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By: sindhu111 (137 month(s) ago)

sir as i having seminar on moleculer basis of plant defense against pathogens pls give me the permission to download this presentation slides thank you

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Defense mutualisms: 

Defense mutualisms Many examples of insect-plant defensive mutualisms. Particularly common for fast-growing tree species with sufficient carbohydrate resources to provision mutualists Plant-fungal mutualisms may be much more widespread and important, but are much less conspicuous and therefore poorly studied

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Cecropia (Moraceae) Neotropics (61 spp) - Hollow stems inhabited by Azteca spp. Ants -prostomata (thin wall) -Glycogen rich food bodies (Mullerian bodies) produced at petiole base Macaranga (Euphorbiaceae) South East Asia (~300 spp) - Obligate relationship? Crematogaster ants live in hollow stems -prostomata (thin wall) -Beccarian bodies produced on leaves and stipules

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Bull-horn Acacia species (Americas, Africa Pseudomyrmex ants (in central America) Obligate mutualism? Ant acacias lack alkaloid defenses present in species lacking ant mutualists Ants are extremely aggressive predators What about pollination? (Willmer 1997)

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Acacia produces a chemical signal that repels ants from young (receptive) flowers allowing pollination (Wilmer and Stone 1997, Nature 388:165-7)

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Ants have a positive effect on seed set by removing seed predators

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Tococa shrubs have hollow stems and provide food bodies for Myrmelachista ants (Morawetz et al. 1992, Renner and Ricklefs 1998) Ants kill insect herbivores and competing plants! Tococa grows clonally and is able to form large patches (up to 30 m diameter) completely free of other plant species

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Seedlings turned to mush in 3 hours!!!!

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Endophytic fungi as mutualists Endophytes = fungi that inhabit plant parts without causing disease Present in all plant species examined: liverworts -> angiosperms Endophytes are mega-diverse in the tropics: Arnold et al (2000) isolated 347 distinct genetic taxa of endophytes from 83 leaves from 2 tropical tree species… >50 % of taxa were only collected once... What are they doing in there???

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Arnold (2003) Looked at endophytes associated with cocao Plants (Theobroma cacao) Endophytes are horizontally transmitted (acquired through the life time of the leaf) Arnold was able to grow endophytes in the lab and then use them as an inoculum source to infect sterile (uninfected) leaves

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Black pod disease of cacao caused by infection by Phytophthora capsici Black pod and witches broom (a fungal disease) has led to large declines in cacao production

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Asked: Are endophytes effective in protecting cacao plants against pathogens? Compared incidence of foliar pathogen damage and leaf mortality in cacao plants +/- endophytes and +/- a foliar pathogen Phytophthora an important pathogen of cacao (‘black pod’) A cocktail of 7 endophyte spp applied to leaves significantly reduced severity of pathogen damage

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Clay and Holah (1999) Looked at an endophyte in a successional field community Neotyphodium coenophialum is an endophytic fungus that grows intercellularly through Tall Fescue (Festuca arundinacea). Fungus is host-specific and vertically transmitted with seeds. Infected plants are more vigorous, more drought resistant than uninfected plants, and TOXIC - cattle and horse poisoning. Tall Fescue is a european grass introduced to N. America. Becomes dominant in pastures it invades

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In Indiana established 8 plots (20 x 20 m) mown and cleared, sown with infected (+E) or uninfected (-E) Fescue. Grassland community established composed of Fescue and other spp germinated from seed bank. Species diversity declined in +E plots overtime relative to -E plots, 6 species were restricted to -E plots after 3 yr

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Gallery (in review): Association of fungi with seeds in the soil Fungi associated with low seed viability = pathogens? Fungi assoc. with high viability = mutualists?

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Freeman and Rodriguez (1993): The heart-warming tale of a reformed pathogen... Notorious filamentous fungal pathogen: Colletotrichum magna wanted for causing anthraconose disease in cucurbit plants. Member of a large group of pathogens capable of infecting the majority of agricultural crops worldwide Infection occurs when spores adhere to host tissue, enter a cell and subsequently grow through the host leaving a trail of necrotic tissue. Plants die within a week.

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Plants infected with path-1 were subsequently protected from disease symptoms produced by the wild-type, and were immune to disease caused by an unrelated pathogenic fungus, Fusarium oxysporum Freeman and Rodriguez suggest that infection by path-1 primes host defenses, activating them against subsequent infection by pathogens Considerable potential to tailor endophytes as biocontrol agents? path-1: a single locus mutant of the wild type of C. magna infects the host and spreads (albeit more slowly) through out the host without killing it and without necrosis. path-1 does not sporulate and lives as an endophyte

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Transport mutualisms Pollination and seed dispersal - have received more attention than most other mutualisms from community ecology perspective Pollinator mutualisms: Wind pollination is quite restricted (prevalent in grasses). Benefits to pollinators include pollen, nectar, fragrances (Euglossine bees), oviposition site and food supply for larvae Pollination mutualisms could be significant to community structure if pollination limitation occurs. Some evidence that certain groups are limited: ephemeral spring flowers in eastern USA (Motten 1983)

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Also true for seed dispersal mutualisms. “Dispersal Limitation” may be critical to species coexistence in diverse plant communities. Lots of effort expended searching for pollination and dispersal ‘syndromes’ (flower and fruit characteristics that are predictive of the principle taxa of pollinators and dispersers). A few traits are somewhat predictive (colour, size, scent) but in most cases mutualisms are diffuse: multiple pollinators and dispersers predominate.

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Co-evolved pollinator/disperser systems are rare - why? Classic example: Calvaria major - large seeded tree species endemic to Mauritius Some good examples of complex co-evolved pollinator mutualisms Yucca flowers - Tegeticula moths Ficus spp and fig wasps (Agaonidae) (Herre 1996)

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Fig inflorescence = synconium Individual flowers are on the inside Female wasp enters the fig through the ostiole carrying fig pollen which is deposited on some flowers in the fig Meanwhile, the wasp also lays eggs on a proportion of the flowers in the fig. The developing wasps induce galls which nourish larval development. New-born male figwasps are wingless. They fertilize the new female wasps, chomp a hole in the ripe fig for females to leave and die inside

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Life-cycle for new-world (monoecious) figs Female wasp + pollen enters fig Lays eggs inside some ovules - larvae feed on fruit tissue Male wasps are wingless, hatch And mate with females inside synconium Females hatch, covered by pollen, fly out of synconium

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Phenomenally complicated system: Tight coevolution: single wasp species per fig species. Phylogenies of figs and wasps match... Pollination mutualism (wasps get food for development, fig gets extraordinarily effective pollinator - gene flow >100 km? (Nason et al. 1998) Mutualism costs: Provisioning of larval development Maintaining fig temperature optimal for wasp development (Herre and West 1997) Mutualism conflict: production of fig seeds and fig wasps are negatively correlated Many, many other intricacies...

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