March 2020 - 18

Wild tomatoes resist devastating bacterial canker
By Krisy Gashler
Cornell University
Many New York tomato growers are
familiar with the scourge of bacterial
canker - the wilted leaves and blistered fruit
that can spoil an entire season's planting.
For those whose livelihoods depend on
tomatoes, this pathogen - Clavibacter
michiganensis - is economically
devastating.
In a new paper, Cornell researchers
showed that wild tomato varieties are
less affected by bacterial canker than
traditionally cultivated varieties. The
paper, " Characterizing Colonization
Patterns of Clavibacter michiganensis
During Infection of Tolerant
Wild Solanum Species, " published
online in November in the journal
Phytopathology.
Co-authors were Christine Smart,
professor of plant pathology and
plant-microbe biology in the College
of Agriculture and Life Sciences; F.
Christopher Peritore-Galve, a doctoral
student in the Smart Lab; and Christine
Miller, a 2018 Smart Lab undergraduate
summer intern from North Carolina
State University.
tomato gets infected, it can spread from
plant to plant.
" Bacterial canker certainly can cause
the complete loss of a field of tomatoes,
and we see outbreaks of the disease
every year, " Smart said. " Growers
use disease management strategies,
including spraying plants with copperbased
products; however, once there
is an outbreak it's difficult to control
bacterial canker. "
To combat diseases, plant pathologists
and breeders often look for varieties
that are resistant, but among tomatoes
traditionally grown for market, there are
none with genetic resistance to bacterial
canker. So Peritore-Galve, Miller and
Smart went back to the beginning.
Tomatoes are native to the Andes
Mountains region of South America,
where wild species have been free to
evolve for thousands of years. Recently,
plant breeders have identified wild
tomatoes that seem to be less susceptible
to bacterial canker and are resistant to
other pathogens.
The team wanted to understand how
bacteria spread and colonize in wild
tomatoes versus cultivated ones. They
zeroed in on the plants' vascular systems -
specifically their xylem vessels.
Like individual veins in a human,
xylem vessels transport water and
nutrients from soil throughout the
plant. The team found that in cultivated
species, bacterial canker spreads
everywhere, while in wild species the
bacteria remain confined to certain
xylem vessels without moving much into
A cultivated tomato infected by bacterial
cankers. Photo: Chris Peritore-Galve
" Bacterial canker is pretty bad in
New York, " Peritore-Galve said, " but
it's distributed worldwide, everywhere
tomatoes are grown. "
The pathogen causes wounding and
is spread by wind-blown rain; if one
surrounding tissues.
" The wild tomatoes, for some reason,
impede the ability of the bacteria to
move up and down through the plants,
which reduces symptoms - in this case,
leaf wilt, " Peritore-Galve said.
This is the first study ever confirming
that wild tomatoes are susceptible to
bacterial canker, though the infection is
Martha Sudermann, right, and Chris Peritore-Galve, graduate students in the lab of plant
pathology and plant microbe biology professor Chris Smart, examine tomatoes growing in
a greenhouse at Cornell AgriTech in Geneva. Photo: Allison Usavage/Cornell University
less severe than in cultivated varieties.
But while a severe infection causes fewer
symptoms in the wild plant, it can still
cause lesions on the fruit.
Even so, a tomato variety with
resistance to the bacteria could still be
very helpful for tomato growers, said
Chuck Bornt, vegetable specialist with
Cornell Cooperative Extension's Eastern
New York Commercial Horticulture
program. Bornt works extensively with
New York tomato growers.
" Many times, it's not the fruit
symptoms that cause the issue, " Bornt
said, " it's the wilting of the plants or
the plugging of the xylem cells that
cause the plant to lose foliage, which
then exposes the fruit to sun scald and
other issues. ... Infected fruit are also
an issue, but in my opinion it's these
other issues that have more impact. "
This work was supported by funding
from the USDA National Institute of
Food and Agriculture. VGN
16 | VegetableGrowersNews.com
http://www.VegetableGrowersNews.com
March 2020

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