Grass pea (Lathyrus sativus cv. Ceora) − adaptation to water deficit and benefit in crop rotation MARCAL GUSMAO M.Sc. School of Earth and Environmental Sciences Faculty of Sciences The University of Adelaide This thesis is presented for the degree of Doctor of Philosophy of The University of Western Australia Faculty of Natural and Agricultural Sciences School of Plant Biology and The UWA Institute of Agriculture December 2010 i Abstract Grass pea (Lathyrus sativus cv. Ceora) is a multipurpose grain legume with an indeterminate growth habit. Adaptation of grass pea to water deficits and its potential rotational benefits in the Mediterranean-type environment of southern Australia are not well understood. The first objective of the thesis was to identify adaptation mechanisms of grass pea to water deficits. This was done by imposing water deficit during the reproductive period on plants grown in pots in a glasshouse. In the first experiment, a moderate water deficit was imposed on Ceora and a well-adapted field pea (Pisum sativum cv. Kaspa), by reducing soil water content from 80 to 50% field capacity (FC) during seed filling. Water deficit decreased pre-dawn leaf water potential (Ψ) of Ceora and Kaspa, as well as stomatal conductance (gs) of Ceora, but no reduction in photosynthesis occurred. Water deficit reduced green leaf area of Ceora resulting in 30 and 24% reduction in plant dry mass and seed yield at maturity, respectively. Seed size and harvest indices (HI) of Ceora did not differ between the treatments. Ceora produced more dry matter than Kaspa in both treatments, but produced 22 (control) and 33% (water deficit) lower seed yields. Kaspa had higher HI and water use efficiency for grain than Ceora. In the second experiment, severe water deficit was imposed on Ceora plants by withholding water from first flowering until Ψ fell to -3.12 MPa, when the plants were rewatered. At maturity, dry matter, seed yield and harvest index decreased by 60%, 87% and 67%, respectively, compared with the control. Flower production stopped at Ψ -1.8 MPa. At Ψ=-1.5 MPa, only 25% of the total flowers produced filled pods (compared with 95% in the control) and the rest aborted as flowers (48%) and pods (27%). Filled pods had more aborted ovules resulting in 29% less seeds per pod than the control. Water deficit reduced pollen viability (from 88 to 75%) and germination (from 53 to 28%) compared with the control. Of the germinated pollen, pollen tubes reaching the ovary were reduced by water deficit from 70 to 39% compared with the control. Seed size did not differ between the treatments. A second objective of the thesis was to assess the effect of a grass pea crop on soil N and P availabilities, and the persistence of this effect over the summer period. This was done by comparing growth, dry matter and N and P uptake of wheat plants in soil collected from plots previously grown to grass pea or wheat at Cunderdin in the ii Western Australian grain belt. Soil from each plot was sampled monthly from Nov 2008 to Feb 2009. Wheat was grown in pots containing these soils with no fertiliser (control), with N or P, or with N and P combined. After four weeks in a controlled environment room, with pots well-watered at 75% FC, wheat after grass pea produced greater dry mass (12%) and green area (16%) than wheat after wheat. The addition of N or combined N and P fertilisers reduced the beneficial effect of grass pea to the subsequent wheat crop. Wheat shoot N content was higher after grass pea than after wheat. Wheat shoot P content was higher after grass pea than wheat at the first sample date, but the opposite occurred at the last sampling. This study showed that under moderate water deficit, grass pea avoids dehydration through a reduction in green leaf area and stomatal conductance. This enables plants to maintain the water status and photosynthesis of the remaining green leaves to support seed yield. High seed loss under severe water deficit was due to the cessation of flower production, reduced pollen fertility and high flower, pod and ovule abortion. Nonetheless, grass pea was able to produce some seed by concentrating limited resources to a smaller number of viable pods. The plants also matured early to escape drought. These adaptation strategies are important in southern Australia where rainfall in the growing season is variable and terminal drought is a common feature. Growing wheat after grass pea resulted in increased growth and N uptake compared with wheat after wheat. Thus, use of grass pea in the rotation could enhance soil N availability and growth and yield of subsequent cereal crops. iii Table of Contents Content Page Abstract ………………………………………………………………………….. ii Acknowledgements ……………………………………………………………... ix Statement of candidate contribution ………………………………………....... xi Chapter 1. General introduction ………………………………………………. 1 Chapter 2. Literature review 2.1 Introduction ………………………………………………………………....... 5 2.2 Taxonomy and common names of grass pea (Lathyrus sativus) …………...... 5 2.3 Description of L. sativus ……………………………………………………... 5 2.4 Origin and distribution of L. sativus …………………………………………. 6 2.5 Uses, production, toxicity and detoxification of L. sativus ………………...... 7 2.6 Environmental effect on ODAP concentration and breeding for low ODAP concentration of L. sativus …………………………………………………… 11 2.7 Achievement and recommendations for new cultivar of grass pea developed in Western Australia ………………………………………………………….. 12 2.8 Plant-soil water relations …………………………………………………….. 12 2.9 Crop adaptation to water deficits …………………………………………...... 14 2.10 Morphological adaptation mechanisms …………………………………...... 15 2.11 Physiological adaptation mechanisms to water deficits …………………..... 18 2.12 The effect of water deficit on yield, yield components and harvest indices… 22 2.13 Water use and water use efficiency (WUE) ………………………………… 24 2.14 The effect of legumes on growth, N and P uptake and yield of subsequent cereal crops ………………………………………………………………….. 26 2.15 Conclusion ………………………………………………………………...... 28 Chapter 3. Grass pea avoids dehydration and escapes drought under moderate water deficit during reproductive period Abstract …………………………………………………………..………………. 29 3.1 Introduction ………………………………………………………………....... 30 3.2 Materials and methods ……………………………………………………...... 33 3.3 Results ……………………………………………………………………....... 37 3.4 Discussion ……………………………………………………………………. 47 3.5 Conclusion …………………………………………………………………... 53 Chapter 4. Grass pea tolerates severe water deficit and sets normal sized seed when the deficit is relieved Abstract ……………………………………………….………..………………… 54 4.1 Introduction ………………………………………………………………...... 54 4.2 Materials and methods ……………………………………………………..... 56 4.3 Results ……………………………………………………………………...... 62 4.4 Discussion …………………………………………………………………… 77 4.5 Conclusion …………………………………………………………………... 85 iv Table of Contents (Continued) Content Page Chapter 5. Grass pea enhances growth and N uptake of a subsequent wheat crop Abstract ……………………………………………………………..……………. 86 5.1 Introduction ………………………………………………………………....... 86 5.2 Materials and Methods ……………………………………………………...... 89 5.3 Results ……………………….……………………………………………...... 92 5.4 Discussion ……………………………………………………………………. 98 5.5 Conclusion …………………………………………………………………… 102 Chapter 6. General discussion 6.1 Introduction ………………………………………………………………....... 103 6.2 Adaptation of grass pea to water deficits …………………………………….. 103 6.3 Soil N and P availability under grass pea crop ………………………………. 108 6.4 General conclusion …………………………………………...……………… 109 References ……………………………………………………………………...... 110 Appendices ………………………………………………………………………. 124 v List of Figures Figure Page Figure 3.1 Daily maximum and minimum growing season glasshouse temperatures (oC) ………………………………………………………………… 37 Figure 3.2 Cumulative transpiration of Ceora (LS) and Kaspa (FP) ……………. 39 Figure 3.3 Soil-plant water relations: gravimetric soil water content for Ceora (a) and for Kaspa (b), pre-dawn leaf water potential for Ceora (c) and for Kaspa (d), and leaf relative water content for Ceora (e) and for Kaspa (f) ……………... 40 Figure 3.4 Stomatal conductance and net photosynthesis for Ceora (a, c) and for Kaspa (b, d) ………………………………………………………......................... 41 Figure 3.5 Osmotic potential for Ceora (a) and for Kaspa (b) ……………........... 42 Figure 3.6 Plant height and node number for Ceora (a, c) and for Kaspa (b, d) ……………………………………………………………………………………. 42 Figure 3.7 Green leaf area development and dry matter production for Ceora (a, c) and for Kaspa (b, d) …………………………………………………………… 44 Figure 3.8 Root dry matter for Ceora (a) and Kaspa (b) …………………............ 44 Figure 3.9 Dry matter partitioning (g plant-1) of Ceora and Kaspa ………........... 45 Figure 4.1 Daily maximum and minimum growing season glasshouse temperatures (oC) .................................................................................................... 62 Figure 4.2 Pot weight during the water deficit treatment ……………………….. 63 Figure 4.3 Pre-dawn leaf water potential (Ψ) ……………………………............ 64 Figure 4.4 Relationship between pre-dawn Ψ and gravimetric soil water content during the treatment period (82 to 100 DAS) ……………………......................... 64 Figure 4.5 Growth of grass pea: a) at first flowering (82 DAS) when water stress was imposed, b) difference between control and water deficient plants at the lowest Ψ (-3.12 MPa) (100 DAS) just prior to rewatering, and c) appearance 6 days after rewatering (Ψ = -1.4 MPa) (106 DAS) when regular watering (to 80% FC) was applied ………………………………………………………………….. 65