New perspectives on ancient Mars

Mars was most active during its first billion years. The core, mantle, and crust formed within approximately 50 million years of solar system formation. A magnetic dynamo in a convecting fluid core magnetized the crust, and the global field shielded a more massive early atmosphere against solar wind stripping. The Tharsis province became a focus for volcanism, deformation, and outgassing of water and carbon dioxide in quantities possibly sufficient to induce episodes of climate warming. Surficial and near-surface water contributed to regionally extensive erosion, sediment transport, and chemical alteration. Deep hydrothermal circulation accelerated crustal cooling, preserved variations in crustal thickness, and modified patterns of crustal magnetization.     

A “curious blend”: The successful farmer in American farm magazines, 1984–1991

Mass media images offer audiences models for how to perform the social roles they depict. Opinions and other attributes of credible media models may likewise be embraced by audience members seeking to identify with those models. Thus farm magazine narratives about “successful” farmers may encourage readers to model or aspire to featured farmers' production and management techniques and ascribe legitimacy to models' responses to current agricultural issues. However, production of agrarian images in the mass media — including images of farms, farmers, and farmers' values — are inevitably biased such that media representations of successful farmers selectively present objective characteristics in terms of the media's own ideological frameworks, which in turn reflect the dominant ideology of the social relations in which the media are engaged. As a first step in identifying farm magazines' role in creating social models for farmers, this study analyzes articles featuring “successful,” “leading,” or “innovative” farmers in leading agricultural magazines. The featured farmers are categorized according to enterprise characteristics and characterizations of them and their management philosophies. Findings show that farmers in farm magazines have larger than average operations and are portrayed in a way that blends a “farming as business” orientation with more conventional agrarian values but that generally omits non-business aspects of farm life.     

Potential of wild germplasm for increasing yield of grain sorghum

Summary Sorghum [Sorghum bicolor (L.) Moench] backcross populations containing 3 to 50% wild germplasm were evaluated in south central India for grain yield and nine related traits. No individual BC₀F₂- to BC₂F₂-derived lines were high transgressive segregates for grain yield. Only 1.5% of all BC₃F₂- or BC₄F₂-derived lines were transgressive segragates, with 26% higher mean grain yield than their respective recurrent parents. The ten highest-yielding BC₂F₂- to BC₄F₂-derived lines per mating having parent CK60B yielded an average of 14% more than CK60B, which was, at the 5% level, a statistically significant difference. However, the increased yield was associated with increased plant height. The highest-yilding lines from RS/R/A2725 x virgatum and RS/R/A2725 x verticilliflorum were an average of 13.5% higher-yielding than RS/R/A2725 (a significant difference) and were equal in plant height. Selection increased BC₂ mean grain yields by 6 to 27%. Population mean yield, mean yield of selected lines, and frequency of high-yielding lines were highest in the BC₄.Journal paper no. 380, ICRISAT, Patancheru, India; Journal paper no. J-11114, Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, USA.     

Relationship among planted and harvested kernel weights and grain yield and protein percentage in winter wheat

Summary Wheat (Triticum aestivum L.) kernel weight is an important yield component and seed quality factor that appears to be declining with recent cultivar releases in the major U.S. wheat region. The objectives of experiments were to detmrmine the relationship between planted and harvested 1000-kernel weights and their effect on grain yield and grain protein percentage. Twelve popular hard red winter wheat cultivars were grown with recommended practices at 10 Kansas locations for three years. Rank correlation coefficients between kernel weights and grain yields and protein percentages were calculated.Correlations of planted and harvested kernel weights over all cultivars with grain yield were inconsistent, being positive for some locations and years and negative for other locations and years. Planted kernel weights and grain yields of individual cultivars were not related, but harvested kernel weights and grain yields were correlated positively for eight of the 12 cultivars. Harvested kernel weights and grain protein percentages frequently were correlated positively at individual locations, but always were correlated negatively for individual cumtivars. It was concluded that high stable harvested wheat kernel weight is important as a component of grain yield under a range of environments and that improving this trait would benefit all segments of the wheat industry.Contribution No. 84-395-J, Department of Agronomy, Kansas State University, Manhattan, Kansas 66506 USA.     

Direct and indirect selection for grain yield in oats (avena sativa L.)

Direct and indirect selection for increased grain yield were carried out on a population of 678 F₂-derived lines of oats. A selection intensity of 10% was used with direct selection (selection for grain yield itself) and with indirect selection using three criteria, harvest index, vegetative growth rate, and the index of harvest index + vegetative growth rate. Expected gains from 1978 evaluations were compared to actual gains measured in 1980. Actual grain yield increases were 4, 8, 7, and 6% from selection via harvest index, vegetative growth rate, grain yield, and harvest index + vegetative growth rate, respectively. Thus, indirect selection via vegetative growth rate gave a greater increase in grain yield than did direct selection. Heritability values computed via components of variance ranged from 0.50 to0.57 for the three traits, harvest index, vegetative growth rate, and grain yield, whereas regression heritabilities ranged from 0.41 to 0.55. Realized heritabilities were 0.33, 1.00 and 0.89 for the three traits, respectively. Selection via all criteria caused significant changes in nearly all agronomic traits except weight per volume. Vegetative growth rate, which gave the greatest gain in grain yield, caused less drastic changes in days to anthesis, plant height, biological yield, and vegetative yield than did direct selection for grain yield.     

Structure of variation among morphological and physiological traits in three pearl millet composites

Summary 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 S₀ spaced-plants from each composite were evaluated for 20 traits, and random samples of 289 S₁ progenies from each composite were evaluated for 18 of these traits. Factors extracted in S₀ and S₁ 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 the Biological Yield and also, but with opposite signs, on the Dry Matter Partitioning factor. The traits having large loading 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 S₁ with parental S₀ 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.