Sub division Basidiomycetes
Class Teliomycetes
Order Uridinales
Members of order uridinales are commonly known as rust fungi because of characteristic rust like reddish-brown colour of their spores . They may be autoecious ( complete their life cycle on a single host , example Puccinia butleri ) or heteroecious ( complete their life cycle on two hosts , example Puccinia graminis ) . Rusts may be microcyclic ( only one type of dikaryon spores , example Puccinia malvacearum ) or macrocyclic ( more than one type of dikaryon spores , example Puccinia graminis ) .
Puccinia ( Family Pucciniaceae )
Many species of Puccinia cause rust diseases in cereal crops . Puccinia striiformis is causal organism of Yellow rust of wheat . Puccinia graminis is the causal organism for black rust or stem rust of wheat and other cereal crops . P. graminis is a composite species . It has been divided into 6 strains each having a different cereal host eg. P. graminis tritici ( on wheat ) , P. graminis secalis ( on rye ) . Each strain has several physiological races .
Puccinia shows phenomenon of biological specialization ( specific host is infected by specific pathogen ). It means Puccinia graminis tritici will infect only wheats not any other cereal crops . Symptoms appear on leaves and stem . Spores come out by rupturing epidermis of the tissue .
It is a macrocyclic , heteroecious fungus . Although Puccinia graminis can survive in the absence of alternate host , its life cycle is completed only when both hosts are available .
There are 5 spores fromed in life cycle of puccinia -
On primary host wheat ( Triticum aestivum )
1. Uredospore
2. Teleutospore
3. Baisidiospore
On alternate host Barberry ( Berberis vulgaris )
4. Pycnidiospore
5. Aeciospore
Uredospores - Mycelium produced by germination of aeciospores enters through stomata on wheat plants . They develop uredospores . Uredospores are stalked , unicellular and binucleate . They develop in groups called uredosori . Uredosorus shows reddish brown rust like appearance . They germinate and germ tubes develop in appressorium ( vesicle like structure ) . Intracellular hyphal branches develop from appressorium . Uredospores are capable of reinfcting wheat plants .
Teleutospores - At the end of wheat season uredosori are converted into teleutosori . Teleutosori appear as black raised streaks . Group of cells called telia produces teleutospores . Teleutospores are stalked , bicelluar , each cell with 2 nuclei and black in colour . 2 nuclei fuse to form synkaryon . Teleutspores are incapable of reinfecting wheat plants .
Basidiospores - Teleutospores remain dormant during summer season and basidiospores are not formed until rainy season . In spring season teleutospores germinate to form germ tube of limited growth called promycelium or epibasidium . Diploid nucleus moves in promycelium and undergoes meiosis . It forms 4 haloid basidiospores , two of + strain and two of - strain . Basidiospores survive only for few days and they perish in the absence of alternate host . They are discharged by explosive mechanism and are disseminated by wind .
Pycnidiospores - Basidiospore infects and germinates on upper surface of Barberis leaf . They produce mycelium of + and - strains . They form spermogonia or pycnidia of + and - strains . They are produced in spermogonium . Spermogonium opens on the upper surface of leaf by ostiole . Pycniophores are arranged like a palisade layer on inner surface of spermogonium . Pycniophores abstracts many small uninuclear pycniospores . They are ooze out through ostiole . Each spermogonium has receptive hyphae and spermatium of either both + or both - strains . Receptive hyphae and spermatium of two opposite strains undergo spermatization . Spermatization is a type of sexual reroduction . It results in formation of dikaryotic mycelium . It is also called diploidization .
Aeciospores - When dikaryotic mycelium formed by spermatization reaches on the lower surface of barberry leaf they form aecial cups . Aecial cup has aeciophores which produce binucletate aeciospores . They are dispersed by winds .
Annual recurrence of wheat rust in India
K C Mehta worked on the recurrence of rust in India while he was at Agra . There is no role of Berberis in the recurrence of wheat rust in India . Uredospores present on wheat or collateral hosts in hill areas are responsible for recurrence of the disease .
Difference between rust and smuts
1. Rust may be autoecious or heteroecious but smuts are always autoecious .
2. Rust symptoms appear as coloured pustules while smut symptoms appears as black powdery mass .