ORIGINAL PAPER 24-epibrassinolide increases growth, grain yield and b-ODAP production in seeds of well-watered and moderately water- stressed grass pea Jun-Lan Xiong 1,2 • Hai-Yan Kong 1 • Nudrat Aisha Akram 3 • Xue Bai 1 • Muhammad Ashraf 4 • Rui-Yue Tan 1 • Hao Zhu 1 • Kadambot H. M. Siddique 2 • You-Cai Xiong 1 • Neil C. Turner 2,5 Received: 11 March 2015 / Accepted: 27 May 2015 Ó Springer Science+Business Media Dordrecht 2015 Abstract 24-epibrassinolide (EBL) is a growth regulator that promotes crop growth and yield, especially under water stress, but its effect on grass pea (Lathyrus sativus L.), a legume crop widely recognized as adapted to rainfed environments, is unknown. The aim of the present study was to investigate the effect of exogenously-applied EBL on growth, yield and accumulation of b-N-oxalyl-L-a, b- diaminopropionic acid (b-ODAP)—a neurotoxin that can induce lathyrism in animals and humans—in grass pea under well-watered (WW) and water-stressed conditions. The first experiment conducted in a growth chamber showed that EBL application increased plant height and leaf area of well-watered [WW, 85 % field capacity (FC)] grass pea seedlings and in those in which the soil dried from 85 to 30 % FC. In two pot experiments conducted under a rainout shelter, three water regimes—soil water contents maintained at (1) 85 or 80 % FC, (2) 50 % FC, and (3) 35 % FC—were imposed. In the first rainout shelter experiment, root/soil drenching with EBL significantly increased aboveground dry weight (DW) and water use efficiency (WUE) compared with plants without EBL at 85 and 50 % FC, but did not significantly affect grain yield. In a second rainout shelter experiment, water treatments were imposed from the vegetative phase to maturity and EBL treatment significantly increased aboveground DW, grain yield, b-ODAP concentration and amount, and WUE in the 80 and 50 % FC water regimes. It is concluded that exogenously-applied EBL can stimulate growth and WUE in grass pea when WW and moderately water stressed, and also stimulates b-ODAP production such that the concen- tration in the grain is similar or even higher. Keywords Stomatal conductance  Plant height  Leaf area  Water use efficiency  Growth regulator  Grain number Introduction Grass pea (Lathyrus sativus L.) is an important legume crop mainly grown in South Asia and Ethiopia, and to a lesser extent in China, the Mediterranean region and Eur- ope (Campbell et al. 1994). It has a seed protein content of up to 30 % and is grown for both animal feed and human food (Ramakrishna and Adiga 1975; Enneking 2011). Grass pea has a reputation for its resistance to a variety of biotic and abiotic stresses such as drought, cold, and waterlogging (Berger et al. 1999; Cocks et al. 2000; Cal- dero´ n et al. 2012), features that may lead to its expansion in semiarid areas of the world which are predicted to become Electronic supplementary material The online version of this article (doi:10.1007/s10725-015-0087-1) contains supplementary material, which is available to authorized users. & You-Cai Xiong xiongyc@lzu.edu.cn & Neil C. Turner neil.turner@uwa.edu.au 1 State Key Laboratory of Grassland Agroecosystems, Institute of Arid Agroecology, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu Province, China 2 The UWA Institute of Agriculture, The University of Western Australia, M082, Perth, WA 6009, Australia 3 Department of Botany, GC University, Faisalabad 38040, Pakistan 4 University College of Agriculture, University of Sargodha, Sargodha 40100, Pakistan 5 Centre for Plant Genetics and Breeding, The University of Western Australia, M080, Perth, WA 6009, Australia 123 Plant Growth Regul DOI 10.1007/s10725-015-0087-1