College Station July 2006

1. 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). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Evaluation of Soil from Selected Sites for Suppressiveness against the Reniform Nematode A.F. Robinson1J.M. Bradford2, S.M. Greenberg2, C. Overstreet3, G.B. Padgett4, S.R. Stetina5, A. Westphal6, and T.A. Wheeler7 1USDA-ARS, College Station, TX,2USDA-ARS, Weslaco, TX, 3LSU AgCenter, Baton Rouge, LA, 4LSU AgCenter, Winnsboro, LA, 5USDA-ARS, Stoneville, MS, 6Purdue Univ., West Lafayette, IN, 7Texas A&M University, Lubbock, TX 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. Preliminary Test Rio Grande Valley 1999 College Station July 2006 Final nematode population (nem/100 cm3) Fresh root weight (g) Brush Area 0-30 cm North Farm 45-105 cm North Farm Oil Well Field Nogales Field Levy Wieden Field Oil Well Field Nogales Field Brush Area Levy Wieden Field 0-30 cm North Farm 45-105 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). College Station October 2006 Plants at the end of the experiment. No obvious plant growth suppression for any treatment.