Peanut (Arachis hypogaea L.) is an important grain legume whose yield is often limited by water deficits because it is commonly grown in regions with intermittent rainfall and on sandy soils with low water-holding capacity. Annual peanut yield loss due to drought worldwide has been estimated at US$520 million (Sharma and Lavanya 2002). To increase yields, it is essential to develop genotypes that can sustain growth and yield when subjected to water deficit (Sinclair and Vadez 2012). The two plant traits, which are the topic of this book, have been identified in peanut to result in conservative use of water and allow sustained growth during drought: (1) earlier closure of stomata in the soil drying cycle resulting in decreased daily transpiration rate and (2) limited-transpiration rate (TRlim) under high atmospheric vapor pressure deficit (VPD) (Devi et al. 2009, 2010).
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