Avenue of Penetration by Plant Pathogen
Avenue of Penetration by Plant Pathogen
Avenue of Penetration by Plant Pathogen
Direct though surface Cutinized Non-cutinized Surface surface Epidermis a)Root hairs b) Needles c) Nectories d) Buds e) Stigma ends f) Anthers. (Indirect though Openings) Natural opening Artificial a) stomata a) Wound b) Lenticels b)Stalk ends c) hydathode c) insect injury.
Directly through epidermis ( Cutinized structure ) : In this case most of fungi like rust, downy mildew, powdery mildew, leaf spotting fungi entres directly by production of enzymes that macerate the host tissue. Entry though non cutinized surfaces:
a)
Root hairs: The several soil borne plant ophogen, which attack.
The
roots enters through the root hairs (like fusarium where as the root rotting fungi directly macerate the succul ant non cutinized host tissue by production of enymes (like rhizoctonia Sp ). The pathogen of finger & toe disease or cruciform (Plasmodiophora harassicase enters through the root hairs. Apart form this various in smut diseases where the infection in systematic the pathogen entres through root thairs & along with plant grows & produces symptoms only at the time of flowering eg. Sunt of wheat, smut of Jowar.
b)
Needle: Infection through needlepoint is of special significant in which blister rust of pines caused by cronortium ribicola which uses these points for entry inside host.
c)
Nectaries ; This is a favarable avenue for the infection in a few cases because of non-cuti9nized surface & surface secretion. The pathogen
like Venturia inagequalis causes the apple scab & the bacterium Erwinia amylovora causing fire blight of apple & pears, the pathogen enters through nectaries.
d)
Buds: The certain rust fungi uromyces pisi (Rust of pea) & Taphrina deformans (peach leaf curl) the pathogen entrs through the buds & causes diseases.
e)
Stigma: The stigma of the flower are highly receptive organs for the entry of the pathogen because of their eruct positi8on & the sugary secretion produced by them. The sugary secretions attract the flies and insects & along with them they brought the fungal spore that infects through stigma.
The most of the pathogens that infects through the stigma are Loose sumt of Wheat (ustilagotritici) Long smut of Jawar Ergot of bajara ( claviceps microcephala ) Bunt of rice ( Neovosia horrida )
f)
Anthers: The pathogen Botrytis anthopola which causes blossom blight of red clover infecte the host through anthers.
The mechanism of
penetration through thedifferent host differs from pathogens to pahtogens. The uredospore of puccinia graminis tritici enters through, stomata at early hours of day where lot of dew present & stomata opens. Apart form rust many fungi like downy mildew of grape,while rust, cercopora sp. Etc. Entrsthrough stomata. The bacterial plant pathogens entres mostly through stomata absorbtion & suction.
are generally present on the stem tubers. The most of pathogen get assess through this natural opening ex. Guava canker (Pestalotia psidi) koleroga of arecanut (Phytophtora areca), common scab of potato (Streptomyces scabies)
c) Hydathodes: Hydathodes are structured through which water is
discharged form the interior of leaves. Hydathodes are the only means of entry for certainbacteria for ex. Erwinia amylovora ( soft rot), Xanthomonas campestri PV campestri s (Black rot of cbbage)
d) Trichome: The bacterium corynebacterum michiganes which causes
The most of fungal & bacterial plants pathogens enters through wound caused by nematode. In case of yellow ear rot of wheat caused by the bacterium corynebacterium paitioi nematode Anguina tritici ( Ear coloccle of Wheat ) plays an important role in transmissions infection process. Many of fungal soil borne plant pahtogen which causes wilt (Fusarium oxysporum entres through wound caused nematode Meloidogyne sp.
For ex. In late blight of potato, the infected tuber acts as the sourve of primary inoculum, which incite the disease & once the plant infected the spores produced by pathogen on infected host spread by means of wind water spread the disease in population (secondary infection) In the absence of cultivated hosts the pathogen over winter or over summer survive in or ont the wild hosts which act asresorvoin of primary source of inoculum can be considered in three groups.
i)
by Xanthomonas compestries p.v.citri the pathogen surivive in crop debrise & soil. ii) Wild host of same familles (collateral host) In case of blast of paddy (Pyricularia oryzae) the pathogen survive over winter on the grass host & when themain host is presnet in the field it attack the host. iii) Wild host of other families (Alternate host). Alternate hosts are those host on which the wheat rust pahtogen (Puccinia gramints tritici) survive on the allternate host barberry. In many other fungi Rhizoctonia solani, sclerotuim rolfsii they have rather a wide host range & thus alternate host may come into play in their survival.
iv)
Per petuatioin in Prepenetration parts: Most of the pathogen such as suckers in banana,
Most of the pahtogen loose sumt of wheat (ustilago tritici) the pathogen survive in the seed internally & acts as source of primary inoculum. Bean Mosaic virus also survive through the seed.
pahtogens produces the various typos dormant structures. These dormant structures of survival can be classified in the following manner (1) Soil borne fungi Dormant spores (coned chalmydospore oospore, perithecia etc. Candid- by cercopora sp.altearia sp. Chalmydospore by Fusarium sp.
Oospores by Pythium, phytophorta SP. Perithecium by venture inequalis a) Other formant structures such as thicked hyphen & chlorite Thickened hyphae. Sclerotic by Rhizoctonia & Sclertium sp. ii) Seed borne fungi a) dormant spores on seed coat In case of through of jawar (sphacelothecasorghi) spore are present on seed coat in the form of chalmydospore. b) Dormant mycelium under the seed coat or in the embryo: In addition topsail & seed the dormant organs of fungi can also be present on the host, In case of downy mildew, powdery mildew the dormant mycelium of fungis present on the affected twigs or may be embodied in host tissue. Polymorphism: An organism having several (many) sperm forms in the life cycle is called saw polymorph & thephenomenon of several. Spores produced by an organism are called polymorphs for ex. Typical rust fungus produces five types of spores. Viz. Pycniospores, ciospores uredosproes, telio spore & basidiospores. Fusarium sp. Produces Micro coned, macrocondidia & chalmydospore I addition to sexual spores. Polymorphism monitions infection chain & persistence of mycelium through periods of draught,desi cantion & freeing polymorphic fungi can adopt rigoros conditions & can have more successful life, free form uncertanities and risk involved in monomorphic fungi . Physiological specialization (Ref Variability. )
Factors affecting the survival of plant pathogens in soil Most of the factor likehigh temperature, irradiation, desiccation, anaerobiosis, toxic chemicals, lack of nutrients, antagonism, perdition, affects the growth & survival of the pathogen in the soil. Terminology used in Plant Pathology (Glossary): Acervulus : Asubepidermal, Saucer-shaped, asexual fruiting Body producing candid on short condo on short conidiophore Achlorophyllus: Without chlorophyll. Aeciospore: binucleate spore produced in aqueous. Anisogamous planogametes; motile gametes that are morphologically simillar but differ in size. Alternate host: The host belongs to different family than that of main host.