Tropical Fruit Diseases - Hawaii Tropical Fruit Growers

Tropical Fruit Diseases
Dr. Lisa Keith
Research Plant Pathologist
Tropical Plant Genetic Resource Management Unit
USDA-ARS, PBARC
Tropical Fruit Growers Conference
September 30, 2006
Tropical Fruit Diseases
• Rambutan disease surveys were conducted and a variety
of fungal pathogens were isolated and identified as the
causal agents of fruit and leaf lesions. Our overall goal is
to gain a better understanding of what fungi affect
rambutan fruit quality and determine if pathogen
management practices can result in improved fruit
quality. The fungi identified included Lasmenia,
Colletotrichum, Phomopsis, Lasiodiplodia and
Pestalotiopsis. Growth studies at a variety of
temperatures were conducted to determine if certain
temperatures could suppress disease. Disease incidence
was compared for six rambutan varieties. Fungal isolates
were also evaluated for sensitivity to fungicides
registered for use in Hawaii.
Tropical Fruit Diseases
• Until recently, lychees in Hawaii were relatively free of
pre-harvest diseases affecting fruit or foliage. This
research aims to benefit the lychee industry in Hawaii by
establishing the extent of disease problems, raising
awareness of the incidence and damage, and eventually
evaluate some potential control measures. Since growers
may be unaware of the symptoms of lychee diseases and
consider them as an unspecified “blemish”, it was felt
that growers would immediately benefit from accurate
identification and early intervention.
Rambutan – Nephelium lappaceum
Common Field Symptoms
Rambutan
Day 0
Day 7
Day 9
Disease progression of a natural field sample
Rambutan – Main Fungi
Artificial inoculations showing symptoms
Lasmenia, 7 days
Pestalotiopsis, 7 days
Phomopsis, 5 days
Colletotrichum, 5 days
Lychee – Litchi chinensis
Common Field Symptoms
20X lesion
magnification
Common Field Symptoms
Kaimana
Lychee – Koch’s Postulates
Main fungi on lychee include Colletotrichum,
Phomopsis, Lasiodiplodia, and Pestalotiopsis
Kwai Mi Pink
Lychee – Susceptibility Study
Colletotrichum
Phomopsis
Pestalotiopsis
Lasiodiplodia
Kaimana/Kwai Mi Pink, Non-wounded/Wounded, 7 days
Conclusions
• Similar symptoms for numerous fungi
• Pathogens can affect several hosts
• Multiple factors contribute to the
onset of disease
• Fungi were identified morphologically
and molecularly
Conclusions
• Differences in growth depending on
temperature
• Trilogy does not appear effective for
control of fungal pathogens on rambutan
• Differences in variety susceptibility
• Fungi can cause significant losses
Goals/Impact
• Characterize host-pathogen interactions
• Develop disease control methods
• Evaluate how pre-harvest practices affect
post-harvest quality
• Additional fungicide trials; field trials
• Determine resistant varieties
The Team