SURVIVAL OF SOIL BORNE PATHOGEN

FACTORS INFLUENCES SURVIVAL OF SOIL BORNE PATHOGEN:

1. The pathogen structures by which survival occurs in soil.
2. The environmental conditions affecting the duration of survival of this structures in soil and those affecting their generations. The environmental conditions are soil temperature, soil moisture, soil pH, organic matter etc.
3. The factors contributing to the reproduction or inhibition of durable stages (Resting stage). The reproduction factor affects soil borne microorganisms, which affects survival factor.
4. The precise micro habited in which activities and survival occurs.
5. The host range: The host range and the affect of non susceptible crops or the survival. Pigeon pea root secrets funagin toxin, which kills Fusarium.
6. The relative degree of saprophytic ability.
7. The substrate saprophytically utilized in soil and the stage succession on that.

Information on those points would contribute toward a more scientific basis for biological control of soil borne pathogen.

DURATION OF SURVIVAL OF SOIL BORNE PATHOGEN:

1. Fusarium oxysporum f. sp. Lini: Up to 50 years at resting condition. Normally saprophytically without reproduction. If host become available then germinate.
2. F. oxysporum f. sp. cubense: Up to 40 years. Attacks banana.
3. Phytophthora capsici: Up to 5 months.
4. P. infestans: up to 77 days. Remain in soil with crop residue. Primary infection occurs in seed.
5. P. parasitica var. nicotiana: Up to 3 years. Attacks in tobacco.
6. Rhizoctonia solani: Up to 6 years. 
7.  Nematode: In general 25-40 years.
8. Bacteria: For long time. It produce endospore which can remain in soil for long.
9. Virus: Up to 9 years.

MODE OF SURVIVAL:

Fusarium oxysporum: Mainly it is parasitic in nature but in cases can show saprophytic nature.

Sclerotia: Produced when host is unavailable.

Chlamydospore: maybe intercalary or terminal. If at middle then termed as intercalary.

VARIATION AND SURVIVAL IN SOIL:

Variation: Variation is a process by which an organism make a new pathotype, which may be done by physiological and morphological change.

Inactive survival	Variation mechanism	Active survival
+	Mutation	+
-	Hybridization	+
-	Heterokaryosis	+
-	Parasexuality	+

          Mechanisms of Variation of Soil Borne Pathogen         :

          Mutation:

          An abrupt heritable or genetical change in a gene, or an individual as a result of an alteration in a gene, or chromosome, or of an increase in chromosome number. Variation comes in variety. Pathogens produce many new pathovar.

          Hybridization:

          Process of production of offspring from two different individuals.

          Heterokaryosis:

       Process of development of heterokaryotic mycelium from two different homokaryotic (where mycelium of a fungi have genetically identified nucleus) mycelium.

         

                   Heterokaryotic mycelium:

                   When mycelium of a fungi contains distinct type of nucleus.

          Heterokaryosis may originate in different ways-

1.     By the generation of heterokaryotic spore.

2.     By the introduction of genetically different nuclear into a homokaryon.

3.     By mutation in a multinucleate homokaryon.

4.     By fusion of cell nuclear in haploid homokaryon.

Parasexuality:

          Parasexuality may be defined as a sexual stage in which plasmogamy, karyogamy, haploidization take places but not at a specific points of times in the life cycle of organism. E.g. parasexulity is observed in Deutaromycotina.

         Some terms:

         f.sp. = formae species

         var. = variety

         pv. = patho var.

         e.g. 1. Fusarium oxysporum f.sp. lycopersici

               2. F. o. f.sp. cubense

               3. Xanthomonas campestris pv. oryzae

              4. X. c. pv. oryzicola

         Variation of pathogen is occurred from race.