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 C, eight of the nine cultivars expressed a restricted transpiration rate at high VPD. However, at C none of the cultivars exhibited a restriction of transpiration rate at high VPD. No differences were found among the nine cultivars in their response to soil drying. 1. Introduction Peanut (Arachis hypogaea L.) is often grown under rainfed conditions on soils with limited water-holding capacity. Hence, an ability to sustain development and growth under water deficit is important for commercial cultivars. While studies have examined traits to enhance peanut performance under water-limited conditions, there is no report specifically on genetic variability among cultivars used commercially in southeast USA. This study was designed to examine specific drought-tolerant traits in nine commercial peanut cultivars. 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 [1, 2]. Without sensitivity to increasing VPD, plants will have continually increasing transpiration rates with increasing VPD [3]. One possibility, however, is for plants to limit transpiration to a maximum rate when VPD becomes high. Such behavior is observed as midday stomata closure. This trait has the benefit of conserving soil water during periods of high VPD so that it might be available for use later in the season if soil water deficits develop. Such a response of transpiration to VPD has been previously identified in some genotypes of soybean (Glycine max (Merr.) L.) [4–6], sorghum (Sorghum biocolor L.) [7], and pearl millet (Pennisetum glaucum (L.) R.Br) [8]. A sensitivity of transpiration to VPD has also been recently reported in peanut. Jyostna Devi et al. [9] studied seventeen peanut breeding lines and commercial lines used in India. They found that nine of the lines had a
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