A Goldilocks Genetic Strategy to Combat Tomato Yellow Leaf Curl Disease

My favorite part of the arrival of spring is getting back to the garden – especially tomatoes. But I’ve learned not to plant too soon, especially in my neck of the woods where snow can come as late as May.

Starting seedlings indoors is fine, but you can’t cheat by buying a plant already festooned with fruits, which I unfortunately smugly did last year. One-by-one, the beautiful tomatoes turned red and quickly rotted from the bottom up into brown mush.

So I was intrigued by a study just published from professor Sota Koeda and graduate student Moeno Shimoide at the Graduate School of Agriculture at Kindai University in Japan, in the journal Euphytica. They tackled begomoviruses, a large group of pathogens known to decimate crops of beans, squash, cassava, cotton and tomatoes, causing tomato leaf curl disease. Whiteflies transmit it in the southern US as far north as North Carolina, and in the Caribbean, Mexico, Southeast Asia, Japan, and the Mediterranean.

Infected plants are stunted and festooned with upward curling, yellowing young small leaflets, and halted flowering.

But nature may have provided a tool to save domesticated tomatoes from yellow leaf curl disease. Certain wild relatives of tomatoes carry resistance genes, which are introduced into cultivars to protect them. A more-is-better approach is to breed in variants of six specific resistance genes, called Ty-1 through Ty-6, into tomato cultivars. But that can harm crop plants too, a phenomenon known as linkage drag.

The new work finds that the magic number of protective genes is two – either Ty-1 or Ty-3, plus Ty-6.

“To control aggressive begomoviruses distributed in Southeast Asia, which are one of the most virulent species globally, relying on a single resistance gene common in Europe and Japan is insufficient. Thus, determining which combinations of resistance genes are necessary and sufficient for effective control is important for breeding tomatoes with enhanced viral resistance,” said Koeda.

First, they tested a trio of resistance genes that differed the most in DNA sequence from each other. They used common Japanese varieties with tomato yellow leaf curl virus resistance, as well as fancier ones from World Vegetable Center specifically bred to be highly resistant to the disease. And it turned out that plants that carried the Ty-1 and Ty-6 genes, or Ty-3 and Ty-6, fared best. Four didn’t improve resistance to the virus.

“Our study suggests that the introduction of fewer resistance genes than expected can substantially enhance resistance. It offers a promising approach for improving tomato varieties while balancing resistance, productivity, and fruit quality. Overall, our findings may provide valuable guidance for enhancing begomovirus resistance in other crops and represent a discovery that could contribute to the long-term stable production of food,” said Koeda.

I live in the northeast so my plants won’t encounter this type of virus, but I can appreciate the difficulty of launching each spring’s tomato crop – a sudden rainstorm early in the season can wipe out hours of work instantly. But there’s nothing better than harvesting an armful of tomatoes, especially heirlooms, from a garden into the fall.