César G. López

Dehydrin expression and drought tolerance in seven wheat cultivars

rarely receives additional moisture during emergence. The lack of precipitation during seedling emergence The winter wheat (Triticum aestivum L.) producing region of the represents a major cropping risk to producers. ConseU.S. Pacific Northwest (PNW) is subject to periods of water deficit during sowing and grain filling. Improving the genetic adaptation of quently, there is need to improve the genetic tolerance wheat to drought stress represents one of the main objectives of of wheat to drought at the seedling stage. regional breeding programs. One biochemical response to dehydrative Plant breeding efforts to improve drought tolerance stress is the accumulation of a family of proteins called dehydrins, would be aided by the identification of biochemical which are believed to protect membranes and macromolecules against markers associated with improved field performance denaturation. Although previous studies demonstrated the accumulaunder drought conditions. Dehydrins, also known as tion of dehydrins in drought-stressed wheat, little was known about late embryogenesis abundant (LEA) D11 (Dure, 1993) the relation of dehydrin expression to acquisition of drought tolerance proteins represent potential markers. Dehydrins are in specific varieties adapted to the PNW. We characterized dehydrin members of a family of proteins that are expressed after accumulation during the exposure of seven cultivars (‘Connie’, ‘Gene’, ‘TAM105’, ‘Rod’, ‘Hiller’, ‘Rhode’, and ‘Stephens’) to progressive plants are exposed to stresses with a dehydrative compodrought stress in four separate experiments. The objective was to nent. This family of proteins is characterized by the identify differences in the nature or timing of dehydrin expression in presence of a consensus amino acid sequence (EKK these cultivars and to learn whether dehydrin expression was associGIMDKIKELPG) near the carboxy terminus (Close ated with the acquisition of stress tolerance during seedling developet al., 1993). Dehydrins can be detected by means of ment. Expression of a 24-kDa dehydrin was observed in Connie, antibodies prepared against this consensus sequence TAM105, and Gene after 4 d of stress and at subsequent sampling (Close et al., 1993) and have been identified in at least dates while no dehydrins were detected in nonstress control plants. 30 diverse plant species including wheat (Campbell and Dehydrin expression was significantly delayed in the remaining cultiClose, 1997). vars. The presence of this dehydrin was related to acquisition of drought tolerance characterized by a greater maintenance of shoot An association between tolerance to stresses with a dry matter production in Connie, TAM105, and Gene. Although the dehydrative component (drought, freezing, or salinity) role of these proteins remains unknown, their association with stress and the expression of dehydrin proteins has been obtolerance suggests that dehydrins might be used to improve the adaptaserved in some crop species. Houde et al. (1992) found tion to drought. that the expression of a specific dehydrin (WSC120) accompanied the development of freezing tolerance in eight species of Gramineae. Tolerance to chilling temperatures during emergence was correlated with the M wheat-producing regions of the world are expression of a 35-kDa dehydrin in two genetically simisubject to water deficits during some part of the lar cowpea [Vigna ungiculata (L.) Walp] sublines that growing season (Moustafa et al., 1996). The impacts of differed in their expression of this dehydrin (Ismail et al., these water deficits on grain development and yield 1997). Lim et al. (1999) also found a positive association depend on their severity and the stage of plant growth between cold hardiness and a dehydrin protein in Rhoduring which they occur. Seedling emergence is one dodendron. Danyluk et al. (1998) showed that the stage of growth that is sensitive to water deficit. In WCOR410 dehydrin protein accumulated near the Mediterranean environments like the PNW, dry condiplasma membrane during cold acclimation of wheat and tions during emergence and early growth along with low suggested that this accumulation protected the integrity temperatures during winter and high temperatures and of the plasma membrane when plants were subjected increasing water demands at the end of spring, result to stress. Zhu et al. (2000) reported increased expression in low yields because of the inability of plants to produce of dehydrin genes during the development of freezing adequate dry matter (Regan et al., 1992). Many productolerance in a more tolerant barley (Hordeum vulgare ing regions of the world, including the PNW are subL.) cultivar Dicktoo relative to that which occurred in jected to water deficits during the seedling stage since ‘Morex’, a less tolerant variety. Cellier et al. (1998), winter wheat is sown during autumn into dry soil and using two sunflower (Helianthus annuus L.) inbred lines, one tolerant and one susceptible to drought stress, showed a higher accumulation of mRNA transcripts Cesar G. Lopez, Catedra de Mejoramiento Vegetal, Facultad de Ciencias Agrarias, Universidad Nacional de Lomas de Zamora, Ruta 4 corresponding to HaDhn1 and HaDhn2 genes in the Km. 2, Llavallol, 1832, Buenos Aires, Argentina; Gary M. Banowetz, tolerant line that was associated with cellular turgor USDA/ARS, 3450 S.W. Campus Way, Corvallis, OR 97331; C. James maintenance under drought stress. Peterson, Department of Crop and Soil Science, Oregon State UniverAlthough genotypic differences in dehydrin expressity, Corvallis, OR 97331-3002; Warren E. Kronstad (deceased), Department of Crop and Soil Science, Oregon State University, Corvallis, sion have been demonstrated in responses to cold and OR 97331. Received 8 July 2002. *Corresponding author banowetg@ drought tolerance, it is important to study the expression ucs.orst.edu). of dehydrins in relation to changes in leaf water potential when seedlings are exposed to drought. The purpose Published in Crop Sci. 43:577–582 (2003).

Using mixing ability analysis from two-way cultivar mixtures to predict the performance of cultivars in complex mixtures

Cultivar mixtures are an alternative to monoculture for crop production. Methods for predicting the performance of cultivars in mixtures would facilitate the identification of the best cultivars for mixture formation. A prediction method [Theor. Appl. Genet. 81 (1991) 265] based on the combining ability analysis proposed by Gardner and Eberhart [Biometrics 22 (1966) 439] model II was evaluated for mixtures. Mean values for percent diseased leaf area (DLA) and yield under disease (YUD) of five club wheat cultivars and all possible two-way mixtures (across three Oregon locations) were used to estimate the relative contribution of each cultivar to the mixture mean (Ii) and the predicted mean of all possible mixtures (Ym) according to the MFC method. Estimated Ii and Ym were compared to actual mixture means. Ii allowed identification of the best cultivars for mixture formation for both DLA and YUD. Actual and predicted rank correlation coefficients for DLA and YUD of complex mixtures (more than two components) were highly significant (P<0.01) for the mean of the three environments (0.87 and 0.78, respectively) and for the mean of the two most relevant environments (0.83 and 0.93, respectively). Similar results were obtained when Ii and Ym were estimated from the means of the cultivars in pure stand (instead of being estimated from the mixing ability analysis). This was due to the relatively small competitive effects (hi) of the cultivars compared to their additive effects (vi). We extended our analysis to data from a yield study of two-way mixtures of eight soybean cultivars [Crop Sci. 29 (1989) 885; Agron. J. 81 (1989) 559], where additive and competitive effects had similar magnitude. Actual and predicted mixture means could not be compared because only two-way mixtures were included in the study. In this case, the mean yield of the cultivars in pure stand was not a good predictor of the performance of cultivars in mixtures. Ra 604, the third highest yielding cultivar, had a positive additive effect (vi=53.8kg/ha), but a highly negative competitive effect (hi=−49.7kg/ha) that resulted in a negative contribution (Ii) to yield when mixed with the other soybean cultivars. Additive (vi) and competitive effects (hi) must be considered to obtain superior mixtures, and the advantage of Ii is that it takes into account both effects (Ii=12vi+(k−1/k)hi, k is the number of cultivars). The MFC method may be a useful tool to select desirable cultivars to obtain complex mixtures.

The Genetic Architecture of Maize (Zea mays L.) Kernel Weight Determination

Individual kernel weight is an important trait for maize yield determination. We have identified genomic regions controlling this trait by using the B73xMo17 population; however, the effect of genetic background on control of this complex trait and its physiological components is not yet known. The objective of this study was to understand how genetic background affected our previous results. Two nested stable recombinant inbred line populations (N209xMo17 and R18xMo17) were designed for this purpose. A total of 408 recombinant inbred lines were genotyped and phenotyped at two environments for kernel weight and five other traits related to kernel growth and development. All traits showed very high and significant (P < 0.001) phenotypic variability and medium-to-high heritability (0.60−0.90). When N209xMo17 and R18xMo17 were analyzed separately, a total of 23 environmentally stable quantitative trait loci (QTL) and five epistatic interactions were detected for N209xMo17. For R18xMo17, 59 environmentally stable QTL and 17 epistatic interactions were detected. A joint analysis detected 14 stable QTL regardless of the genetic background. Between 57 and 83% of detected QTL were population specific, denoting medium-to-high genetic background effects. This percentage was dependent on the trait. A meta-analysis including our previous B73xMo17 results identified five relevant genomic regions deserving further characterization. In summary, our grain filling traits were dominated by small additive QTL with several epistatic and few environmental interactions and medium-to-high genetic background effects. This study demonstrates that the number of detected QTL and additive effects for different physiologically related grain filling traits need to be understood relative to the specific germplasm.