P. R. Beuselinck

Quantitative Conversion of Phytate to Inorganic Phosphorus in Soybean Seeds Expressing a Bacterial Phytase

Phytic acid (PA) contains the major portion of the phosphorus in the soybean (Glycine max) seed and chelates divalent cations. During germination, both minerals and phosphate are released upon phytase-catalyzed degradation of PA. We generated a soybean line (CAPPA) in which an Escherichia coli periplasmic phytase, the product of the appA gene, was expressed in the cytoplasm of developing cotyledons. CAPPA exhibited high levels of phytase expression, ≥90% reduction in seed PA, and concomitant increases in total free phosphate. These traits were stable, and, although resulted in a trend for reduced emergence and a statistically significant reduction in germination rates, had no effect on the number of seeds per plant or seed weight. Because phytate is not digested by monogastric animals, untreated soymeal does not provide monogastrics with sufficient phosphorus and minerals, and PA in the waste stream leads to phosphorus runoff. The expression of a cytoplasmic phytase in the CAPPA line therefore improves phosphorus availability and surpasses gains achieved by other reported transgenic and mutational strategies by combining in seeds both high phytase expression and significant increases in available phosphorus. Thus, in addition to its value as a high-phosphate meal source, soymeal from CAPPA could be used to convert PA of admixed meals, such as cornmeal, directly to utilizable inorganic phosphorus.

Fatty Acid Profiling of Soybean Cotyledons by Near-Infrared Spectroscopy

Genetically improved soybean grain often contains altered fatty acid profiles. Such alterations can have deleterious effects on seed germination and seedling development, making it necessary to monitor fatty acid profiles in follow-up physiological studies. The objective of this research was to quantify the five fatty acids in soybean (Glycine max) cotyledons using near-infrared (NIR) spectroscopy. Soybean cotyledon samples were dried, ground, and scanned with visible and NIR radiation from 400 to 2500 nm, and reflectance was recorded. Samples were also analyzed by gas chromatography (GC) for palmitic, stearic, oleic, linoleic, and linolenic acids and total oil; GC data, expressed as actual concentration and proportion of total oil, were regressed against spectral data to develop calibration equations. Equation statistics indicated that four of the five fatty acids could be predicted accurately by NIR spectroscopy; the fifth fatty acid could be determined by subtraction. Principal component analysis revealed that most of the spectral variation in this population was due to chlorophyll absorbance in the visible region. Therefore, the spectra were trimmed to include the NIR region only (1100–2500 nm), and a second set of equations was developed. Equations based exclusively on NIR spectra had equal or greater precision than equations based on visible and NIR spectra. Principal component analysis and partial least squares analysis revealed that even after trimming, at least 90% of the spectral variation was unrelated to fatty acid, though variation from fatty acid was identified in the second and third principal components. This research provides an NIR method for complete fatty acid profiling of soybean cotyledons. Equations were achieved with NIR spectra only, so spectrophotometers that analyze both the visible and NIR regions are not needed for this analysis. In addition, equations were possible with a 250 mg sample, which is one-tenth the normal sample size for this analysis.

Birdsfoot Trefoil, A Valuable Tannin-Containing Legume for Mixed Pastures

Introduction Legumes are important components of pastures. Legumes not only fix atmospheric nitrogen (N2) for their own use when properly inoculated, they provide nitrogen (N) for associated grasses and forbs. A range from 150 to 240 lb N per acre is needed to equal the contribution of legume N in legume-grass mixtures (14). Using a legume reduces the purchase and application costs of N fertilizer and may reduce soil acidification and N losses to the environment. Many legumes are deep-rooted and therefore more drought-tolerant than grasses. Under grazing, legumes are more commonly used as a component of mixtures with grasses than as monocultures. This is because fibrous-rooted grasses are valuable sources of soil organic matter, they provide better protection from soil erosion, are more resistant to grazing and treading damage than legumes, and well-managed grass-legume mixtures provide more-thanadequate levels of crude protein (CP) for highly productive livestock. Legumes have higher nutritive value and voluntary intake than grasses (18), and steer gains are higher on legume-grass mixtures than on N-fertilized grass monocultures (14). However, most legumes can cause bloat. In a uniform stand, a maximum of 50% bloat-causing legume is considered bloat-safe, but bloat has been reported in mixtures with less than 15% bloat-causing legume where selective grazing could occur (30). The low digestibility of tropical legumes has been attributed to their high tannin content (53). Well-managed temperate grass-legume pastures, however, can have excessive CP and therefore animal performance can benefit from the presence of moderate concentrations of condensed tannins that control bloat and decrease ammonia and methane production in the rumen while increasing rumen undegradable protein (58). There are several species in the genus Lotus that produce condensed tannins in high enough concentrations to influence herbage digestibility and animal performance. Big trefoil (Lotus uliginosus Schkur.) produces concentrations of tannins at levels high enough to be considered an antiquality component (2). In contrast, birdsfoot trefoil (L. corniculatus L.; BFT) has lower herbage tannin concentration, but levels can be high enough to be beneficial. This review will discuss agronomic aspects of BFT and assess studies that have compared the livestock production value of BFT with forages that contain little or no condensed tannin. Many studies of tannins in BFT have been carried out in New Zealand with sheep, but studies with cattle are included where available.

Genetic diversity and virulence of Rhizoctonia species associated with plantings of Lotus corniculatus

Species of Rhizoctonia cause a blight of Lotus corniculatus, a perennial forage legume. We characterized genetic variation and virulence in populations of R. solani and binucleate Rhizoctonias associated with diseased L. corniculatus in field plantings over several years. Isolates of anastomosis groups AG-1 and AG-4 accounted for the R. solani recovered from diseased leaf and shoot tissues. Isolates of binucleate Rhizoctonia were recovered predominantly from soil and associated plant debris. Isolates of R. solani were more virulent on leaves and shoots of L. corniculatus than were binucleate Rhizoctonia isolates. Numerous unique DNA restriction patterns were observed among binucleate isolates and anastomosis groups of R. solani. Variation in restriction patterns was greater among isolates of AG-1 from the lower plant canopy than from the upper canopy. No restriction pattern was shared by any isolate from AG-1 and AG-4. Allelic and genotypic heterogeneity of AG-1 isolates were also greater in the lower plant canopy. Binucleate isolates exhibited greater heterogeneity than AG-1 isolates from either canopy region. L. corniculatus offers significant opportunities for investigating temporal and spatial dynamics of genetic structure of Rhizoctonia populations in perennial plant systems.

Cattle Preferentially Select Birdsfoot Trefoil from Mixtures of Tall Fescue and Birdsfoot Trefoil

When birdsfoot trefoil (Lotus corniculatus L.) is interseeded into tall fescue (Festuca arundinacea Schreb.) pastures, animal performance often exceeds that expected based on forage samples taken from the pasture. This may be due to cattle (Bos taurus) preferentially selecting birdsfoot trefoil from mixed pastures. Our objective was to investigate the selectivity for birdsfoot trefoil by cattle grazing tall fescue-birdsfoot trefoil pastures. Treatments were ‘Phyter’ tall fescue sown in a monoculture and in mixtures with ‘ARS-2622’ and ‘Norcen’ birdsfoot trefoil. Beef heifers fitted with esophageal cannulas grazed pastures in the spring and autumn of 1998 and again in spring 1999. In the tall fescue-birdsfoot trefoil mixtures, the amount of birdsfoot trefoil on-offer showed a 73% reduction during the study, but the amount of birdsfoot trefoil in esophageal samples declined by an average of only 22%. Although the percentage of birdsfoot trefoil in mixed pastures often declines over time, its value may be underestimated because animals selectively graze this species when its proportion in pastures is low.