Modern tomatoes can’t get the same boost from soil microbes as ancient ancestors


WEST LAFAYETTE, Ind. – Tomato plants are particularly vulnerable to leaf diseases which can kill them or affect yield. These problems require a number of pesticides in conventional crops and make organic production particularly difficult.

A team of scientists led by Purdue University has evidence that tomatoes may be more susceptible to these types of diseases because they have lost the protection offered by certain soil microbes. Researchers found that wild relatives and wild-type tomatoes that associate more strongly with a positive soil fungus grow, resist disease onset, and fight disease much better than modern plants.

“These fungi colonize wild-type tomato plants and boost their immune systems,” said Lori Hoagland, associate professor of horticulture. “Over time, we have selected tomatoes for their yield and flavor, but it seems they have inadvertently lost their ability to benefit from these soil microbes. “

Post-doctoral researcher Hoagland and Purdue Amit K. Jaiswal inoculated 25 diverse tomato genotypes – a range of wild types to older and more modern domesticated varieties – with Trichoderma harzianum, a beneficial soil fungus often used to prevent malicious fungal and bacterial diseases.

In some wild-type tomatoes, researchers have found up to 526% more root growth in plants treated with the beneficial fungus compared to those that were not treated, and up to 90% in height. plant in addition. Some modern varieties had up to 50% more root growth, but others showed no increase. The height of modern varieties has increased by about 10-20%, much less than the wild types.

The researchers then introduced the plants to two pathogenic pathogens – Botrytis cinerea, a necrotrophic fungus that causes gray rot, and Phytophthora infestans, a mold that causes potato blight in the 1840s.

Wild types showed increased resistance up to 56% and 94%, respectively, to Botrytis cinerea and Phytophthora infestans. However, Trichoderma actually increased disease levels in certain genotypes, typically in modern plants.

“We found a significant response to beneficial fungi in wild type plants, with increased growth and disease resistance,” Jaiswal said. “As we moved across the spectrum to domesticated varieties, we saw less benefit.”

The research was conducted through the Tomato Management and Biological Improvement Project (TOMI), led by Hoagland, with the aim of improving organic tomato production and disease resistance. Funded by the US Department of Agriculture National Institute of Food and Agriculture, the TOMI team includes researchers from Purdue, the Organic Seed Alliance, North Carolina State University, University of Wisconsin-Madison, North Carolina A&T State University, and Oregon State University.

Hoagland said his team wanted to identify the wild-type tomato genes responsible for interactions with soil microbes and reintroduce them into current varieties. The hope is to keep the characteristics that growers have selected for thousands of years while also picking up those that make plants stronger and more productive.

“Plants and soil microbes can coexist and enrich each other in many ways, but we have seen that the plants we selected for certain traits broke that relationship. In some cases, we were able to find that adding what should have been beneficial microbes actually made some domesticated tomato plants more susceptible to disease, ”Hoagland said. “Our goal is to find and restore the genes that can give these plants the natural defense and growth mechanisms they had so long ago.”

Writer: Brian Wallheimer; 765-532-0233; [email protected]

Sources: Lori Hoagland; 765-494-1426; [email protected]

Amit Jaiswal; [email protected]


ABSTRACT

Domestication of tomato attenuated reactivity to a soil microbe beneficial for promoting plant growth and inducing systemic resistance to leaf pathogens

Amit K. Jaiswal, Tesfaye D. Mengiste, James R. Myers, Daniel S. Egel and Lori A. Hoagland

doi.org/10.3389/fmicb.2020.604566

Crop domestication events followed by targeted breeding practices have been critical in improving desirable traits and adapting cultivars to local environments. Domestication has also resulted in a sharp reduction in genetic diversity among modern cultivars compared to their wild relatives, although the effect this may have on the tripartite relationships between plants, beneficial underground microbes, and aerial pathogens remains. undetermined. We quantified plant growth performance, basal resistance and induced systemic resistance (ISR) by Trichoderma harzianum, a beneficial soil microbe against Botrytis cinerea, a necrotrophic fungus and Phytophthora infestans, a hemi-biotrophic oomycete, in 25 diverse tomato genotypes. Wild tomato relatives, local tomato varieties and modern commercial cultivars that have been conventionally or organically selected, together representing a domestication gradient, were assessed. The relationships between the base and the ISR, the physiological state of the plant and the phenolic compounds were quantified to identify potential mechanisms. Trichoderma improvement of shoot and root biomass and ISR to both pathogens in a genotype specific manner. In addition, improving plant performance in response to Trichoderma gradually diminished along the domestication gradient. Wild relatives and local breeds were more susceptible to Trichoderma, resulting in greater control of leaf pathogens than modern cultivars. The rate of photosynthesis and stomatal conductance of some tomato genotypes were improved by Trichoderma while the nitrogen status of the leaves of the majority of tomato genotypes was not altered. There was a negative relationship between basal resistance and induced resistance for both diseases, and a positive correlation between Trichoderma-ISR at B. cinerea and an increased total flavonoid content. These results suggest that domestication and breeding practices altered the responsiveness of plants to beneficial soil microbes. Further studies are needed to decipher the molecular mechanisms underlying the differential promotion of plant growth and resistance among genotypes, and to identify molecular markers to incorporate selection for reactivity into future breeding programs.

Agricultural communications: 765-494-8415;

Maureen Manier, Head of Department, [email protected]

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