Citrus Propagation and Disease in California – Your Questions Answered by Dr. Georgios Vidalakis

September 17, 2019 0 By Stanley Isaacs


– Hi I’m Dan Willey, the fruit mentor. I’m here at the historic 1907 Riverside Citrus Experiment Station
to present your questions on citrus propagation and disease to Dr. Georgios Vidalakis, professor and extension specialist from
the Department of Microbiology of the University of
California, Riverside. Georgios is the Director of the Citrus Clonal Protection Program, a historic program that has been providing disease free citrus budwood
for more than 80 years. – Welcome, Dan. – [Dan] Thank you. – Welcome to the 1907
Citrus Experiment Station. The birthplace of the University
of California at Riverside. This building is over a
hundred years old now. So, Dan, I hear you have
some questions for me. – Yes, the first question is on the prohibition of grafting
with backyard budwood. Could you explain that and
when that will be over? – That’s a good question, Dan. I think a better way to see
this is not something temporary. It didn’t just appear. This kind of rule has been
in place since the 1930’s when we made the scientific discovery right here at the Citrus
Experiment Station that if you collect
budwood from a sick tree and you propagate trees with that budwood, those trees are also going to be sick. So in the case of plant pathology these regulations are science based. It is not just a random
governmental agency saying you cannot do this
or you can’t do that. These days because we’re battling another very important and
catastrophic citrus disease, the huanglongbing disease of citrus or citrus greening disease, it was very important to
remind the people in California that we should not propagate citrus trees from random sources because
those sources could have, not only huanglongbing but many,
many other citrus diseases. So I do not expect an expiration. This is how we should propagate trees. We should propagate
trees from mother plants that have been produced in a program like the Citrus Clonal Protection Program that we are visiting here today, where scientific developments
over the last 80 years have given us the technology
to produce strong, healthy mother plants for everybody to use and propagate their trees. – What is the risk if
someone takes citrus cuttings from their own property and propagates them to another
citrus tree on their property? – That’s a very good question, Dan. But always, you know, in questions of risk they’re complicated. So let me give you an example. The first HLB tree in
the state of California was a backyard tree that had
23 different grafts on it. And that was local varieties
in that neighborhood and a local person was
making those propagations. And that was the first
huanglongbing tree in our state. With the spread of the
vector of the disease this Asian citrus psyllid all over our state using budwood from trees
that have been exposed to the disease and the
vector and keep propagating that material and propagating
the disease in your back yard. I don’t think it’s a very good idea. You can always go and buy
a nice, strong healthy tree from a nursery or get
clean budwood from the CCPP and start a beautiful healthy
tree in your back yard. – How does using CCPP budwood help someone in an area where Asian citrus psyllids and or huanglongbing are already present? – Because HLB has been
reported in your area, it doesn’t mean that all
the trees in your property have the disease. So you have to make sure
you don’t bring the disease into your property with
budwood that is not clean. So you have to make sure
you use clean budwood, in this case from CCPP, and that way you are
propagating clean trees. So the psyllid that it’s
also based on the question is in your area cannot take
the disease from your trees and move it to other
trees in your property or further out in other properties. So it’s always the best
practice to use clean budwood when you make trees for your backyard, regardless if you are in an area with HLB or the Asian citrus psyllid. – Several people have
asked me to do a video on air layering citrus. Could you explain why
that’s not a good idea. – The disease principles are the same between air layering and using budwood. If the mother tree you are
using to make your air layers has a disease the new
trees you are going to make with air layering are also
going to have the disease. So you’re keep propagating
a disease in your property and also if an insect vector
comes through your property it can spread the disease
more within your property or to other properties. Also, self rooted citrus trees, trees that they are not
grafted on rootstocks usually are weaker trees,
less productive trees that don’t live as long as other trees. The citrus practice has
changed from self rooted trees since the 1800’s because
the trees that they were not propagated on rootstock, they were very sensitive
to soil borne diseases and they had all sorts
of production issues. So in general air layering
from your own back yard trees is not a good idea. – Are there any HLB resistant rootstocks or scions available, and if so
how can the public get them? – Right now there is no
resistant scion variety or rootstock to HLB. As soon as the research
has discovered or developed such a variety we will
make sure we will create a clean source for it at the CCPP and we will make it
available to everybody. Some reports from experimental hybrids or from commercial
citrus outside California where the disease is widespread, they indicated there is some
varieties and some rootstocks that they behave a little bit better under the disease pressure. But these are not standalone observations. These varieties are grown
into very sophisticated and complex production systems. It’s not a classic system where you have a resistant variety and without
any special manipulation is resistant to the disease. Unfortunately we do not
have anything like that right now in our hands. – How can people have their trees tested and treated for disease? – In the case of HLB, if any of you think you have a sick tree, an HLB tree in your backyard, please call immediately the hotline of the California Department
of Food and Agriculture. In any other case, but including HLB, the University of California Agriculture and Natural Resources,
UCANR, has in every county, has a farm advisor locally. UCANR and I think I have
their handbook here, UCANR also has this beautiful
program, the Master Gardeners, and there are very
knowledgeable people trained by the University of California, and they know very well
how to advise homeowners about all sorts of crops, not only citrus. In terms of treatment for
HLB and for other diseases in the same category, what we call graft transmissible diseases. Diseases that they are
introduced into a tree by propagation. There is no treatment. That’s why we always say
you need to make your tree with clean budwood. That way you do not introduce
diseases in your tree because after and if
you introduce diseases there is no treatment for your tree. – Will citrus germinated from
seed be resistant to disease? – Growing a citrus tree
from seed doesn’t affect the resistance to diseases. You cannot make a tree
resistant to a disease, in this case HLB or in
general for any other disease, just because you’re growing it from seed. There is no change in the
sensitivity of a citrus in a disease because it grows from seed. – Can HLB be spread by municipal compost? – So Dan if we talk about
fresh, green, yard waste, then HLB risk, yes there is a risk there because you can move the
pathogen around and the psyllid. But after that yard waste
has been processed properly, and has been composted
you essentially have soil. So the HLB risk from composted
materials is very, very low. – For the remainder of the
questions we put on lab coats and went out to the CCPP greenhouse. If I graft CCPP budwood
to my infected tree will that cure the tree? – So if you graft CCPP
budwood on a sick tree, let’s say this budwood
here is CCPP budwood and this is the tree in your property, this is a sick tree trunk and
these are sick tree roots, what is going to happen is
that no, the CCPP budwood will not cure your tree. Actually the disease from the roots and the trunk of your tree will make the CCPP budwood also sick. – If an HLB infected tree is removed and a new tree is planted in its place, will the new tree be infected? – The key element to the
answer to this question Dan, is stump removal. You cannot just cut with
a chainsaw your tree and then leave on the ground
the stump of the rootstock. And this is a beautiful
example in this pot where we had three plants
that we finished working with, and we decapitated you can
see the stumps of the seedling in this pot, and in this stump right here you can see shoots coming out in this one all fully developed shoot
here and two more shoots here. And what’s happening is the
stump pushes this young shoot and this young shoot will do
two things in your property. They will keep the roots
under the ground alive of the sick tree, and if you come and plant your new tree, healthy tree next to
them the roots may graft and the roots from the
sick tree could transmit the disease to the clean tree. But most importantly these
young shoots will attract the Asian citrus psyllid. And the Asian citrus psyllid
will pick up the disease from the shoots, from the
stump of the sick tree and transmit it to your new tree, or to other trees in your
property or beyond your property. So it’s very important to
have complete stump removal and complete tree removal
if a tree is sick with HLB before you plant a new
tree in the same spot. – Can citrus diseases be spread by seed? – Huanglongbing is not
transmitted by seed. There is other diseases
however that can be transmitted by seed. There’s a very well-studied
case of a virus that was actually discovered last year in California for the first time. And a citrus seed has
many different layers and different parts. And in most cases, the citrus pathogens could
be in one part of the seed, but it cannot find its
way to the growing plant and infect the plant. So a pathogen or a disease
could be seed-borne, could be part of the seed, but it’s not seed transmitted. It cannot make the plant that
growing out of the seed sick but nevertheless there is citrus diseases that can be seed transmitted. Huanglongbing is not
one of those diseases. – How much does it cost to produce budwood compared to how much
people pay for budwood? – Production of clean budwood
requires a lot of resources. Our program operates
with 14 different people. We have another 20 people
doing research for us. Students to develop new
technologies for diagnostics and budwood therapy. We operate at three different
locations and facilities where everything begins
here at the Rubidoux Quarantine Facility we’re
standing in front of future budwood sources. And as you can see, in these labels here, and these code numbers
there is an indication that this specific budwood source tree in the last two years
from 2017 went through introductory propagation and therapy and eventually was tested negative for all non-citrus diseases in the
variety index screening as this code numbers indicate. And we also operate a diagnostic
and research laboratory at the main UC Riverside campus, and we also have our foundation facility which maintains over
1,000 trees of 400 plus different citrus varieties
for budwood distribution. Our annual budget is a little
bit less than $1 million, that’s operational budget. In addition to that there
is overhead expenses and facilities expenses and so on. And our income from
budwood sales last year was a little bit over $74,000. And as you can imagine,
$74,000 can barely cover salaries and benefit of one person and they’re by far less what is required to produce clean budwood
source for citrus. – [Dan] Click the video
on the screen now to watch the next interview in this series. Thanks so much to Georgios, and I will see you in the next video.