Rootstocks Offer Production Attributes

Tomato Rootstocks Grafting

By Jessica Theisman, Associate Editor

California Ag Today recently spoke with Brenna Aegerter, a UC Cooperative Extension farm advisor in San Joaquin County, about grafting rootstocks to tomato plants.

“Rootstocks are cut below the cotyledons, while the scions are cut above the cotyledons at an angle,” she said.

These two plants are then clipped together and go into a high humidity healing chamber for about one week.

Aegerter explained that, “In the beginning, there is no light. They gradually increase the light because they do not want to stress the plants, and so if those two angles match … then everything grows back together.”

Each tomato plant can differ depending on the rootstock that it has been grafted to. Different rootstocks have varying levels of resistance to disease and pests. Rootstock resistance does have an effect on crop yield. If all of the fruiting varieties had the nematode resistance gene, they could potentially improve their yields.

There is great success rate on grafting these tomato plants.

“We have had pretty good success, 90 percent and up,” Aegerter said.

The remaining 10 percent is because the angles were not matched up quite right and there is not enough contact between the two tissues.

“Rootstocks are for the most part, hybrids between our cultivated tomato and wild tomato species,” Aegerter explained.

Wild tomatoes are used often to bring in new genetic material due to their diversity and natural resistance. Depending on the type of tomato that is being used, the resistance can differ.

The fruiting varieties are resistant, but are resistant to a shorter list of diseases.

“These root systems are are bigger, the crown is bigger, and sometimes they aren’t even purely resistant to the disease, but just by virtue of the fact that they grow faster, they can outgrow it,” Aegerter said.

Working on Nematode Resistant California Commercial Carrot

Nematode Resistant California Commercial Carrot On Its Way?

By Jessica Theisman, Associate Editor

Phil Simon is a carrot breeder and geneticist with the USDA Ag Research Service based at the University of Wisconsin. He produces the vast majority of carrots for the consumers throughout the nation. A big goal is to find a commercial carrot variety that is root-knot nematode resistant. Nematodes are a soil-borne, microscope, worm-like organism destroying production in some fields. Through lots of research, the carrot industry is getting closer to a resistant variety.

The first resistance gene was first discovered in 1992 in a Brazilian variety that may have some genetic resistance. The resistance was discovered by using derivatives from the Brazilian variety crossed with California-adapted carrots. This is all being done with, “the idea of moving that resistance gene into a carrot that’s suitable for California in terms of shape, size, flavor, and productivity,” Simon said.

The Brazilian variety is not suited to California because it is shorter and wider. It does not look like a California carrot, and it bolts very easy, which means it flowers and goes to seed. But with the Brazilian carrot having nematode resistance, it is also heat-tolerant, which is great news for us in California, especially with the rising temperatures.

It is said that California is getting closer and closer to getting its own commercial variety. “We’ve also found genes for resistance in other carrots from around the world, from Syria, China, Europe, and we intercrossed those also into California, so we’re putting a couple of genes in,” he said.

With all of these genes, this makes for an even stronger and durable resistance to nematodes.