Sarocladium oryzae (Sawada) W. Gams & D. Hawksworth

California Pest Rating for
Sarocladium oryzae (Sawada) W. Gams & D. Hawksworth
Pest Rating: A

 


PEST RATING PROFILE
Initiating Event:

In August 2014, during a routine Controlled Import Permit inspection, Anthony Jackson, USDA APHIS PPQ WR, sampled rice seedlings imported from Spain and grown under post quarantine permit conditions in a greenhouse in Pleasant Grove, Sutter County, California.  A fungal pathogen, Sarocladium oryzae was detected in the sampled seedlings and identified by Cheryl Blomquist, plant pathologist, CDFA.  This identification marked the first detection of S. oryzae in California.  Later, in October 2014, the same pathogen was again detected by Suzanne Latham, plant pathologist, CDFA, in rice seedlings grown in the same Pleasant Grove greenhouse.  Subsequently, all post quarantine rice seedlings held at the greenhouse were destroyed by steam sterilization at the CDFA Plant Pathology Laboratory.   The fungal pathogen was assigned a Q (temporary) rating which is reassessed herein for the proposal of a permanent rating.

History & Status:

Background:  Sarocladium oryzae is a fungal pathogen that causes the sheath rot of rice disease.  Historically, the pathogen was initially described as Acrocylindrium oryzae by Sawada in 1922 from Taiwan.  In 1956, a species which caused symptoms similar to Sarocladium oryzae, was named by Gams and Hawksworth as S. attenuatum.  However, genetic and biochemical analyses revealed no differences between S. oryzae and S. attenuatum and subsequently the latter species was declared a synonym of S. oryzae (Bridge et al., 1989).  Sarocladium oryzae belongs to the order Hypocreales in the class Sordariomycetes, Phylum Ascomycota.

Hosts: Oryza sativa (rice) is the main host. However, rice cultivars differ in their susceptibility to the pathogen.  Other naturally infected hosts include O. rufipogon (wild rice) and grasses: Hymanchne assamica, Leersia hexandra, Panicum walense.  Other hosts include monocot weeds found in rice fields which may serve as a natural source of inoculum for infection of rice: Cyperus iria (rice flat sedge), C. tenneriffae, C. difformis (small-flowered nut sedge), Echinochloa crus-galli (barnyard grass), Eleusine indica (goose grass) and Monochoria vaginalis.  Also, Echinochloa colona (jungle rice)Other monocot agricultural crops include millets, sorghum and maize. Several weeds and wild rices are included experimental, greenhouse-tested hosts (CABI, 2014; EPPO, 2014).

Symptoms:  The pathogen mainly attacks the uppermost leaf sheaths which enclose young panicles at the booting stage.  Lesions develop, initiating as irregular spots 5-10 mm, which become dark lesions, sometimes oblong, with brown margins and light-brown centers or grayish-brown throughout. Lesions may coalesce and cover most of the leaf sheath.  Young lesions bear whitish, powdery fungal growth on the outer and inner sides of affected sheaths, while old lesions have less or no fungal growth and appear as dry, brownish lesions with the enclosed rotted panicle. When infected early, young panicles remain compressed within the sheath, do not develop and rot, or only partially emerge from the sheath.  Outside the rotted sheath, partially emerged spikelets/grains are dark brown, chaffy and partially filled.

Infected seeds are usually symptomless and germinate normally.  Sometimes, primary and secondary leaves wither prematurely due to S. oryzae infection (CABI, 2014).

Damage Potential:  In India, rice yield losses of 10-26% and 50% are reported (Chakravarty and Biswas, 1978; CABI, 2014).  In Taiwan, 3-20% incidence of sheath rot disease have been observed reaching 85% in susceptible varieties.  Losses include production of fewer spikelets per panicle, lower grain weight of diseased panicles, and increased grain chaffiness. In India, 70% disease severity with 15-35% grain chaffiness, and 100% seed sterility in severe cases has been reported (CABI, 2014).

Disease Cycle: Sarocladium oryzae survives as mycelium on and in seeds.  Fungal inoculum or spores (conidia) from several infected weed hosts are capable of infecting rice.  The pathogen invades rice through the stomata and wounds and grows intercellularly within vascular and mesophyll tissues.  Additionally, wounds created in rice plants facilitate infection and disease development.  This is particularly true of wounds caused by mites, stem borers, mealy bugs, and rice bug.  The incidence and severity of sheath rots of rice disease is favored at 20-30°C and 65-85% relative humidity.

Transmission:  Seed – the pathogen is externally and internally seedborne.  Sachan and Agarwal (1995) found S. oryzae within the seedcoat, endosperm and embryo of discolored seeds however the pathogen may also be detected on seeds that are not discolored. S. oryzae may also be spread through infected straw and plant parts – leaves, seeds, flowers, inflorescences, cones, and calyx.

Worldwide DistributionAfrica:  Burundi, Cameroon, Cote d’Ivore, Gambia, Kenya, Madagascar, Niger, Nigeria, Senegal, Tanzania; North America: Mexico, USA; Central America: Cuba; South America: Argentina, Brazil, Colombia, Venezuela; Asia:  Bangladesh, Brunei Darussalam, China, India, Indonesia, Iran, Japan, Malaysia, Nepal, Pakistan, Philippines, Saudi Arabia, Sri Lanka, Taiwan, Tajikistan, Thailand, Uzbekistan, Vietnam, Oceania: Australia.  In the USA it is reported as being widespread, and specifically present in Louisiana (CABI, 2014; EPPO, 2014).

Official Control: Sarocladium oryzae is on the “Harmful Organism List’ for Honduras and Peru (PCIT, 2014). The species is currently listed as a Q rated pest for California.

California Distribution: Sarocladium oryzae is not present in California.

California Interceptions:  Prior to its current detection in Sutter County (see ‘Initiating event’) Sarocladium oryzae has not been detected in incoming plant shipments to California.

The risk Sarocladium oryzae would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

High (3) likely to establish a widespread distribution in California.

Risk is High (3) – If allowed to enter California, Sarocladium oryzae is capable of establishing a widespread distribution in the States rice cultivated acreage.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Medium (2) Rice is the major host of the pathogen and is grown in significant acreage in California.  Other hosts include several weeds that are capable to harboring inoculum for rice infections.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

High (3) has both high reproduction and dispersal potential.

Risk is High (3) – Long distance spread is mainly through infested seed.  Infected plant parts and rice straw also serve as significant means of spread.  Potentially, conidia may be moved over short distances via winds, and wind-blown water droplets.  

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

High (3) causes 3 or more of these impacts.

Risk is High (3) – The pathogen could significantly impact rice production in California by lowering crop yield and value which would result in the loss of markets.  Additionally, certain species of mites and stem borers have been reported to harbor large numbers of fungal spores (conidia) and spread the pathogen to non-infected plants thereby, increasing the incidence of the sheath rot of rice disease.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2) – Several species of natural grasses and wild rice are hosts of Sarocladium oryzae. If these hosts are infected they may significantly impact the ecosystem of a natural environment. 

Consequences of Introduction to California for Sarocladium oryzae:

Add up the total score and include it here. (Score)

-Low = 5-8 points

-Medium = 9-12 points

High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Sarocladium oryzae to California = (13).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is not established (0).

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 13.

Uncertainty:

Sarocladium oryzae has not been previously detected in California.  The initial detection recorded in this report was made in a greenhouse and subsequently all rice plants within the greenhouse were destroyed.  No targeted surveys of natural environments, rice fields or seed rice storage facilities have been conducted for the detection of this pathogen within California.  If detected, the proposed rating may alter.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the sheath rot of rice pathogen, Sarocladium oryzae is A.

References:

CABI.  2014.  Sarocladium oryzae full datasheet report.  Crop Protection Compendium.  www.cabi.org/cpc/.

Chakravarty, D. K, and S. I. Biswas. 1978. Estimate of yield loss in rice affected by sheath rot. Plant Disease Reporter, 62:226-227.

EPPO.  2014.  Sarocladium oryzae (SARMOR).  European and Mediterranean Plant Protection Organization PQR database.  http://www.eppo.int/DATABASES/pqr/pqr.htm.

Farr, D.F., & Rossman, A.Y. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved December 4, 2014, from http://nt.ars-grin.gov/fungaldatabases/.

Groth, D.  1992.  Sheath rot.  In, Compendium of Rice Diseases edited by R. K. Webster and P. S. Gunnell.  The American Phytopahtological Society, Minnesota, USA: 25.

PCIT.  2014.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp .

Sachan, I. P., and V. K. Agarwal. 1995. Seed discolouration of rice: location of inoculum and influence on nutritional value. Indian Phytopathology, 48(1):14-20; 17 ref.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.


Comment Period:

The 45-day comment period opened on Monday, October 12, 2015 and closed on November 26, 2015.


Pest Rating: A


Posted by ls