Ex.No. 4                                   Study of club root of cabbage

Taxonomic position                                                                                                                   

 Domain : Eukarya                                                                                                                                            Kingdom: Protozoa                                                                                                                                           Division : Plasmodiophoromycota                                                                                                                        Class: Plasmodiophoromycetes                                                                                                           Order: Plasmodiophorales                                                                                                                 Family: Plasmodiophoraceae                                                                                                          Genus: Plasmodiophora                                                                                                                                    Species: brassicae                                                                                                                               Disease name: Club root of cabbage or Finger and Toe disease (M.S.Woronin)

Symptoms: Spindle shaped or club shaped swellings occurs in the roots and rootlets. The swellings are due to Hypertrophy and Hyperplasia.                                                                                                Hypertrophy – Excessive growth due to enlargement of cells                                                        Hyperplasia – Enlargement of tissue as a result of increase in number of cells               Plasmodium – A multinucleate mass of protoplasm

Resting spore – Cyst; Asexual spore : Zoospore

Primary phase                                                                                                                                       1. Infection of the root hairs takes place during the seedling stage                                                                        2. The resting spore penetrates the root hair and develops in to uninucleate plasmodium                       

3. The plasmodium cleaves into multinucleate portions and each portion is surrounded by a membrane and develops in to a sporangium                                                                                                         4. Each sporangium forms 4-8 uninucleate, anteriorly biflagellate zoospores (Hyaline, spherical)                5. Zoospores infect the host and they fuse in pairs to produce zygote

Secondary phase (forming club shaped roots)                                                                                           1. The zygote settles on the root hair and enters the cells of cortex                                                            2. It forms a multinucleate secondary plasmodium.                                                                               3. Karyogamy takes place and the secondary plasmodium becomes a diploid plasmodium

4. Cruciform nuclear division                                 

5. Meiosis fallows and the resulting haploid nuclei multiply by mitotic division and by cleavage of the               cytoplasm, wall formation, several uninucleate haploid resting spores are formed.                                         6. The secondary plasmodium induces swellings of the infected cells (Hypertrophy and Hyperplasia)             7. After death and decay of the roots, resting spores are enter the soil, until the host is available.