Alan G. Taylor

Combining effective strains of Trichoderma harzianum and solid matrix priming to improve biological seed treatments

In all crop-pathogen combinations, Trichoderma strains increased stands relative to the untreated control and were as effective as the chemical fungicides, even in the absence of solid matrix priming. Priming of seeds treated with Trichoderma strains increased plant stands in solid infested with F. graminearum and P. ultimum but not in soils infested with R. solani or S. rolfsii. In soils infested with P. ultimum, strain T95 generally gave the poorest results, T12 was intermediate, and the progeny strains (22 and 106) gave improved stands

Production of Conidial Biomass of Trichoderma harzianum for Biological Control

Abstract Fungi in the genus Trichoderma are promising biological control agents (bioprotectants) against plant diseases. Biomass used for biological control must be inexpensive to produce. It should be capable of being dried with retention of a high level of germinable propagules, be insensitive to environmental fluctuations (e.g., temperature and humidity), and possess a long shelf life. In this work, we show that the minimal media Czapek Dox and Richards medium supported a high level of conidial production of T. harzianum , but that overall yields were low. The addition of V8 juice to these media increased yields by 8- to 16-fold, but only 1 to 10% of the conidia produced were viable after vacuum drying. The addition of an osmoticum, i.e., polyethylene glycol (PEG), MgCl 2 · 6H 2 O, or mannitol, to Richards medium with V8 juice (RM8) provided a high level of conidial production, and the conidia were resistant to drying in vacuum. Conidial preparations from RM8 + PEG were less variable in numbers of colony-forming units per gram than those from RM8. Further, spores produced in RM8 + PEG in the laboratory were more effective than spores produced in a commercial fermenter in a medium without added osmoticums in protecting cucumber seeds and seedlings against attack by Pythium ultimum . Spores produced in RM8 + PEG had higher levels of trehalose than those produced in RM8; the higher trehalose levels may be associated with the superior level of performance and the desiccation tolerance of spores produced in RM8 +PEG.

SMP: Solid matrix priming of seeds

The purpose of these studies was to develop the technique of solid matrix priming (SMP) and then evaluate its ability to improve seedling establishment of small-seeded vegetable crops under either sub- or supra-optimal temperatures. SMP is a process in which seeds are mixed with a solid material and water in known proportions. This mixture allows the seeds to imbibe and attain a threshold moisture content, but prevents radicle emergence. The solid material used in these studies was a ground Leonardite Shale, “Agro-Lig”, which was a friable material and had a high water-holding capacity. The water potential of the Agro-Lig was determined after SMP and the osmotic potential accounted for >97% of the total water potential, which was attributed to solutes from the Agro-Lig and seed leachates. The matric potential contributed <1.5% of the total water potential. Seedling emergence studies were conducted on primed tomato (Lycopersicon esculentum), carrot (Daucus carota) and onion (Allium cepa) seeds sown in an artificial soil media in flats maintained at 2010°C with a 12-h photoperiod. The priming treatments consisted of polyethylene glycol 8000, inorganic salts and SMP. All priming treatments decreased the time for 50% seedling emergence and increased the plant dry weight compared with the non-treated controls for each crop. The seedling emergence characteristics of SMP-sown seeds were superior to, or equal to, conventional solution priming treatments. In addition, lettuce (Lactuca sativa) seeds were primed with solutions or SMP and later germinated at 35°C in the dark. All priming treatments overcame thermodormancy.

Conidial Biomass and Desiccation Tolerance of Trichoderma harzianum Produced at Different Medium Water Potentials

Abstract Fungal biomass to be used for biological control of plant pathogens must be economical to produce, able to withstand desiccation, and stable under storage conditions. Polyethylene glycol (PEG) 200 was added to modified Richards medium (RMS) to create different medium water potentials for producing Trichoderma harzianum. Water potentials of RM8 and RM8 with 6% (v/v) PEG 200 were −0.82 and −1.88 MPa, respectively. As medium water potentials were lowered with increasing concentrations of PEG 200 in RM8, the biomass dry weights decreased. However, conidial density and colony forming units (cfu) in the dry biomass were significantly improved to a maximum at −1.88 MPa. The total cfu number (biomass dry weight × cfu/g) in the dry biomass produced in RM8 at −1.88 MPa was increased on the average about 14-fold over that produced in RM8 alone. Although the cultivation temperatures did not affect the yield of the biomass, raising the cultivation temperature to 30°C and lowering the medium water potential to −1.88 MPa at 24 h of fungal growth enhanced conidial formation and cfu numbers after drying. Under these growth conditions, conidiophores were formed within 12 h after PEG 200 was added; intensive conidiation occurred within 48 h and reached the maximum level in 84 h of incubation. Trehalose levels have been correlated with desiccation tolerance of T. harzianum. The concentration of trehalose in the dried conidial biomass produced in this manner was higher than that produced in RM8 alone, and the germination percentage of the dried conidia was 65%.

Electrical impedance spectroscopy in relation to seed viability and moisture content in snap bean (Phaseolus vulgaris L.)

A method, electrical impedance spectroscopy (EIS), is introduced to study seed viability non-destructively. Snap bean (Phaseolus vulgaris L.) seeds were studied by EIS to determine the most sensitive EIS parameter(s) and the optimal range of moisture content (MC) for separation of viable and non-viable seeds. Hydrated seeds exhibited two impedance arcs in the complex plane at the frequency range from 60 Hz to 8 MHz, and impedance spectra of viable and non-viable seeds differed. The hydrated seeds were best-modelled by an equivalent electrical circuit with two distributed circuit elements in series with a resistor (Voigt model). Moisture content and seed viability had strong effects on the EIS parameters. The most sensitive EIS parameters for detecting the differences between viable and non-viable seeds were the capacitance log(C 2 ), the resistance R 2 , the resistance ratio R 2 /R 1 and the apex ratio, which all represent specific features of the impedance spectrum. The highest differentiation in the EIS parameters between the viable and non-viable seeds occurred in partially imbibed seeds between MC of 40 and 45% (fresh weight basis).

Control of corn flea beetle and Stewart's wilt in sweet corn with imidacloprid and thiamethoxam seed treatments.

Abstract Two field-plot experiments were conducted in western and central New York to evaluate imidacloprid and thiamethoxam seed treatments for control of corn flea beetle, Chaetocnema pulicaria Melsheimer, and Stewarts bacterial wilt in three varieties of sweet corn. Seed treatments significantly reduced flea beetle feeding injury to leaves in all varieties and reduced disease incidence 37–83% in the susceptible variety ‘Sprint’. Seed treatments did not control Stewarts wilt as effectively as genetic resistance. Disease incidence in the resistant varieties ‘Dynamo’ and ‘Bonus’ was relatively low (⩽5%) with or without a seed treatment. Additional on-farm evaluations conducted in western New York confirmed the results obtained from our field plots with incidence of Stewarts wilt ≈88% lower in imidacloprid-treated fields compared with non-treated fields. Laboratory germination tests indicated that seed treatments with imidacloprid may have some phytotoxic effects, depending on sweet corn variety and vigor of the seed lot. A general recommendation is that only high quality seed lots should be treated with imidacloprid and that carry-over seed should not be used.

Liquid coating formulation for the application of biological seed treatments of Trichoderma harzianum

Abstract Seed coating formulations were developed for application of biological control agents (bioprotectants) to seeds. Cucumber ( Cucumis sativus L.) seeds were used as a model system to evaluate the efficacy of the bioprotectant, and soil infested with Pythium spp. was used in a laboratory bioassay. A liquid coating formulation that contained a suspension of an aqueous binder (Pelgel or Polyox N-10), a finely ground solid particulate material (Agro-Lig or muck soil), and a bioprotectant, Trichoderma harzianum strain 1295-22, was developed. A continuous, uniform coating of T. harzianum were also formulated as a dry treatment (powder coating). Efficacy of the T. harzianum applied with either liquid coating or powder coating was enhanced compared to that of a slurry application of T. harzianum in binder. High humidity post-treatment of liquid-coated seeds improved plant stands compared to liquid-coated seeds alone. Stands obtained from sowing liquid-coated seeds were comparable to those from seeds treated by solid matrix priming. No differences in field emergence between biological seed treatments and chemical treatments were measured in 1989 or 1990. In conclusion, the liquid coating formulation enhanced efficacy of T. harzianum when seeds were sown in a Pythium -infested soil in a laboratory bioassay. The coating provided a physical barrier that delayed the pathogen attack and resulted in a conducive environment for T. harzianum growth.

Influence of Soil Water Repellency on Seedling Emergence and Plant Survival in a Burned Semi-Arid Woodland

High intensity wildfires in semiarid shrub and woodland plant communities can leave ecosystems incapable of self-repair and susceptible to weed invasion. Subsequently, land managers need effective restoration tools to reseed native vegetation back into these degraded systems. In order to develop successful post-fire restoration approaches in these communities, it is critical that we understand the mechanisms that impair reseeding success. Our objective was to quantify the influence of soil water repellency on seedling emergence and plant growth in a greenhouse study using soil cores obtained from beneath burned Juniperus osteosperma trees. Soil cores were seeded with either Elymus wawawaiensis or Agropyron cristatum, and watered with either a high (watered daily) or a low water regime (watered every 5 days). During the first watering event, water repellency was ameliorated in half the cores by adding a wetting-agent comprised of alkylpolyglycoside-ethylene oxide/propylene oxide block copolymers. Results showed that water repellency reduced seedling emergence and seedling survival by decreasing soil moisture availability. Wetting-agents improved ecohydrologic properties required for plant growth by decreasing runoff and increasing the amount and duration of available water for seedling emergence, survival, and plant growth. These results indicate that soil water repellency can act as an ecological threshold by impairing establishment of reseeded species after a fire. Where restoration efforts are limited by soil water repellency, wetting agents have the potential to improve the success of post-fire reseeding efforts. Future work is needed to validate these findings in the field.

Semipermeable Layer in Seeds

Semipermeability may be defined as the ability of seed coverings to allow water uptake and gas exchange, while solute diffusion is restricted or prevented. The presence and location of a semipermeable layer was studied in seed coats of cabbage, leek, onion, tomato, and pepper. Morphological studies did not reveal a semipermeable layer in cabbage seed coats, and all subsequent research was performed on seeds of the other four species. Electron microscopy studies revealed that the semipermeable layer is located at the innermost layer of the seed coat just next to the endosperm. Ultrastructurally, the layer was similar for the four species, typically amorphous, highly compact, but easily distinguished from the remainder of the seed coat and endosperm tissue. The layer was permeable to water while inhibiting uptake of lanthanum salts. Histochemical analysis revealed that the semipermeable layer in seed coats of leek and onion was composed primarily of cutin, while in tomato and pepper the layer was composed of suberin.

Electronic structures of carbazole and its derivatives: A Semi-empirical study on the substitution effects of carbazole.

The electronic structures of carbazole, N-phenylcarbazole (NPC), cyanophenylcarbazole (CPC) and N-ethylcarbazole (NEC) have been calculated using the quantum chemical semi-empirical MINDO/3 method. In this paper, electronic ground states and first singlet excited states of the systems mentioned were investigated. It is observed that the excitation energy of carbazole based on the calculated difference in heats of formation agrees quite well with experimental data obtained from supersonic expansion studies. Calculated energy levels of molecular orbitals and their graphical forms are used qualitatively in elucidating the S0 → S1 excitation electronic origin red shifts observed in carbazole derivatives with respect to the electronic origin of the parent carbazole. It is noted that the red shifts are not just a result of the destabilization of the HOMO of carbazole but are also determined by the nature of the substituting moieties. It is also observed that the LUMO of CPC is not derived from the parent carbazole which partially explains the difference in electronic behaviour as compared with the other derivatives.