Recurrent Selection for Kernel Weight in Spring Wheat

reported grain yield increased 3.9 and 7.4% cycle 1, respectively, over two cycles of selection in barley Increasing kernel weight has been proposed as a method to increase (Hordeum vulgare L.). Durum wheat (Triticum turflour extraction in spring wheat (Triticum aestivum L.). Recurrent selection was initiated to increase kernel weight while maintaining gidum L. var. durum) grain yield improved 6.3% cycle 1 genetic variation for the unselected traits. Our objectives were to after two cycles of recurrent selection (Olmedo-Arcega determine (i) genetic gain for kernel weight after eight cycles of et al., 1995). In spring wheat, Delzer et al. (1995), reselection, (ii) the indirect effects of the selection for kernel weight ported a gain of 2.7% cycle 1 for grain protein after on other agronomic traits, kernel morphology, milling fractions, and four cycles of selection. grain protein concentration, and (iii) the level of genetic variability Long-term results from recurrent selection programs among lines within selection cycles for kernel weight and unselected involving autogamous crops are limited. A recurrent traits. Ten lines, selected for high kernel weight, were originally inselection program for grain yield in oat (Avena sativa termated to form the base population. About 20 F2 plants with the L.) was initiated in 1968 and has completed seven cycles highest kernel weight were selected ( 2% of the population), and (DeKoeyer and Stuthman, 1998). Parents for Cycle 7 about three of their F3 progeny were intermated to form the next produced 21.7% more grain than the parents of Cycle cycle. This procedure was repeated for eight cycles, with an average of 60 crosses per cycle. Forty random lines from each cycle were used 0, which is nearly a 2.5% yield gain per cycle. to evaluate agronomic traits in three environments. Kernel weight Single trait selection programs often alter other unseincreased linearly at about 4.5% cycle 1. Cycle means did not differ lected traits, reducing the usefulness of this strategy for plant height and grain yield, but tillers per square meter and for cultivar improvement. Recurrent selection for grain kernels per spike decreased 2.4 and 1.6% per cycle, respectively. yield in oat resulted in increased kernel number and Spikelets per spike, kernels per spikelet, test weight, and days to kernel weight, but delayed heading by almost 2 d and heading decreased, whereas spike length increased in response to increased plant height (Payne et al., 1986). Parlevliet selection for kernel weight. The proportion of bran and shorts deand van Ommeren (1988) reported that although grain creased, and flour extraction and grain protein concentration inyield was increased in spring barley, adverse effects, creased 0.58 and 0.16% cycle 1, respectively. No clear trend towards such as a greater susceptibility to lodging, were also decreased genetic variance for kernel weight was observed since gain detected. Delzer et al. (1995) reported reduced grain was linear over eight cycles. The observed gain from selection and heritability estimates point to kernel weight being controlled by sevyield, taller plants, and later heading after four cycles eral genes with small effects. Selection for increased kernel size in of recurrent selection for grain protein content in spring this population resulted in increased flour yield. wheat. Worzella (1942) and Boyce (1948) reported that kernel weight was quantitatively inherited, but postulated R selection is a cyclical breeding strategy major effects by a few genes. Sharma and Knott (1964) designed to accumulate favorable gene combinareported that kernel weight was moderately to highly tions while maintaining genetic variability within a popheritable (0.37–0.69), depending on the method used ulation. This procedure is used extensively in allogato estimate the heritability. Kernel weight was low to mous species. Initial studies using this procedure were moderately and positively correlated with grain yield reported before 1920 and its effectiveness has been docbut negatively correlated with both kernels per spike umented in the literature (Hallauer, 1985). Recurrent and number of tillers (Hsu and Walton, 1971; Knott and selection has not been as widely used in autogamous Talukdar, 1971). species because of the amount of labor required to inIn 1967, a recurrent selection program was initiated termate selected lines and the difficulty associated with to increase kernel weight in spring wheat, leading to a producing adequate quantities of seeds for progeny evalusubstantial increase in kernel weight after the first four ations. cycles of selection (Busch and Kofoid, 1982). This popuReported responses in small grains to recurrent seleclation has completed its eighth cycle of recurrent selection have been positive (Carver and Bruns, 1993); howtion. Our objectives were to determine (i) genetic gain ever, most were short term, usually involving less than for kernel weight after eight cycles of selection, (ii) the five cycles (Goldringer and Brabant, 1993). Parlevliet indirect effects of the selection for kernel weight on and van Ommeren (1988) and Marocco et al. (1992) other agronomic traits, kernel morphology, milling fractions, and grain protein concentration, and (iii) the level J.J. Wiersma, Dep. of Agronomy & Plant Genetics, Northwest Reof genetic variability among lines within selection cycles search and Outreach Center, Univ. of Minnesota, 2900 University Ave., Crookston, MN 56716; R.H. Busch, USDA-ARS, Plant Science for kernel weight and unselected traits. Unit, 411 Borlaug Hall, Univ. of Minnesota, 1991 Upper Buford Circle, St. Paul, MN 55108; G.G. Fulcher, Dep. of Food Science & Nutrition, MATERIALS AND METHODS Eckles Ave., St. Paul, MN 55108; G.A. Hareland, USDA-ARS Spring Wheat Quality Lab., Fargo, ND58105. Contribution from Minnesota The recurrent selection program was initiated by screening Agric. Exp. Stn., Scientific Journal Series no. 99113037. Received 17 about 100 cultivars and breeding lines for high kernel weight. Sept. 1999. Corresponding author ([email protected]). Abbreviations: DIA, digital image analysis. Published in Crop Sci. 41:999–1005 (2001).