The Other CSI

Catriona is currently finishing a thriller and a Sisters in Crime Report and getting ready to go to Britain in two weeks' time to launch a mystery and attend Harrogate, so she has stepped aside to let a real investigator take the reins. (She only writes about it, you know.)

Dr Neil McRoberts, UC Davis

Forensic science has been delivering ratings toppers and bestsellers for years. But here’s something new: a wave of attacks sweeping the nation, millions of helpless victims, a complex legal tangle, the very latest in DNA-based investigations, and sniffer dogs too.

It’s the other CSI: Citrus Science Investigation.

With geeky, corduroy-clad plant-pathologists in place of Kay Scarpetta.

Citrus trees around the world are being killed by a bacterial disease first named in Chinese as Huanglongbing (HLB) or “yellow dragon” disease. Infected trees produce elongated shoots on which the leaves grow at a slightly tilted angle and are yellow rather than green. If you squint at shoots of this type and use a little imagination they do sometimes give the impression of the scaly neck of a golden dragon.

Once a tree is infected with the HLB bacterium a slow death is inevitable. There is no cure, none of the varieties of citrus we eat have useful levels of resistance, and long before an infected tree finally dies its fruit becomes inedibly sour and unpleasant-tasting.

Florida was the first of the US’s major citrus-producing states to detect HLB, back in 2005. In the decade since then it has spread to every county of the state and caused the Florida orange juice industry to shrink to a third of its former size. Citrus trees in private gardens are no less at risk and everything is pointing to a future in which Floridians will no longer be able to pick fresh oranges from their own trees to squeeze for their breakfast juice, or grow their own grapefruit to go with it.

A similar fate awaits other citrus-growing states. HLB has been detected in backyard trees in LA.

One of the problems is that HLB is an invisible killer; infected trees don’t show symptoms for months or even years. Meanwhile the disease spreads to all neighbouring trees, which in turn harbour their secret and keep the spread spreading. Not surprisingly, major efforts are being made by state and federal government departments and by the citrus industry to track down the tree killer and stop it.

photo-credit Steve Garnsey USDA-ARS

Thankfully, the presence of the bacterium can be confirmed through the use of DNA detection methods, in which minute traces can be detected with CSI-like precision. But this is where our disease detective story has the potential to turn into a legal drama. Trying to persuade a grower to kill a healthy-looking tree, perhaps one heavy with valuable fruit, is far from easy and experience with other diseases shows a history of legal challenges as well as quarantine programs that become mired in litigation.

And there’s another problem: a tissue sample taken early enough to be useful in stopping the spread has to be taken from precisely the right spot of the tree where the bacterium is at work. By the time the tree is infected enough for any old sample to do, it’s too late.

Luckily, infected trees smell bad before they look bad . . . to the right kind of very sensitive nose. Enter the sniffer dogs.

Just as dogs can be trained to detect explosives, drugs, and cancer, so they can be trained to detect HLB and the training program, based in Florida, has so far done just that with 10 dogs – mostly German Shepherds – and has 10 more coming. The dogs romp through a citrus orchard until they detect the presence of the disease, then they sit down and won’t budge unless they are rewarded with a few moments of play with their favorite toy.

Mira, Coast-to-Coast K9

The dogs, the citrus growers, federal and state legislators, and those corduroyed plant pathologists are all working hard. But in the meantime a killer is at large.

 

Comments

[Charlaine Harris]

Well, I never! As Monty Python might say. I guess there's no use asking the trees to spit into a vial so their DNA can be identified . . .

[Ann Mason.]

I say we build a fence around Florida and keep foreign bacteria out of the country.

Or shoot them. It's my constitutional right.

Love, Donald

[catriona]

(Neil) Too late, Ann. It's all over Texas and it's arrived in California. It's spread by psyllids and they can fly.

[catriona]

(Neil) You're right, Charlaine. Trees take the fifth a lot too.

[Dean James]

I suppose it's just as well, then, that I don't drink orange juice...

[Neil]

Not drinking orange juice does mean you dodge one of the main impacts of HLB, but citrus oils and other flavourings derived from the fruit are some of the most widely used ingredients in the food industry. And let's not even think about the consequences for those who like a G&T, martini, or Margarita...

[Susan]

I'm running right out to build a fence around my orange tree and make florida pay for it.

(Thanks, Neil, for a great primer.)

[Elaine Viets]

Thanks right, blame the victim, poor old Florida. Once again, it's foreigners causing this -- the Plantagents!

[Elaine Viets]

I meant, the Plantagenets. See, they made me mess this up.

[catriona]

Hi all. Glad my substitute kept you entertained!

[Hank Phillippi Ryan]

This is so fascinating. And chilling. It's only one example of how we have no control. Thank you, dear Neil! I think.

[Hank Phillippi Ryan]

We had boxwood psyllids, and the garden person said--oh, they;ll just go away.

[Dana]

Thanks for a compelling (and kinda scary) post, Neil! Eek! But very cool science!

[Cherie O'Boyle]

Fascinating. The wonder and joy of dogs never ceases to amaze. My border collies and I have only been learning nose-work for a few weeks, but if you ever need to find birch, cloves,...or the cat, we've got you covered.