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Date: February 1, 2008
Source: The Statesman [edited]
<http://www.thestatesman.net/page.arcview.php?clid=23&id=215566&usrsess=1>

Drizzling and prolonged foggy weather caused extensive damage to thousands of hectares of potato cultivation in Birbhum [district] this year [2008]. The district expected 20 lakh [2 million] tonnes of production but according to the district agricultural authority, production would be reduced by a huge percentage due to the rough weather right before harvesting. Adding to the problem, a bulk of the produce has become victim to the late blight, leafroll virus, and bacterial wilt.

Birbhum cultivated more than 20 000 hectares (49 421 acres) of potato across 19 blocks, but this year [2008] the cultivation area has been increased by 5000 hectares (12 355 acres). According to a senior agricultural officer of Birbhum: "10 out of 19 blocks are worst hit due to the calamity. Though the disease was curable to some extent, the stored produce got badly damaged." He also said that [district] officials have already visited several blocks recently to prepare a final report on the damage. The potato farmers of the district alleged that due to ignorance of such diseases they are incurring huge loss every year. "Potato cultivations need proper treatment on time to prevent damages from such diseases but due to lack of proper guidance from the district agricultural department the farmers are facing difficulties to deal with these diseases," alleged a farmer.

Mr Prasun Kanti Ghosh and Mr Joydev Fulmali research scholars of Visva-Bharati's Agricultural department, who are doing research work of potato in different fields said, "The farmers need to observe the symptoms of the diseased plants regularly and then consult with the agricultural officers for proper treatment of the diseases."

[Byline: Sabyasachi Roy]

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Late blight

Potato late blight (PLB) is caused by the fungus _Phytophthora infestans_, which can also infect other solanaceous crops such as tomato or eggplant. It is one of the most important potato diseases worldwide affecting both leaves and tubers. It is favoured by cool, moist conditions. The fungus is spread by plant material (including seed tubers), wind and water. Solanaceous weeds can serve as pathogen reservoirs. Other fungi and bacteria often invade blight-infected tubers resulting in total tuber breakdown. Late blight is a concern in many countries because new and even more virulent strains are emerging, some of which can destroy a potato plant within hours.
Disease management includes preventative fungicide treatments of seed tubers as well as fungicide sprays of crops. In India, infected seed potatoes are typically the main source of disease inoculum, and losses of up to 75 percent have been reported previously in some areas. Several PLB resistant varieties are being deployed around the country and a forecasting model has been developed to determine the timing of fungicide applications.

Leafroll

_Potato leafroll virus_ (PLRV; genus _Polerovirus_) is a destructive pathogen causing reduction in yields and poor quality tubers.
Symptoms include curling and chlorosis of leaves and stunting of plants. In storage, infected tubers often develop "net necrosis"
(brown strands beneath the skin), depending on potato cultivar and storage conditions. PLRV can also affect tomato and a number of solanaceous and cruciferous weeds. The virus is transmitted by aphids, with _Myzus persicae_ being the most efficient vector, as well as seed tubers. Chronically infected plants growing from infected tubers are a main source of PLRV in commercial potato fields. Disease management includes clean planting material, removal of pathogen and vector reservoirs (volunteer potatoes, weeds), phytosanitary measures, and vector control. Potato cultivars with different levels of susceptibility to PLRV, including some which do not develop net necrosis, are available.

Bacterial wilt

This disease is also called brown rot and is caused by _Ralstonia solanacearum_ race 3, which is widely distributed in warm temperate areas. The effect on food- and seed-potato industries can be substantial, and tomato crops are also susceptible. Symptoms include wilting, stem discolouration, brown internal staining of tubers, and plants may die. Symptom expression is favoured by temperatures above
15 deg C (59 deg F). The bacteria may also latently infect tubers without causing symptoms and can survive in seed tubers during storage. The pathogen is spread by mechanical means (including insects), contaminated equipment, infected plant material (including seed tubers), and water. Solanaceous and other weeds and volunteer potatoes may serve as pathogen reservoirs. Yield losses are mostly caused by tuber rotting and, in many warmer areas of the world, brown rot is one of the main limiting factors in potato production.

Although the weather patterns have obviously been very unfavourable for the crop, there appear to be some problems that need to be addressed urgently in the region. These seem to include the use of infected seed tubers, lack of efficient phytosanitary measures, and suboptimal control of pathogen reservoirs. The call for more training and support for the local farmers also appears to be justified.

Maps
India:
<http://www.globalsecurity.org/military/world/india/images/IndiaMap_tourism.gif> 
and
<http://healthmap.org/promed?v=22.9,79.6,5>
West Bengal districts:
<http://www.mapsofindia.com/maps/westbengal/westbengal-district.htm>
Assorted maps of Birbhum via:
<http://birbhum.gov.in/MAPS/Map_index.html>
Worldwide distribution of _R. solanacearum_ race 3 (September 2006):
<http://www.eppo.org/QUARANTINE/bacteria/Ralstonia_solanacearum_race3/PSDMS3_map.htm>

Pictures
PLB symptoms:
<http://www.sciencedaily.com/images/2007/01/070102132649.jpg>  (tuber) and
<http://www-biol.paisley.ac.uk/bioref/Chromista/potato_blight.jpg>  (leaf)
PLRV symptoms:
<http://www.gov.mb.ca/agriculture/crops/potatoes/images/bda04s07-p27.jpg> 
(tuber) and
<http://www.gov.mb.ca/agriculture/crops/potatoes/images/bda04s07-p26.jpg> 
(leaf)
Brown rot symptoms:
<http://www.eppo.org/QUARANTINE/bacteria/Ralstonia_solanacearum/PSDMSO_images.htm> 
and
<http://www.redepapa.org/murcha.jpg>

Links
Late blight information, history and background:
<http://www.apsnet.org/online/feature/lateblit/>,  and
<http://www.olympusmicro.com/micd/galleries/brightfield/potatoblight.html>
Management of potato diseases including early and late blights:
<http://archives.eppo.org/EPPOStandards/PP2_GPP/pp2-02-e.doc>
Late blight information and resources via:
<http://www.potato.org.uk/department/knowledge_transfer/fight_against_blight/advice_blight.html>
_P. infestans_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=232148>
Information on PLRV:
<http://www.wsu.edu/~potatoes/leafroll.htm>  and
<http://www.uidaho.edu/ag/plantdisease/potnet1.htm>
PLRV taxonomy:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.039.0.02.001.htm>
Brown rot disease information:
<http://www.defra.gov.uk/planth/brownrot.htm>
Description and taxonomy of _R. solanacearum_:
<http://expasy.org/sprot/hamap/RALSO.html>  and
<http://www.ebi.ac.uk/2can/genomes/bacteria/Ralstonia_solanacearum.html>
History and description of races:
<http://www.eppo.org/QUARANTINE/bacteria/Ralstonia_solanacearum/pm7-21(1)%20PSDMSO%20web.pdf>
List of potato diseases and pathogens:
<http://www.apsnet.org/online/common/names/potato.asp>.  - Mod.DHA]