Roots 'n' Shoots: October 2013

Saturday, 19 October 2013

Eggplant Rust – Disease of the Month

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).



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.

Eggplant Rust
Topside of leaf
Puccinia substriata
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.

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.

Dead eggplant rust (red arrows)
Re-infection and the amount of spores that survive to the next season is reduced by controlling the fungus early in the season when symptoms are noticed (spring). You will never be able to eradicate rusts completely from an area as other hosts plants may distribute wind blown spores into your garden from a distance and spores will always be present in the soil. This control is for seasonal use to decrease the total damage caused to your crops and food production.

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

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.


References

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 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...).

 
Teleospores of Wheat Rust
Puccinia graminis



Have you noticed eggplant rust on your plants?

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Please share with fellow gardening enthusiasts via the various sharing buttons at the end of posts/pages! Else you can vote for posts through the Google reactions bar at the end of articles. To stay up to date I have provided several reader and social networking platforms with which to subscribe: TwitterPinterestRSS Feed Reader or Email/Follow directly using the Blog Followers widget on the left hand side toolbar. Thank you for reading and please feel free to ask if questions arise - I appreciate comments and ideas too! 😆
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Friday, 18 October 2013

Breaking News: Update on Bee Colony Failure

The first time I reported on bee colony failures was during January of 2012. Hot from the press was scientific studies on a parasitic fly of Honey Bees, Apocephalus borealis. Also known as the Zombie fly, Apocephalus borealis can cause Colony Collapse Disorder (CCD) and was proposed to be one of the many factors that influence colony failures.

Nature reported (17 Oct 2013) of a new study done on the causes of colony collapse. John Bryden and colleagues (6 Oct 2013) described a system of sub-lethal stresses exerted on bee colonies can cause collapse when the colony's threshold (breaking-point) is reached.

They maintain that no single factor is a direct cause of colony failure. Instead several stress factors act on bee colonies that are detrimental, but not lethal. These indirectly pile up and sooner-or-later the colony cannot maintain itself and results in collapse at unpredictable times. Examples of stress factors can be combined scenarios of habitat loss, pesticide use, pathogens and parasites. Worker bee memory, foraging capability, and mobility are effected when exposed to field concentrations of pesticides. Pathogens and parasites have also been shown to influence body temperature regulation and energy levels as well as impairing learning of infected bees. This does not result in bee deaths, but decreases the efficiency and viability of the colony as a whole.

To investigate their hypothesis they modelled sub-lethal stress (SLS) on several healthy and impaired bumble bee colonies belonging to the Bombus terrestris species. The bees were fed sucrose treated with sublethal concentrations of neonicotinoid pesticide (higher than that received in the field). All of the colonies' bee numbers expanded during initial growth stages, but later only untreated colonies kept expanding. Colony growth decreased in treated colonies, due to bees becoming behaviourally impaired and colony performance decreased. Subsequently, treated colonies became unsustainable and collapsed at random intervals.

The SLS model created from the data allowed the scientists to predict what would happen at field-level exposure to pesticides. Their SLS model showed variable outcomes (some colonies continued growing, whereas others failed) depending on the type and amount of additional stressors. They showed that non-lethal levels of pesticides alone would not cause colony collapse. This provides an explanation for why no single factor could be attributed to colony collapse in the past. Rather, multifactorial stress can cause colony failure as a result of the critical stress level being reached through the accumulation of sublethal factors.



Original Article: 

J. Bryden, Gill R. J., Mitton R. A. A., Raine1 N. E., and JansenV. A. A. (2013) Chronic sublethal stress causes bee colony failure. EcologyLetters. doi: 10.1111/ele.12188.

This is an open article and is freely available to the public.

Nature Article: Why bee colonies collapse



Previous Post: Colony Collapse Disorder - 05 Jan 2012

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Please share with fellow gardening enthusiasts via the various sharing buttons at the end of posts/pages! Else you can vote for posts through the Google reactions bar at the end of articles. To stay up to date I have provided several reader and social networking platforms with which to subscribe: TwitterPinterestRSS Feed Reader or Email/Follow directly using the Blog Followers widget on the left hand side toolbar. Thank you for reading and please feel free to ask if questions arise - I appreciate comments and ideas too! 😆
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Saturday, 5 October 2013

Orchid Exhibition 2010

The amateur orchid cultivators’ guide book (1900)

Some more old photos I dug up! J This time it was at the Safari Garden Center (Lynnwood, Pretoria) with some of the orchid specimens that were competing at the 20th World Orchid Conference in Singapore 2011.



Website

Orchids belong to the Orchidaceae family and is one of the largest families of flowering plants. Charles Darwin studied orchids, specifically their pollination mechanisms. Some of the orchids trap insects and the only way out deposits pollen onto the insect body. Others mimic receptive female insects, visually and by smell, particularly wasps – the males pollinate the flower during an attempt to mate with it … nasty orchids! Never kept orchids myself, I think they are too fussy J


I think I left my brain at home that day, because I did not take my camera with. So the photos below are from my cell phone – the best ones – and I don’t know any names, common or scientific J Enjoy.







At least I managed to nab a few postcards of the 20th WOC in Singapore, 14-23 November 2011.










What do you think about orchids? Do you keep any orchids?



_________________________________________________________________________________
If you enjoy the content please share with fellow gardening enthusiasts via the various sharing buttons at the end of posts/pages! Else you can vote for posts through the Google reactions bar at the end of articles. To stay up to date I have provided several reader and social networking platforms with which to subscribe: TwitterPinterestRSS Feed Reader or Email/Follow directly using the Blog Followers or Follow Your Way widget on the left hand side toolbar. Thank you for reading and please feel free to ask if questions arise - I appreciate comments and ideas too! J
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The Shroom
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