Group Title: Immokalee ARC research report
Title: Late blight of tomato seedlings
Full Citation
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 Material Information
Title: Late blight of tomato seedlings
Series Title: Immokalee ARC research report - University of Florida ; SF1975-1
Physical Description: 3 leaves : ; 28 cm.
Language: English
Creator: Blazquez, Carlos H.
Agricultural Research Center (Immokalee, Fla.)
Donor: unknown ( endowment )
Publisher: Agricultural Research Center, IFAS, University of Florida
Place of Publication: Immokalee, Fla.
Publication Date: April, 1975
Copyright Date: 1975
Subject: Tomatoes -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: C.H. Blazquez.
General Note: Caption title.
General Note: "April, 1975."
 Record Information
Bibliographic ID: UF00094214
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 406511153

Full Text
I Jot)




C. H. Blazquez

In recent years there has been a considerable increase in the production of
tomato seedlings in greenhouses for transplanting to fields. The growing of seed-
lings in various types of trays greatly facilitates planting in the field and allows
growers greater flexibility in scheduling planting, plus a savings in the cost of
seed. Transplants generally produce a more uniform stand when compared with direct
field seeding. Transplanting also permits the growers later planting dates both in
the fall of the year, to escape hotter temperatures, and in the spring, to reduce
the possibility of losses due to frost damage.

The growing of seedlings in greenhouses with modern techniques such as auto-
mated planting, fertilizing, and good pesticide appl.caton permits more accurate
quality control and the capability of correcting rapiidd, ye~a b s encountered.
However, the high population of single varieties inig7L d8e r te ential
danger for the rapid outbreaks of both insect pests, such as p ,1 diseases,
such as late blight.

The purpose of this report is to describe experiments wi tht o see ings
which will assist growers and agribusiness representatives in recognizing e
symptoms of late blight (caused by the fungus Phyt6 h1gra lnfestans d. B on
tomato seedlings. .'i l Of j-f


Walter tomato (Lycopersicon esculentum L) seedlings were grown in Speedling
trays (manufactured by Leisey &Todd of Sun City, Fla.) in a plastic covered green-
house with a wooden frame until they were five inches high. In a randomized and
replicated experiment, four replicates of six plants each were inoculated in a moist
chamber with P. infestans from two different hosts and transferred to a saran house
with 60% light transmission. Observations were made every six hours during the
light hours. No observations were made at night.

Inoculation.--Late blight infected leaves from Walter tomato plants and Sebago
potato plants were collected from three different fields in Collier County and
brought to the Research Center in Immokalee. Sporangia of the fungus growing on
lesions on the lower surface of the infected leaves were brushed from the lesions
with steam sterilized camel-hair brushes and applied to water droplets on leaves of
tomato seedlings. Microscopic observations of the brush-tip depositions to water
droplets indicated that there were approximately 8 to 15 sporangia per high power
field (650X) of a compound microscope. The seedlings had been previously sprayed
with a mist nozzle to cover the surface of the leaves with water droplets, and care
was taken to touch the leaves with the brushes without brushing. After inoculation,
each group of seedling plants was covered with plastic bags for a period of 24 hours.
Following this period they were placed in a moist chamber with an intermittent mist
_ applicator.



The symptoms observed on the Walter tomato seedlings were as follows: The
first visible symptom observed was a slight water-soaked brownish discoloration on
the rachis of the inoculated leaflets followed by the appearance of a darker brown
discoloration on the leaflet, petiole, or stem. The infected leaflet rapidly began
to wilt and as the dark brown discoloration increased in length down the petiole,
the other leaflets curled inward. The increasing dark discoloration of the stem
preceded a slow collapse of the petiole and the complete wilting of the inoculated
young leaflets. This was followed by the increasing discoloration of the main stem
and distribution both upward and downward from the point of leaf petiole attachment.
There appeared to be no difference in susceptibility between the different ages of
leaves (Table 1), as the pathogen was capable of killing the three types of leaves
inoculated and, in fact, the entire plants without any significant differences.
As the infection progressed down the stem, the dark brown discoloration changed to
a purplish-brown tinge of the main stem. Any leaves and stems above the purplish-
brown discoloration collapsed completely, although they remain attached, giving a
stringy or thread-like appearance to the collapsed and doubled over plant top. The
pathogen will kill the entire stem down to within two inches above the soil line.

No tip or marginal lesions, such as those associated with chemical or fertilizer
burns, developed on any of the leaflet types inoculated. All inoculated plants
collapsed in a similar fashion 3 to 3 1/2 days after inoculation, while the uninocu-
lated plants remained healthy throughout the experiment. The dead top remained
attached to the dying stem until the entire stem turned into a slimy mass of decayed
tissue four days after inoculation.


Walter tomato seedlings were quite susceptible to infection by sporangia of
P. infestans. The symptoms produced by the infection were similar to those produced
in older plants with the exception of sporangial formation. Tomato seedlings were
killed rapidly by both the tomato and potato strains of P. infestars.

Late blight symptoms were quite distinct from those produced by soil-borne
organisms such as Fusarium wilt caused by Fusarium oxysporum f. lycopersici Sacc.
and bacterial wilt caused by Pseudomonas solanacearum.

The symptoms observed on inoculated plants were similar to those previously
described by other researchers.


Table 1. Tomato seedlings killed with two strains of the late blight organism
Phytophthora infestans d. By three and a half days after inoculation.

Percent tomato plants
killed per replicate
Isolate Type of leaflet A B C D Total

P. infestans Young 100 100 100 83 96a
(tomato) Intermediate 100 100 100 100 100a
Mature 83 100 100 83 92a

P. infestans Young 100 100 100 100 100a
(potato) Intermediate 83 100 83 100 92a
Mature 100 100 83 100 96a

Inoculated (water only) Mature 0 0 0 0 Ob

Uninoculated Mature 0 0 0 0 Ob

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