Puccinia Classification Kingdom- Fungi Division- Basidiomycota Class- Pucciniomycetes Order- Pucciniales Family- Pucciniaceae Genus- Puccinia Puccinia

Genus Puccinia consists of more than 4000 different species all of which are plant pathogens. These are known to cause rusts in both monocotyledons and dicotyledons. Major pathogen, P. graminis (Stem rust) affects cereal crops such as wheat, barley etc. Some other species are- P. recondita (Brown rust), P. asparagi (Asparagus rust), P. psidii (Guava rust) etc.

Structure of Puccinia  The vegetative structure of Puccinia is represented by both mono and dikaryotic mycelium. Generally the dikaryotic mycelium with two nuclei are found in primary host Monokaryotic mycelium with single nuclei are found in secondary host. Mycelium is formed of septate, tubular hyphae. Puccinia graminis It is an obligate parasite of wheat causing stem rust disease. Its life cycle consists of two hosts namely, Wheat – Primary host Barberry – Secondary host Stem rust affects parts of plants that are above ground. Stem rust on wheat In wheat it results in formation of brown to black elongated pustules. In Barberry flask shaped Pycnia at dorsal and aecia on ventral side forms. Infection of P. graminis results in retarded growth and reduced seed size in wheat. In north India it appears in March while in south it appears at the end of November. Stem rust on Barberry

Image source: https://www.mindenpictures.com/search/preview/black-stem-rust-puccinia-graminis-on-wheat-ear-and-grains-usa/0_80113653.html https://pnwhandbooks.org/node/2207/print Fig 1: Life cycle of P. graminis in Wheat and Barberry https://i.pinimg.com/originals/e2/fb/35/e2fb352fb297508257dcfe7606db8334.png Life Cycle P. graminis is a macrocyclic rust. consisting of five stages of growth.

Host Growth Stage Characteristic feature

Wheat Uredo Stage . Formation of single celled, binucleated uredospores on stalk. . Uredospores form germ tube that apply pressure on epidermis breaking it and forming uredinia. . Uredospore germinate and forms mycelia. Telial Stage (Black . Teleutospores formation from uredospore in unfavourable condition stage) of growth. . Each cell has single germ pore and two nuclei. . Karyogamy leads to formation of diploid nucleus. . Spores rests until favourable condition.

Basidial Stage . Formation of haploid basidiospores by meiosis. . Ejection of spores that are carried out by wind to secondary host. . Infects barberry forming haploid mycelia.

Barberry Pycnidial Stage . Formation of specialised Pycnia or spermatia. . Pycnia produces haploid pycniospores and receptive hyphae. . Dispersed by insects, Pycniospores fertilise receptive hyphae of another plant forming dikaryotic mycelia. Aecial stage . Formation of dikaryotic aeciospores from mycelia. . Chain like aeciospores are carried by wind to infect cereal host. https://ars.els-cdn.com/content/image/3-s2.0-B9780123820341000013-f01-11- 9780123820341.gif https://1.bp.blogspot.com/-FRDrXkA02bE/WBt02AvaXQI/AAAAAAAAD1U/JpI3Vpy3- zE3rRTnmEm5nvzret4r3QCjACLcB/s640/graphical%2Brepresentation%2Bof%2Blife%2Bcycle%2B of%2Bpuccinia.jpg Uredospore: Dikaryotic containing two un-fused, haploid nuclei in one cell; formed on individual stalks ; spiny and brick-red; the only type of spores in the rust fungus life cycle that are capable of infecting the host on which they are produced Teleutospore: Dark brown or black; stalked, two – celled; spindle shaped; with thick, black and smooth wall; the only form in which Puccinia graminis is able to overwinter independently of a host; undergoes karyogamy and meiosis. Basidiospore: haploid products of meiosis; thin-walled and colourless; cannot infect the cereal host, but can infect the alternative host Pycnidiospore or spermatia: pycniospore can fertilise a receptive hypha of the opposite mating type, leading to the production of a dikaryotic mycelium Aecidiospore: Dikaryotic, Round, yellowish red, unicellular, binucleate, thick walled with 6 germ pores, produced in chains; able to germinate on the cereal host but not on the alternative host

Source: https://en.wikipedia.org/wiki/Stem_rust

https://www.biologydiscussion.com/fungi/puccinia-graminis-introduction-vegetative-body-and-life- history/46690 https://www.biologydiscussion.com/fungi/puccinia-graminis-introduction-vegetative-body-and- life-history/46690 https://www.biologydiscussion.com/fungi/puccinia-graminis-introduction-vegetative-body-and- life-history/46690 https://www.biologydiscussion.com/fungi/puccinia-graminis-introduction-vegetative-body-and- life-history/46690 https://4.bp.blogspot.com/-rI5E3rljWL0/XBx3p-0CSfI/AAAAAAAAAmQ/vALaOJ7J2AkGwO- j5pYXisaN4G6qPZfmwCLcBGAs/s1600/6.%2BAeciospores.jpg Rust hazards Plants infected with Puccinia shows poor development Reduced seed size Broken epidermis makes plant susceptible to dessication and fungal infection. Defoliation in severe cases.

Disease control Immediate removal of infected leaves. Avoiding growing alternate host nearby primary host plant. Use of fungicides such as sulphadiazine, nickel sulphate etc. Use of resistant variety of plants.