College Station July 2006 College Station October 2006 Evaluation of Soil from Selected Sites for Suppressiveness against the Reniform Nematode A.F. Robinson 1 J.M. Bradford 2, S.M. Greenberg 2, C. Overstreet 3, G.B. Padgett 4, S.R. Stetina 5, A. Westphal 6, and T.A. Wheeler 7 1 USDA-ARS, College Station, TX, 2 USDA-ARS, Weslaco, TX, 3 LSU AgCenter, Baton Rouge, LA, 4 LSU AgCenter, Winnsboro, LA, 5 USDA-ARS, Stoneville, MS, 6 Purdue Univ., West Lafayette, IN, 7 Texas A&M University, Lubbock, TX Picture No. Soil tested Nematode population (vermiform/gram) Percent of Fibermax 832 Percent suppression 111D Sweet Potato, NE Louisiana St. Joe, Louisiana Gin Ridge North East Research Station Panhandle Field, **5248 5Rapides Parish, Bill Poole Farm, Field BP-1, **3941 6Morehouse Parish, Boyd Holley Farm, Field-Big Cat, *6337 7Rapides Parish, Bill Poole Farm, Field PV, **3466 8Morehouse Parish, B. Turner Farm, Field 104, **5446 9Rapides Parish, Dean Lee Research Station, Sweet Potato, East Baton Rouge, Burden Plantation, May 14, Rapides Parish, Bill Poole Farm, Field RB-3, Rapides Parish, Bill Poole Farm, Field JP, ** Concoudia Parish, VanGilden Farm, Field P14-1, Franklin Parish, Ken Thornhill Farm, Field Test 201, Russ Hayes198* North Farm, cm North Farm, 0-15 cm14**595 18USDA at Stoneville Fibermax 832, susceptible control, no supplement Fibermax 832, susceptible control, extra set of 6 reps27592 N/A GB713, resistant control, no supplement27**991 N/A Delta Pine 16, extra susceptible control, 6 reps replicates per treatment * Denotes means significantly differ from Fibermax 832 at P = ** Denotes means significantly differ from Fibermax 832 at P = Plants at the end of the experiment. No obvious plant growth suppression for any treatment. Preliminary Test Rio Grande Valley 1999 Reproduction of Rotylenchulus reniformis under cotton after 14 weeks in non-treated or autoclaved portions of six soils in a greenhouse trial (LSD for treatment*soil). Final nematode population (nem/100 cm 3) Oil Well Field Nogales Field Brush Area Levy Wieden Field 0-30 cm North Farm cm North Farm Cotton root fresh weight after 14 weeks in Rotylenchulus reniformis infested non-treated or autoclaved portions of six soils in a greenhouse trial (LSD for treatment*soil). Fresh root weight (g) Oil Well Field Nogales Field Brush Area Levy Wieden Field 0-30 cm North Farm cm North Farm Experimental: Soil was collected from cotton fields in Louisiana, Mississippi, and South Texas where the reniform nematode (Rotylenchulus reniformis) was present at lower population densities than expected based on soil texture, cropping history, and infestation levels in nearby fields. In preliminary tests conducted in the Rio Grande Valley in 1999, soil was autoclaved (gray bars) for 30 minutes on 2 consecutive days, or not autoclaved (white bars), placed directly into greenhouse pots and planted to susceptible cotton for 14 weeks. In tests conducted at College Station in 2006, soil was mixed 1:20 (July test) or 1:10 (October test) with a fine sand supplemented with vermiculite and balanced nutrients, and placed within 0.5 liter pots that were planted to susceptible cotton cv. Fibermax 832. Two weeks after planting, each pot was inoculated with 4,000 vermiform R. reniformis, and 7 weeks after inoculation, three cores were removed from each pot to evaluate nematode populations in pots. Nematode population densities were measured by counting vermiform stages collected by Baermann funnel extraction. Results: In 1999, autoclaving greatly increased final nematode populations for all sites except the brush area. Root biomass differences were too small to explain the effect. In 2006, transferable agent(s) in soil from eight fields suppressed populations measurably (P = 0.05). Strong suppression (36-95%) was obtained with soil from North Farm. Surface soil (0-15 cm) from the North Farm suppressed populations 95% in the second test, compared with 91% for the resistant control, G. barbadense GB-713; population suppression values measured for North Farm surface soil in the 1999 and July 2006 test were 90% and 80% respectively. Suppression values for deeper soil from North Farm in the 1999, and the July and October tests of 2006 were 95%, 36%, and 38%. Conclusion: Our results indicate the presence of a transferable agent in North Farm soil that suppresses R. reniformis at higher concentrations in the top 30 cm than below 30 cm. The level of suppression observed in one test was comparable to that obtained with one of the best sources of host plant resistance within Gossypium. Suppression in upper soil layers at North Farm is consistent with numerous previous observations of greater nematode populations deep in the soil than near the surface at this site. Further research is merited. Soil type Nematode population (vermiform/gram of soil) Percent of Fibermax 832 Percent suppression Lubbock Station Lamesa Panhandle North Farm, cm North Farm, 0-15 cm USDA at Stoneville Fibermax GB replicates per treatment *No treatment means significantly differ from Fibermax 832*