Radiation Use Efficiency in Cotton: Effect of Environment and Plant Growth Regulators Evangelos Gonias, Derrick Oosterhuis, Androniki Bibi and Bruce Roberts University of Arkansas Department of Crop, Soil and Environmental Sciences

Introduction Crop growth depends on: Amount of intercepted radiation Time allowed for growth Fraction of intercepted radiation (f) calculated by the Beer’s law: f = I/I0 = e-k·LAI Cotton canopy extinction coefficient (k): 0.56-0.87 (Sinclair and Muchow, 1999) (Monsi and Saeki, 1953) (Constable, 1986; Rosenthal and Gerik, 1991; Sadras and Wilson, 1997)

Radiation Use Efficiency (RUE) Effectiveness of a crop to convert intercepted radiation to dry matter. Amount of dry matter produced per unit of radiation intercepted (g·MJ-1). Correlation described as linear. Cotton RUE: 1.31 to 1.92 g·MJ-1 of intercepted PAR. (Monteith, 1977) (Rosenthal and Gerik, 1991; Pinter at al., 1994; Sadras and Wilson, 1997)

Factors affecting RUE Biotic stress: Abiotic stress: Spider mites reduced cotton growth without reduction in light interception. Abiotic stress: Salinity reduced RUE of soybean by 40%. Water deficit reduced RUE by 54% and 64% for two peanut cultivars. Increasing vapor pressure deficit decreased RUE. (Sadras and Wilson, 1997) (Wang et al., 2001) (Collino et al., 2001) (Stöckle and Kiniry, 1990)

Vapor pressure deficit (VPD) VPD>1 kPa decrease leaf photosynthesis in wheat. Increasing VPD decreased RUE by a slope of: 0.65 and 0.85 g·MJ-1·kPa-1 for sorghum and corn. 1.48 g·MJ-1·kPa-1 for potato. 0.53 g·MJ-1·kPa-1 for barley and wheat (solar). (Leach, 1979) (Stöckle and Kiniry, 1990) (Manrique et al., 1991) (Kemanian et al., 2004)

Effect of VPD on RUE RUE at high VPD expressed as percentage of RUE at the lower VPD. (Summarized by Kiniry et al., 1998) Crop Low VPD High VPD RUE References - kPa - - % - Maize 1 2.5 75 Bunce, 1982 0.8 2.0 84 Morison and Giford, 1993 0.4 1.9 93 Dai et al., 1992 2.7 79 “ 3.5 64 1.25 4.0 48 El-Sharkawy et al., 1985 Sorghum 74

Studies Effect of environment on radiation use efficiency of cotton. Effect of plant growth regulators on radiation use efficiency of cotton.

Measurements Data recorded between pinhead square stage (PHS) and three weeks after flowering (FF+3). Measurements: Light interception (weekly) Dry matter (every 10-15 days) Weather data: Temperature Relative humidity Photosynthetically active radiation

Effect of environment Hypothesis: Objective: Radiation use efficiency of cotton differs among geographic locations due to differences in environmental parameters (i.e. vapor pressure deficit). Objective: Determine and compare the radiation use efficiency of cotton in Arkansas and California.

Materials and Methods Locations: Years: 2006 and 2007 Marianna, AR (Cotton Branch Station, UA) Fresno, CA (Dr Bruce Roberts, CSU) Years: 2006 and 2007 Cultivar: DP444BR Populations: 5 plants / m2 10 plants / m2 5 replications

RESULTS

Weather Data 2006 Average values between pinhead square stage and three weeks after flowering. Location VPD Tmax Tmin RH PAR kPa Cº % MJ·m-2 Marianna, AR 1.68 33.1 21.3 67.5 10.12 Fresno, CA 2.92 37.7 19.3 43.7 13.30 P-value <0.001 0.002

Weather Data 2007 Average values between pinhead square stage and three weeks after flowering. Location VPD Tmax Tmin RH PAR kPa Cº % MJ·m-2 Marianna, AR 1.35 32.5 21.3 75.5 8.75 Fresno, CA 2.49 34.2 15.9 44.9 12.91 P-value 0.020 <0.001

Vapor Pressure Deficit Daily vapor pressure deficit for Marianna, AR and Fresno, CA between pinhead square stage and three weeks after flowering. 2006 2007

Radiation Use Efficiency Across Years No significant YearRUE interaction (P=0.9246)

Effect of Plant Growth Regulators Hypothesis: Plant growth regulators affect crop growth and canopy dynamics and therefore alter radiation use efficiency of cotton. Objective: Determine the effect of plant growth regulators on radiation use efficiency of cotton.

Materials and Methods Location: Fayetteville, AR (University of Arkansas Agricultural Research and Extension Center) Years: 2006 and 2007 Cultivar: DP444BR Populations: 10 plants / m2 5 replications in a RCB design Treatments (applied at PHS, PHS+10 days and FF): Untreated control Mepiquat chloride at 8 oz/acre

Mepiquat Chloride 1,1-dimethylpiperidinium. Gibberellins inhibitor. Height reduction, earlier maturity and a small yield advantage. Reduced leaf expansion and shorter main-stem and branch internodes. Changes in leaf coloration to a darker green and effect on specific leaf weight. (Oosterhuis et al., 1991) (Walter et al., 1980; Reddy et al., 1990) (Gausman, 1980)

RESULTS

Effect of PGR treatment on growth parameters Measured at first flower, 2006 Treatment Height LAI Dry Weight cm — g·m-2 Untreated control 85.18 2.54 352.7 Mepiquat chloride 72.59 1.98 282.6 P-value 0.002 0.007 0.017

Effect of PGR treatment on dry matter partitioning Measured at first flower, 2006 Treatment Leaves Stems Fruit % Untreated control 40.75 52.19 7.06 Mepiquat chloride 42.63 50.18 7.19 P-value 0.067 0.014 0.894

Effect of PGR treatment on light Interception 2006 2007 Intercepted Radiation (MJ·m-2) 2006 2007 Untreated control 204.3 233.0 Mepiquat chloride 201.0 218.4 P=0.463 P=0.012

Effect of PGR treatment on canopy extinction coefficient (k) Across Years No significant YearRUE interaction (P=0.343)

Radiation Use Efficiency Across Years No significant YearRUE interaction (P=0.182)

Conclusions (Environment) Radiation use efficiency of cotton grown in Arkansas and California differed significantly in one of the two years of the study and across years. The California location had higher day temperature, incoming radiation and vapor pressure deficit. The Arkansas location had higher night temperature and relative humidity. Increasing vapor pressure deficit decreased radiation use efficiency of cotton by a slope of 0.47 g·MJ-1·kPa-1.

Conclusions (PGR) Mepiquat chloride: Decreased height, leaf area and dry matter of cotton and changed the partitioning of dry matter. Decreased light interception in 2007. Increased the canopy extension coefficient (k) Increased radiation use efficiency in 2006.

QUESTIONS ?