Relationship Between Root Biomass and Water – Nitrogen Uptake and Grain Yield in Bread Wheat ‘Pavon 76’ and Its 1RS Translocation Lines J.G. Waines1, B. Ehdaie1, A. Hoops1, D. Merhaut1, L. Jackson2, K. Brittan3, M. Canevari3, B. Marsh3, D. Munier3, J. Schmierer3, R. Vargas3, and S. Wright3 1Dept. of Botany & Plant Sciences, University of California Riverside, 2Dept. of Plant Sciences, University of California Davis, 3University of California Cooperative Extension ABSTRACT We investigated the effect of root biomass and branching on water and nitrogen (N) absorption, drainage and grain yield in bread wheat (Triticum aestivum L.) Experiments in sand tubes confirmed rye (Secale cereale L.) 1RS translocation lines had larger root biomass than Pavon 76 wheat, which were significantly positively correlated with grain yield at low and high N levels. Root biomass was positively correlated with root, stem, grain, and plant N content. The amount of solution absorbed during early grain filling was positively correlated and amount of leachate negatively correlated with root biomass. Leachate N concentration was negatively correlated with root biomass. In field trials, 1RS translocations only effected yield increase in 50% of irrigated experiments. INTRODUCTION Nitrogen fertilizer is the most expensive and important nutrient to raise crop plants. The N-use efficiency (NUE, the ratio of grain N yield to supplied N) of wheats grown in California is about 51% (Ehdaie et al., 2001). This inefficiency contributes substantially to environmental pollution and in economic loss to farmers. MATERIALS and METHODS Glasshouse Experiment - Pavon 76 and its 1RS translocation lines (Lukaszewski 1993), namely 1RS.1AL, 1RS.1BL, and 1RS.1DL, were grown at optimum level (HN) and at low level (LN) of N solution in a tube experiment in a glasshouse at the University of California, Riverside, using a randomized complete block design with four replications. Seeds from each genotype were soaked and germinated in water in Petri dishes on 10 March 2006. Five days later, seedlings with similar growth were transplanted in polyethylene tubing bags sleeved into polyvinyl chloride (PVC) tubes, 80 cm long and 10 cm in diameter. Two drainage holes were made at the bottom of each bag and were covered with a filter paper before being filled with 7.750 kg of dry silica sand # 30 with 24% field capacity (w/w). Each bag was well-irrigated with half-strength Hoagland solution provided in glasshouse before transplantation and this solution was used during the experiment to irrigate tubes under high N. This nutrient solution was diluted with tap water in the ratio of 1:1 to provide nutrient solution to irrigate tubes under low N. Samples of tap water and nutrient solution were taken regularly during the experiment to determine N content. During early grain filling, leachate was collected for 5 days from each tube, measured, and samples were taken for N content. Each plant received 25 l of nutrient solution which supplied 2400 mg N to each plant in HN and 1500 mg N to each plant in LN. At maturity, the shoots were excised at the shoot/root interface. Grain yield and roots were dried and weighed. Nitrogen content in tap water and leachate was analyzed in D. Merhaut’s laboratory at UC Riverside and N content in plant samples and leachate was analyzed at ANR Analytical Laboratory at UC Davis. The data were subjected to trend analysis (Draper and Smith, 1981). Field Evaluation – The genotypes were included in the University of California Cooperative Extension cereal evaluation tests in 2004-2005 growing season at two locations in irrigated and two locations in rainfed experiments. In 2005-2006, the genotypes were evaluated in six locations in irrigated and two locations in rainfed experiments. RESULTS Glasshouse Experiment – The 1RS translocations produced more root biomass than Pavon in both LN and HN treatments (Fig. 7, horizontal axis). Solution uptake and leachate during early grain filling were, positively (Fig.7) and negatively (Fig. 8) correlated with root biomass, respectively. Grain yield (Fig. 9), plant N content (Fig. 10), and grain N content (Fig. 11) were positively correlated with root biomass. Leachate N concentration during early grain filling was negatively correlated with root biomass in LN and HN (Fig. 12, shown for HN ). Field Evaluation – Grain yield of 1RS.1BL (3.6 t ha-1) was greater than that of Pavon 76 (2.9 t ha-1) by 24% in irrigated experiment at Kings in 2004-2005 growing season. In 2005-2006 growing season, grain yield of 1RS.1BL (4.0 T ha-1) was greater than that of Pavon 76 (3.5 t ha-1) by 14% in irrigated experiment at Sacramento and grain yields of 1RS.1DL in irrigated experiments at Madera (5.0 t ha-1) and at Kings (4.6 t ha-1) were greater than that of Pavon 76 (4.1 t ha-1) at both locations by 23% and 11%, respectively. Differences among the four genotypes for grain yield were not significant under rainfed conditions in both growing seasons. Fig. 1. Set up of the PVC tubes and a bucket and a PVC ring used to collect leachate during early grain filling. Fig. 2. Each PVC tube is sitting on a ring of PVC in each bucket to collect leachate. Fig. 3. Seedlings at 3-leaf stage are growing in sand tubes. Fig. 4. Plants near physiological maturity. Fig. 5. Root system being washed and sand removed from roots. Fig. 6. Washed root systems of five mature bread wheat genotypes. Conclusions: 1- The 1RS translocations had larger root biomass than Pavon 76. 2- Trend analysis indicated lines with larger root biomass absorbed more N in both N treatments and had less N in drainage water. 3- In 50 % of the irrigated field trials, one 1RS line had grain yield greater than Pavon 76 by at least 11%, but not in rainfed trials. Implications: Increased N absorption & mobilization due to greater root biomass may result in: increased grain yield and grain protein content, reduced application of N, less N leaching into ground water and air, thus decreasing N pollution, and d) improved N sustainability. Acknowledgement: This study was partially support- ed by a UC ANR Core Issue Grants Award in 2005. Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig.11 Fig. 12 References Draper, N., and H. Smith. 1981. Applied regression analysis. 2nd ed., John Wiley & Sons, New York. Ehdaie, B., and J.G. Waines. 2001. Sowing date and nitrogen effects on dry matter and nitrogen partitioning in bread and durum wheat. Field Crops Res. 73:47-61. Lukaszewski, A.J. 1993. Reconstruction in wheat of complete chromosomes 1B and 1R from the 1RS.1BL translocation of ‘Kavkaz’ origin. Genome 36:821-824.