-_._--~--_ .__._ -- ---_._----~
ABSTRACT
Plant growth is influenced by a number of factors. To reduce environmental factors, growth stimulating microbes were tested in vitro. Pot trials comprising perennial (Lolium perenne L.) and annual ryegrass (L. multiflorum Lam.) were established within a greenhouse (QC and RH% controlled) at the University of Natal, Pietermaritzburg. The trials were to determine the potential of formulations of Bacillus subtilis Ehrenberg &
Cohn. and Trichoderma harzianum Rifai for growth stimulation.Plant counts(%)and leaf measurements (mm) (6-20 days post seed inoculation) showed increased growth associated with microbial treatments. Increased leaf length of perennial ryegrass treatment the microbes was significantly (P~0.05) different to the control treatment. The application of MICROBOOST®increased microbial activity in that root lengths of annual ryegrass were significantly (LSD(0.05)
=
6.69) greater than treatments with no MICROBOOST. Microbial efficiency was also determined in vivo, using experimental plots at Cedara (29032'S,3001TE)of perennial ryegrass, fescue (Festuca rubra L.) and bentgrass (Agrostis stolonifera L.). Formulations of growth stimulating microbes: B.
subtilis, T. harzianumand Gliocladium virens J.H. Miller, J.E.Gidens, A.A. Foster & von Arx., were applied to seeds as a dusting at planting,and at 10 day intervals for 10 weeks after planting. Growth stimulation was measured as increased plant counts (%), as well as root and shoot lengths (mm). Growth responses between the two trials differed, as did responses for the duration of the trial. Interms of increased germination rate, microbial treatments, with the exception of G. virens, ranked highest for growth simulation. At trial termination, significant (P~0.05) differences in the final plant count were noted. This
indicated the potential for increased establishment associated with the microbe-based treatments. Non-significant (P~0.05) differences in growth at 6 days after planting, indicated that microbes had little effect on germination rates. Microbe-based treatments caused increased root and shoot lengths. Mean root and shoot lengths for the three grass types were significantly (P~0.05) increased. MICROBOOST had no significant (P~0.05)effect on microbial activity in terms of increased germination rates, but root and shoot lengths were significantly (P~0.05) increased. Growth stimulation associated with the microbe-based treatments was also observed by increased weed growth.
5.1 INTRODUCTION
The concept of using biological control agents (BCAs) was first recognised when researchers discovered that supposedly healthy plants were stunted by the activity of a number of root pathogens (Baker, 1992). Over the years this has led to renewed interest in biological control, withvarious investigations on disease control and growth stimulation incited by antagonistic microorganisms. It is assumed that antagonistic microbes colonize the rhizosphere following inoculation forming a close relationship with the plant's roots (Schroth and Becker, 1990). Upon COlonization these microorganisms may cause plant growth stimulation (Kapulnik, 1996; Harman 2000). Commonly documented as growth promoting BCAs are Trichoderma harzianum Rifai strains. These are known toincrease germination, seedling emergence and establishment (Raviv et al., 1998), as well as improve dry weight of shoots, stems and roots under both greenhouse and field conditions (Windham et al., 1986; Kleifeld and Chet, 1992). Commercial application includes the amendment of planting media or seed treatments (Knudsen et al.,1991) resultingin growth stimulation, as well as disease control of soilborne pathogens (Agrios, 1997).
The aim of these trials was to determine the growth stimulation potential of experimental formulations of antagonistic microbes on grass species both in vitro and in vivo. Growth stimulation was determined as an increase in germination or plant emergence,
establishment rates and increased root and shoot lengths. The potentially adverse effect of increased weed growth associated with microbial amendments was also determined.
It is assumed that growth stimulation could be due to colonization of the plant's rhizosphere by antagonists resulting in increased moisture and nutrient uptake by the plant (Cook, 1990).Antagonist colonization of the rhizosphere also potentially protects against soil pathogens which would reduce plant growth potentials (Harman, 2000).
In terms of growth stimulation, microbial formulations were applied to cool season grasses: Perennial Prelude 11 ryegrass (L. perenne L.), Junior fescue (F. rubra L.) and Crenshaw bentgrass (Agrostis stolonifera L.). Although temperate grasses are not that widely used in KwaZulu-Natal for turf establishment, cool season grasses were chosen due to the trial period falling over winter.In KwaZulu-Natal, plants are exposed to limited moisture (averaging 85mm), extreme daily temperatures (6.0 -20.30C) and severe frost (441 chill units) during the winter months (Camp, 1995). Temperate grasses are able to maintain active growth during the winter months and are tolerant of severe frost. Of these, bentgrass is more widely used on golf greens,while ryegrass and fescue are used to oversaw rugby fields (Tainton and Klug, 2002).
Due to the BCAs used being experimental formulations, the recommended application rates were tested. The method and rate of microbial application plays a vital role in the establishment and maintenance of the mended antagonistic population (Fravel, 1992).Too Iowa population would not stimulate growth,while too high a population would exceed the carrying capacity of the rhizosphere (Papavizas, 1985; Handelsman and Stabb, 1996). Microbial activity is also dependent on nutrient competition on the rhizosphere (La, 1998). The application of MICROBOOST, a microbial activator, was therefore also tested. The assumption was that MICROBOOST causes a large boost of the multiplication of the antagonist.
The future success of BCAs is dependent on the stability of antagonists once inoculated into an environment where fluctuating extremes will be experienced (Koch, 1999).