Test is next Thursday, Feb 12

• All the material on the website is on the exam including the lecture on Feb 5.

• Material covered on Feb 10, will be not be on the first exam.

Today

• Fungal like organisms

Some of this lecture material was created by U. of Arizona, Purdue and AVRDC

KSU

Purdue

Cabbage

Horseradish

AVRDC

AVRDC

Kingdom ChromistaOomycetes

Not true fungi – phylogenetically unrelated to Ascomycetes, Basidiomycetes, Zygomycetes, and Chytridiomycetes

Characteristics (generalizations)1. Mycelium is coenocytic (without

crosswalls) 2. Hyphal wall is composed of cellulose3. Produce oospores (sexual spore)

as a resting stage

Slide courtesy of Barry Pryor, U. Arizona

4. Produce zoospores (motile) or similar non-motile asexual spores in sporangia

5. Most are diploid (2N) – whereas most true fungi are haploid

6. Sexual reproduction by gametangial contact between oogonia & antheridia

Characteristics, continued…..

Slide courtesy of Barry Pryor, U. Arizona

Oomycetes cause two types of general diseases

1. Diseases affecting plant parts in the soil or in contact with soil

2. Diseases that affect above ground parts – leaves & stem

Both categories require the presence or abundance of water

Slide courtesy of Barry Pryor, U. Arizona

I. Aphanomyces spp. – root rots

II. Pythium spp. – damping –off; root rots & soft rots

III. Phytophthora spp. root rots; damping-off, blights; other rots

IV. Downy Mildews*: foliage blights

V. White Rusts*: foliage diseases

*Obligate parasites

Primary groups of Oomycetes

Slide courtesy of Barry Pryor, U. Arizona

Caused by many Pythium spp.P. ultimum, P. debaryanum, and P. viole are some common species

Damping off1. Seeds fail to germinate2. Before emergence (pre-emergence damping off)3. Seedling emerged are usually attacked from the roots first.

Invaded areas become water soaked and discolored. The base of the stem becomes thinner and the seedling falls over.

Pythium seed rot, damping off, root rot, and soft rot

Slide courtesy of Barry Pryor, U. Arizona

Pythium blight of cereals & grasses

•Empty patches in field or on lawn

•Stunted growth or delayed maturation

•Several species of Pythium cause diseases, but other organisms can cause similar symptom

Slide courtesy of Barry Pryor, U. Arizona

Plant Pathology, G.N. Agrios

Zoospores Liberated

http://www.apsnet.org/online/Archive/2003/IW000025.asp

Diseases on many types of plants and is similar to Pythium. Species of Phytophthora are important pathogens of woody ornamentals, field crops, ornamental plants, fruits, etc.

Phytophthora Diseases

examples:P. fragariae – red stele of strawberryP. sojae – soybean root rotP. infestans – late blight of potatoP. ramorum – sudden oak death

General Symptoms of Diseases Caused by Phytophthora

* Root or lower stem rots* Loss of feeder roots* First symptoms are drought wilt or mineral deficiencies

Generally – high soil moisture + cooler temperatures promote disease - < 23ºc

Annuals or tree seedlings may be killed in days or weeks. Older plants exhibit sparse foliage, dieback of branches or twigs, and/or yellow leaves – sometimes collar rots and necrosis of lower stem

Slide courtesy of Barry Pryor, U. Arizona

Late blight of potatoPhytophthora infestans

Symptoms – water soaked lesions on lower leaves brown blighted areas within + indefinite borders – worse in wet, cool weather.

Can affect leaves & tubers (purple, stinky rot)

Control – sanitation, resistant varieties, timed chemical sprays

Slide courtesy of Barry Pryor, U. Arizona

Late blight of potato: Phytophthora infestansDisease cycle

Downy Mildews- obligate biotrophic parasites- foliar blights- produce sporangiophores + sporangia in very characteristic ways for each genus of downy mildew.

examples:Pseudoperonospora cubensis – downy mildew of cucurbitsPlasmopara vitacola – downy mildew of grape

Slide courtesy of Barry Pryor, U. Arizona

Haustoria of P. viticola

Slide courtesy of Barry Pryor, U. Arizona

Symptoms are small, chlorotic spot on both sides of leaves.

Signs are sporangiophores that emerge through the stomates. The underside of the leaf turns white.

Spots later may coalesce and form large necrotic areas in severe infections, plants may be defoliated.

The pathogen can also attack the fruit and the budwood. The budwood will allow the pathogen to overwinter in the vineyard.

Downy mildew of grape: Plasmopora viticola

Slide courtesy of Barry Pryor, U. Arizona

Sporangiophore emerging from stomataSlide courtesy of Barry Pryor, U. Arizona