Transcript Slide 1
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 Horseradish AVRDC Cabbage AVRDC Kingdom Chromista Oomycetes 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 cellulose 3. Produce oospores (sexual spore) as a resting stage Slide courtesy of Barry Pryor, U. Arizona Characteristics, continued….. 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 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 Primary groups of Oomycetes 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 Slide courtesy of Barry Pryor, U. Arizona Pythium seed rot, damping off, root rot, and soft rot Caused by many Pythium spp. P. ultimum, P. debaryanum, and P. viole are some common species Damping off 1. Seeds fail to germinate 2. 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. 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 Phytophthora Diseases 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. examples: P. fragariae – red stele of strawberry P. sojae – soybean root rot P. infestans – late blight of potato P. 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 potato Phytophthora 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 infestans Disease 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 cucurbits Plasmopara vitacola – downy mildew of grape Slide courtesy of Barry Pryor, U. Arizona Haustoria of P. viticola Slide courtesy of Barry Pryor, U. Arizona Downy mildew of grape: Plasmopora viticola 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. Slide courtesy of Barry Pryor, U. Arizona Sporangiophore emerging from stomata Slide courtesy of Barry Pryor, U. Arizona