Benghal Dayflower (Commelina benghalensis L.) Seed Viability and Impact on Dispersal Mandeep Riar 1, Janet F. Spears 1, Joseph C. Burns 1, Theodore M. Webster 2, Danesha S. Carley 3 and Thomas Rufty 1, (1)Crop Science, North Carolina State University, Raleigh, NC, (2)USDA-ARS, Tifton, GA, (3)Integrated Pest Management, North Carolina State University, Raleigh, NC Introduction Benghal dayflower (Commelina benghalensis L.) is a federal noxious weed possessing many unusual features that contribute to its competitiveness and the severity of its infestation. It is only marginally controlled by glyphosate in Georgia (Culpepper et al., 2004), and produces both aboveground and subterranean seeds in dimorphic flowers, varying in size depending on their position on the plant (Maheshwari and Maheshwari, 1955). Fragments of stem can produce roots at nodes and give rise to new plants from as deep as 2 cm below the soil surface (Budd et al., 1979). Livestock and farm products such as hay can be important dissemination methods that allow movement of weed seeds from one area to another. Seeds of some weed species disintegrate during animal digestion and pose no serious threat of seed dispersal. But the microbial digestion can break down dormancy mechanisms of other weed seeds, increasing seed germination. The purpose of this series of experiments was to examine the viability of Benghal dayflower seed that were subjected to extended periods of burial in soil, animal digestion, and simulated high temperatures, captured in hay bales. Methods Experiment 1: Benghal dayflower seed viability after long periods of soil burial- In North Carolina and Georgia, packets of Benghal dayflower seeds containing 3: 1 ratio of large and small subterranean seed were buried 20 cm deep in soil for five years, starting in 2004 and Packets from each start year were exhumed at 12, 18, 24, 30, 36, 48, 60 months after burial. The seeds were checked for decay and viability of undamaged seeds was checked using Tetrazolium chloride test. References Results Conclusions Experiment 3: Benghal dayflower seed viability under simulated rumen digestion- Large and small aerial seeds of Benghal dayflower and five other common weed species were placed in filter bags and kept in rumen fluid in glass jars. The jars were kept at 39.5°C inside an incubator for hours. Seeds were removed at 12, 24, 48 and 96 hours and checked for survival and germination. Undamaged seeds were germinated in Petri dishes for 8 days. Fig. 2. Viability of (A) Aerial large (B) Aerial small (C) subterranean large and (D) subterranean small seeds after exposure to a range of simulated hay bale temperatures. Duration of treatment (Days) Fig.1. Percent of viable Benghal dayflower seeds in (A) North Carolina start year 2004 (B) NC start year 2005 (C) GA start year Benghal dayflower seeds lose viability at a faster rate in soil in a warmer climate than in milder climates(Fig.1). Benghal dayflower seed banks in North Carolina will have longer persistence than those in Georgia. All types of Benghal dayflower seeds remain viable at 45 and 50°C temperatures found in uncovered hay bales for at least 14 days. The higher hay bale temperature of 65°C kills the seeds much faster than lower temperatures (Fig.2). Rumen digestion for up to 48 hours enhances germination of large aerial seeds (Fig.3A). Digestion duration of 12 and 24 hours also increases the seed germination (data not shown here). Germination of small aerial seeds is also enhanced by digestion of any duration compared to the control (Fig.3B). The process of digestion in rumen generally lasts for hours. Thus, dispersal of viable Benghal dayflower seeds via ruminants is very likely. Budd, G. D., P.E.L. Thomas, and J.C.S. Allison Vegetative regeneration, depth of germination and seed dormancy in Commelina benghalensis L. Rhod. J. Agr. Res. 17:151–153. Culpepper, A. S., J. T. Flanders, A. C. York, and T. M. Webster Tropical spiderwort (Commelina benghalensis) control in glyphosate-resistant cotton. Weed Technol. 18:432– 436. Maheshwari, P. and J. K. Maheshwari Floral dimorphism in Commelina forskalaei Vahl and C. benghalensis L. Phytomorphology 5:413–422. Experiment 2: Benghal dayflower seed viability under simulated hay bale temperatures- Temperatures were recorded in round hay bales at depths of 20.3, 40.6 and 60.9 cm from the outer surface during August-October, 2009 at CEFS, Goldsboro, NC. These recorded temperatures were simulated in growth chambers. Large and small aerial seeds of Benghal dayflower were exposed to a range of these temperatures. These seeds were tested for viability at 1, 3, 7, 14 and 21 days. Fig.4. (A) Temperature measurements in hay bales (B) Damaged Benghal dayflower seed embryos at 65°C after 3 days (Pictured after Tetrazolium chloride test). Temperature probes in an uncovered hay bale AB Damaged seed embryos 45°C 50°C 65°C 50°C 45°C 50°C 65°C 45°C 50°C 65°C A B C D Seed viability (%) Days after digestion Fig. 3. Germination of (A) large and (B) small aerial Benghal dayflower seeds after rumen digestion. A B A A B C Y= exp ( X) R 2 =0.83 Y= X R 2 =0.97 (Large seeds) Y= X R 2 =0.83 (Small seeds) Y= X R 2 =0.95(Large seeds) Y= X R 2 =0.81(Small seeds) Seed viability (%) Duration of burial (Months)