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Date: Wed 3 Jun 2009
Source: South Asia Partnership Pakistan, The Dawn report [edited] <http://sappk.wordpress.com/2009/06/03/spot-blotch-a-new-wheat-crop-disease/>

Spot blotch: a new wheat disease

Farmers in Sindh found that the yield was contrary to their [high] expectations. A large number of growers from Punjab are also reported to have disease [in their crops]. Some areas have been badly affected with significant losses in yield, while other areas are less affected.

Losses depend on various factors such as early start of disease, late planting, varieties sown, temperature and humidity, etc. Most of the crops planted late have been affected seriously. The losses due to this problem have been estimated at about 2 million tons, or between 8-10 percent.

The author travelled to various farms in Sindh and Punjab in March and early April [2009]. The symptoms included black irregular spots on leaves. The affected leaves looked as if they were dried and devoid of chlorophyll. Powder of leaf rust was not observed in the wheat fields. Powdery mildew was also not serious in the affected areas.

Samples of leaves from different districts were sent to the National Agricultural Research Centre, Islamabad. The disease was identified as "_Bipolaris sorokiniana_" spot blotch, also known as helminthosporium leaf blight (HLB). It mostly occurs in India, Bangladesh, and Nepal. In Pakistan, it was observed on a small scale in the past. It re-appeared here during 2008/2009. HLB is a seed, soil and air borne disease. The current occurrence seems to be air-borne with origin of spread presumably being coastal areas of India and Bangladesh.

It is not possible to eliminate the most susceptible wheat variety "Bhakkar-02" which is covering about 50 percent of the area in southern Punjab and Sindh. Spot blotch can be controlled in the most effective and cheapest way by the introduction of resistant wheat varieties. During the visit it was observed that 4 wheat varieties, that is, TJ-83 and TD-01 from Sindh, and Serhar-06 and Fareed-06 from Punjab had the ability to resist this disease. Seed treatment should be applied strictly for its control in future.

[Byline: Manzoor Hussain]

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[Spot blotch of wheat and barley is caused by different strains of the fungus _Cochliobolus sativus_ (synonym _Bipolaris sorokiniana_).
The pathogen is also associated with root rot, seedling and head blights, and black point of kernels. It causes significant yield losses in both crops and has been recognised as the major disease constraint to wheat cultivation in the warmer eastern plains of South Asia. Infection early during the cropping cycle leads to more serious losses, and plants subject to other stress factors are more susceptible. Outbreaks are favoured by warm temperatures and high relative humidity.

The fungus survives on crop debris, and several grass species may serve as reservoir hosts. Spread occurs with infected seeds, soil or other material, and by wind. For disease management an integrated approach is recommended including crop rotation, cultural practices, removal of pathogen reservoirs, fungicide treatments of seed and crops, and use of resistant crop varieties.

In the story above, India and Bangladesh are suggested as likely sources of the emergence of spot blotch in Pakistan. However, since no facts are presented it cannot be excluded that the current outbreak may have originated from other areas or even from infected seed.

Maps of Pakistan:
<http://www.lib.utexas.edu/maps/middle_east_and_asia/pakistan_pol_2002.jpg>
and <http://healthmap.org/r/00tj>

Pictures of spot blotch symptoms
Wheat leaves:
<http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm2394/$FILE/c85.jpg>,
<http://www.cropdiseasescouncil.ca/image/diseases/spot-blotch.jpg>, and <http://gallery.cimmyt.org/main.php?g2_itemId=997>
Wheat head:
<http://gallery.cimmyt.org/main.php?g2_itemId=1000>
Barley plants:
<http://www.ipmcenters.org/cropprofiles/docs/Graphics/WAbarleySpotBlotch.jpg>
Infected kernels (black point):
<http://ipm.illinois.edu/diseases/series100/rpd115/115-2.gif>

Links
Information on spot blotch of wheat and barley:
<http://ohioline.osu.edu/ac-fact/0051.html>,
<http://www.lumrix.net/health/Spot_blotch_(wheat).html>,
<http://www.ipmcenters.org/cropprofiles/docs/wabarley.html>,
<http://ipm.illinois.edu/diseases/series100/rpd115/index.html>,  and <http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm2394>
_Cochliobolus sativus_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=285403>.
- Mod.DHA]