Pythium root necrosis of oats

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PTTHIUM ROOT HICROSIS W

OATS

bf M m w m w, Welch

A Thesis Submitted to the Sradmfce faculty for the Degree of # § § » * OF «XH»Stf»r Major Subject: Plant P&tholQgy

loura State College 1942

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On Seed and on Young fteedliagp Prior to Imergeno# 0# ©olcoptlle and Suberownal Interned®....

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Ob Primary and Secondary Moots *

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:9m foliage * * * * ♦ ♦ . v . *' ■. * . •. * ..

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Prevalence and Identity o f Pythium m the loot# ■ of Oat Seedlings* ............ .

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Fact ora Affecting the. Pathogenicity of Fythtuia ■ on the Oat Plant, . . . . , . . . . . . . . . .

IV

Period of incubation of the organism in artificially infested soil . . . . . . , , it The pathogenicity of Pythium on plants grown from different numbers of seeds per pot . . 20 The pathogenicity of Pythium an plants grown in soil infested with different amounts of Inoculum .................. ..28 The res pons# of oat plants grown fro® primary and secondary seeds. . . . . . . ........ 26 The relative response of plants grown from one-, three- and five-year-old seed. . . . ti The iffeet of Temperature on the Germination of ©at Seed Sewn In Pythlum-Infested Soil. . . . .

23

The effect of temperature on tbm growth

rate of P^ debaryanum . . . . . . >

...»

SI

The Pathogenicity of P*. deharyanua on Boots of Oat Seedlings . . . . . . . . . . . . ........

SI

Reaction of 116 Varieties of Oats to P. . . . . . . . . . . . . . . . debarvanum . . .

40

'"Y’T; 3 5 0 4 —

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Page EXPERIMENTAL RESULTS (Continued) Reaction mi Six Species mi 1 1 M Oats to P. Ambmwmmxm » . * * * ♦ . . * . # * . . . . . .

Decreased Tie 3d In Variety Swedish Select Caused ty Is.debary&oum. . • * « • ,. . . . . . . . . .

46 .

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Prevalence of PytM.ua in the Roots of Green and Yellowed Oat Plants Found In the Field. . . , . .

5-5

Mutrient Deficiencies in Relation to the loot Vecrosis of tele* . • * . • . . . . • . . . . . .

58

The effect of nutrient deficiencies on in­ fected and non-infected plants grown in quarts sand. . ................. . . . . . . The response of the varieties Boone end Marion, grown in field plots heavily in­ fested with Pythium, to certain fertilizer amendments . . . . . . . . . . . . . . . . . The response of Boone and Marion, grown on Buchner sand treated with chloroplcria, to certain fertilizer amendments. . . . . . . . The influence of certain fertilizers, broad­ cast and drilled with the seed, on the root necrosis of oats. * * * * . . . . . . . DJSSdfS'SfG® .w .-*e .:w .w* . .*W’.s? . . .... a® — w— w.e**’ . . ’W • . w* . m

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85 m

Oats in the seedling and boot stages often are yellow

and stunted, and the lower leaves say he brown and dead. These systems occur to seme extent each year and say he ob­ served in oat fields throughout the state. 'At heading bias the yellow, stunted oat plants tend to regala their normal . green color ant seemingly recover from the diseased seedling condition.

Srowers long have'recognised that this yellowed

and stunted condition of oats during the early spring resulted in a reduction of the eat crop. Several years* observations indicate that even though the

above described symptoms occur sash year, they are most pro­ nounced when conditions .are unfavorable for the 'rapid growth

of the 'let plant.

The yellowing and stunting of oats in April

and .Say has been thought to be a result of one or more condi­ tions, such as cold weather, excess moisture., deficient nitrogen, lack of aeration, root parasites, etc,., but few.data have been obtained supporting, any one of these theories.

la 1922 dram and Rostrup (2) briefly reported that a 'root blight caused by JhrKh&wi debaryanua lease and species of W m m t i m m had been

Benmark.

found in sows oat and barley fields 'in.

Subramanlaa (14), Robertson (11), Vanfcorpool ant

Truseott '{'11:1, Brandenburg (1), and Ho and Melhua {11 also reported finding species of Pythium parasitic on cut roots.

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Ion® Of tl»»«® Investigator*., however, studied the Interaction of tii® host and «em»&i organism or the effect of environmental M M i i t t a M on tl» activity of Pythian oa the roots of oat plants.

A detailed study was undertaken in the spring of liSS to determine whether the roots of field grown oat plant® w«r« parasitised, and if so, how extensively and hy what pathogen or pathogens.

The preliminary results of this investigation

indicated that species of Pythina war® parasitizing the roots and wight h® partially responsible for th® follag® symptoms

so evident during April and Hay*

It then seemed necessary to

study the host-parasite relationship and to determine the effect of the pathogen on th® growth and- development of the plant itself.

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S fM ffO M S

Pythlam is strictly ft seed and 'root parasite on oats, but the siiwiiad and yellowed •condition ■mi ■Infeebed plants is ' common,

these- symptoms are thought to be the result ©f root

tmfaebioas because they ere not ceased by the presence ©f the parasite la the tissues Of the aerial pert* ©f infected pleats, the pathogen itself is restricted' to the base of th© stem and to those parts of the pleat that m m h e l m the surface «f the

soil.

Symptoms that are found on the glumes, the endosperm,

the developing embryo of germinating seed an# os primary end secondary roots are caused by the direst action of the pathogen,

fis© yellowing and stmtliag of the aerial parts of Infested plants is ©eased indirectly by the aotioa of the pathogen on the roots. ■

'So Seed end ©a Young Seedlings frier to Jteergence flat seed ■sows in soil infested with Pythltm debaryanam lease, and under ©©nditions favorable for the pathogen, may be Ottaeleed soon «fter planting.

'If conditions following sowing

%

are sash that seed require one week or longer to germinate,

■*fhe -smther considers germination to. be ©©mpleis when radiele growth ins become evident; following this, the devel­ oping eahryo is considered a seedling. .

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-4

the seed m j be rotted and the stand reduced.

fh© glumes of

.rottod seed are blackish brown .in color but remain intact and. vil«i» feboij? .originai shapa as shown in fig* l,C.

goto th*

bright color of glumes of uaplaated seed in fig:* 1,A and alight discoloration of glume* of aood planted tn'stsrtic soil,,,

fig* 1, 1. fhe interior of the rotted aood may be soft and mushy anft may haw# a putrid odor,

if th® infected glumes are

removed fro® the oary ops is and the embryo examined, It may show tint .m® embryo was atteckfWi and killed before any apparent development had tsten place (fig* 1, S).

In such

m s e c the dead embryo appears as a dark-brown spot .at the basal end of the caryopsis. . It frefmently Is shriveled wad distorted in step® and stands out in sharp contrsst to the lighter brown

color of the endosperm.

Vote contrast between normal seed,

fig* It b, and Infected seed, fig. 1, 1. the developing seedling often is killed between the time the plumule end the radicle begin to develop and the time the cole optile appears

above the .surface of the soil Cfig* I# f* •# K, D *

©wing

this time the organism M y attack the developing .radicle be­ fore ■the primary roots are visible and kill than before they

have reached a length of 1/2 cm* is the roots are killed the organism grows up into the vascular plate and may grow into the eoleeptile and its enclosed leaves*

Infected parts usually

become brown in color and distorted in shape*

*ete difference

in color and extent of root system @f hesltliy anaSUag* fig. 1, 1 as © c®pared with fig* i, i*

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-5

Pig. 1. Symptoms caused b y Pythium debaryanum on oats. A, unplanted oat seed. B, a seed planted In steamed soil. C, seed planted in Pythium-infested soil. D, normal seed, glumes removed, showing white color of uninfected embryonic tissues, E, seed with discolored and dead embryo. F, G, H, I, young seedlings infected with Pythium; glumes removed except in H. J, K, normal seedlings showing no infection. L, Pythiuminfected seedling showing the early stages of root infection. M, infected seedling showing adherence of soil particles to infected parts of the roots. N, 0, seedlings showing Pythium lesions on the coleoptile. P, Pythium-infected seedlings showing late stages of primary root necrosis and infected subcrownal internode. (Drawn by Marie A. Corkle.)

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Qa Col® opt lie ancI fmberowisal Interned® Pyfchiuai infection on- the developing eolooptile of young seedlings causes tit* appearance of typical blaeMsh-brown lesions, which may be found at any place on the eoleoptile but usually are restricted to its lower half*

Such lesions are

shown in fig. 1# I f 0.’ 'the lesions are snail* circular, darkbrown Spots, tint seldom exceed f mm. in diameter*

la seme

eases, however, long, linear, dark-brown lesions are found that may be 1/2 to 1 inch in length.

These lesions extend

longitudinally up and dean the surface of the eoleoptile. this type of lesion apparently is sensed by the elongation of a eoleoptile on which a circular lesion has developed prior to elongation.

Both types of lesions usually a r e .restricted to

the surface of the eoleoptile because the pathogen rarely pene­ trates the eoleoptile tissue to attack the leaves and stem inclosed within.

After the eoleoptile emerges and the first

leaf is formed, eoleoptile lesions may be found above the soil surface*

If Infection occurs at the time radicle growth has been initiated, the pathogen may grow upward Into the soberownal internode.

If such an Infested seedling emerges, the sub­

erownal internode may reach a length of 1 Inch or more, de­ pending upon the depth the seeds are planted in the soil,

fhe

entire suberownal intemode, extending from the primary roots

to th© erovnai node, may be Infested and killed (fig. 1, P).

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file pathogen attacks the lower end of the suberowaai interoode and spreads up th# internod© to til© crownal node.'^Th® in­ fected tissue t i m a dark orown, withers, end shows typical damping-off symptoms*

The crownal nod® establishes Itself at

the soil surface, and secondary roots develop from it*

Fythlua

infection seldom 'has been observed above the crownal node, but

It h is been found at the base of the stem immediately above the soil surface*

In such instances the base of the stem may

become discolored and shriveled.

6n Primary and Secondary Roots dnder conditions favorable for P* debaryanuia the primary

roots any be infected as soon as they emerge from the germi­ nating seed (fig. 1, 0, Hj.

The first symptom on an infected

root la a water-soaked, translucent area (fig* 1, lt)« This water-soaked area increases in sis© and its center become®

discolored.

At first it is a very light shad© of brown, but

it gradually changes to reddish brown and finally to dark brown In color.

Vote the dead root tips in fig. 1, &»

to'■

fig* 1, E is shown the root system of a healthy seedling ■of the same age aa the seedling shown In the fig* 1, L. The structure of primary roots permits lesions to spread

rapidly, but mider conditions favoring maximum root growth they seldom succeed in. reaching the growing, point*

On. the

other hand, If seed is germinated at 15°C. ear below,.the rate

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■ -» -

of root growth 1# reduced to the extent that

M 7 fee infected and MIMA*

m

entire root

At temperatures Higher them

li%. lesions -ere restricted to the upper three-fourths of a root, and the growing point 1* not infected because it ©an. out­ grow the parasite.

Under these conditions mew infections

©eeur Immediately behind the growing point on the stationary parts of the root, and by the time a typical brown lesion has

developed the growing point his advanced several centimeters. In such roots trams location is decreased, ami the terminal

portion of the root dies. Young seedlings growing at temperatures of l$'®f» or below

may have me, two, or even three dead primary roots, each of which may be less than an last in length.' These infacted primary roots are reddish brown throughout, slightly enlarged -and irregular in shape,

frimordia of breach roots may be

attacked and killed before the young branch root has broken

the epidermal layers of the small primary root, these pristerdla never develop, but 'the resultant mailings m u s e the infected primary root to be irregular in shape (fig. 1, 1). & digging and washing Infected 'roots it is difficult to remove the soil particles from the infected areas.

Th© soil particles

.are matted and stuck to the surface of the lesion by th# mycelium of the parasite. The- adherence of -soil particles to the infected roots, as shown is fig. 1, If, is strikingly characteristic of the disease and may be used as the best -

diapieetie symptom when searching for Pythium root injury.

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M

removing the soil particles the diseased cortical tissues

are easily lorn.

Wreat"ear® must h e :taken la digging and

washing plants fear examination because severely diseased rents

are easily broken and destroyed. The primary rent system of a normal oat seedling has three primary rents*

If m e or- mere of these roots are

destroyed hy Pythtua, the seedling m y produce additional roots. Toung seedlings hare been found in the field with seven primary

roots.. This excessive production of roots retards and weakens the' growth of the plant and makes it more susceptible to attack by Pythlaau : Wader these conditions oat seedlings m y be killed before they establish an efficient root system. Lesions found on secondary roots are similar to those already described on primary roots but are aore H al t ed in ex­

tent. The- pathogen dees not spread so rapidly through the tissue of' the larger, tougher secondary roots as In the primary roots* - 'in the: field typical root symptoms of Pythium infection

c m be found best on the primary root system.' During the seedling stage environmental factors usually favor the develop­ ment of Pythium. the roots of the plants are mall and young, and symptoms are very pronounced*

As the plants mature, en­

vironmental faetors usually are less favorable far the develop­

ment of the pathogen, other organisms become active ant Pythium is no longer readily 'detected*

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.fe Foliage Oat plants growing In Pythiua-inf eated sell may show stunting, yellowing and dying of th® basal Isa*©#.*, Stunting begins when the plants are in the seedling stags and becomes Increasingly pronounced until heading time.

Stunted seedlings

during the first two week# of growth are normal green in color and can 'he Identified only hy their reduced sis* and infected roots. After two to three weeks, the hasal ieawe# of th# in­ fected plants hegia to die from the tip# hack, and the terminal leawes turn light yellow*

Seder field conditions yellowing

becomes very pronounced when the pint# are four to elk weeks

old. At this time the hasal leaves ere dying, end stunting is most pronounced.

Stunting .end 'yellowing is' most 'prevalent

during « cold spring. following end stunting of oat plants was general through­ out many fields’in IfSi.

In such fields, ell pleats seemed to

be equally effected end no differences were found between

plants, growing on high, well drained lend and those 'growing on low, poorly drained land*

3fe 1939, however, yellowing and

stunting was restricted to spots.- Such spots varied from one to several yards in diameter and usually were eonflaed to lew, poorly drained areas.

Spots containing yellow, stunted plants

were surrounded by normal appearing green plants, and the region of transition fr«* yellow plants to green plants was distinct. As the season -advanced and the plants began to head,

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■li­ the fallow spats disappeared because th© plants tended to regain their normal green color and stunted condition,

more or less screenad the

the development of th* stunted plants,

however, was mutch slower than that of the adjacent green plants. Stunted, yellowed plants •tiller from one to 'two weeks

later than normal plants.: fillers- that appear under these conditions usually 'dry up and die before they complete develop­ ment.

Under field conditions yellowed plants seldom have more

than one e*3».fe«fc may possess one to several partially devel­ oped, dead'tillers. foliage symptoms caused by Pythium are difficult to dis­ tinguish from these caused by certain mineral deficiencies. Hoffer {$) shewed that a nitrogen deficiency produces a

-yellowish green foliage in. oats.,, that a phosphorous deficiency retards growth, and reduces stooling, and that a potassium deficiency -may cause elder leaves to turn yellow and to die from the tip ends..

Because of this similarity, foliage

symptoms should he used only as a supplementary method few diagnosing Pythium root necrosis.

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- 12-

/ ;-'g g m v n m u . B i s u m

Prevalence and Identity of Pythium on the Hoots of Oat Seedlings After Investigations proved tint JV debaryanuia sensed root lesions on oat seedlings In the greenhouse wad la the field,

m

attempt was made to trace the prevalence of the path­

ogen in th® field during the growing season,

la 1910 and 1919

isolations sere made from the field grown oat 'plants at weekly or bi-weekly intervals during the entire growing season.

In­

fected plants were taken fro® the field, the dirt was washed thoroughly ftp®® their roots and isolations were made from the

lesions found on the lafeete# roots. One-half to one-inch pieces of an infected root were placed beneath 2 par sent agar-agar la a petpi dish, 'the solidified agar was lifted with'a specially flattened needle according to Meredith (10), wad the infected root placed be­ neath it.

This method of leelatien reduced bacterial contami­

nation to a minimum because any organism growing from the in­ fected root tod to grow through the thick layer of plain agar before an- Isolate could be obtained.

Fythlua grew « t of the

Infected root ant through the agar layer' in 43 hours or less.

All other' organisms present in the Infected roots had slower growth .rates, this difference la growth rate provided an easy method of separating Pythium Isolates’from other organisms.

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■ the isolation studies were started m April-1, '1833* this time 85 Isolates ■» f i obtained frost M

At '

isolations and tl,

©p 91.3 per cant ©f the isolates, were Identified as Pythium.

Ha Kay 13, ft Isolates were obtained from 61 isolations and 46, or ft.3 far. ©ant or th* isolates, were Pythiunu

On Kay ft, S4

isolatss were Obtained fro® 100 isolations and 41, or 48.8 par cent of the isolatss, were Pythium.

On dun® 1, 24 isolates

were Obtained from it Isolations and only six,, or ii per cent of the isolates, wer* Pythium,

On June S3, 17 isolates wars

obtained fro© 83 Is©lations, but Pythlust was not present.

Simi­

lar results were obtained in 1939 when 293 isolations were made between lay 1 and d m® it.

fhe results for 1938 and. 1939 ar*

summarized in table 1.

It 1938 and 1939 the early isolations yielded the highest ■percentage* of Pythias Isolates. ■ Xte fact, .fythit» was prac­ tically the only organism that ©©aid be isolated during the

first weeh of May in I M S end 1939. fhla fact suggested that Pythium was th® initial causal agent of the root injury. .As the seasons advanced, however, M e isolation of Pythium from diseased roots became increasingly difficult. fhs .data In

table. 1 show that la £838 and 1939 each mmmsalve date at which Isolations were made yielded a lower percentage of Pythium, and ©a the final date a® .Pythium Isolates were ob­ tained.

.la addition to each saaeacalwn data .of isolation'yielding a 'decreased ■ percentage of Pythium Isolates.,, a. higher percentage

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6,2 6,3 6.4 7.2 3,4 6.6 6.3 7.9

5.6 8.0 6.2 6.3 6.6 7.2 6.9

4. satlva (A. ©rient&lis I 1593 1362 1365 807 291 1864 1609 1606 1612 1604 1602

Oriental Carton Mo. 748 Carton Ho. 784 Black Rival Black Tartar Carton Cray Selsure Golden Giant Carton fellow Sparrowbill Storm Ming

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6.3 7.6 7.2 7.4

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fable i (Coatlamed)

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Variety

Non-infested loan

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Infested

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:Boot * fop j§tnd jgjpeotlatgfootfei3^*5®®1sgrowths growth 4. ntida

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6.0 l.§

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A. midibreuia ti§§

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Least difference for significance « 2.S ©». (root}.

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-AS-

Cheek*

Coast Black shewed definite root lesions.

■f M ;variety fmsh-'jKaek, most resistant of the IAS ■■ tarUfeiia to Sythlust, was selected for th® eoaparisen with

efthc# nrialiii.

flue toast difference for sipdurtmme#' in

stsctn root growth was §*-§■ w u

Bins® Coast Black haft a mean ■

root growth of 11.2 cm. , alt the varieties that ha# a m a n

mot'-grmttrof ':'B*7 cm. or ever were as resistant as Coast Black variety,

fhe interval 11.2 to 8.7 included the follow­

ing varieties?

Black Algerian, Early Bed Bastproof, Bed Bast*

proof* feed Algerian, Belar, Culred, Victoria, feakiwi, SoarI a®, Almria, Culberson, lowar, Canadian and Anthonf.

Of these 14

varieties, 9 belonged to Arena bvzantlne and 5 belonged to A. satlva.

The only varieties that were considered ho he

possible sources of resistance were Coast Black, Black

Algerian* Ssrly led Inetpreef, M l Algerian and' luakura, , fh# other 11C varieties were too susceptible to PythluiB damage to he included in any breedingspreiraia to develop resistant varieties*

fhe reaction of these varieties was similar to.

that:of variety Ray' (fig. #}*

B e a c t i m of Sir Species of Wild Oats to fv, debarvanuai Sir species of wild oat3 were grown and tested as de­ scribed in the above experiment,

fw© selections of Avena ■

abysstnlea and three selections of A ^ ludoviolnla.were in­ eluded*

Avena nudlbrevla and A. wieetll had 7 haploid

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-4 7 -

Pig. 6.

Pythium injury to Hay oats.

Infected plants on right.

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cteraaosernes x A. teartestea and .A, abyss inlea had 14 faaplold

e b B m m m M f sad A&

atarllta lad 11 haploid

Iadovlelnla and

chromosomes. 'the reactions are presented in table 9.

fable f. Relative Resistance of Six Species of Wild Oats Representing the f# 14, and 91 Baploid.Chromosome ©roups

s

i

|*1* t ■ Variety

■ lh u *

^

2455 A. nuditerevis 246? 2108 2519

1994 2321 2050 1781 2723

A. A. A. A. A. it e A.

ion-infested

'lStendsKoot

*

t

Infested

*Sfea«d*loot

.•? » ****,g p o a th ig ro w th s

28 30 barbate abyssinica SO abyssiaica 3© wiestli 17 27 lmdevieiaia * Dorian 14 * of Sthlopia 30 sterllla(alger)29

8.9 8.7 9.9 9.1 9.7 12.0 9.2 12.0 14.5

5*6 6.4 7.7 7.1 3.7 6.7 4.5 6.0 9.8

8 fet

*g ro w th :g r o w th

If • tl .ft so

7 tl 14

m m.

5.5

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4.9 7.5

' 8.5 4.4 t.$ 8.6 10.2 12.4

6.3

2:.5 6.3 5.3 6.4 . 6.9

least difference for significance s !.,# «»• (root).

■ A n analysis of variance shewed that there- were highly significant differences is species reaction to Pythium.

S&ete

species m s attacked by the.organism tut A ^ abyssimlca. A* Iadov Iclnla and JU sterllla were somewhat resistant* . la general, both wild species and cultivated varieties that be­ longed t# the 21-chromosome group tended1to tee more .resistant

then members of the 14- or 7-cto ernesone groups* This tendency was very pronounced In the 11© varieties listed. In table 8, which ehcwe that, the five meet resistant varieties belonged

to the 21-ehreoiOsem© * A^ teysantine group.

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-4 9 -

BeereaeeilT M A to Variety Swedish Select ©onset. hy ?. debary&nu®

1# obtain soma idee. e£ fythiwsto ability to decrease yield,- the- variety Swedish Seleet was grown to maturity to infested soil,

the plants were grown in one-gallon stone

Jars, and the soil moisture was held at §5 per eent of the water holding oapaeity or below.

lach Jar contained cm equal

amount of steamed greenhouse soil, whleh had a water holding capacity of 42 per cent and a field capacity of 22 per cent

Ifigured m . « dry weight basis),

The soil to eaeh pot was

tofeeted with on® unit of Inoculum and was mulched with onohalf toeh of ground oork to reduce evaporation.

pots of un infested soil were held as- ©hacke.

Additional

Fifteen seeds

were sown per pot, but each pot was thinned to the first five plants to emerge*

to .toes of the infested pots only three

seedlings were produced.

Consequently, three pots contained

only three plants at maturity.

The pots were weighed daily

and the water required to bring the moisture content back to

ft per sent or to $3 per -sent of the water holding capacity was sided. ~ The plants wore grown to soil to which the soil moisture never exceeded, the field percentage. The experiment was storied on January 1©, 1938, and ties temper* hero of the greenhouse was held at 15°C. until the

first week to larch. By this ttoe it was impossible to main­ tain a 15°C. temperature throughout the day because of higher

air temperatures.

Fortunately, these higher temperature

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conditions approached those fo\md in the field, i.e., the seed was pleated in cold soil, hut 'the tempera tore increased os the. growing season advanced. A comparison of height and degree of tillering la in­ fested and non-infested soil showed that the check plant* tended to have tetter rate* of growth from the seedling stage

to maturity (table 10).

"M general,

the infected plants were

two weeks behind non-infected la relation to top growth and

the production of tillers.

Figaro

1 shows the

difference

that existed between infected end non-infected plants at maturity. When mature, the plants were washed from the pots and dried at 100°C.

the dry weights obtained showed that the

average development of the non-infested plants was approxi­ mately twiaa that of .'infested, plants regardless ©f whether

total dry weights per plant, total root weights per plant or total top weights per plant were compared.

Blfferenees in

yteld'were correspondingly as great since the cheek plants yielded 82.8 to 88.4 seed* per- plant and the Pythium-infested Plante yielded only 28.3 t© 44.1 seed* per plant.

Such dif­

ferences Indicate that under certain environmental conditions Pythian may be a very important factor in datepsfctSng She development and yield of the '©at plant*

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i@ © * A ana fallowed Oat Plants Found to the Field

The ®p#eai and yellow spotted oettdlttom -of oat field® to

tli«:state of lew®, m i erred to emitter to thia paper, becomes evident during toe latter part of May-

to 1938, 1939 and

1940 yellow are*® began to appear to ©at field® throughout

the' etate about lay IS, Bay lf# and lay 26, respectively,

the

•potted condition eaeb season became progressively more pro­ nounced until the plant® began to head.

At heading time the

yellowed plants regained their green color and could be located

only^by their reduced alee-

Isolations were made each year

from green and yellowed plants found to the same field to an

effort to determine if the fungus flora of yellowed plants differed from that of normal appearing, green plant*, fable II present® data typical of theme obtained fro® several field® to If3® and 1939.

the green plants yielded the higher peroestage of fythtom Isolate®,

to 1938 toe green plant® yielded 58.8 .per ©eat

Fythtom isolates and the yellowed plants 40.f per ©eat.

Simi­

lar result# were obtained to 1939 when 31.2 per ©eat of the isolate® from green plants were Pythian ae compared with 14.2 per ©eat from yellowed plants, fhe chi-square values indi­ cated that there-*®® no significant difference- between the Fythtom populations of the yellowed and green plants but, to

1938 and 191®, such data were collected repeatedly fro® field® of oats when yellowing we® most pronounced.

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