Mobility Why some of the endophytes were so successful in suppress- ing Fusarium and ear rot has to do with mobility. In particular, Raizada says they observed how one strain (known as M6, de- rived from finger millet) respond to infection by leaving the root system to coat the exterior of the plant. It also promoted root hair growth. Both factors combined, says Raizada, create an ideal habitat within which the edophyte can capture and kill the pathogen. “It’s actually mobile; Some of these mi- crobes have little tails whihc they use to seek and destroy pathogens,” he says.
The overall goal of this research was to develop an in-season spray or a seed coating containing the microbes that could prevent and suppress the establishment and spread of myco- toxins. If commercialised, such a tool would also have greater longevity than standard fungicides. Grain growers could em- ploy it in conjunction with chemical solutions for a multi- pronged attack strategy. Currently the university is working with the private sector to make this happen.
Barriers to commercialisation There are some notable barriers to commercialisation, though. Delivering endophytes via seed coating – theoreti- cally the ideal system – is inherently less effective than in-season applications made directly to corn ear silks and wheat heads. Indeed, bacteria delivered through seed coat- ing did not appear to effectively colonise the plant in the field. The researchers are not entirely sure why this is the case, although they suspect it’s due to a combination of pressures – specifically fluctuating environmental conditions and the sheer volume of more competitive, already-naturalised mi- crobes present in the soil. “If we spray directly onto the plant, we do see more success.” Raizada adds that inadequate stor- age during transportation and on the farm are an even great- er barrier. As with some other biologicals, poor storage com- monly means growers are applying dead or low-activity
products. Raizada says the ideal solution to both issues would be improved seed formulations – that is, something that bet- ter protects the endophytes in storage and prevents them be- ing outcompeted in the soil. “If there’s some formulation that allows the microbes to be coated on the seed and can also tolerate poor storage conditions, that would be the best solu- tion.” The cost of the endophytes should not be prohibitive for farmers. “Theoretically, the microbe itself is very inexpensive. We haven’t worked out the exact cost, but Its certainly competitive with fungicides,” Raizada says.
Variability problems Apart from the recent greenhouse tests at the University of Guelph, three additional field trials were conducted over two years. The results were not as positive – year-on-year variabil- ity in the corn crop itself was a problem, as was inherently low Fusarium pressure in the wheat plots – but professor Raizada reiterates that these and other variability problems are typical of in-field microbial studies. The most important revelation, he says, is how effective these microbes can be. In- deed, replicated field trials with corn showed three promising bacterial endophytes , with one strain in particular reducing (DON) mycotoxin accumulation by up to 65%.
The M6 strain of endophyte, labelled with green florescent protein. It co- exists with maize and wheat plants.
Spraying fungi- cides on wheat may be (partly) replaced by spraying endo- cytes, or by coat- ing seeds with these natuarlly occurring organisms.
▶ ALL ABOUT FEED | Volume 28, No. 9, 2020
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PHOTO: UNIVERSITY OF GUELPH
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