substrate all-trans geranylgeranyl diphosphate, represents a so far unidentified class of tricyclic diterpene carbon skeletons with an unusual tricyclic spiro-hydrindane structure. Protein targeting and administration of stable isotope precursors indicate that rhizathalenes are biosynthesized in root leucoplasts. TPS08 expression is largely localized to the root stele, suggesting a centric and gradual release of its diterpene products into the peripheral root cell layers. We demonstrate that roots of Arabidopsis tps08 mutant plants, grown aeroponically and in potting substrate, are more susceptible to herbivory by the opportunistic root herbivore fungus gnat (Bradysia spp) and suffer substantial removal of peripheral tissue at larval feeding sites. Our work provides evidence for the in vivo role of semivolatile diterpene metabolites as local antifeedants in belowground direct defense against root-feeding insects.

Goosegrass [Eleusine indica (L.) Gaertn.] remains problematic for bermudagrass [Cynodon dactylon (L.) Pers.] turf managers due to the ineffective, selective control of mature plants with available POST herbicides and lack of sufficient residual activity from those herbicides to control seedling plants. Topramezone controls mature E. indica, but past efforts to suppress potential injury to bermudagrass turf have been inconsistent. We hypothesized that metribuzin at 210 g ai ha−1 in admixture with topramezone would improve bermudagrass tolerance while conserving mature E. indica control. In preliminary field studies, metribuzin mixed with topramezone at 1.2 or 2.5 g ae ha−1 applied twice at a 3-wk interval reduced bermudagrass injury and white discoloration compared to topramezone applied alone, but metribuzin did not safen bermudagrass to mesotrione. Topramezone at 3.7 g ha−1 plus 210 g ha−1 metribuzin applied twice at a 3-wk interval offered improved bermudagrass tolerance while it still controlled mature E. indica during fifteen field and two greenhouse studies in Virginia. This program offered a 10-fold decrease in suprathreshold duration of white-discoloration compared to topramezone alone at 6.1 g ha−1. Bermudagrass absorbed three times less radioactivity than E. indica at timings up to 48 h after treatment with 14C-topramezone. Bermudagrass also metabolized twice as much topramezone compared to E. indica at 48 h after treatment. Metribuzin reduced 14C absorption by approximately 25% in both species. These studies confirm the performance of a novel, low-dose topramezone plus metribuzin program for mature E. indica control in bermudagrass turf, and suggest that selectivity between bermudagrass and E. indica to topramezone is due to differential absorption and metabolism. The fact that metribuzin reduces topramezone absorption in both species suggests that it may help reduce bermudagrass phytotoxic response to topramezone, but its role in altering selectivity between bermudagrass and E. indica may be due to other factors.

No abstract

Peer-reviewed research is not available to explain Polygonum aviculare L. (prostrate knotweed) control in Cynodon dactylon (bermudagrass) turf, yet P. aviculare is common and troublesome in managed C. dactylon turf. Six experiments were conducted to determine control options for P. aviculare in C. dactylon golf roughs managed in Hanover, VA. Studies evaluated hormone, photosystem, and ALS inhibiting herbicides. Among a group of eighteen herbicide treatments, only six controlled P. aviculare over 80% and these included single products or mixtures containing 2,4-D, dicamba, metsulfuron, or chlorsulfuron. Imazaquin, quinclorac, and triclopyr caused transient C. dactylon injury. Treatments dependent on bromoxynil, triclopyr, clopyralid, quinclorac, metribuzin, rimsulfuron, imazaquin, foramsulfuron, flazasulfuron, trifloxysulfuron sodium, or sulfosulfuron are unlikely to adequately control P. aviculare in C. dactylon turf.

Can. Ent. 102: 1554-1558 (1970) A gelatine-based diet for rearing the onion maggot, Hylemya antiqua (Meigen), that contains sucrose, evaporated milk, yeast hydrolysate, wheat embryo, cellulose powder, n-propyl disulfide, water, and antibiotics is described. Three consecutive generations reared on this medium were equal in puparial weights, percentages of pupation, adult emergence, and egg hatch, to those reared on onion bulbs. The procedure is simple and two man-hours per week is sufficient for producing 1000 maggots daily.