1. Mobilization of Stem Reserves in Diploid, Tetraploid, and Hexaploid Wheat B. Ehdaie, G.A. Alloush and J.G. Waines Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, U.S.A. ABSTRACT One accession (G3489) of wild diploid wheat (Aegilops tauschii, genome DD) with tough spike, a tetraploid durum wheat, Westbred Turbo (Triticum turgidum L. var. durum, genome BBAA), and four hexaploid bread wheats (T. aestivum L., genome BBAADD); including a landrace (No. 49), a tall old wheat (Maringa), and a semidwarf (Express), and a dwarf wheat (Yecora Rojo), were evaluated for main stem length, weight, water-soluble carbohydrate (WSC) content, WSC specific weight (stem WSC content / stem length), and WSC concentration (stem WSC content / stem weight) in well-watered and droughted field experiments with four replications across two years. Stem maximum WSC content was 102 mg in diploid, 957 mg in tetraploid wheat, and ranged from 446 (Maringa) to 695 mg (No. 49) in hexaploid wheat. Stem mobilized WSC was the lowest in diploid (72 mg), highest in tetraploid wheat (823), and it ranged from 374 mg (Maringa) to 561 mg (Express) in hexaploid wheat. These preliminary results indicated that the DD genome might depress WSC-related traits in hexaploid wheat. More diploid, tetraploid, and hexaploid wheats should be evaluated to determine the effect of DD genome on WSC-related traits. INTRODUCTION In semiarid regions, rainfall decreases and soil evaporation increases in spring when wheat crops enter the grain-filling period. Wheat crops often experience water deficit and heat stress during grain growth and development which limit productivity (Ehdaie and Waines, 1989). Grain growth and development in wheat depend on C from three sources: (1) carbohydrate produced after anthesis and translocated directly to the grains, (2) carbohydrate produced after anthesis, but stored temporarily in the stem before being remobilized to the grains, and (3) carbohydrate produced before anthesis stored mainly in the stem and remobilized to grains during grain filling (Kobata et al., 1992). Genotypic variation for stem dry weight and WSC content exist in bread wheat (Ehdaie et al., 2006 a, b). A preliminary study was conducted to quantify main stem reserves using stem dry weight and WSC content and to estimate stem reserve mobilization in the ancestors of hexaploid wheat. MATERIALS and METHODS Accession (G3489) of wild diploid wheat (genome DD) with tough rachis, a tetraploid durum cultivar, ‘Westbred Turbo’ (genome BBAA), and four hexaploid bread wheat cultivars (genome BBAADD); including a landrace from Iran, ‘No. 49’, a tall old cultivar from Brazil, ‘Maringa’, and a semidwarf and a dwarf cultivar, ‘Express’ and ‘Yecora Rojo’, both CIMMYT-derived wheats grown locally in California. Field experiments were planted in 1997 and in 1999 at the Moreno Farm of the University of California Agricultural Experiment Station, Moreno Valley, CA., using a split-plot design with four replicates. The main plots consisted of two irrigation treatments; well-watered and droughted treatments. The split-plot consisted of the genotypes. In the 1997 season, plants in well-watered treatment received 496 mm of water and rain and those in droughted treatment received 430 mm of rain and water. In the 1999 season, plants received 332 and 270 mm of water and rain, respectively. Each plot consisted of six rows, 5 m in length. Interrow spacing was 20 cm and interplant spacing was 3 cm. In each plot, 30 to 40 main tillers from the two middle rows were tagged as spikes emerged from the flag leaf sheath. Three tillers were harvested at random at anthesis and at 10-day intervals after anthesis from the soil surface. After each harvest, spikes, leaf blades and leaf sheaths were removed and main stems were immediately dried at 80 °C for 48 h. Main stem maximum weight and maximum WSC content were determined. Mobilized dry mater and WSC in the main stem was estimated as the difference between postanthesis maximum and minimum weight and maximum and minimum WSC content, respectively. The data was subjected to ANOVA (Steel et al., 1997). Mean values averaged over irrigation treatments and years are reported. RESULTS and DISCUSSION Stem weight and WSC content were correlated (Fig. 1); thus only WSC-related traits are reported. Stem WSC content at anthesis was highest for Westbred Turbo and lowest for Ae. tauschii, whereas, those of the bread wheats were in between (Fig. 2). Stem maximum WSC content was reached 10 d postanthesis for Westbred Turbo, No. 49, and Ae. tauschii, whereas for Express, Yecora Rojo, and Maringa it was reached 20 d postanthesis (Fig. 2). WSC content per unit stem was the highest for Westbread Turbo followed by Yecora Rojo, Express, No. 49, Maringa, and Ae. tauschii (Fig. 3). Modern short-statured bread wheats had more WSC content per unit stem than the old tall ones. Similar trends were observed for stem WSC concentration (Fig. 4). Stem mobilized WSC was highest in Westbred Turbo (823 mg) and lowest in Ae. tauschii (72 mg), whereas those of bread wheats ranged from 315 mg (Maringa) to 561 mg (Express) (fig. 5). These preliminary results indicated that the DD genome might depress WSC-realted traits in hexaploid wheat. More diploid, tetraploid, and hexaploid wheats should be evaluated to determine the effect of DD genome on WSC-related traits. ACNOWLEDGEMENT : We acknowledge support from the Southwest Consortium. RERENCES Ehdaie, B., and J.G. Waines. 1989. Adaptation of landrace and improved spring wheat genotypes to stress environments. J. Genet. Breed. 43:151-156. Ehdaie, B., G.A. Alloush, M.A. Madore, and J.G. Waines. 2006 a. Genotypic variation for tem reserves and mobilization in wheat: I. Postanthesis changes in internode dry matter. Crop Sci. 46:735- 746. Ehdaie, B., G.A. Alloush, M.A. Madore, and J.G. Waines. 2006 b. Genotypic variation for tem reserves and mobilization in wheat: II. Postanthesis changes in internode water-soluble carbohydrates. Crop Sci. 46:2093-2103. Kobata, T., J.A. Palta, and N.C. Turner. 1992. Rate of development of postanthesis water deficits and grain filling of spring wheat. Crop Sci. 32:1238-1242. Steel, R.G.D., J.H. Torrie, and D.A. Dickey. 1997. 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