Eggplant Rust at a
glance
Type
of Damage
|
Stunted growth, leaf blight
|
Plant
Symptoms
|
Bright orange blisters under leaves
|
Favourite
Plant
|
Common & African eggplant
|
Control
|
Difficult (Sulphur based products)
|
 |
| Eggplant Rust Puccinia substriata Pearl Millet Rust |
Quick Intro
This is a recently identified rust problem on eggplants. Pearl Millet Rust (Puccinia substriata var. substriata), the same fungus that infects Pearl Millet (Pennisetum
glaucum), has been recorded infecting eggplant (since 2006). Here I provide you with a
complete profile on what is currently known about this disease.
Science Stuff
The family Pucciniaceae contains several pest fungi of grain crops, which belong to the Poaceae family (the grass family). The Puccinia
genus contains a very large number of species and 'variants'. 'Variant' being a rust of
the same species but might differ in spore morphology or ecology. I will be
discussing Puccinia substriata var substriata, Puccinia substriata var penicillariae
and Puccinia substriata var indica.
Hosts
Puccinia substriata var substriata infects the ‘common’ eggplant (Solanum melongena) and its horticultural
rootstock, the turkey berry (Solanum
torvum). This species was often confused with Aecidium
tubulosum, but has now been confirmed to be the same species through
inoculation experiments (Ref 1).
Puccinia substriata var penicillariae infects the ‘common’
eggplant from Brazil. Again confusion resulted in the same fungus been given two species names. Therefore, Puccinia substriata var indica is the same species as Puccinia substriata var penicillariae.
No symptoms of Puccinia substriata
var penicillariae infection was
noticed on Solanum americanum (American nightshade), Solanum sisymbriifolium (Sticky
Nightshade), Solanum tubersonum (Potato) or Solanum paniculatum (Jurubeba, a nightshade) after inoculation and therefore these species of Solanum are not considered host plants (Ref 2).
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Puccinia substriata var substriata and Puccinia substriata var penicillariae infect the same host plants and have similar life cycles, they only differ by geographical dispersal. Puccinia
substriata species occur in Africa, North America, Central America, USA,
Mexico, Caribbean and South America (Ref 2 & 3).
Aecidium cantanese (potato
deforming rust) is another similar rust species that has been recorded on the African eggplant (Solanum macrocarpon)
in Benin during 2011 (Ref 4).
It has also been shown that the Puccinia grass-infecting (or Poaceae-infecting) rusts are evolutionarily distinct from the Puccinia hardwood-infecting (or Junaceae & Cyperaceae-infecting) rusts (Ref 5 & 6).
Life Cycle (Ref 2)
Rusts are ‘simple’ fungi with very complicated life cycles. They can
reproduce asexually (without a compatible partner) and sexually (with the fusion of
gametes). The mechanism of reproduction, their morphology and cytological structures define their growth/life stages. Typically rusts have five distinct life stages,
but I am just going to discuss three.
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| Eggplant Rust Topside of leaf Puccinia substriata |
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| Eggplant rust Underside of leaf Puccinia substriata |
Pearl millet rusts are heteroecious, meaning they require two host
species to complete their life cycle.
The initial host, AKA alternate host, is infected early in the growing season, usually during spring. This will be the eggplant (Solanaceae) host. During this stage mature teliospores from the previous seasons’ rust growth infects the eggplant leaves. These germinate and grow on the eggplant host, in what is known as the Aecial stage (asexual). Aecia are cup shaped and grow into the leaf tissue. They cause local necrosis (cell death) and stunt the host plant. As they mature they will burst open and release aeciospores.
Aecioposres disperse with the wind and fall upon the next host, AKA definitive host, such as Pearl Millet where sexual reproduction takes place. Aeciospores germinate and grow as Uredinia. The Uredinial stage remains asexual and bolsters the rust population by infecting new pearl millet hosts with Urediniospores. Towards the end of the growing season, in late summer, Uredinia mature and become Telia. Telia cause the most damage to the host plant. Necrotic lesions increase in size, connect and coalesce. At this stage the rust causes large scale necrosis and leaf blight (dropping of dead leaves). Telia also burst open to disperse teliospores. Teliospores are thick, black structures that are able to overwinter and are almost impossible to kill. Teliospores will then infect the alternate host come spring.
The initial host, AKA alternate host, is infected early in the growing season, usually during spring. This will be the eggplant (Solanaceae) host. During this stage mature teliospores from the previous seasons’ rust growth infects the eggplant leaves. These germinate and grow on the eggplant host, in what is known as the Aecial stage (asexual). Aecia are cup shaped and grow into the leaf tissue. They cause local necrosis (cell death) and stunt the host plant. As they mature they will burst open and release aeciospores.
Aecioposres disperse with the wind and fall upon the next host, AKA definitive host, such as Pearl Millet where sexual reproduction takes place. Aeciospores germinate and grow as Uredinia. The Uredinial stage remains asexual and bolsters the rust population by infecting new pearl millet hosts with Urediniospores. Towards the end of the growing season, in late summer, Uredinia mature and become Telia. Telia cause the most damage to the host plant. Necrotic lesions increase in size, connect and coalesce. At this stage the rust causes large scale necrosis and leaf blight (dropping of dead leaves). Telia also burst open to disperse teliospores. Teliospores are thick, black structures that are able to overwinter and are almost impossible to kill. Teliospores will then infect the alternate host come spring.
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| Pearl Millet rust life cycle Start at 'Initial innoculation' at the top left-hand side |
The rust infection is more abundant, grows more aggressively and inflicts more damage to crops at each stage its life cycle, from the alternate host towards the definitive
host. Therefore effective control is applied during the correct stage of the life cycle and when both the alternate and definitive hosts are treated. All stages are similar in terms of their growth, eruption of mature structures and the release of wind dispersed spores.
Control
Rusts are hard to control and several chemical treatments exist.
Sulphur containing fungicides prevent spore germination and stunts the growth of the rust. I
have developed an organic treatment of eggplant rust using lavender, rosemary and
sulphur. Check out my Pest Control: Eggplant Rust section for the recipe and an in-depth explanation as to why it works.
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| Dead eggplant rust (red arrows) |
Preventative Tips
ü Avoid overwatering of plants
ü Avoid wetting leaves
ü Decrease crop planting density
ü Increase air circulation between plants
ü Rotate crops
Something Interesting: Saint
Anthony’s Fire
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| Claviceps purpurea Köhler's Medizinal-Pflanzen in naturgetreuen Abbildungen mit kurz erläuterndem Texte 1887 Kurt Stuber's online library |
Rusts are related to another crop pest known as the Smuts, such as Claviceps purpurea.
Claviceps purpurea is an ergot fungus that grows on rye and other cereals. The fungus infects the ears of rye and produces a black growth filled with toxic alkaloids. When you eat grains infected with ergot fungus you become intoxicated with the alkaloids and will suffer neurological symptoms. During the Middle Ages and medieval times people suffering from ergotism believed themselves to be on fire; they will strip, run down the walkways, yelling as they ran and other people would merely think them bewitched. The monks belonging to the Order of St. Anthony were very adept at treating the poisoning and soon people identified the source. Thus, the disease caused by ergot fungi became known as Saint Anthony's Fire.
Claviceps purpurea is an ergot fungus that grows on rye and other cereals. The fungus infects the ears of rye and produces a black growth filled with toxic alkaloids. When you eat grains infected with ergot fungus you become intoxicated with the alkaloids and will suffer neurological symptoms. During the Middle Ages and medieval times people suffering from ergotism believed themselves to be on fire; they will strip, run down the walkways, yelling as they ran and other people would merely think them bewitched. The monks belonging to the Order of St. Anthony were very adept at treating the poisoning and soon people identified the source. Thus, the disease caused by ergot fungi became known as Saint Anthony's Fire.
Ref 2: De O. de Carvalho, A. et al (2006) Description of the
life-cycle of the pearl millet rust fungus– Puccinia
substriata var. penicillariae with
a proposal of reducing var. indica to
a synonym. Mycopathologia 161: 331-336
Ref 3: Roberts, P. D. et al(2012) Rust detected on eggplant (Solanum melongena) in Southwest Florida. Report
Ref 4: Beed F. et al (2011) First report of Aecidium cantenese (potato deforming rust) on Solanum macrocarpon (African eggplant) in Benin. New Disease Reports 23 (12).
Ref 5: Dixon, L. J. et al (2010) Phylogenetic relationship of sugarcane rust fungi. Mycol Progress 9: 459-468
Ref 4: Beed F. et al (2011) First report of Aecidium cantenese (potato deforming rust) on Solanum macrocarpon (African eggplant) in Benin. New Disease Reports 23 (12).
Ref 5: Dixon, L. J. et al (2010) Phylogenetic relationship of sugarcane rust fungi. Mycol Progress 9: 459-468
Ref 6: Maier, W. et al (2007) Polyphyly and two emerging
lineages in the rust genera Puccinia
and Uromyces. Mycol Research 111(2):
176-185
Last Comments
It seems that the Puccinia
species are increasing in their geographical spread and that their distribution is no
longer restricted to Africa and the Western Hemisphere, but they have now been
recorded in Europe as well (Ref 3).
Please note that any herbs or vegetable crops that are grass-species (Poaceae family) can become infected with rusts and their control will be similar to that of eggplant (sulphur-based treatments). Rust infection can occur on lemongrass and any cereal crop (maize, rye, barley, rice...).
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| Teleospores of Wheat Rust Puccinia graminis |
Have you noticed eggplant rust on your plants?
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