White rust of crucifers

White rust, caused by Albugo candidans, is a crucifer disease that results in yield loss, root injury, and a decline in market quality.

1. White Rust of Crucifers
Dr.ChinnamaniPrasannakumar
AssistantProfessor
PG&ResearchDepartmentofBiotechnologyandMicrobiology
NationalCollege(Autonomous)
Tiruchirappalli,TamilNadu-620001,India

2. Crucifers
Cruciferousvegetables
arevegetablesofthe
familyBrassicaceaewith
manygenera,species,
andcultivarsbeing
raised for food
productionsuchas
cauliflower,cabbage,
kale,gardencress,bok
choy,broccoli,Brussels
sprouts,mustardplant
andsimilargreenleaf
vegetables.

3. Causative agent
Whiterust,causedbyAlbugocandidans,isadiseaseofcrucifers
thatcausesyieldlossthroughdefoliation,rootinjury,and
reductionofmarketquality.
Spinach,horseradish,andmustardareaffectedmoreseriously
thanothercrucifers.

4. Albugocandidans
Albugocandida,commonlyknownaswhiterust,isaspeciesofoomycete
inthefamilyAlbuginaceae.
A.candidaisanobligateplantpathogenthatinfectsBrassicaceae
speciesandcausesthediseaseknownaswhiterustorwhiteblister
rust.
Clade:SAR
Phylum:Oomycota
Order:Albuginales
Family:Albuginaceae

5. Life cycle

6. Theprimaryinfectionoccursduetooosporesperennatinginthesoilor
duetomyceliumperennatingonperennialhosts.
Theseserveasprimaryinoculumwhentheenvironmentalconditionsare
favourable.
Oosporesgerminateinpresenceofwatertoformavesicleinwhicha
largenumberofzoosporesareformed.
Thesezoosporesswiminafilmofwaterandlandonthesuitablehost,
germinatebygermtubes,enterthehostandestablishinfection.
Themyceliuminthehostisintercellularwithglobosehaustoria.
Soonthemyceliumafterabsorbingnutrientsandfoodmaterialsfromthe
host,accumulatesbelowthelowerepidermis.
Conidiophores,whichareclavate,andformedatthetipofhyphae,begin
toproduceconidiosporangiainbasipetalsuccession.
Thepressureofthesebreaksopenthelowerepidermisandwhiterust
symptomsbecomeapparentontheleaves.

7. The
conidiosporangia
produced during
earlyphaseofthe
growing season
cause secondary
infectioninthehost.
Theseareblown
awaybywindorany
otheragency,land
onthehostsurface
andgerminateto
formzoospores.
The zoospores
germinate by
formationofgerm
tubeswhichenter
thehostandcause
secondaryinfection.
Iftheconditionsare
favourable,thisis
repeated.
Whentheconditionsbecomeunfavourableorduringthelaterphaseofthegrowingseason,
thefungusbeginssexualreproductionproducingoospores.Theseoospores,beingthick-
walled,canwithstandtheunfavourableconditions.

8. Symptoms of White Rust Disease
The disease affects all the aerial parts of the plant, the roots
are not attacked.
Symptoms may appear as a result of two types of infection:
1)Local infection
2) Systemic infection

9. Local infection
Isolatedspotsorpustulesappearonleavesorstemsorinflorescence.
Thepustulesareofvariablesize,measuring1-2mmindiameterandare
raisedshinywhiteareas.
Thesemayariseincloseproximityandcoalescetoformlargeirregular
patches.
Usually,thepustulesappearincircularorconcentricarrangementwith
oneortwocentralareas.
Thehostepidermisrupturesexposingwhitepowderymassconsistingof
sporesofthefungus.
Pustulesoccurringonleavesareusuallyconfinedtothelowersurface
only.

10. Systemic infection
Youngstemsandinflorescenceareinfected.
Thefungusbecomessystemicinthesepartsandtheaffected
tissuesarestimulatedtovarioustypesofdeformities.
ThemostprominentisHypertrophyoftheaffectedparts.
DuetoHypertrophyandHyperplasiaoffloralparts,theseshow
swellingsanddistortion.
Thepeduncleandpedicelmaybecomeenormouslythickened
upto12-15times,thenormaldiameter.
Floralpartsbecomefleshy,swollen,greenorvioletincolour,the
stamensfallingoffearly.

11. Thepetalmayturngreensepallikeandstamensandcarpelsarealso
convertedtoswollenleaflikestructures.
Theovulesareusuallyatrophiedasalsothepollengrainsresultingin
totalsterility.
Pustulesmayalsoappearontheseparts.
However,theaffectedpartsarefullofoosporesandstarch.
Whenthesystemicinfectionhastakenearly,thegrowthoftheentire
plantischecked,stuntedandonlysmallleavesmaybeformed.

12. Control Measures of White Rust Disease
Cleancultivationanddestructionofweedshouldbepracticed.
Croprotationwillavoidthesoilborneprimaryinoculum.
Sprayingwith0.8percentBordeauxmixtureorDithaneM-45(0.2%)
maybeundertakentocheckthespreadofthedisease.
Diseaseresistantvarietiesbepreferred.