Commercial peanut cultivars in the USA are often grown under soil and environmental conditions resulting in intermittent periods of water deficit. Two plant traits have been identified that result in conservative use of water and allow sustained growth during drought: (1) restricted transpiration rate under high atmospheric vapor pressure deficit (VPD) and (2) earlier closure of stomata in the soil-drying cycle resulting in decreased daily transpiration rate. The objective of this study was to investigate whether there was diversity in these two putative traits for drought resistance among nine US commercial peanut cultivars. When the response to VPD was measured at an average temperature of
Peanut (
One putative drought-tolerant trait is to limit transpiration rate by having a decreased stomatal conductance under conditions when atmospheric vapor pressure deficit (VPD) is high [
A sensitivity of transpiration to VPD has also been recently reported in peanut. Jyostna Devi et al. [
A second putative trait to confer drought tolerance involves the response of transpiration rate to soil drying. In general, transpiration rate is unaffected by soil drying until the soil dries to a volumetric water content where the rate of water uptake from the soil requires that transpiration rate be limited [
The response of transpiration to soil drying has also been studied among peanut genotypes. Jyostna Devi et al. [
Although Jyostna Devi et al. [
Peanut material used in the following study was commercial varieties obtained from USDA, Agricultural Experimental Research Station, Dawson, Georgia. The nine cultivars used in this study are listed in Table
Date of sowing, experimental dates, and environmental conditions during the measurements of response to vapor pressure deficit (VPD), minimum and maximum VPD, and temperature.
High Temperature experiment | ||||||
Genotype | Date of sowing | Date of measurement | VPD (kPa) | Temperature (°C) | ||
Minimum | Maximum | Minimum | Maximum | |||
AP 3 | Jul 10th, 2008 | Aug 14th & 15th, 2008 | 1.04 | 3.36 | 29 | 36 |
AT 3085 | Jul 10th, 2008 | Aug 12th & 13th, 2008 | 0.77 | 3.27 | 28 | 34 |
C 76-16 | Jul 10th, 2008 | Aug 12th & 13th, 2008 | 0.85 | 3.58 | 29 | 36 |
C 99R | Jul 10th, 2008 | Aug 14th & 15th, 2008 | 1.10 | 3.27 | 29 | 35 |
FL 07 | Sep 19th, 2008 | Oct 26th & 27th, 2008 | 1.15 | 3.32 | 29 | 35 |
GA 04S | Jul 10th, 2008 | Aug 12th & 13th, 2008 | 0.90 | 3.29 | 28 | 34 |
GA 06G | Jul 10th, 2008 | Aug 12th & 13th, 2008 | 0.89 | 3.08 | 29 | 35 |
Tifrunner | Sep 19th, 2008 | Oct 26th & 27th, 2008 | 1.31 | 3.24 | 29 | 35 |
York | Jul 10th, 2008 | Aug 14th & 15th, 2008 | 0.90 | 3.29 | 29 | 35 |
Low Temperature experiment | ||||||
AP 3 | Jan 16th, 2009 | Feb 27th & 28th, 2009 | 0.92 | 3.02 | 23 | 27 |
AT 3085 | Jan 16th, 2009 | Mar 2nd & 3rd, 2009 | 0.86 | 3.06 | 22 | 27 |
C 76-16 | Jan 16th, 2009 | Mar 2nd & 3rd, 2009 | 0.96 | 3.01 | 22 | 27 |
C 99R | Jan 16th, 2009 | Feb 27th & 28th, 2009 | 0.85 | 3.02 | 23 | 27 |
FL 07 | Jan 20th, 2009 | Mar 6th & 7th, 2009 | 0.85 | 3.19 | 23 | 28 |
GA 04S | Jan 16th, 2009 | Mar 2nd & 3rd, 2009 | 0.83 | 3.21 | 23 | 28 |
GA 06G | Jan 16th, 2009 | Mar 2nd & 3rd, 2009 | 0.82 | 3.01 | 23 | 27 |
Tifrunner | Jan 20th, 2009 | Mar 6th & 7th, 2009 | 0.98 | 3.05 | 23 | 27 |
York | Jan 16th, 2009 | Feb 27th & 28th, 2009 | 0.82 | 3.08 | 23 | 27 |
Transpiration response of individual peanut plants in response to various atmospheric VPD was measured in the same chamber system described by Jyostna Devi et al. [
The evening before testing the VPD response, all pots were fully watered and left to drain overnight. The following morning, the soil surface around the plant was sealed with aluminum foil to prevent soil evaporation. A 254 mm diameter lid of a food container (Rubbermaid Commercial Products LLC, Winchester, VA) with an opening cut out of the center for installation over the plants was attached to the toilet flange that had been attached to the top of the pot. The 5.4 L translucent food container was then inverted over the plant and attached to its lid to form the VPD chamber. A 12 V, 76 mm diameter computer box fan (Northern Tool and Equipment, Burnsville, Minn, USA) was mounted on the chamber wall to mix the air inside the chamber. A pocket humidity/temperature pen (Extech Instruments, League City, Tex, USA) was placed through a slit in the side wall of each container to record temperature and humidity.
Different humidity levels were established around the plants in the chamber by pumping air into the container using different flow rates and sources of air [
Since there were twelve VPD chambers and data were obtained for three or four replicate plants of each cultivar, it was necessary to do the measurements in batches. The cultivars were randomly assigned to a batch. The dates for the measurement of the transpiration response for each cultivar, and the range of VPD to which the plants were exposed are given in Table
Two experiments were performed on the cultivars. The first experiment was a summer sowing and the plants were grown in the greenhouse for 35 to 40 d. The second experiment used plants grown in the greenhouse during the winter, and as a result the overall average temperature in the greenhouse to which the plants were exposed was less than in the first experiment. Consequently, the plants in the second experiment developed more slowly in the second experiment than in the first experiment and the plants were allowed to grow 40 to 50 d before measuring their VPD responses.
Data from all plants of each genotype on the two measurement days were combined to perform a two-segment linear regression (Prism 2.01, GraphPad Software Inc., San Diego, Calif, 1996) for transpiration rate versus VPD. If the slopes of the two segments were significantly different (
Two experiments were conducted to measure the FTSW threshold for decline in transpiration rate with soil drying for the same nine cultivars used in the VPD study. The plants were grown in 200-mm diameter plastic pots filled with garden soil. A total of 12 replicate pots were established for each cultivar. The seeds were inoculated with rhizobia to ensure adequate nodulation as described above. The plants were grown in a greenhouse subjected to natural solar radiation with air temperature regulated at 27°C day/21°C night. The plants were grown for approximately 35 d under well-watered conditions. The experimental dry-down period was from 11 to 25 June 2008 for the first water-deficit experiment and from 22 April to 5 May 2009 for the second water-deficit experiment (WD2).
The plants were fully watered the evening before the experiment began. After draining overnight, the pots were enclosed in white plastic bags and sealed around the plant stem to prevent soil evaporation. A small tube was inserted along the plant stem in each plastic bag to allow rewatering of the pots. The pots were weighed after enclosing in plastic bags and this value was recorded as the initial pot weight. Thereafter, the pots were weighed every morning beginning approximately at 09:30 EST. Daily transpiration amount was calculated as the difference in weight on successive days.
Six pots were maintained in a well-watered state throughout the experiment by adding water each day to return pot weight to 100 g less than the initial weight. Six pots were subjected to slow soil drying. To avoid rapid imposition of stress and to homogenize the development of drought stress across replicated plants, the decrease in soil moisture of each pot was limited to a net loss of 70 g per day by adding water if necessary to maintain the maximum targeted water loss. The experiment was terminated when the soil water content in drought-stressed pots decreased to a level where daily transpiration rate was less than 10% of the well-watered plants [
The transpiration data were analyzed by the procedure previously described by Sinclair and Ludlow [
The values of TR varied among individual plants, in part because of plant size differences. To decrease plant-to-plant variations and to facilitate comparison among cultivars, a second normalization was done. This second normalization for each plant was done by dividing the daily transpiration ratio (TR) by the mean TR of that same plant during the first 3 days of the experiment when the soil still had a high water content. This ratio was identified as the normalized transpiration ratio (NTR) and its value during the wet phase of the dry-down cycle for each plant by definition was therefore centered on a value of 1.0.
The total transpirable soil water available to the plant in each pot was calculated as the difference between the initial and final pot weight for the entire period of soil drying. The use of transpirable soil water as the basis of comparing plant response to soil drying under a range of conditions has been effectively used in a number of studies [
In the VPD experiments, air flow rate and air source were successfully manipulated to achieve a range of humidities in the VPD chambers. The minimum and maximum VPD obtained across all cultivars were 0.77 kPa and 3.58 kPa, respectively (Table
The response to VPD in all cultivars was well expressed by linear regression analysis as exemplified by cultivars AP3 and C 76-16 in Figure
Linear regression analysis of response to vapor pressure deficit based on the results from the High Temperature experiment. The number of data for each cultivar is listed in the column labeled
High temperature experiment | |||||||
Genotype | Slope 1 ± S.E. | Break point ( | Confidence limit of | Slope 2 ± S.E. | |||
AT 3085 | 18 | 21.5 ± 6.41 | 1.81 ± 0.23 a | 1.41 to 1.94 | 3.32 ± 3.55 | 0.79 | 0.71 |
C 99R | 18 | 22.8 ± 2.63 | 1.94 ± 0.11 a | 1.71 to 2.17 | 3.63 ± 1.87 | 0.88 | 0.94 |
GA 06G | 18 | 21.0 ± 5.70 | 2.03 ± 0.12 ab | 1.58 to 2.48 | −2.90 ± 6.89 | 0.92 | 0.61 |
Tifrunner | 18 | 31.5 ± 5.30 | 2.10 ± 0.08 b | 1.95 to 2.26 | −10.10 ± 3.22 | 0.92 | 0.80 |
AP 3 | 18 | 15.8 ± 2.99 | 2.10 ± 0.14 ab | 1.78 to 2.41 | −3.19 ± 3.00 | 0.72 | 0.81 |
C 76-16 | 18 | 35.1 ± 3.97 | 2.17 ± 0.16 ab | 1.80 to 2.53 | 1.53 ± 4.87 | 0.94 | 0.92 |
GA 04S | 17 | 16.0 ± 2.39 | 2.17 ± 0.19 ab | 1.75 to 2.59 | −1.27 ± 3.82 | 0.64 | 0.86 |
FL 07 | 18 | 22.8 ± 3.53 | 2.25 ± 0.13 b | 1.96 to 2.54 | −6.19 ± 3.40 | 0.87 | 0.89 |
Slope | |||||||
York | 16 | 22.3 ± 0.92 | −20.0 ± 2.25 | 0.89 | 0.97 |
Transpiration rate versus vapor pressure deficit (VPD) for cultivars AP3 and C 76-16 in High Temperature (HT) and Low Temperature (LT) experiments.
In those cultivars in the HT experiment with a BP, the slope of transpiration rate per unit leaf area above the BP was much less than the slope at VPD less than the BP (Table
The results for the LT experiment were quite different from those of the HT experiment. In the LT experiment, all cultivars were described by a single linear regression over the entire range of VPD (Table
Linear regression analysis of response to vapor pressure deficit based on the results from the Low Temperature experiment. The number of data for each cultivar is listed in the column labeled
Low temperature experiment | |||||
Genotype | Slope ± S.E. | ||||
AT 3085 | 18 | 11.6 ± 0.46 | −7.73 ± 0.96 | 0.66 | 0.98 |
C 99R | 18 | 12.9 ± 1.30 | −6.48 ± 3.15 | 0.49 | 0.93 |
GA 06G | 17 | 14.7 ± 1.89 | −14.3 ± 4.54 | 0.97 | 0.80 |
Tifrunner | 18 | 24.9 ± 2.04 | −19.7 ± 4.49 | 0.79 | 0.92 |
AP 3 | 17 | 18.1 ± 1.93 | −11.1 ± 4.32 | 0.62 | 0.85 |
C 76-16 | 18 | 27.1 ± 0.96 | −21.7 ± 2.13 | 0.80 | 0.99 |
GA 04S | 18 | 15.4 ± 2.17 | −14.7 ± 5.31 | 0.95 | 0.80 |
FL 07 | 18 | 18.7 ± 0.85 | −16.7 ± 1.78 | 0.89 | 0.98 |
York | 16 | 26.3 ± 1.15 | −27.0 ± 2.67 | 1.02 | 0.97 |
The commonly observed initial plateau in transpiration response followed by a linear decrease with further soil drying was observed for all peanut cultivars in these experiments. The FTSW threshold for the decline in transpiration rate with drying soil was not significantly different among cultivars in either experiment (Table
Results from the two deficit experiments (WD1 and WD2) showing the FTSW-threshold for the decline in transpiration rate. Values followed with the same letter are not statistically different on LSD (Least Significant Difference) values calculated using Tukeys method (
Genotype | WD1 | WD2 |
---|---|---|
AP 3 | 0.46 a | 0.42 a |
AT 3085 | 0.46 a | 0.43 a |
C 76-16 | 0.46 a | 0.41 a |
C 99R | 0.47 a | 0.42 a |
FL 07 | 0.44 a | 0.43 a |
GA 04S | 0.46 a | 0.40 a |
GA 06G | 0.46 a | 0.44 a |
Tifrunner | 0.45 a | 0.42 a |
York | 0.43 a | 0.42 a |
L.S.D. | ||
P |
Unless transpiration is restricted by stomata conductance, plant transpiration is anticipated to increase linearly with increases in the atmospheric vapor pressure deficit [
The marked difference in response to VPD for eight commercial cultivars in this study between the two experiments may be a crucial result of this study. The major environmental difference between the two experiments was the ambient temperature to which the plants were exposed (Table
A hypothesis to explain the temperature sensitivity could be the involvement of aquaporins. Aquaporins are critical for high rates of water transport between cells [
Possible temperature acclimation in the transpiration response observed here could be an important asset for these commercial cultivars. These cultivars with the temperature acclimation have the capability to have restricted transpiration rate under high VPD when temperatures are high. These conditions would exist when the demand for water is high and potential water loss from the plants is high. The cultivars acclimating to a high temperature with a BP in the VPD response appeared to have the capability to switch to a water-conserving mode and decrease the risk of water deficits developing in the soil. Under cooler temperatures, stomata remained open under all VPD conditions so that CO2 assimilation is not restricted under these conditions. Clearly, more research is required to explore the acclimation possibilities in these cultivars and to understand the consequences on crop water use and yield.
The general transpiration response to FTSW was similar to previous reports and was similar among these nine commercial cultivars. The threshold for the decline in transpiration rate was observed at a threshold FTSW of slightly greater than 0.4 for all cultivars in both experiments (Table
Overall, these results do not highlight any major differences among the nine US commercial peanut cultivars in their response to either VPD or soil drying. The one exception was that York sustained a continuing increase in transpiration with increasing VPD in the HT experiment. This result indicates that York may have an aquaporin population somewhat different from the other eight cultivars. The general uniformity of results for these two drought traits among the commercial cultivars indicates that a possibility exists for developing differences in the expression of the two putative traits for enhanced peanut drought tolerance. Jyostna Devi et al. [