START: 01 MAY 2002 TERM: 30 APR 2004 FY: 2003 GRANT YR: 2002
GRANT AMT: $150,000
INVESTIGATOR: Caruso, F.
PERFORMING INSTITUTION:
CRANBERRY SUBSTATION
UNIV OF MASSACHUSETTS
AMHERST, MASSACHUSETTS 01003
INFECTION BIOLOGY OF KEY CRANBERRY FRUIT ROT PATHOGENS
NON-TECHNICAL SUMMARY: Cranberry fruit rot is a destructive disease in the field before harvest and in storage after harvest. It is especially problematic in Massachusetts and New Jersey, but losses can also occur in Wisconsin and the Pacific Northwest. Little is known about the epidemiology of fruit rot due to its complexity. There are at least 15 different species of fungi that cause the disease and the spectrum of fungi vary from year to year and location to location. The lack of knowledge about the disease is a key barrier to IPM implementation. The objectives of this project are to investigate whether cranberry fruit exhibit a distinct period of susceptibility during early development. It is believed that infections occurring during this period have a high probability of eventually rotting fruit, whereas infections occurring later in the season have a lower probability of rotting fruit. If this is the case, growers should only need to apply fungicides for disease control only during this critical period, and applications later in the season could be eliminated. In the Northeast, fungicide programs could be reduced from 3-6 applications to 1-3 applications. This cost reduction is critical to the cranberry grower, because hard economic times have caused considerable alterations in pest management. The project will include experimental research and field demonstrations. The new knowledge on the biology of these key pathogens will provide a foundation for the development of future predictive models for fruit rot.
OBJECTIVES: 1. Determine the important sources of inoculum of the fruit rot fungi 2. Characterize infection structures and latent forms for the fruit rot fungi 3. Determine the timing of infection by the fruit rot fungi
APPROACH: Four key species of fruit rot pathogens will receive the focus: Coleophoma empetri, Colletotrichum gloeosporioides, Phyllosticta vaccinii and Physalospora vaccinii. Different plant tissues will be collected at different times to determine the overwintering inoculum. Samples will be visually inspected and spores will be examined under the microscope. Tissues will be incubated in moist chambers and visually inspected on a regular basis for the presence of inoculum. Spore traps will be utilized to determine which of these fungi produce aerial inoculum. Units will also be set up to determine which fungi are dispersed by water splash. Flowers and berries will be inoculated with these fungi to determine whether a latent phase exists in their life cycle(s). Plant tissues will be sampled, stained, mounted and examined for infection structures. As symptoms of rot develop, berries will be regularly sampled to follow the progression of infection. Specific RNA probes will be utilized to detect these fungi in symptomless berries. Experiments will be conducted under both controlled laboratory and field conditions. Field plots will address the exact timing of infection of these fungi. Eight schedules of two Bravo applications will be examined, wherein the flowers and berries are sprayed from early bloom through berry development. Tissues will be sampled and half will be cultured, while the other half is evaluated by reverse dot blot hybridization. Fruit rot infection in these plots will be evaluated.
PROGRESS: 2002/05 TO 2004/04
Leaves and stems, berries, and the duff layer were sampled both years from pre-bloom
to post-bloom and either incubated in moist chambers or plated directly to determine
which fungi were present on what tissue as inoculum. Colletotrichum was found
primarily on 2nd and 3rd year stems and occasionally on 2nd and 3rd year leaves
in NJ and was hardly ever detected in MA and WA. Phyllosticta was detected on
1st, 2nd and 3rd year leaves and 2nd and 3rd year stems in MA and NJ. Physalospora
was detected on 2nd and 3rd year leaves in MA and NJ. Coleophoma was only detected
on 3rd year leaves and stems in MA but at very low levels. Some of the above
fungi were also detected in the duff layer, but saprophytic fungi made quantification
very difficult.Spore traps were operated from April to September in WA and MA
adjacent to the fungicide timing trials. Pitfall traps were also employed in
both locations to trap waterborne spores. Spore trappings on the tapes, rotorods,
and in the filtrates will be analyzed by the reverse dot blot hybridization
(RDBH) assay.In the greenhouse, groups of young green berries and older blushed
berries were inoculated with either Colletotrichum, Fusicoccum, or Coleophoma.Final
rot incidence was too low (0-4%) at harvest to discern differences between young
and older fruit inoculated with any fungus.A subset of berries were examined
by scanning electron microscopy and light microscopy to visualize fungi in fruit.
Hyphae often were not visible in inoculated fruit.Younger berries rotted more
quickly than older berries, and Colletotrichum was a more aggressive fungus
than Fusicoccum.The fungi colonize the calyces of young berries and invade through
the stylar scar.Fungicide timing trials were established in both years.Chlorothalonil
was applied to provide protection of the flowers and berries during different
portions of the crop season. Each treatment consisted of a two-spray schedule
with sprays seven days apart, with the first treatment spray applied at 5% open
blooms and the final treatment spray applied post-bloom. Field and storage rot
were evaluated, and rotted berries were cultured to determine which fungi were
responsible for rot in each treatment. Rot levels in WA were very low and there
were no differences between the different fungicide schedules in both years.
In MA in 2002, all fungicide schedules provided excellent field and storage
rot. In 2003, field and storage rot increased when the first fungicide was applied
after most berries had set. In NJ, based on similar trials, the majority of
infections occur prior to fruit set.Flowers and berries were sampled on a weekly
basis in MA, NJ and WA from a second set of untreated plots solely used for
sampling. Fungi were cultured from half of the samples and the other half was
frozen. These samples will also be analyzed by the RDBH assay to compare fungal
presence in these samples at different times during fruit development. Phenological
data were compiled during the entire growing season so that fungi detected could
be linked to a particular developmental stage. Fruit rot estimations were also
compiled on a weekly basis, beginning at fruit set until harvest.
IMPACT: 2002/05 TO 2004/04
Growers will be able to achieve good control of fruit rot with fewer fungicides.
Important information will be learned about the basic biology of the fruit rot
fungal pathogens. The usefulness of the DNA reverse hybdridization dot blot
assay will be confirmed. Information will be learned about the latent phase
of certain fungi in the cranberry plant.
PUBLICATIONS: 2002/05 TO 2004/04
No publications reported this period
PROJECT CONTACT:
Name: Cromack, P.
Phone: 413-545-2771
Fax: 413-545-5910
Email: pcromack@fnr.umass.edu