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As an attempt to estimate fruit production in carob tree (Ceratonia siliqua L.) under Mediterranean conditions, several multiple linear regression models were elaborated by Correia et al. (p. 1577–1583) on the basis of leaf nutrient concentrations. Two dates of leaf sampling were studied: autumn and winter. The best estimation model indicated that 92% of yield variation may be related to N, P, K, Mn, and Fe leaf concentration values. The equation obtained was validated by means of an independent data set.
Growth and Spectral Vegetation in Durum Wheat
Destructive sampling for biomass assessment of crops is tedious and time consuming, so some vegetation indices based on spectral reflectance have been proposed as an alternative method. Aparicio et al. (p. 1547–1555) investigated the usefulness of normalized difference vegetation index and simple ratio as total dry matter and leaf area index predictors. The best growth stages for measurements were 65 and 75 of Zadock's scale, and their suitability depended on the range of variability within experimental data. Their value as indirect genotypic selection criteria is discussed.
Drought-Adaptive Traits in Upland Rice
Extensive research has gone into putative drought-adaptive traits that differ among tolerant and susceptible rice cultivars. While ample genetic variation exists for such traits, the adaptive value of the trait in different drought environments is often unclear. A range of rice (Oryza sativa L.) lines and cultivars were evaluated by Lafitte and Courtois (p. 1409–1420) in nine environments that differed in water supply, and the interaction between genotype and environment was examined relative to selected morpho-physiological traits. For this set of lines, positive interaction with stress environments was found in lines that had high root pressure and long roots, but those lines tended toward drought-susceptible aboveground traits. Maturity was a critical factor in determining how genotypes interacted with environments.
Solanum tuberosum vs. Andean populations
A study by Raker and Spooner (p. 1451–1458) tests the genetic difference between landrace populations of Solanum tuberosum subsp. tuberosum and subsp. andigena Hawkes using nuclear DNA microsatellites. In mixed populations, subsp. tuberosum was distinguished from subsp. andigena and other wild species. These results support the genetic difference of these two populations and their recognition at some classification level.
Adaptation of Forage Legumes to Acid Soils
Although much is known about adaptation of forage species to acid and calcareous soils, relative adaptation of some species and adaptation of cultivars within species have not been thoroughly studied. The soil-on-agar technique, based on growth of the primary root in an acid, Al-toxic soil, characterizes relative acid-soil adaptation of small-seeded species and cultivars. The procedure by Voigt and Mosjidis (p. 1631–1639) correctly identified the superior acid-soil adaptation of ‘AU Dewey’ birdsfoot trefoil (Lotus corniculatus L.). Acid-soil adaptation of kura clover (Trifolium ambiguum M. Bieb.) was superior to that of white clover (T. repens L.). Among kura cultivars, Cossack, developed from a germplasm selected in Utah, was less acid-soil resistant than Rhizo, developed in Kentucky.
Orchardgrass and Ryegrass Carbon Isotope Discrimination
Water-use efficiency is important in the selection of grasses for pastures in semiarid regions of western North America. Jensen et al. (p. 1498–1503) evaluated cultivars of orchardgrass (Dactylis glomerata L.), perennial (Lolium perenne L.) and intermediate ryegrass (L. xhybridum Hausskn), and festulolium [xfestulolium braunii (K. Richt.) A. Camus.] under a line-source irrigation system for carbon isotope discrimination (
) to determine relationships between and dry matter (DM) yield and trends in across four water levels (WL2, wettest to WL5, driest) under frequent defoliation. Consistent differences were found between orchardgrass and the ryegrasses for when averaged across water levels. Within orchardgrass and ryegrasses, nonsignificant negative correlations between DM yield and were observed at higher water levels; however, as water stress increased, positive correlations were found between and DM yield in the ryegrasses.
Synchronous Flowering and Fruit Set in Soybean
Seed number in grain crops is related to photosynthesis during flowering and podset, but the mechanisms responsible for this relationship are not well understood. Egli and Bruening (p. 1535–1540) used a girdled-node system to evaluate the relationship between the timing of flower development and seed number in soybean [Glycine max (L.) Merr.]. Photosynthetically isolated single and multi-node treatments fed by a single leaf were used to vary flower number while maintaining a similar-sized source. All nodes on the multinode treatment flowered at the same time and total flower production was 68% larger than the single-node system which resulted in more pods (36–94%) and more seeds (36–78%). The response of pod and seed number to synchronous flowering suggests that the timing of flower development may play a significant role in determining reproductive success.
Predicting Intake of Bromegrass by Ruminants
Voluntary intake by ruminant livestock can be predicted by chemical and physical characteristics of feeds. Casler (p. 1427–1433) conducted divergent selection for a chemical (neutral detergent fiber, NDF) and a physical (particle size reduction index, PSRI) measure of intake in smooth bromegrass (Bromus inermis Leyss). Both traits were heritable, resulting in significant gains, although gains were greater for PSRI than for NDF. Selection for NDF resulted in consistent and opposite changes in PSRI, while selection for PSRI resulted in little or no change in NDF. The concentration of NDF seems to be one of several possible mechanisms causing genetic variation for PSRI. Loci that regulate NDF also control PSRI, acting pleiotropically, but PSRI appears to be governed by additional loci that regulate other plant traits.
Adaptation of Festulolium to Northern Climates
Festulolium [Festulolium loliaceum (Hudson) P.V. Fournier], a hybrid between meadow fescue (Festuca pratensis Huds.) and Italian ryegrass (Lolium multiflorum Lam.) or perennial ryegrass (L. perenne L.), is a highly nutritious and palatable pasture grass that has insufficient cold tolerance for long-term survival in pastures of the northern USA. Casler et al. (p. 1421–1426) documented improved freezing tolerance associated with natural selection for survival in field plots. Selections had increased forage yield, averaged across 13 locations from Minnesota to Virginia, and increased persistence across the locations with the most severe winter conditions. One cycle of phenotypic selection for surviving festulolium plants at multiple locations increased freezing tolerance, which led to increased adaptation of festulolium to northern USA locations.
Semidwarf Wheat Cultivars
The success of the Green Revolution can be partially attributed to the development and widespread use of semidwarf cultivars of wheat (Triticum aestivum L.). Compared with normal or tall genotypes, the advantages of semidwarf genotypes include higher harvest index, yield per plant, and yield per hectare, while the disadvantages are associated with reduced test weight and protein content but, more importantly, shorter coleoptiles which can result in unacceptable stands especially when planted under low soil moisture conditions. Pereira and coworkers (p. 1483–1487) examined the effect of temperature and gibberellic acid in the seed germination medium on the coleoptile length of tall, semidwarf, and dwarf isolines of two cultivars. The results indicated that coleoptile length in tall and semidwarf genotypes in certain genetic backgrounds could be increased by the application of gibberellic acid, suggesting that preplanting seed treatments with growth hormones may improve seedling establishment.
Breeding Strategy for Fusarium Resistance in Barley
Design of an efficient breeding strategy for developing Fusarium head blight (FHB) resistant barley (Hordeum vulgare L.) cultivars is dependent on knowing (i) the heritability of FHB resistance and accumulation of deoxynivalenol (DON), a mycotoxin contaminant produced by Fusarium graminearum Schwabe, and (ii) the correlated response of other traits when Urrea and coworkers (p. 1404–1408) select for reduced FHB. Field studies in FHB disease nurseries using ‘Foster’/CIho 4196 were conducted to gain this knowledge. Heritability of FHB severity and DON accumulation was moderate. On the basis of information obtained on correlated responses, development of FHB resistant lines derived from crosses to CIho 4196 with acceptable DON accumulation and days to heading is obtainable, but development of FHB resistant plants with acceptable plant height will be difficult.
Apomixis in Buffelgrass
Molecular tools are being applied to begin dissecting the genetic elements controlling apomixis. In this study, Jessup et al. (p. 1688–1694) established a linkage map of the apospory region in buffelgrass [Pennisetum ciliare (L.) Link syn. Cenchrus ciliaris L.]. Apospory mapped to a single locus in a region having disomic inheritance and suppressed recombination, and comparative mapping revealed the possibility of polyphyletic origins for apomixis. Allelic interactions through female gametophytes were found to affect offspring survival in buffelgrass. These results indicate the valuable contribution that buffelgrass genomics offers to marker-assisted breeding and map-based cloning of apospory.
Testing for Presence of Endophytes in Tall Fescue
Utilization of nontoxic endophytes in tall fescue (Festuca arundinacea Schreb.) provides persistent pastures associated with endophyte without the toxic effects on livestock. These value-added products are proprietary and, thus, must have a rapid reliable mechanism of testing to document presence in seed and vegetative tissues for quality control and compliance by those who utilize these products. Hill et al. (p. 1627–1630) developed a monoclonal antibody-based test which is capable of differentiating a nontoxic endophyte in tall fescue seed and vegetative tissue from other nontoxic and naturally occurring endophytes. These results demonstrate the specificity of monoclonal antibodies, provide a powerful isolate-specific diagnostic tool for commercial analysis of a nontoxic endophyte, and can largely replace the need for expensive RFLP analysis.
Aluminum Tolerance in Wheat
A better understanding of aluminum tolerance in wheat (Triticum aestivum L.) will enhance efforts to develop varieties more tolerant to acid soils. Tang et al. (p. 1541–1546) examined the physiological basis of Al tolerance in near-isogenic lines (NILs) that harbor single major Al tolerance genes from ‘Atlas 66’ but are not as Al-tolerant. The NILs released more malate from their root tips than their Al-sensitive recurrent parents, but less than Atlas 66. Thus, more than one gene is present in Atlas 66 that influences malate-mediated Al tolerance. Higher levels of Al tolerance are obtained if all of the relevant Atlas 66 genes are present.
Site-Specific Farming with Maize
Site-specific farming (SSF) requires the identification and management of biotic and abiotic factors affecting crop productivity. Predicting effects of interactions between these factors on crop productivity is a major challenge. Monitoring crop growth can form the basis for managing SSF, since the plant integrates factors affecting its growth. Machado et al. (p. 1564–1576) conducted a growth analysis in maize (Zea mays L.) at geo-referenced locations. Water, soil, arthropods, and disease effects on corn growth were evaluated. Measured parameters forecast grain yields better in 1998, a dry year, than in 1999, a wet year. Trends in net assimilation rate that matched trends in yield were evident before the 12-leaf stage, making net assimilation rate a potentially useful measurement for early in-season management decisions. Information on biomass, although obtained later, may be used for both in-season and the following season's management decisions.
Fresh- vs. Field-Cured Hay
Singer (p. 1656–1661) evaluated the extent of change in fresh vs. field-cured grass hay quality, mineral, and NO-3-N concentrations under rain-free conditions. Differences in orchardgrass (Dactylis glomerata L.), smooth bromegrass (Bromus inermis Leyss.), and timothy (Phleum pratense L.) between fresh and field-cured forage were detected, with orchardgrass having the greatest consistency and smooth bromegrass the least. The results demonstrate that under rain-free, field-curing conditions, changes in grass quality, mineral, and tissue NO-3-N concentrations occur.
Regulators of Voluntary Food Intake in Ruminants
During the history of ruminant nutrition, many factors have been proposed as regulators of voluntary feed intake (Fisher, p. 1651–1655). Factors controlling ruminant intake should be assumed to function with multiple interactions. A number of feedback regulators such as distension, protein, and energy should be considered in the context of their interacting regulatory effects when attempting to predict intake. In spite of these difficulties, knowledge of theoretical feedbacks has already been used to modify ruminant feeding strategies. In the future, novel mathematical and experimental approaches will be needed to properly consider each feedback signal in light of the other feedbacks.
Related articles in Crop Science:
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