May 20, 2019
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No pesticides required; research offers a possible genetic resistance to plant disease


In Biology Department Chair Dr. James Prince’s research laboratory,
Heather Brewer is preparing a nutrient-rich substance the root-rot
disease-causing agent will be grown in. Prince’s lab is working on
a solution to root rot, one of the most important pepper diseases
in the world.
Johnathan Wilbanks / The Collegian

Peppers — an ingredient in so many American dishes are being threatened by a plant disease that is costing farmers a significant amount of money.

Root rot of pepper plants infects more than 50 plant species. Innate genetic resistance, meaning disease resistance that is literally incorporated into the plant itself, is one of the ultimate goals of genetics professor and Biology Department Chair Dr. Jim Prince.

Prince, along with two students, is working on an environmentally friendly solution that could potentially eliminate the use of pesticides. This solution involves genetic resistance without harmful chemicals.

“We have peppers that can naturally resist disease,” Prince said.

Root rot, a type of water mold, destroys a number of plants including squash, cucumber, honeydew melon, tomato, eggplant, pumpkin and watermelon. Chemicals and well-drained soil are a couple of the control measures currently used for plant disease.

The disease means plant destroyer in Greek, and is caused by a pathogen known as Phytophthora Capsici.

The elimination of pesticides is not only healthier for consumers, but it can also reduce the use of pesticides that can be detrimental to the environment and increase the yield of pepper crops.

Prince exposes his pepper plants in the green house to a disease-causing agent that is a water mold. The agent was formerly thought of as a fungus but it’s a slightly different organism.

The disease predominately attacks peppers growing in low areas where moist soil is abundant. The spores can move within the water and infect a large number of plants.

“It’s probably the most important pepper disease in the world,” Prince said.

Prince said plants that resist disease are bred with plants that don’t resist disease.

Once offspring of the plants is produced, Prince said that they can follow the genetics of a certain trait in subsequent generations.

“We can simultaneously do that with DNA markers, and then see which markers associate with the trait,” Prince said. “We can produce maps of the chromosomes with little blips on it that say, ‘Hey, there’s a gene that controls this resistance in this area.

An ideal situation for Prince would be to produce plants which are resistant to multiple diseases without the use pesticides. “So you don’t have to spray chemicals,” Prince said.

As an adjunct to the pepper research, Prince is starting a next-generation gene sequencing project.

A research group at UC Davis has produced a densely populated molecular map of with approximately 4,000 markers. This is helpful for Prince and his team because they are able to view the hundreds of individual markers on each chromosome, whereas before this work was produced the team had about ten markers located.

“I’m hoping that this next-gen sequencing project may help illuminate some genes that we don’t even know about,” said Prince.

Biology graduate student Pierre Boivin is trying to find different spots on the genome that correspond to agricultural interests, such as total yield, germination rate and fruit characteristics. This means he is trying to locate each part of the gene that gives a code for desired qualities in a plant.

“What I’ve done is basically grow four different genotypes of pepper, which each have different characteristics,” said Boivin.

Some of these genotypes code for faster growth or better fruits. A genotype is a fancy word for physical traits that may or may not be expressed in an outward appearance. Similar to a lineage that gives a person certain physical features similar to their parents.

“What I will be doing is RNA extraction from all four genotypes and sending it in to UC Davis to get sequenced… comparing all four and looking at where the differences lie and which sites in the genome actually correspond to that trait.”

Biology graduate student Heather Brewer is dealing directly with the water mold. “I work with the pathogen that infects chili and bell peppers,” Brewer said. She screens different types of plants against inbred lines of pepper.

Brewer uses plants that are resistant to the pathogen and those who are susceptible to come up with a scale of disease manifestation. A certain location on a gene has been found to have a correlation with disease resistance in the plants.

“We found that a locus [location of a genetic code] isn’t necessarily attributed to resistance in all peppers. That’s normal to find, because resistance to disease isn’t just associated with one gene. There’s multiple gene interactions that lead to different resistances and susceptibilities.”

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