Characterization of Phytophthora resistance in soybeancultivars/lines bred in Henan province

Jiqing Zhang • Suli Sun • Guiqing Wang •

Canxing Duan • Xiaoming Wang • Xiaofei Wu •

Zhendong Zhu

Received: 3 February 2013 / Accepted: 28 November 2013 / Published online: 15 December 2013

� Springer Science+Business Media Dordrecht 2013

Abstract Deployment of resistant soybean cultivars

is the most effective and economical method of

controlling Phytophthora root rot (PRR) incited by

Phytophthora sojae, and characterization of Phytoph-

thora resistance of the soybean cultivars greatly

facilitates the effective utilization. The objective of

this study was to characterize the resistance phenotype

in 30 soybean cultivars/lines bred in Henan province

and 4 ancestral cultivars which were inoculated with

26 P. sojae pathotypes. The 34 soybean cultivars/lines

showed 34 different reaction types of resistance to 26

P. sojae pathotypes. The reaction types produced on

the cultivars/lines were compared with those produced

on the differential lines to postulate which Rps gene

was present. The gene Rps5 and Rps3a or gene

combination Rps3a?5 were postulated to be present in

Zhoudou17 and Zheng77249, respectively. The other

32 cultivars/lines exhibited novel reaction types that

were different from known single or two Rps gene

combinations. The cluster analysis of the reaction

types revealed 10 groups among the 34 soybean

cultivars/lines, 17 differentials and the cultivar Wil-

liams at the similarity coefficient 0.6540. This study

indicated that Phytophthora resistance was extremely

diverse in this region. The cultivars/lines with broad

spectrum resistance could provide effective sources of

resistance for the control of PRR in the future.

Keywords Cluster analysis �Gene postulation �Phytophthora resistance � Soybean � Reaction

type

Abbreviations

D Day

DPI Days post inoculation

I Intermediate

PRR Phytophthora root rot

R Resistant

Rps Resistance to Phytophthora sojae

S Susceptible

Introduction

Phytophthora root rot (PRR), caused by Phytophthora

sojae Kaufmann & Gerdemann, is one of the most

destructive diseases on soybean (Glycine max (L.)

Merr.) (Schmitthenner 1999). Under saturated soil

conditions, P. sojae produces zoospores that infect

soybean plants throughout the growing season,

J. Zhang � S. Sun � C. Duan � X. Wang �X. Wu � Z. Zhu (&)

MOA Key Lab of Soybean Biology (Beijing),

The National Key Facility for Crop Gene Resources

and Genetic Improvement, Institute of Crop Science,

Chinese Academy of Agricultural Sciences,

12 Zhongguancun South Street, Beijing 100081,

People’s Republic of China

e-mail: zhuzhendong@caas.cn

G. Wang

Agricultural Science, Liaocheng University,

Liaocheng 252059, People’s Republic of China

123

Euphytica (2014) 196:375–384

DOI 10.1007/s10681-013-1040-x

resulting in pre- and post-emergence damping-off,

root and stem rot, yellowing and wilting of lower

leaves, and the death of soybean plants (Schmitthenner

1999). Yield loss due to PRR may be as high as 10 to

40 %, and severe infection can result in a total yield

loss under an epiphytotic condition (Anderson and

Tenuta 2003; Li and Ma 1999).

Deployment of race specific single gene resistance

to P. sojae in soybean cultivars has been the primary

method for PRR control (Schmitthenner 1999). The

Rps genes, which interact with P. sojae in a gene-for-

gene model, have been utilized extensively in com-

mercial soybean cultivars in Northern America (Dor-

rance and Schmitthenner 2000; Slaminko et al. 2010).

The first Rps gene, Rps1, was identified in the 1950s

(Bernard et al. 1957). To date, twenty Rps genes/

alleles at 14 genomic loci distributed on six different

chromosomes have been identified (Fan et al. 2009;

Sugimoto et al. 2012; Sun et al. 2011; Wu et al. 2011;

Yao et al. 2010; Yu et al. 2010; Zhu et al. 2007). In

contrast, partial resistance, which is caused by multi-

ple genes, has been used to a limited extent on

soybean, because the partial resistance is not enough

to prevent significant yield losses under high inoculum

densities and adverse environmental conditions.

Phytophthora resistance conferred by several Rps

genes, such as Rps1k, Rps1c and Rps1a, has provided

effective protection against the diverse P. sojae pop-

ulations (Malvick and Grunden 2004; Slaminko et al.

2010). However, the continuous use of these genes has

promoted selection of races or pathotypes capable of

overcoming them in the pathogen population (Grau

et al. 2004). New Rps1k-virulent P. sojae populations

have been reported (Dorrance et al. 2003; Malvick and

Grunden 2004), although the widespread resistance

provided by Rps1k has remained effective in most

soybean production areas (Slaminko et al. 2010).

Generally, single Rps gene has been effective for 8 to

15 years (Dorrance et al. 2003; Schmitthenner 1985).

Phytophthora sojae is highly diverse with at least

55 described races (Grau et al. 2004). Additional

pathotypes that have not been assigned a race number

have also been reported worldwide (Dorrance et al.

2003; Malvick and Grunden 2004; Zhu et al. 2004).

Chen et al. (2008) and Zhu et al. (2003) reported that

the known Rps genes, except Rps1c and Rps1k, were

not effective against the Chinese P. sojae populations.

Therefore, new sources of resistance need to be

identified to cope with complex populations of P. sojae

in China. Gene postulation provides for quick identi-

fication of the probable Rps gene and discovery of

novel genes in the soybean cultivars and germplasms.

Chen et al. (2008) postulated that Rps1a, 3c, 4, 5 were

present in 13 soybean cultivars/lines and that 15 two-

gene combinations occurred in 33 soybean cultivars/

lines. Xia et al. (2011a) showed that Rps1k, 3b, 4, 6

were present in 9 soybean cultivars/lines and that 13

two-gene combinations occurred in 12 soybean culti-

vars/lines.

Although it is one of the major soybean production

regions in China, there have been no reports of PRR in

the Henan province. Recent research indicates that

many soybean cultivars/lines bred in this region have

resistance to P. sojae (Chen et al. 2008; Tang et al.

2010; Xia et al. 2011a). However, comprehensive

information on the Phytophthora resistance of soybean

cultivars/lines bred in this region is lacking. The

objectives of this study are to characterize the

resistance phenotype of soybean cultivars from Henan

province in order to identify potential sources of

resistance for control of PRR in the future.

Materials and methods

Plant material

Thirty soybean cultivars/lines bred in Henan province

were provided by Professor Weidong Li and

Dr. Weiguo Lu in Henan Academy of Agricultural

Sciences, China. The four ancestral parents Qihuang1,

Qihuang13, Shandongsijiaoqi, and Zaofeng1 were

obtained from the Institute of Crop Science, Chinese

Academy of Agricultural Sciences.

A set of 17 differential lines possessing a single Rps

gene and were utilized to confirm the pathotype of the P.

sojae used for screening the thirty-four soybean culti-

vars/lines (Table 1). The susceptible cultivar ‘Williams’

(rps) was used as a control for inoculation efficiency.

Inoculum and inoculum preparation

The twenty-six P. sojae pathotype was confirmed by

means of the hypocotyl inoculation method (Dor-

rance et al. 2008). All isolates were obtained from a

single oospore. The pathogen was transferred to

petri dishes containing Carrot-Agar medium 1 week

prior to inoculation. The inoculum slurry was

376 Euphytica (2014) 196:375–384

123

Ta

ble

1R

eact

ion

typ

eso

f1

7d

iffe

ren

tial

lin

esin

ocu

late

dw

ith

26

of

Ph

yto

ph

tho

raso

jae

pat

ho

typ

es

Cu

ltiv

ar(R

ps)

Pat

ho

typ

es

PsH

LJ5

PsH

LJ3

PsJ

MS

3P

sJL

1-1

PsH

LJ1

PsH

LJ4

PsA

H4

PsJ

L4

-3P

sGZ

2P

sJL

3-2

PsS

X1

PsJ

S4

PsJ

L4

-1

Wil

liam

s(r

ps)

SS

SS

SS

SS

SS

SS

S

Har

lon

(1a)

RS

SS

RS

RS

SS

SS

S

Har

oso

y1

3X

X(1

b)

RR

RR

RS

RS

RS

SS

S

Wil

liam

s79

(1c)

RR

RS

RR

RS

SS

SS

S

PI1

03

09

1(1

d)

RS

RR

RR

RR

SR

SS

R

Wil

liam

s82

(1k

)R

RR

RR

SR

SS

SS

RS

L7

6-1

98

8(2

)S

RS

RR

RS

RR

RR

SR

L8

3-5

70

(3a)

RR

RR

RR

SR

RR

RR

R

PR

X1

46

-36

(3b

)R

RR

RR

RR

RR

RR

SR

PR

X1

45

-48

(3c)

RR

RR

SR

RR

RR

RR

R

L8

5-2

35

2(4

)R

RR

RR

RS

RR

RR

RR

L8

5-3

05

9(5

)R

RR

RR

RS

RS

RR

SR

Har

oso

y6

2X

X(6

)R

RR

RR

RR

RR

RR

RR

Har

oso

y(7

)R

RR

RS

SR

RR

SS

RR

PI3

99

07

3(8

)R

RR

RR

RR

RR

RR

RS

Yo

ub

ian

30

(YB

30)

RR

RS

RR

RR

RR

RR

R

Zao

shu

18

(ZS

18

)R

RR

RR

RR

RR

RR

RR

Yu

do

u2

5(Y

D2

5)

RR

RR

SR

RR

RR

RR

R

Cu

ltiv

ar(R

ps)

Pat

ho

typ

es

Ps4

1-1

PsA

H3

PsT

A3

PsA

H1

PsF

JP

sJS

9P

sJS

7P

sJS

8P

sMC

1P

sJN

4P

sJS

2P

sAH

6P

s23

Wil

liam

s(r

ps)

SS

SS

SS

SS

SS

SS

S

Har

lon

(1a)

SS

RR

RR

SR

SR

SS

S

Har

oso

y1

3X

X(1

b)

RR

SR

SR

RS

RS

SS

S

Wil

liam

s79

(1c)

RR

RR

RR

RR

SS

SR

S

PI1

03

09

1(1

d)

SR

RS

RS

SS

RS

RS

S

Wil

liam

s82

(1k

)R

SR

RR

RR

RS

RS

RS

L7

6-1

98

8(2

)S

RR

SR

RR

RS

SR

SS

L8

3-5

70

(3a)

RS

SS

RS

SS

RR

SS

S

PR

X1

46

-36

(3b

)S

RR

RR

SS

SS

SS

RS

PR

X1

45

-48

(3c)

SR

SR

RS

SS

SS

SS

R

Euphytica (2014) 196:375–384 377

123

prepared by the pulp refining method (Joyong,

Bejing). The slurry was then transferred to 5 mL

syringe for application.

Experimental design

Fifteen seeds of each cultivar/line were planted in

11.5 cm in diameter paper cups filled with a medium

of vermiculite and grass-lime (1:1). Plants were

grown in the greenhouse under a 14 h photoperiod

with temperatures ranging from 25 to 30 �C. For each

series of 34 cultivars/lines evaluated against each

pathotype, the 17 differential lines and the susceptible

Williams were included to verify the success of the

inoculation. The tested cultivars/lines, the differential

lines and Williams were randomized within each

replication. Three replicates of the experiment were

conducted.

Phytophthora inoculation, disease assessment

and gene postulation

Seedlings were inoculated using the hypocotyl inoc-

ulation technique (Haas and Buzzell 1976). An

incision about 1 cm long in the hypocotyl of the

14-day-old seedling below the cotyledonary node was

made and approximately 0.2 mL of inoculum slurry

was placed in the wound. The inoculated plants were

placed in a mist room with a relative humidity of

100 % and an average temperature 25 �C for 2 days.

They were then moved to a greenhouse with an

average temperature of 25 �C.

The resistance phenotype of each cultivar/line to

each P. sojae pathotype was determined based on the

data from the three experimental replications 6 days

post inoculation (DPI). A cultivar/line was classified

as resistant (R) if greater than 70 % of the plants lived.

A cultivar/line was rated as susceptible (S) if less than

30 % of the plants lived. And a cultivar/line was

determined as intermediate (I) type when plants had a

survival range of 30 to 70 % (Chen et al. 2008). The I

reaction was combined with R reaction for classifica-

tion of reaction types according to previous report by

Kyle et al. (1998).

According to the gene-for-gene hypothesis, resis-

tance gene or gene-combination in each cultivar/line

was postulated by comparing their reaction types to

the 26 P. sojae pathotypes with those of the differen-

tial lines with known Rps genes (Chen et al. 2008).Ta

ble

1co

nti

nu

ed

Cu

ltiv

ar(R

ps)

Pat

ho

typ

es

Ps4

1-1

PsA

H3

PsT

A3

PsA

H1

PsF

JP

sJS

9P

sJS

7P

sJS

8P

sMC

1P

sJN

4P

sJS

2P

sAH

6P

s23

L8

5-2

35

2(4

)R

SS

SS

SS

SS

SS

SR

L8

5-3

05

9(5

)S

SS

SS

SS

SS

SS

SS

Har

oso

y6

2X

X(6

)R

SS

SS

SS

SS

SS

SS

Har

oso

y(7

)S

SS

RS

RR

SS

SS

SS

PI3

99

07

3(8

)S

RS

SR

SR

SS

SR

SS

Yo

ub

ian

30

(YB

30)

RS

SS

SS

SS

RR

SS

S

Zao

shu

18

(ZS

18

)R

RR

SS

SS

RS

SR

SR

Yu

do

u2

5(Y

D2

5)

RR

RR

SR

RR

RR

SS

S

378 Euphytica (2014) 196:375–384

123

Statistical analysis

In this study, the data of reaction types of 34 cultivars/

lines to 26 P. sojae pathotypes were further analyzed

and characterized their clustering situation for com-

paring with those of 17 differential lines carried

known Rps genes. The cultivars/lines that had R and I

phenotypes to P. sojae pathotypes challenges were

recorded as ‘‘1’’. The cultivars/lines that had the S

phenotype to P. sojae pathotypes challenges were

recorded as ‘‘0’’. A genetic similarity coefficient

matrix was then used to construct a dendrogram by the

un-weighted pair-group method using the arithmetic

averages (UPGMA) algorithm, and employing the

Sequential, Agglomerative, Hierarchical, and Nested

(SAHN) clustering procedure of the NTSYS-pc ver.

2.11 software (Rohlf 2000).

Results

The reaction types of 17 differential lines and

Williams to 26 P. sojae pathotypes are listed in

Table 1 for comparison with the cultivars/lines

reaction types. Thirty-four cultivars/lines produced

34 different reaction types to the 26 P. sojae

pathotypes (Table 2). The 34 soybean cultivars/lines

evaluated were all resistant to more than 3 P. sojae

pathotypes (Table 2). Seven soybean cultivars/lines

were resistant to between 3 and 9 P. sojae patho-

types, and twenty-one cultivars/lines were resistant

to between 10 and 20 P. sojae pathotypes. Eight

soybean cultivars/lines were resistant to more than

21 of the 26 P. sojae pathotypes. And, most

importantly, one soybean cultivar, Yudou2, showed

resistant to all P. sojae pathotypes (Table 2), which

indicated that Yudou2 was the novel and valuable

material.

The comparison between reaction types of culti-

vars/lines and the differential lines to the 26 P. sojae

pathotypes determined the results of the gene postu-

lation in each cultivar/line (Table 2). Zhoudou17 were

elicited an reaction type RRRRRRSRSRRSRSSS

SSSSSSSSSS to the orderly 26 P. sojae pathotypes,

PsHLJ5, PsHLJ3, PsJMS3, PsJL1-1, PsHLJ1, PsHLJ4,

PsAH4, PsJL4-3, PsGZ2, PsJL3-2, PsSX1, PsJS4,

PsJL4-1, Ps41-1, PsAH3, PsTA3, PsAH1, PsFJ,

PsJS9, PsJS7, PsJS8, PsMC1, PsJN4, PsJS2, PsAH6

and Ps23, which was consistent with the reaction type

of the differential line L85-3059 carrying Rps5.

On this basis, Zhoudou17 was postulated to have

Rps5. In a similar fashion, the cultivar Zheng77249

was postulated to have Rps3a or gene-combination

Rps3a?5, because its reaction type was corresponding

to the differential line L83-570 containing Rps3a or

combination of reaction types of L83-570 and L85-

3059 carrying Rps5. However, it was not possible to

postulate which resistance genes/alleles are present in

the remaining 32 cultivars/lines because their reaction

types were not consistent with any differential line

carrying single previously identified Rps gene or two-

gene combinations. In such cases, more than two

possible Rps gene combinations or unidentified Rps

gene were present due to the novel reaction types of

these 32 cultivars/lines to the 26 P. sojae pathotypes.

Cluster analysis based on the reaction types

revealed 10 arbitrary groups, A, B, C, D, E, F, G, H,

I, and J among the 34 soybean cultivars/lines, 17

differentials and the cultivar Williams at the similarity

coefficient 0.6540 (Fig. 1). Group A included only one

cultivar Williams, which was susceptible to the 26

P. sojae pathotypes Group B had three cultivars

including differential lines, Harlon (Rps1a), Wil-

liams79 (Rps1c), and Williams82 (Rps1k). Group C

included two differential lines, Harosoy13XX (Rps1b)

and Harosoy (Rps7). Groups E, F, G, I and J also

included cultivars Yudou27, Zheng120, Yudou 6,

Shandongsijiaoqi (Sdsjq) and Yudou21, respectively,

which were respectively resistant to 8, 9, 8, 3, 3

P. sojae pathotypes. And two lines Zheng90007 and

Zheng87260 fell into group H.

Among the 10 groups, group D was the biggest one,

including 2 cultivars/lines (Zhoudou17 and

Zheng77249) with postulated known Rps genes, 25

cultivars/lines with unknown Rps genes, and 12

differential lines. The 25 cultivars/lines formed sev-

eral subgroups in this study. Anyway, based on the

coefficient, Zheng135 and Zaofeng1 shared a higher

similarity with PI 103091 (Rps1d). Yudou18 and

Zhoudou18 shared a higher similarity with L83-570

(Rps3a), and Yudou22 shared the higher similarity

with L85-2352 (Rps4) and Harosoy62XX (Rps6).

Chihuangdou shared a higher similarity with L85-

3059 (Rps5). Yudou3, Yudou12, Zheng85558 and

Yudou11 shared a higher similarity with PRX146-36

(Rps3b) and PRX145-48 (Rps3c). The 3 cultivars/lines

Yudou13, Yudou15, Yudou29 shared a higher simi-

larity with Yudou25 (RpsYD25).

Euphytica (2014) 196:375–384 379

123

Discussion

Following the Flor’s hypothesis (Flor 1955), the

method of gene postulation by the gene-for-gene

specificity to hypothesize which resistance gene might

be present in the cultivar/line has been used widely to

search the resistance gene in some major crops, such

as leaf rust resistance genes in wheat cultivars (Yuan

Table 2 Reactions of 34 soybean cultivars/lines to 26 Phytophthora sojae pathotypes and postulated Rps genes

Cultivar/line Pedigree of cultivar/line Reaction typea No. of

resistance to

pathotypes

Postulated

gene

Qihuang1 Not available RRRRRRRSRSRRRRSRRRRRRRRSSR 21

Qihuang13 Qihuang1/Yeqi1 RRRRRRRRRRRRRRRRRRRRRRRSRR 25

Zheng7104 Qihuang13/Miyangshuibaidou RRRRRRRRRRRRRRRRRRRRRRSSRR 24

Shandongsijiaoqi Not available SSSRRSSSSSSSSSSSSSSSSRSSSS 3

Zaofeng1 Juxuan23/5905 RRRRRSRRRRSRRSRSSRSSSRSSSS 14

Zheng135 Shandongsijiaoqi/Zaofeng1 RSRRRSRRRRRSRSSSSRSSSRSSSS 12

Zheng77249 Zheng135/Sidou2//Zheng7104/Xudou1 RRRRRRSRRRRRRRSSSRSSSRRSSS 16 Rps3a?5

Yudou3 Zheng135/Sidou2 RRRRRRRRRRRRRSRRRRSSSRSSSS 18

Yudou2 Zheng7104/Huaxiandalvdou RRRRRRRRRRRRRRRRRRRRRRRRRR 26

Zheng84285 Yudou2/line (un-named)//Zheng77249 RRRRRRSRRRRSRRSSSSSSSSRRSS 14

Yudou12 Yudou2/Zhengchangjiao10//You82-10 RRRRRSRRRRRRRRRRRRSSSRRSSS 19

Yudou11 Zheng77249/Kai80-7 RRRRRRRRSRRSRRRRRSSSSRRSSS 17

Yudou15 Zheng77249/Yi7914-3-1 RRRRRRRRRRRRRRRSRSRRRRRSSR 22

Yudou18 Zheng77249/Yuejin5//Zhongdou19 RRRRRRSRSRRRRRSSSSSSSRRSSS 14 Rps5??

Yudou13 Zheng77249/Yuejin5//Haijiao07 RRRRRRRRRRRSRRRSRSRRRRRSSS 20

Yudou23 Yudou13/Lu851 RSRRRRRRSSRRRRRRRSRRRRRSSS 19

Zheng120 Yudou23/Kefeng35//Yudou22/Yudou10 SSRRSSSRRSRSRRSSSSSSSRRSSS 9

Zheng90007 Yudou18/Zheng84285 RSRSRSSSSRSSRSSSSSSSSRSSSS 6

Yudou22 Yudou18/Zheng84174 RRRRRRSRSRRRRRSSSSRSSSSSSS 13 Rps5??

Zhoudou17 Yudou22/Zhou94(23)-111-5 RRRRRRSRSRRSRSSSSSSSSSSSSS 10 Rps5

Yudou21 Yudou10/Yudou6 SSRRSSSRSSSSSSSSSSSSSSSSSS 3

Chihuangdou Not available RRRRRSSRRRRSSSSSSRSSSSSSSS 10

Yudou24 Yudou10/Yudou15 RSRRRRRRRRRRRRRRRSRRRRRRSR 23

Zhoudou11 Yudou24/Yudou11 RSRRRRRRRRRRRRRSRSRRRRRSSR 21

Zhoudou12 Yudou24/Yudou12 RRRRRRRRRRRRRRRSRSRRRSRRSS 21

Zheng97196 Yudou25/Zheng93048 RSRRRRRRRRRRRRRSRSRSRRRSSR 20

Zheng92116 Yudou25/Zheng506 RRSRRRRRSRRRRRRSRSRRRRRSSR 20

Yudou6 Shang7608/Zhou7312 SRRRRSRSRSRSSSSSSRSSSSSSSS 8

Yudou26 Yudou6//Yudou10/S0114 RRRRRRRSRSRRRRSSSSSSSSRSSS 13

Yudou27 Zheng86481/Zheng85212 SSRRSRSRSRSSRRSSSRSSSSSSSS 8

Zheng87260 Zheng80024/Zhengchangjiao01 RSRRRRSSSSSSRSSSSSSSSRSSSS 7

Yudou29 Zheng87260/Zheng85212 RRRRRRRRRRRRRRRSRSRRRRRSSS 21

Zhoudou18 Zhou9521-3-4/Zheng94059 RRRRRRRRSRRRRRSSSSSSSRRSSS 15

Zheng85558 Not available RRRRRRRRRRRRRRRSRRSSSRRSSS 19

a Means: The reaction type is a combination of all resistance phenotype of a soybean cultivar/line to 26 P. sojae pathotypes, PsHLJ5,

PsHLJ3, PsJMS3, PsJL1-1, PsHLJ1, PsHLJ4, PsAH4, PsJL4-3, PsGZ2, PsJL3-2, PsSX1, PsJS4, PsJL4-1, Ps41-1, PsAH3, PsTA3,

PsAH1, PsFJ, PsJS9, PsJS7, PsJS8, PsMC1, PsJN4, PsJS2, PsAH6 and Ps23 in given order

380 Euphytica (2014) 196:375–384

123

et al. 2007), powdery mildew resistance genes in

wheat varieties (Cao et al. 2010), and Phytophthora

resistance genes in soybean (Chen et al. 2008; Xia

et al. 2011a, b). In this study, the gene Rps5 was

postulated to be present in Zhoudou17, and the gene

Rps3a or gene combination Rps3a?5 was postulated

in Zheng77249. The other 32 reaction types produced

in the remaining 32 cultivars/lines reacting to the 26

Fig. 1 Dendrogram of the 34 soybean cultivars/lines, 17

differential soybean lines with known Phytophthora resistance

genes in soybean and Williams, the control line for inoculation

efficiency, using the un-weighted pair-group method with

arithmetic averages (UPGMA) cluster analysis method. The

Sdsjq in this figure is the abbreviation of cultivar

‘‘Shandongsijiaoqi’’

Euphytica (2014) 196:375–384 381

123

P. sojae pathotypes were distinct from the known

Rps genes, which deduced that the 32 cultivars/lines

possessed novel Rps gene or gene combination.

Lohnes et al. (1996) evaluated the reactions of 726

accessions from China to four races of P. sojae and

found that there were a large number of Phytophthora

resistant accessions in central China, especially in

Anhui provinces. Kyle et al. (1998) also found that a

high frequency of Phytophthora resistant accessions

from southern China, including Hubei, Jiangsu and

Sichuan provinces were resistant to different P. sojae

pathotypes. Xia et al. (2011a) reported that 80.13 % of

156 tested soybean resources were resistant at least

one of 13 P. sojae pathotypes and 90 different reaction

types were elicited in their study. Thus, it is apparent

that Phytophthora resistance was relatively common

in Chinese soybean germplasms. Some soybean

cultivars/lines from the Henan province were also

included in the evaluation by Chen et al. (2008) and

Tang et al. (2010). The results of this research

combining with previous studies indicated that soy-

bean cultivars/lines bred in this region had broad

spectrum resistance to P. sojae. Due to the appeared

numerous reaction types, it was proposed that Phy-

tophthora resistance of soybean in Henan province

was extremely diverse.

Depending solely on the reaction types, it was

difficult to postulate resistance genes for all of the

soybean cultivars/lines. With the addition of the

pedigree, we could postulate the resistance genes

present in some soybean cultivars/lines. The pedigree

of Yudou 18 was bred though Zheng77249/Yuejin5/

Zhongdou19 (Table 2). Zheng77249 and derived

Yudou 18 were different in the susceptibility/resis-

tance to pathotypes PsGZ2 and PsFJ, thus Yudou18

could contain the Rps3a or Rps3a?5, or other new Rps

genes combination due to the genetic backgrounds.

And Yudou22 was bred though Yudou18/

Zheng84174. Yudou 18 and derived Yudou22 were

different in reaction type to pathotypes PsJS9, PsMC1

and PsJN4, so the different Rps genes might also be

present in both cultivars. In this study, Zhoudou17

derived from Yudou22 was postulated to contain

Rps5. Therefore, Rps5 was taken as the most likely

gene present in both Yudou22 and Yudou18. In such

cases, we can conclude that the other novel Rps gene

conferring the resistance was also present in Yudou22

and Yudou18 to explain the phenotype. Based on the

pedigree information, we can also speculate the origin

of the Rps gene. Yudou2, Zheng7104, Qihuang13 had

highly similar reaction types, which was the descen-

dant of Qihuang1 with broad spectrum-resistance.

Hence we proposed that Yudou2, Zheng7104 and

Qihuang13 originated from the Qihuang1 might have

one of the same novel Rps genes conferring the

resistance. The difference in resistance might be

caused according to the breeding objective of soybean,

seed yield, seed quality, plant types, lodging resis-

tance, drought tolerance and SMV resistance rather

than Phytophthora resistance. It might induce the

diversity of Phytophthora resistance occurred in this

region. In another case, the excellent characters of the

cross parent might be integrated into the descendant of

the pedigree, which might also contained the Rps gene.

Maybe cultivars/lines contain several resistance genes

or novel Rps genes, which could lead to the resistance

with broad spectrum (Cao et al. 2010).

In theory, both host and pathogen have coevolved

in one region over a long period of time and this

protracted association has led to diversity. Large

quantities of soybean cultivars/lines developed from

Henan province, one of the soybean origins in China,

have been screened for PRR resistance (Chen et al.

2008; Tang et al. 2010; Xia et al. 2011a), though there

has no report about PRR in this region. Maybe the

broad spectrum of Phytophthora resistance in soybean

cultivars prevents P. sojae infection and the symptoms

of PRR do not appear. This information also provides a

rationale for collecting P. sojae pathotypes to inves-

tigate PRR. By researching the diversity of avirulent

gene in P. sojae pathotypes, the relationship between

the soybean resistance and P. sojae in this region will

be better explored.

In previous studies, Chen et al. (2008) reported that

Zhoudou12, Yudou29, and Zheng97196 contained the

postulated gene combination Rps1c?8 or Rps1k?8.

Yudou23 and Yudou26 contained an unknown Rps

gene, and Yudou21 did not confer resistance to 12

P. sojae pathotypes. Tang et al. (2010) postulated that

Yudou 26 contained the gene Rps5. They determined

that Zheng135 was susceptible to six P. sojae path-

otypes, and that Zhoudou11, Qihuang1, and Yudou12

elicited new reaction types that might contain novel

Rps genes. However, Xia et al. (2011a) suggested that

Qihuang1 and Yudou12 might contain two-gene

combinations. The above cultivars/lines also evalu-

ated in this study had been postulated to carry

the unknown Rps genes. The difference in gene

382 Euphytica (2014) 196:375–384

123

postulation may be caused by the different P. sojae

pathotypes used in different studies (Chen et al. 2008;

Tang et al. 2010; Xia et al. 2011a). There are still some

cultivars/lines generated novel reaction types in Xia’s

report and in our study, such as Yudou18, Yudou22

and Zaofeng1. It is conceivable that these cultivars

contain new Rps gene. In this study, the differential

lines were resistant to only between 9 and 21

pathotypes, but some cultivars/lines tested could

provide resistance to more than 21 P. sojae patho-

types, including Yudou2, Qihuang13, Zheng7104,

Yudou24 and Yudou15, which explained their broad

spectrum resistance. Moreover, we found that most of

cultivars/lines showed novel reaction types which

suggested that these cultivars might carry novel Rps

genes. Therefore, results of gene postulation indicate

that Phytophthora resistance genes can be an alterna-

tive way for screening soybean cultivars, and can be

useful for evaluation of differential set.

Once resistance of the cultivars/lines are identified,

inheritance studies will be necessary to further identify

the nature of their resistance for verifying whether the

source contains a truly ‘‘novel Rps gene’’. Then, the

confirmed novel gene(s) would provide an alternative

management strategy of resistance in soybean breed-

ing programs for soybean breeders in the future.

Acknowledgments We thank Professor Li Weidong and

Dr. Weiguo Lu (Henan Academy of Agricultural Sciences,

China) for providing the soybean cultivars/lines used in this

study. The work was supported by the Special Fund for Agro-

scientific Research in the Public Interest (201303018) and the

Program of Protection of Crop Germplasm Resources (NB2010-

2130135-25-14) from the Ministry of Agriculture of the

People’s Republic of China.

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