avalon: a new way to keep georgia's pecan crop from scabbing over

Hurricane Michael made landfall in October 2018. According to the National Weather Service, it was the first major hurricane to “directly impact” Georgia since the 1890s. Being a forever agriculture nerd, I was shocked at the affect Hurricane Michael had on farms in south and central Georgia, where high wind gusts hit between 70 and 115 miles per hour. Cotton and pecan crops were the hardest hit. Approximately 51 percent of the pecan crop was directly affected, according to University of Georgia Extension.
 
I recently learned about a newer pecan cultivar, the Avalon, which is touted as one producers should consider as they look to recover from Hurricane Michael. I was intrigued — so I reached out to Patrick Conner, the UGA pecan {and muscadine} breeder who brought this cultivar to life. He was gracious enough to spend a few minutes and answer my plethora of questions about pecans, scab and how the Avalon can help.

DAD: So, first off … how did you become a pecan breeder?
 
Dr. Conner: I came out of a fruit breeding program to get my Ph.D. I was a graduate student at Cornell University in the apple breeding program, and I’ve always been very interested in fruit breeding in particular, because a lot of the quality aspects come into the breeding program … it’s not just yield. After graduating from there, there’s not a lot of fruit breeding programs. The pecans were work similar to what I’ve done in apples.

dr. patrick conner. | courtesy photo

The pecan growers really pushed the University of Georgia to get this breeding program. There was only one other breeding program in pecans in the United States [in Texas]. It’s much drier in Texas in the pecan-growing region, so scab is not as big of a problem there. They released several cultivars for the US pecan industry that were planted on a fairly widespread basis. Some of those were so susceptible to scab they had to cut the orchards down. 
 
From what I’ve gathered, aside from wind damage, it seems that a big concern with how 
Hurricane Michael affected our pecan crop is the spread of pecan scab. What is pecan scab, and why is it so devastating?
 
This was an issue even without the hurricane, but due to the frequency of the rainfall, it just kept raining every day. 

>> Side note: Per UGA Extension, “the amount of rainfall really starts to matter in June, and its importance continues on through the rest of the season until shell hardening occurs (or shortly after shell hardening if you grow a scab-susceptible variety).” Months before Hurricane Michael, Georgia’s pecan-growing region already had a wet 2018, with more than 30 days of “significant rainfall” during the summer months. This provided prime growing conditions for scab.

Pecan scab is a fungal disease and infects the young leaves. It puts black lesions on them and if you get enough lesions on them, the leaves will drop. And it affects the nut shuck the whole year. When the scab infects the shuck … the nut is not able to develop. 
 
It’s a big problem in the Southeast because it needs free water to disperse and germinate on the shucks. When we get thunderstorms in the evening, the leaves stay wet all night. That’s just the perfect way for it to spread.

One of the problems is cultivars tend to become more susceptible to scab over time. Desirable, when it was first released in the 1940s, was extremely resistant to scab and now it’s one of the most susceptible things we grow.
 
In nature, the tree is in balance with the pathogen. If you take pecan scab off one cultivar and transfer it to another oftentimes it can’t infect the cultivar. You don’t get a big buildup of scab most years. But what we’ve done in Georgia is we’ve planted the entire state with just a few cultivars. When you have an orchard and all the trees are the same, the pathogen gets adapted to that cultivar. By reducing the variability from what’s seen in nature to almost no variability in our orchards, we set ourselves up to have a lot of scab.

avalon pecans. | courtesy photo

Tell me a little history of the Avalon pecan. 
 
When we release cultivars, they have to have at least moderately good resistance to scab. We use scab-resistant cultivars, which have existed, but usually you pay a price for that resistance: the nut is small; something is less desirable. 
 
We did a lot of crosses with resistant cultivars, crossing them with things that are higher quality and less susceptible. So out of this cross, which was a cross between Glorida Grande and 

Caddo — with Gloria Grande being large and resistant, but having a thick shell, and ​Caddo is more productive with a thinner shell — this one had fairly large nuts, it did not scab; had decent quality; so we went on to test it. It performed well in our replicated yield trials. Gloria Grande is the female parent and Caddo is the pollen parent.
 
How long did it take for crossbreeding to produce the desired pecan? And why did you decide to use traditional breeding methods instead of using genetic modification or CRISPR technology?
 
Well, this cross was made in the year 2000 and I released it in 2016. Which was actually a little bit shorter than it normally takes. We take a large tree that was already bearing, and you graft on new limbs of the selection you’re trialing. That tree very quickly regrows and acts like a more mature tree.
 
Right now, we don’t have any genetic protocols for pecans. Usually when you’re doing that, you’re tissue culturing, and a pecan is extremely difficult to place through tissue culture. It’s not clear that [a genetically modified pecan] would be allowed to be released, because pecan is a native crop. It’s wind-pollinated and the animals carry it off. So if you were to genetically modify a pecan, it would immediately be out there in the environment.

Other than planting one of the scab-resistant varieties like Avalon, how are growers able to combat scab?
 
It’s primarily through the application of fungicides. … Typically we spray fungicide about every two weeks from first leaf until shell hardening in mid-August. When it rains, you shorten that time period to seven to 10 days.

pecan orchard. | courtesy photo

What’s been the response since Avalon was released? Have people been clamoring for it?
 
Yeah. They’re driving the nurseries crazy because we aren’t able to produce enough trees to meet the demand. Pecan sales have been in a boom for the last five years because of high prices and will continue to be so because we lost so many trees in the hurricane.
 
If people want to switch over to Avalon, and are able to get their hands on some, how exactly does this transition occur? Would they be grafting limbs as was done to create Avalon initially?
 
That’s not really practical on a wide scale. When you change over a tree like that, not only does it take probably an hour or two to do the initial graft, but you have to follow it back and make sure it doesn’t sprout new branches of the original cultivar. If you wanted a new cultivar in general — what growers typically do, unless it’s a disaster you wouldn’t cut down your tree — just plant new trees as you phase out. Over time you’re changing the makeup of the orchard.
 
We’re not telling people to cut down their Desirable orchards … but a lot of them are going to make the choice to plant something else. 
 
You have to contact the nursery at least a year, sometimes two years, before you’re going to plant so you can get on the list of cultivars you want. There are other cultivars that have better levels of resistance, things like a Sumner. I would encourage them not to plant Desirable anymore in the south part of the state — it’s just too difficult to control scab.

>> for more about georgia's pecans ...
UGA Pecan Extension blog
​Georgia Pecan Commission

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