The proportion of total plant N that occurs in the grain of cereals is called the nitrogen harvest index (NHI). Twenty oat (Arena sativa L.) cultivars, 10 with high and 10 with low NHI, were used to study the repeatability of NHI measurements over environments and the association of NHI with certain grain and straw yield characteristics, i.e., mean yield, regression response to environments with differing levels of N availability, and stability of that yield response. The NHI values for the oat cultivars were determined at low N (0 kg ha−1) and high N (224 kg−1 in 1979 and 100 kg ha− in 1981). Adaptation to variable soil N was evaluated in 12 environments with varying N availability for 2 yrs. The NHI values were highly consistent across N levels (r=0.72**, significant at the 0.01 probability level) but less so across years (r=0.57**). The NHI values were less consistent across years at low soil N (r=0.18) than at high (r=0.75**). Selection for NHI in the high N environment gave realized heritabilities of 1.01 for high and 0.85 for low NHI lines. The NHI was positively associated with mean grain yield and response of grain yields to environmental productivity, but was inversely related to mean straw yield.
Mass selection is a technique widely used in both population and pedigree breeding of pearl millet, Pennisetum glaucum (L.) R. Br. To determine the feasibility of mass selecting for 19 agronomic traits of pearl millet, we (i) estimated trait heritabilities on both a singleplant and a progeny-mean basis and (ii) observed responses of Sp rogenies to divergent selection on parental So plants. Fourteen hundred and forty So spaced plants from each of three pearl millet composites were self-pollinated and evaluated for 19 traits at Patancheru, India on a Udic Rhodostaif soil. Random samples of 289 S~ progenies from each So population were evaluated for these same traits in triple-lattice experiments at the same location. Heritabilities estimated on a progeny-mean basis were all significantly (P 0.01) larger than zero. Heritabilities estimated on a single-plant basis were highest for traits such as panicle length (0.64), plant height (0.58), and seed weight (0.52); they were intermediate straw yield (0.40); and they were lowest for grain yield (0.29), threshing ratio (0.24), and harvest index (0.23), averaged across composites. Divergent selection of the highest and lowest decile of So plants identified S~ progenies with significantly (P < 0.05) increased and decreased means, respectively, for panicle and seed characteristics in all composites and for grain yield in two of the composites. Selection for increased efficiency of dry matter partitioning, however, was ineffective. The observed heritability values suggest that mass selection of pearl millet can be effective for all traits examined, with the rate of gain being proportional to the magnitude of those values.
The plant breeder's task of improving and stabilizing many plant traits simultaneously is complicated by interrelationships that occur among the traits . Factor analyses were conducted on three phenotypically diverse pearl millet [Pennisetum glaucum (L .) R . Br .] composites to describe the structure of relationships among yield, morphological, and physiological traits . Approximately 1000 So spaced-plants from each composite were evaluated for 20 traits, and random samples of 289 S, progenies from each composite were evaluated for 18 of these traits . Factors extracted in So and S, populations identified unique sets of traits that were interrelated along axes of (a) biological yield, (b) panicle size, (c) dry matter partitioning and (d) compensation between number and size of seeds . Several plant traits had large loading coefficients on thè Biological Yield' and also, but with opposite signs, on the `Dry Matter Partitioning' factor . The traits having large loadings on these two factors differed between space-planted and normal-density stands, showing that environmental conditions contributed to the associations observed among traits . Correlations of S, with parental So factor scores for the `Biological Yield', `Panicle Size' and `Seed Paramters' factors produced significant correlation coefficients, indicating that these trait complexes had a genetic basis . The implications of these results for millet breeding are discussed .
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