Parasitic Plants - Plant Pathology - Lecture Slides, Slides of Botany and Agronomy

Download Parasitic Plants - Plant Pathology - Lecture Slides and more Slides Botany and Agronomy in PDF only on Docsity! What Are the Causes of Plant Diseases? Parasitic Flowering Plants Docsity.com What Are The Causes of Plant Diseases? Parasitic Flowering Plants What are parasitic flowering plants? • Angiosperms—seeds and flowers like other plants • Biotrophs- obligate parasites • “Extreme weeds”- obtain water, minerals, and photosynthates from their host plants • Produce specialized absorption structures (modified roots) (haustoria)—same as ones used by certain fungi for nutrient-absorption structures Docsity.com What Are The Causes of Plant Diseases? Parasitic Flowering Plants Holoparasites: • Totally dependent on their hosts • Do not produce own food by photosynthesis • Haustoria invade both xylem and phloem of the host to absorb their needs • Very small leaves called scales which are not green • Produce flowers and seeds Docsity.com What Symptoms and Signs Do Parasitic Flowering Plants Cause? Symptoms of affect plants are similar to those of plants growing in intense competition with weeds: • Wilting • Stunting • Nutrient deficiency • Normal branch pattern is affected • Witches’ broom - a proliferation of branches from a central point; common symptom on conifers infected by dwarf mistletoes Docsity.com Dwarf Mistletoe Witches’ Broom www.extension.umn.edu/ gardeninfo diagnostics/ evergreen/spruce/ branchesbroom.htmlDocsity.com Broomrapes Broomrapes (Orobanche spp.): • Usually grow in clumps at the base of the host plants • Root parasites • Vary in color from whitish to pinkish; have verly little green color—do not photosynthesize • Native to warm, dry regions, inc. Calif. • Host plants include: brassica crops , solonaceous crops and sunflower. Docsity.com Btoomtape on Tobacco www.forestryimages.org tl browse detail .cf...m=1440060 Resi ewer ULTT) Docsity.com Dodders Dodders (Cuscuta spp.): • Dependent on host plants and are classified as stem holoparasites • Look like yellow vines growing around the aboveground portion of the host plant • Yet have no contact with the soil • Each stem has numerous haustoria that connects to both the host xylem and phloem Docsity.com Witchweeds Witchweeds (Striga spp.): • “Pretty green plants” with colorful flowers above ground • Aggressive parasites below ground (root hemiparasites) • Absorb water and minerals through a haustoria that penetrates the host roots • Reduces crop yields • Important pathogens on corn, millet, rice, sorghum and sugarcane in Asia and Africa • Introduced into the U.S. (N. Ca. and S. Ca.) in the 1950’s Docsity.com Witchweeds on Corn agspsrv95...wa.g ov.au/ dpsversion02/ 01_plantv...entI D=95&Docsity.com Mistletoes Mistletoes (multiple species): • Parasites of trees Stem parasites connected primarily to the xylem • Two main types: 1. Leafy mistletoes (Phoradendron spp. in N.A. and Viscum spp. in Europe) 2. Dwarf mistletoes (Arceuthobium spp.in the U.S.) Docsity.com Mistletoes Dwarf mistletoes (Arceuthobium spp.in the U.S.): • Dioescious and parasites on conifers (hemiparasites) • Much smaller than Leafy M’s, vary in color, and have smaller leaves called scales • Found in western U.S. and northern Great Lakes and New England; Parasitic plant is the sign of the pathogen Docsity.com Dwarf Mistletoes • Seedlings can photosynthesize (obtain about 40% of their carbon) • Adult plants are dependent on host plants via connections to both xylem and phloem • Seeds are explosively dispersed (one seed per fruit) • In timber monocultures can cause distortion by witches’ brooms and cause reduction in yield and timber value Docsity.com Dwarf Mistletoes Bs Pa “19 \ a ve. @ Pp? Docsity.com Witchweed Seeds ww.invasive.org, 5376862 DIOWSE / detail .cf...m=53768 W) Docsity.com How Do Parasitic Flowering Plants Survive and Spread? Dodder Seeds: • About the same size of many legume crop seeds • Legumes are common host plants • Easily harvested and planted along with the host seeds teachplants.okstat e.edu/ rstnxwddodder/ seed.html Docsity.com How Do Parasitic Flowering Plants Survive and Spread? Mistletoe seeds: • Coated with sticky substance (viscin) that helps the seeds to attach to a new infection site; name of the mistletoe family (Viscaceae) • Birds eat the white berries and the seeds pass through and are deposited • Also stick to some animals and are therefore vectored to new sites • Female plants produce a single seed in each fruit that can be explosively discharged up to 16 m (50 feet) Docsity.com How Are Parasitic Flowering Plants Managed? Management practices are similar to those of free- living weeds: • Avoidance- evaluate planting sites for potential severity of infection • Exclusion- monitoring of imported plant and shipping materials; difficult with seeds which are small; quarantines (one in the Carolinas for witchweed) Docsity.com How Are Parasitic Flowering Plants Managed? • Eradication- 1. Hand-pulling (especially before seeds are produced) 2. Selective herbicides (may harm the host plant) 3. Trap crops are used to reduce the seed population in the soil; 4. Decoy crops; 5. Soil treatment with ethylene ($$) which stimulates witchweed seed germination that can be destroyed before planting 6. Resistance genes for non-selective herbicides Docsity.com How Are Parasitic Flowering Plants Managed? Mistletoe management: 1. Leafy mistletoes: selective pruning; removal of female plants; do not use mistletoe with berries for decorations outside 2. Dwarf mistletoe: Management is more difficult; clear cutting (not always pretty!); fire management vs. Smoky the Bear 3. Biological controls (fungi) are being explored, but none yet to date Docsity.com Witchweed Weed Alert http: //www.wyong.nsw.gov.au/environment/Weeds_category_oné Witchweed.pdf Docsity.com  \ Life Cycle of Dwarf Mistletoe Sceds land on conifer needles Berries mature after 2 more ‘2 Rains wash then onto the twigs hoots first appear y after another 2 years about 2 years later = “wis The seeds germinate and infect the twig Docsity.com