No matter the location, plants can experience stress. This can be in your home garden, the local community garden, or on a farm miles away. Stresses include heat or drought, and they limit a plant performance.

Today’s current varieties of tomatoes – ones grown in gardens and available in produce sections and farmers’ markets – are a bit spoiled. Through thousands of years of cultivation, the root systems of cultivated crops have become “trusting” that people will provide them with the resources they need to grow.

This trust that resources will be available allows tomato plants to increase production of shoots and fruits – increasing yields. However, that tradeoff comes at the expense of root growth. That means that plants are less suited to care for themselves under challenging environmental conditions such as heat and drought.

Fortunately, tomato rootstocks often retain more of the wild traits from their undomesticated ancestors. This means they can be better suited at managing stressful environmental conditions. For those reasons, grafting a desirable cultivar onto a vigorous rootstock is an approach worthy of research and consideration.

Grafting is a common technique used to grow many different types of fruits and vegetables. For tomatoes, a desirable-fruit-bearing scion (the shoot) is placed atop a rootstock (the roots) that contains some other desirable characteristic. This characteristic could be stress tolerance or disease resistance. Humans do the splicing, biology does the healing, and the result is a new grafted plant with the desired characteristics of the grower.

How exactly does the new root system help improve performance in stress conditions like heat and drought? And what traits may they retain from wild ancestors?

Well, certain rootstocks may improve plant performance by enhancing the amount of root biomass used to support shoot function (often referred to as a root-to-shoot ratio). Having more roots per shoot means that under stressful conditions shoots can continue to operate efficiently during the hottest parts of the day and the hottest days of the year.

Rootstocks can change the root architecture, which means they may favor more small lateral roots. Per weight, small lateral roots have more surface area in contact with water and soil. This means they are better at water and nutrient acquisition than thick primary roots and can improve the ability of the rootsystem to maintain the plant’s water demands.

Roots that increase contact with water and soil also improve nutrient acquisition. Improved nutrient uptake can increase the amount that plants grow per unit of water lost. Rootstocks can also improve performance by reducing the uptake and accumulation of salts in the scion. Excess salts increase the osmotic stress that plants encounter and when coupled with heat and drought conditions that can be very detrimental.

The final advantage of using rootstocks is hormone regulation. Plants use hormones to communicate between various organs. Different rootstocks can regulate hormones differently in response to stress conditions. This means that rootstocks that respond more efficiently to changing environmental conditions can improve plant performance under those conditions as well.

Charles Rick was a horticulturist who collected many South American species of wild tomato in the 1950s. His contributions to this collection have provided today’s tomato breeders with a wealth of information. Wild tomato plants continue to survive today because they have efficient responses to environmental conditions. (However, their fruits are often small and bitter-tasting.) But domesticated tomatoes have adapted to the conditions provided by humans. Having a plant that responds to our gardens the way a wild plant would respond to its environment is an important way rootstocks can help growers by improving plant performance under heat and drought conditions.

Answered by Steven Bristow, University of Nevada

Read this blog about tomatoes: vegetable or fruits and to learn about more tomato research!

About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Members are researchers and trained, certified professionals in the areas of growing the world’s food supply while protecting the environment. Members work at universities, government research facilities, and private businesses across the United States and the world.