This document discusses Phytophthora soybean root and stem rot (PSRSR), a major soilborne disease of soybeans caused by the oomycete Phytophthora sojae. PSRSR can attack all parts of the soybean plant and causes symptoms like seed rot, damping off, root and stem rot, stunted growth, and yield losses up to 50%. The disease cycle of P. sojae is described. Resistance to PSRSR in soybeans can take the form of R-gene mediated resistance, partial resistance, or root resistance. Combining different resistance mechanisms, such as partial resistance and R-gene resistance, provides the best protection against this widespread and damaging disease.

1. RESISTANCE AGAINST
PHYTOPHTHORA ROOT AND STEM
(PSRSR) ROT OF SOYBEAN
RUFUS AKINRINLOLA

2.  FOCUS:
 PSRSR and impact on soybean
 The disease cycle of PSRSR
 Resistance to PSRSR
 Conclusion

3.  PSRSR AND IMPACT ON SOYBEAN
 Phytophthora soybean root and stem rot (PSRSR)
 PSRSR is caused by Phytophthora sojae
 First discovered in 1948 Indiana
 PSRSR is a soilborne disease
 Affects all stages of growth
 Optimum temperature: 25-30°C
 Favored by high humidity and rainfall
Dorrance et al, 2007

4.  PSRSR AND IMPACT ON SOYBEAN
 Impacts on soybean
 PSRSR could attack all soybean parts
 PSRSR causes seed rot, seedling damping off, root and stem
rot.
 Causes stunted growth and reduced standing
 Yield loss may be up to 50%
 PSRSR could wipe out susceptible varieties
 PSRSR destroys upto 300 000acres of soybean in Ohio (1970s)
 Worldwide annual loss close to $2 billion (Tyler, 2007) Dorrance et al, 2007

5.  PSRSR AND IMPACT ON SOYBEAN: symptoms
Dorrance et al, 2007
Stem rotSeedling damping
off
Root rot
Stunted growth and reduced standing
Tyler, 2007

6. Spring
Under favorable
wet high
moisture and
warm
temperature
conditions
oospores
germinate and
form mycelia
Mycelia
produce
sporangia
which
releases
zoospores
DISEASE CYCLE PHYTOPHTHORA SOJAE
Causing the Phytophthora root and stem rot
(PRSR) of Soybean
(Glycine max).
Rufus Akinrinlola PLPT
Dead infected
plants residues
remain in the soil
and overwinter
for the next
growing season
Wind and rain splash spread
sporangia and other infective
propagules from infected plant
to initiate secondary infection
in uninfected susceptible host
Secondary
inoculum source
Summer
Fall
Oospores
overwinter in
soil and
debris during
hatch
conditions
Oogonium form by sexual crossing
of hypha and produces the survival
oospores in the soil
Winter
Zoospores swim
towards root
exudates of young
soybean root tips
initiating primary
infection
Attachment, encystment and penetration on
zoospores into root surface induce root rot
and hyphal colonization of the stem induces
stem rot
Hyphal tips of
Mycelia can also colonize
root tips and induce
infection
25 -
30°C
Optimum
temperature

7. Plant
description
polycycl
ic

8.  RESISTANCE TO
PSRSR
 R-GENE MEDIATED RESISTANCE.
 ROOT RESISTANCE.
 PARTIAL RESISTANCE.
Dorrance et al, 2007

9.  RESISTANCE TO PSRSR
R-gene mediated resistance.
 Involves 14Rps
 Expressed as HR
 It’s race specific
 Active from germination
Wu et al, 2010; Dorrance et al, 2007

10.  RESISTANCE TO PSRSR: R-gene mediated resistance

11.  RESISTANCE TO
PSRSR
Partial resistance.
 Race non-specific/horizontal tolerance
 It’s stable and heritable
 It’s a multi-genic trait
 Limits lesion expansion
 Limits severity of root rot
 Limits yields losses Dorrance et al, 2007; Wu et al, 2010

12.  RESISTANCE TO
PSRSR
Root resistance
 Expressed in the root
 It is quantitatively inherited
 It is an incomplete resistance
 It involves several genes

13.  CONCLUSION
 Phytophthora soybean root and stem rot is a major soilborne disease of soybean
 Annual losses due to the disease worth $2billion
 It affects all parts of soybean
 The disease is polycyclic in cycle and mostly initiated by zoospores
 It’s majorly controlled through resistant varieties
 R-gene resistance, partial and root resistance are the major resistance
 Commination of both partial and R-gene mediated resistance gives the best protection

14. QUESTIONS
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15.  REFERENCES
 Dorrance, A. E., Robertson, A. E., Cianzo, S., Giesler, L. J., Grau, C. R., Draper, M. A., ... & Anderson, T.
R. (2009). Integrated management strategies for Phytophthora sojae combining host resistance and seed
treatments. Plant Disease, 93(9), 875-882.
 Dorrance, A. E., Mills, D., Robertson, A. E., Draper, M. A., Giesler, L., & Tenuta, A. (2007). Phytophthora
root and stem rot of soybean. The Plant Health Instructor, 1.
 Tyler, B. M. (2007). Phytophthora sojae: root rot pathogen of soybean and model oomycete. Molecular
plant pathology, 8(1), 1-8.
 Wu, X. L., Zhao, J. M., Sun, S., Yang, F., Wang, Y. C., Gai, J. Y., & Xing, H. (2010). A survey of soybean
germplasm for resistance to Phytophthora sojae. Euphytica, 176(2), 261-268.