The Groundsman

April 2012

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the Groundsman April 2012 FEATURE 31 The battle for the rhizosphere… We take an in-depth look at the complex growth promoting interactions between grass and rhizobacteria - discussing the beneficial effect of the bacteria Bacillus subtilis (Bs) and Bacillus amyloliquefaciens (Ba) Plant growth in soil is influenced by many abiotic and biotic factors. There is a thin layer of soil immediately surrounding plant roots that is an extremely important and active area for root activity and metabolism - known as the rhizosphere. Nearly 40 per cent of the products of photosynthesis are released into the rhizosphere and consequently there is an abundance of micro-organisms present. These micro-organisms are a mixture of both harmful pathogens, including some nematodes and soil borne fungi, such as fusarium, as well as beneficial pathogens which include rhizobacteria. Bacillus is the most abundant genus of bacteria in the rhizosphere and the plant growth promoting activity of some members of the genus has been known for many years. Naturally present in the immediate vicinity of plant roots, B subtilis is able to maintain stable contact with higher plants and promote their growth [1]. It is B subtilis (Bs) and B amyloliquefaciens (Ba), present in the VitanicaRX and Fertilis fertilisers which are considered here. The beneficial effect of B subtilis and B amyloliquefaciens works in two ways, by enhancing plant growth and inhibiting pathogens. Let us first consider the growth promoting benefit which can, in turn, be divided into a few distinct affects. Accumulating evidence indicates that Bs and Ba influence plant growth and development by the production of phytohormones such as auxins, gibberellins and cytokinins that are subsequently plant available. There are a number of metabolites (small molecules) that are released by these strains which increase nutrient availability to the plant. Iron is essential for the growth of all plants and is especially important to turf managers to give a greening effect and an element of disease resistance to turf grass particularly in the autumn; Bs and Ba secrete small iron chelating compounds called siderophores which benefit the plant roots in the immediate rhizosphere. Phosphorus (P) is an important macronutrient that is all too often locked into the soil and unavailable to plants. Bacillus is one of the rhizobacteria that is most efficient at solubilising the insoluble inorganic P of soil to make it available to plants. There are other similar affects too numerous to mention here that all positively influence plant growth. Bs and Ba inhibit pathogens in two ways and the first is very easy to comprehend. Essentially they compete for spaces around the roots and form a barrier which the pathogens, such as soil borne fungi, cannot penetrate. More intriguingly, studies show that the production of antifungal substances gives an antibiotic affect that deters pathogens. Some rhizobacteria, including Bs and Ba, synthesise antifungal antibiotics which inhibit the growth of soil borne fungi in the vicinity. Induced Systemic Resistance (USR): A widespread phenomenon, the concept of ISR centres on a plant's response to a local infection. Infected plants respond with a salicylic-dependent signally cascade that leads to a long lasting disease resistance against fungi, bacteria and viruses [1]. In simple terms, some rhizobacteria including Bs and Ba can simulate this response and lead to an ISR within plants. Plant parasitic nematodes are microscopic roundworm most of which live in the soil and feed on plant roots. Nematodes can be split into two major types, those that target roots cells (Ectoparasitic) and those that access the plant through the roots and migrate to feed in other parts of the plant (Endoparasitic) [2]. The important point is that it is the roots of the plant where nematodes feed or access plants; therefore if we can effectively strengthen the roots in such a way as to deter nematodes of both types, we significantly nullify any population in the soil. The growth promoting effects of Bs and Ba have been shown to help plants better withstand the effects of nematodes. Further study is needed for conclusive proof that the same physical and antibiotic deterrents that work against harmful fungi and bacteria are effective against nematodes, but the hypothesis is that this may well be the case. The gr ef V i tanica RZ owth pr fect of B amyloliquefaciens R6- CDX when nematodes ar omoting e pr esent Contr V i tanica RZ ol The ef fect of B amyloliquefaciens R6-CDX on turf gr owth

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