Biological Foundations 112, Lecture 25


Fungi III

Chapter 28, pages 573-588
Basic Botany-2 20:16-31:38
Five Kingdoms-3 11:25-15:12


Life Cycle of Puccinia (Wheat Rust)

Summary

     1.   Contains two different hosts and four kinds of spores

     2.   The two hosts are:

           a.   Wheat plant

           b.   Barberry plant

     3.   The four spores are:

           a.   Teliospores - black, 2-celled, winters in wheat stubble, dikaryon

           b.   Basidiospores - black, germinates from teliospores, single-celled, haploid, blows to
                                            and infects the barberry in the spring

           c.   Aeciospores - single-celled, dikaryon, develops on barberry and blows to and        
                                         infects the wheat in the spring, initial infectors of wheat plants in the    
                                         spring

           d.   Uredospores - red, single-celled, dikaryon, develops on the wheat, blows to and    
                                          infects other wheat plants, secondary infectors of wheat plants

Events of the Life Cycle

     1.   Teliospores

           a.   Dormant through the winter while lying on the ground at the base of the dead wheat    
                 plant

           b.   Spores are black in color

           c.   Each spore contains two cells

           d.   Each cell of the spore is dikaryon

           e.   Teliospores germinate in the spring by the following process

                 (1)  Each of the two cells forms a diploid nucleus from the two dikaryon nuclei

                 (2)  Meiosis occurs on each of the two diploid nuclei to form four haploid nuclei in    
                       each of the two cells

                 (3)  Each of the four nuclei takes some of the cytoplasm to produce two 4-celled      
                        basidia 

                 (4)  A sterigma is pushed out of each cell by the nucleus to form a basidiospore at    
                        the top of each sterigma

                 (5)  The result is that each cell of the teliospore produces four basidiospores for a      
                        total of eight basidiospores

                 (6)  Of the eight basidiospores, four will be + basidiospores and four will be -

     2.   Basidiospores

           a.   These spores are black and are blown about by the wind

           b.   Some of the basidiospores will land on barberry bushes

           c.   When some moisture is present on the surface of the barberry leaf, the basidiospore  
                 will germinate

           d.   The hypha from the basidiospore penetrates the cuticle and pushes its way into the    
                 midst of the mesophyll but does not go into the inside of the cells of the mesophyll

     3.   Spermagonia or pycnia

           a.   The haploid hyphae that came from the basidiospores form a spermagonium on the    
                 upper surface of the barberry leaf

           b.   Spermagonia are pear-shaped

           c.   Small pore at the top end of the "pear"

           d.   Each spermagonium contains:

                 (1)  Receptive hyphae that fill the inside and extend out through the pore

                 (2)  Spermatia - small spherical structures that are interspersed between the            
                                             receptive hyphae inside the spermagonium

           e.   Because both plus and minus basidiospores germinate on the leaf surface, then both  
                 plus and minus spermagonia are scattered over the surface of the leaf

           f.    Conjugation of spermatia and receptive hyphae:

                 (1)  Spermatia of both plus and minus spermagonia ooze out of the pore at the top of
                        the spermagonium

                 (2)  Spermatia migrate over the surface of the leaf

                 (3)  When plus spermatia come in contact with minus receptive hyphae or visa versa,
                        plasmogamy occurs to form a dikaryon cell

                 (4)  The dikaryon cell divides by mitosis to form a filament of dikaryon cells

           g.   The dikaryon filament grows downward into the spongy parenchyma where it            
                 produces an aecium

     4.   Aeciospores

           a.   Aeciospores are produced in the aecia.  [The aecia are sometimes called cluster      
                 cups
.]

           b.   Single-celled spore

           c.   Dikaryon

           d.   When the spores are mature, they are blown about by the wind

           e.   If the aeciospores lands on a wheat plant the spore enters the leaf through the stoma   
                and there germinates into a hypha - primary infection of the wheat

           f.    The hyphae penetrate individual cells with their haustoria and obtain nourishment        
                directly out of the cell

     5.   Uredospores

           a.   About 10 days after the infection of the wheat by the aeciospores, pustules                
                (uredinia) begin to appear on the surface of the wheat plant leaves just under the      
                epidermis

           b.   The uredospores that the pustule releases are red (rust colored, thus wheat rust)

           c.   Spores are single-celled

           d.   Spores are dikaryon

           e.   These spores blow about in the wind as the pustules open

           f.    Uredospores that land on other wheat plants they infect those plants (secondary      
                 infection
) in the same manner as the aeciospores do to from more uredinia.

           g.   The uredospores as they are produced continue to infect wheat plants while they are  
                 growing and maturing

     6.   Teliospores

           a.   The wheat rust mycelium in the wheat leaf, shifts from the production of uredospores  
                 to the production of teliospores, as the wheat begins to mature and turn from            
                 green to yellow

           b.   Thus it is possible to find both uredospores and teliospores in the same pustule

           c.   Spores are two-celled

           d.   Each cell is dikaryon

           e.   The spores are black

           f.    When the spores are released they fall down on the ground in the stubble of the        
                 wheat where the spores spend the winter


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