S. C. Schank

Nitrogen Fixation in Grasses Inoculated with Spirillum lipoferum.

Field-grown pearl millet (Pennisetum americanum) and guinea grass (Panicum maximum), lightly fertilized and inoculated with Spirillum lipoferum, produced significantly higher yields of dry matter than did uninoculated controls. Up to 42 and 39 kilograms of nitrogen per hectare were replaced by inoculation for pearl millet and guinea grass, respectively. The data demonstrate that nitrogen fixation by these grass-Spirillum systems is efficient and is achieved at a reasonable energy cost to the plant.

Fluorescent antibody technique to identify Azospirillum brasilense associated with roots of grasses

Abstract Bacteria associated with roots of grasses from Florida, Ecuador and Venezuela were isolated and their N 2 -fixing ability was demonstrated by C 2 H 2 reduction assay. The bacterial isolates have been classified as Azospirillum brasilense (formerly Spirillum lipoferum ). These N 2 -fixing isolates have been compared with several Brazilian strains. Fluorescent antibody (FA) techniques were used to assist identifying isolates of N 2 -fixing bacteria from grass roots. Tests with antisera prepared against four strains of Azospirillum were used to define serological groups. Antigen-antibody specificity was demonstrated using both Azotobacter and Azospirillum antisera against known species of other soil microorganisms and numerous unidentified soil bacteria. Several applications of the FA technique are suggested to identify N 2 -fixing bacteria associated with grass roots.

Development and application of RFLP and rapd dna markers in genetic improvement of Pennisetum for biomass and forage production

Abstract The objective of this research was to use new molecular techniques to improve efficiency of traditional breeding programs of Pennisetum for biomass and forage production. Restriction fragment length polymorphic (RFLP) and random amplified polymorphic DNA (RAPD) genetic markers were developed to characterize the Pennisetum purpureum genome and those markers were used to facilitate genetic study and breeding improvement. Standard RFLP and RAPD methodologies were adapted and/or modified to work well with Pennisetum and the DNA marker system was developed. This marker system was used to “fingerprint” the P. purpureum plant introduction collection, to determine the genetic diversity in that collection, to measure heterozygosity of selected lines and to measure hybridization/self fertilization rates using different crossing methods. Linkage relationships were studied between the DNA markers and quantitative trait loci (QTL), especially those loci associated with biomass/forage productivity, conversion to methane and rumen digestibility. Linkage analyses revealed 64 markers were linked to QTL of 26 plant traits. Those QTL-linked markers form the basis for genetic study of important biomasstforage productivity and quality traits. While the research was conducted with biomass for energy objectives, it is equally applicable to forage production and quality.

Peroxidase-antiperoxidase labeling of Azospirillum brasilense in field-grown pearl millet

Abstract Bacterial cells of Azospirillum brasilense (Tarrand) from their natural habitat were labeled with peroxidase-antiperoxidase (PAP), identified, and observed using the transmission electron microscope. Pure cultures of A. brasilense, axenically inoculated pearl millet root samples, and field-grown inoculated pearl millet root samples were embedded in Luffs araldite. Thin sections were treated using the immunological PAP method. Identification was possible because of the heavy outlining of the cells with a dense deposit of osmium. Pleomorphic forms of A. brasilense were observed in axenic pearl millet root cultures. Encapsulated forms were larger than vibrioid forms, and both types reacted with antiserum against the bacterial strain.

Genetic improvement of napiergrass and hybrids with pearl millet

Abstract Genetic improvement of napiergrass (Pennisetum purpureum Schum.) has included both intraspecific and interspecific hybridization. Our main thrust has been on interspecific hybrids between P. glaucum (L.) R.Br. (pearl millet) and P. purpureum, but we have also studied intraspecific hybrids between USDA PI 300086 (cv. Kinggrass) and PI 517947 (cv. Mott). Overall objectives were: (1) to breed higher quality and /or higher yielding napiergrass types that can be planted from seed; (2) to assess the large amount of genetic variability among accessions and hybrids and evaluate traits that can lead to low-cost yield of convertible biomass for energy production. Twenty napiergrass selections were evaluated for bioconversion to methane. These studies included analyses of plant parts for lignin, crude protein and biochemical methane potential.

The influence of shading on associative N2 fixation

SummaryThe effect of reduced solar radiation on associative N2-fixation and plant parameters was studied in three field experiments (1978–80). ‘Gahi-3’ pearl millet (Pennisetum americanum (L.) K. Monch.) field plots were shaded with saran shade cloth that reduced solar radiation by 50% and 75%. Acetylene reduction activity (ARA) was reduced by shading in one of the three experiments. The two non-responding experiments were conducted on a wall-drained, low-activity site (ARA means ranging 17–68 n moles ethylene core−1 h−1), the responding experiment was conducted on a poorly drained, high-ARA site.Shading affected the plants drastically, reducing fresh weight and dry matter yields up to 46% (50% shade) and 57% (75% shade). Shading also reduced dry matter percentage from 19.6 (no shade) to 15.3 (75% shade) and increased nitrogen content from 0.6% (no shade) to 1.53% (75% shading). However, shading did not affect protein yield. Inoculation withAzospirillum brasilense had no measurable effect on yield or acetylene reduction in the first two experiments.In the third experiment, shading reduced mean ARA of inoculated plots over 100% but had no significant effect on control plots. Inoculation significantly increased ARA in the nonshaded plots but not in shaded plots. Acetylene reduction activity was high, with means ranging between 208 and 465 n moles ethylene evolved core−1 h−1. Soil moisture and millet growth stage also affected acetylene reduction activity.

Acetylene Reduction Activity and Non-Structural Carbohydrate Content of Hemarthria Altissima CV. Bigalta, After Defoliation

Cut vs. uncut plants of Hemarthria altissima cv. Bigalta were studied to ascertain if the defoliated plants had significantly lower acetylene reduction activity (ARA) than unclipped plants. (Fig. a). Non-structural carbohydrate determinations were made of dried root samples. Roots sectioned with a freezing microtome were observed to contain starch in the cortical cells in the center of the root. ARA per gram of root, was significantly lower in the cut plants (p=. 02), and percent carbohydrate content was also significantly lower in the cut plants 17 days after clipping (p=. 001). A summary of percent carbohydrates found in the stems, crowns and roots of cut vs. uncut Hemarthria altissima is also shown. (Fig. b). Observations of root and shoot development indicated that cut plants had increased shoot growth, but initiated fewer new roots than the uncut plants. The ARA results are similar to, but at lower rates than reported with legume seedlings (Cralle, Heichel 1981) (Vance et al. 1979) and in field pastures (Halliday, Pate 1976).

Effect of Plant-Derived and other Carbon Substrates on Asymbiotic N2-Fixation

Asymbiotic N2-fixation (also called associative N2-fixation when plants are involved) is highly variable over different sites and conditions but can occur at magnitudes great enough to be agronomically important. We previously reported finding highly active associative N2-fixation sites in a statewide search of Florida. Since energy that drives associative No-fixation is plant derived and restricting, we questioned whether N2-fixing bacteria in those highly active soils could utilize a greater proportion of the substrate in fixing nitrogen than those in low activity soils. We further questioned whether those highly active soils could utilize plant structural carbohydrates to fix nitrogen, and also wanted to get estimates of efficiency of substrate use for fixing nitrogen relative to other metabolic uses.