Las Cruces, New Mexico
February 4, 2009
Source:
American Society for
Horticultural Science
Does hotter mean healthier?
Relationship between chile peppers' heat level and plant disease
resistance studied
Phytophthora blight, caused by Phytophthora capsici, is a major
plant disease that affects many crop species worldwide,
including chile peppers in New Mexico. Farmers' observations
suggested that Phytophthora capsici caused less damage in pepper
crops of the hot pepper varieties than low-heat pepper
varieties.
A study published in the October 2008 issue of
HortScience by
the research team of Mohammed B. Tahboub (postdoctoral
researcher), Soumaila Sanogo (plant pathologist and team
leader), Paul W. Bosland (chile pepper breeder), and Leigh
Murray (statistician) set out to determine whether or not the
severity of Phytophthora blight would be greater in low-heat
than in hot chile peppers.
The most effective means for controlling Phytophthora blight are
chile pepper cultivars that are genetically resistant to the
disease. Some resistant lines have been identified, but
currently there are no cultivars that are resistant to the
blight in all environments.
Chile pepper fruit become infected during prolonged periods of
heavy rain and high humidity in flooded and poorly drained
fields. Prior to this study, there had been no systematic
assessment of the relationship of chile pepper heat level to
chile pepper response to Phytophthora capsici. If such a
connection could be found, information might have been revealed
that would assist breeding programs intended for developing
disease-resistant cultivars of pepper.
Based on documented field observations in New Mexico, Arizona,
and South Carolina, the researchers hypothesized that peppers
that produce high-heat fruits would be more resistant to
Phytophthora blight than low-heat varieties. The study was
conducted by observing infection on both the root and fruit of
different varieties of peppers included.
The results of the study concluded, however, that there was no
relationship between the heat level of the pepper and the
plant's resistance to Phytophthora blight. For example, while
the disease was slowest to develop on the roots of one variety
of jalapeño, it was quickest to develop on the fruit of the same
plant.
Conversely, the disease was faster to develop on roots and
slower on fruit of all other cultivars. As the root of the plant
contains no heat-inducing agents but the fruit does, the slow
development on the root and rapid development on the fruit of
the jalapeño indicates that heat level is not a factor.
The results of this study indicate that factors other than heat
level may be involved in fruit response to Phytophthora capsici.
Genetic differences and cuticle thickness of the plants and
fruits are among other issues that could be relevant, but
further study is warranted.
The complete study is available on the ASHS HortScience
electronic journal web site:
http://hortsci.ashspublications.org/cgi/content/abstract/43/6/1846
Heat Level in Chile Pepper in Relation to Root
and Fruit Infection by Phytophthora capsici
Mohammed B. Tahboub, Soumaila Sanogo, Paul W.
Bosland and Leigh Murray
ABSTRACT
Phytophthora blight, caused by Phytophthora capsici
Leon., is a major plant disease that limits chile
pepper (Capsicum annuum L.) production in New
Mexico. Chile pepper producers in New Mexico report
that Phytophthora blight symptoms appear to develop
slower and its incidence is lower in hot than in
nonhot chile pepper cultivars. There has been no
previous systematic assessment of the relationship
of chile pepper heat level to chile pepper response
to P. capsici. Three hot (‘TAM-Jalapeño’, ‘Cayenne’,
and ‘XX-Hot’) and two low-heat (‘NuMex Joe E.
Parker’ and ‘New Mexico 6-4’) chile pepper cultivars
were inoculated at the six- to eight-leaf stage with
zoospores of P. capsici under greenhouse conditions.
Additionally, detached mature green fruit from three
hot (‘TAM-Jalapeño’, ‘Cayenne’, and ‘XX-Hot’) and
one low-heat (‘AZ-20’) chile pepper cultivars were
inoculated with mycelium plugs of P. capsici under
laboratory conditions. When plant roots were
inoculated, Phytophthora blight was slowest to
develop on ‘TAM-Jalapeño’ in contrast to all other
cultivars. All ‘TAM-Jalapeño’ plants showed wilting
symptoms or were dead 22 days after inoculation
compared with 18, 15, 14, and 11 days for ‘NuMex Joe
E. Parker’, ‘New Mexico 6-4’, ‘XX-Hot’, and
‘Cayenne’, respectively. When fruit were inoculated,
lesion length ratio was significantly higher for
‘TAM-Jalapeño’ fruit than for ‘Cayenne’, ‘XX-Hot’,
and ‘AZ-20’ fruit. Similarly, lesion diameter ratio
was higher for ‘TAM-Jalapeño’ fruit than for fruit
of other cultivars. Furthermore, mycelial growth on
lesion surfaces was more extensive on ‘TAM-Jalapeño’
fruit than on fruit of other cultivars. Results from
this study indicate that there is little or no
relationship between heat level and chile pepper
root and fruit infection by P. capsici. |
Founded in 1903, the American Society for Horticultural
Science (ASHS) is the largest organization dedicated to
advancing all facets of horticultural research, education and
application. More information at
www.ashs.org |
|
