Soil-borne Microorganisms Research Articles

CDNA Sequences of Three Kinds of -tubulins from Rice

Complete nucleotide sequences of three kinds of rice beta-tubulin cDNA clones (pTUB22, R1623 and R2242) were determined. Southern hybridization indicated that these beta-tubulins consist of one gene family. Using RFLP mapping, these three beta-tubulin cDNAs were mapped to different chromosomes indicating at least three loci for the beta-tubulin gene. The deduced amino acid sequences of these cDNAs showed a high similarity to other plant beta-tubulins. The asparagine residue located at the 100th amino acid from the N-terminus of plant beta-tubulins was also conserved with these three beta-tubulins. This asparagine is thought to be responsible for the sensitivity against rhizoxin, the toxin of the pathogen of rice seedling blight, Rhizopus sp. a soil-borne microorganism. Expression of the three beta-tubulin genes was analyzed by Northern blotting and all three clones were expressed in root, the possible target tissue of rhizoxin. These results suggest that these clones are candidates of beta-tubulins targeted by rhizoxin.

Influence of antifungal compounds from a soil-borne actinomycete onFusarium spp. in asparagus

Asparagus decline syndrome is caused by fungal infection of asparagus roots and crowns byFusarium oxysporum f.sp.asparagi (FOA) andF. moniliforme (FM). Several soil-borne microorganisms have been found inhibitory toFusarium pathogens in other crops. A novelStreptomyces spp. (ME2-27-19A) was isolated from asparagus field soil and found to be inhibitory to FOA and FM in vitro. Solvent extraction of ME2-27-19A and Chromatographic purification of the extract yielded compound(s) that were inhibitory to FOA and FM at 40Μg/ml. ME2-27-19A extract produced variable control of FOA and FM in vitro, and was phytotoxic at 1000 (Μg/ml. In soil, ME2-27-19A extract reduced theFusarium population at 100Μg/ml, but also reduced the asparagus shoot length.

Controlling Apple Replant Disease in `McIntosh' Apple Trees on Various Rootstock

Apple replant disease (ARD) adversely affects development and performance of apple trees planted in old orchard soils; it is characterized by stunted tree growth, which reduces orchard profitability (Hoestra and Oostenbrink, 1962; Mai and Parker, 1967). The probable cause of ARD is a complex of soil-borne microorganisms, including parasitic nematodes. The lesion nematode Pratylenchus penetrans is a component of ARD in some soils. Preplant soil fumigation improves root system development, tree growth, and cropping in some orchard sites (Hoestra and Oostenbrink, 1962; Jaffee and Mali, 1979; Mai and Parker, 1970). We examined the effects on tree performance of preplant soil fumigation, a postplant nematicide treatment, and rootstock at the Univ. of Vermont Horticultural Research Center in 1983. Results for 1983–1985 were reported by Costante et al. (1987). We now present results for the final 4 years of the experiment (1986-1989). Trees were on a well-drained Adams loamy sand (pH 6.2) on a 20-year-old orchard site infested with P. penetrans and with a diagnosed replant” disease problem (Costante et al., 1987). Eighty ‘Rogers Red McIntosh’ trees each on semi-dwarfing MM.111, MM. 106, M.7a, or dwarfing M.26 rootstock were planted on 2 May 1984 at 2.4 x 5.5 m spacing, including appropriate buffer areas.

Contribution of soil-borne bacteria to the rotation effect in corn

Few efforts have been directed at understanding how the rhizosphere microbiology of continuous corn may effect crop yields. This relationship may explain, in part, the decreases in yield associated with continuous corn as compared to the corn in rotation with a second crop. This study was conducted to determine the importance of soil-borne microorganisms to yield declines in long term continuous corn. Continuous corn (Zea mays L.) or rotated corn-soybean (Glycine max L.) field plots, established in 1975, under either fall plowing or no-till tillage treatments were used. Treatments consisted of methyl bromide applied at 48.8 g m−2 3 days prior to planting in all four combinations. Total plant samples from both the fumigated and non-fumigated areas were collected 14 days after planting. Rhizosphere bacteria were recovered and tested for their ability to impact plant growth. Bacterial assessments were made in a test tube bioassay where germinated corn was transported in to agar containing a bacterial isolate. In the first year of the study a highly significant interaction of fumigation and rotation was indicated. With fumigation continuous corn yields were similar to that of rotated corn-bean. Rotated corn yields were less affected by fumigation. In the second year, the effects were similar but less significant. Over 130 bacterial isolates were tested for their effect on plant growth. Approximately 22% were able to inhibit plant growth. Of these, 72% were from the continuous corn system. Clearly, the interaction of rotation and yield is at a microbiological level. The suggestion that microorganisms similar to those isolated are responsible for controlling early plant growth in the continuous corn system is indicated.

Microorganisms Associated with Velvetleaf (Abutilon theophrasti) Seeds on the Soil Surface

The relationships between microorganisms and velvetleaf (Abutilon theophrastiMedic. # ABUTH) seeds in contact with soil were studied to determine microbial effects on velvetleaf seed viability. The characteristic seed microbial association persisted on velvetleaf seeds placed on the soil surface during 32 days of incubation. The fungal association comprised ofAlternaria alternata(Fr.) Keissl.,Cladosporium cladosporioides(Fres.) de Vries,Epicoccum purpurascensEhrenb. ex Schlecht, andFusariumspp. was detected on over 50% of the seeds during incubation. Establishment of soil microorganisms on 50% of seeds occurred at only one sampling date. Such establishment was largely unsuccessful due to the effective barrier presented by seedborne microorganisms. Seedborne and soilborne microorganisms were unable to reduce viability of velvetleaf seeds in contact with soil as the total viability of all seeds tested exceeded 90% during incubation. Velvetleaf seedborne microorganisms may augment seed longevity on and in soils by acting as a barrier to potential seed decomposers originating from soil.

Gene Cloning in the Actinomycetes

The production of antibiotics by soil-borne micro-organisms, the actinomycetes, has considerable economic importance. The manipulation of antibiotic producers has become a prime target for the application of recombinant DNA technology. Certain technical requirements have had to be met for gene cloning to be successful in the actinomycetes. These requirements, including the development of cloning vectors and transformation procedures, have been satisfied, in part, for some members of the Streptomyces genus. Some problems including sequence rearrangement and stability of plasmid maintenance are now being recognized. A number of genes have been cloned in Streptomyces and some preliminary results characterizing the gene for a Streptomyces-derived beta-galactosidase-like activity were described.

Biodegradation of entomopathogenic hyphomycetes: Influence of clay coating on Beauveria bassiana blastospore survival in soil

The survival of naked and clay-coated Beauveria blastospores in soil was investigated with an experimental biodegradation method using a trap technique. At various times of incubation, traps were collected to study changes in biomass, inoculum potential, and infection potential of degraded blastospores, and to investigate the colonization of blastospore biomass by antagonistic soil-borne microorganisms. Infection potential was tested on larvae of Plutella maculipennis and Leptinotarsa decemlineata. Naked blastospores were inactivated after 3 weeks incubation, while clay-coated blastospores were still active after 2 months incubation in soil at 20°C. All investigations demonstrated the protective role of clay coating against biodegradation of fungal propagules by soil bacteria and protozoa. Consequently, clay coating of blastospores is proposed for the formulation of entomopathogenic hyphomycetes propagules. Moreover, antagonists implicated in lysis of blastospores, must be considered as an important part of the environmental response to a massive introduction of a fungus used for insect control.

Potential Uses of Nitrogen-Fixing Trees and Shrubs in Commercial Forestry

The potential for commercial utilization of tree and shrub species that can fix molecular nitrogen symbiotically is examined. Recommendations are made for research to speed the practical use in forestry of woody plants that fix nitrogen in combination with specific soil-borne microorganisms.

The effects of soil-borne micro-organisms on the germination of chlamydospores of Tilletia caries and T. foetida

The effects of soil-borne micro-organisms on the germination of chlamydospores of Tilletia caries and T. foetida

The Interactions of Soil-Borne Microorganisms and DCPA

Soil samples with and without a past history of dimethyl-2,3,5,6-tetrachloroterephthalate (DCPA) treatment were obtained from New York. A third sample was obtained from a field in Colorado where DCPA had been ineffective as a herbicide. The populations of bacteria and actinomycetes in these soils were determined and the actinomycetes were more prevalent in the samples with previous DCPA treatment than in untreated samples. Subsequent treatment resulted in an increase in actinomycete population and little change in bacterial population. In pure culture and in soils, the addition of DCPA had no adverse effect upon microbial growth, and several microorganisms appeared to utilize the herbicide as a carbon source. Two degradation products were methyl-2,3,5,6-tetrachloroterephthalate and 2,3,5,6-tetrachloroterethalic acid.