Tropical Fruit Diseases

Dr. Lisa KeithResearch Plant Pathologist

Tropical Plant Genetic Resource Management UnitUSDA-ARS, PBARC

Tropical Fruit Growers ConferenceSeptember 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 FungiArtificial inoculations showing symptoms

Phomopsis, 5 days

Pestalotiopsis, 7 days Colletotrichum, 5 days

Lasmenia, 7 days

Lychee – Litchi chinensis

Common Field Symptoms

20X lesionmagnification

Common Field Symptoms

Kaimana

Lychee – Koch’s Postulates

Kwai Mi Pink

Main fungi on lychee include Colletotrichum, Phomopsis, Lasiodiplodia, and Pestalotiopsis

Lychee – Susceptibility Study

Kaimana/Kwai Mi Pink, Non-wounded/Wounded, 7 days

Colletotrichum Phomopsis

LasiodiplodiaPestalotiopsis

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