Life cycle of phytopthora

Life cycle of phytopthora

1. Life Cycle of Phytophthora  BY JAVED AHMAD Department of Biotechnology, JMI

2. Mycelium of Phytophthora: It is profusely branched and consists of aseptate, hyaline, profusely branched, coenocytic Moderately thick hyphae about 4-8µ in diameter. Glucans is the predominant material in the hyphal wall. Cellulose is a minority component or even lacking altogether. The plasma membrane is distinct and is seen as a dark line at the periphery of the hyphal protoplasm.

3. The cytoplasm contains scattered nuclei, dictyosomes, lomasomes , mitochondria, endoplasmic reticulum, ribosomes and many large vacuoles with lipid inclusions. The fungal hyphae ramify in the intercellular spaces between the cells of the host tissue. These are called the intercellular hyphae.

4. Haustoria of Phytophthora: The haustoria are variously shaped intracellular feeding structures. In P. infestans they are small globes, occasionally short, straight or curved pegs. There may be one or more haustoria in each host cell. The intracellular haustorium relates to the intercellular hypha by a neck-like constriction at the penetration site. Thus the long haustorial stalk or neck usually associated with this organ is lacking.

5. ASEXSUAL REPRODUCTION Because  P. infestans   is a  host-specific parasite , it needs plant tissue to grow in.  Usually, as was the case in  Ireland ,  P. infestans  reproduces asexually. Its life cycle usually begins as the sporangia are carried by the wind, land on plant tissue, and release their zoospores.  This will happen when the conditions are wet and cool and is called indirect germination. These spores are biflagellated —having both a tinsel and whiplash flagellum which is  characteristic of oomycota  and will swim until they encyst in the host.  When conditions are warmer,  P. infestans   will infect the plant by direct germination—that is a germ tube will form from the sporangium and will penetrate the host tissue allowing it to gain  nutrients  from its host. 

6. Sexual reproduction , can and does occur when both  mating types  are present.  The antheridium and oogonium (the only haploid parts in the life cycle of  P. infestans ) nuclei will fuse together (karyogamy) when the antheridium enters the oogonium.  They will form a diploid oospore, which will develop into a sporangium and the cycle will continue as is would asexually.