Impacts on Plant Pathogens - Climate Resilient Agriculture for Ensuring Food Security - page 151

Table 8.1 Estimated potential of pathogens (bacteria, fungi, and viruses) and actual losses in six major crops world-
wide, in 2001-2003 (Oerke 2006 )

Crop losses (%) due to pathogens
Pathogens Viruses

Attainable production
(million tons) Crop Potential Actual Potential Actual

Wheat 785.0 15.6 (12-20) 10.2 (5-14) 2.5 (2-3) 2.4 (2-4)

Rice 933.1 13.5 (10-15) 10.8 (7-16) 1.7 (1-2) 1.4 (1-3)

Maize 890.8 9.4 (8-13) 8.5 (4-14) 2.9 (2-6) 2.7 (2-6)

Potatoes 517.7 21.2 (20-23) 14.5 (7-24) 8.1 (7-10) 6.6 (5-9)

Soybeans 244.8 11.0 (7-16) 8.9 (3-16) 1.4 (0-2) 1.2 (0-2)

Cotton 78.5* 8.5 (7-10) 7.2 (5-13) 0.8 (0-2) 0.7 (0-2)

*Seed cotton

of the fungus Aspergillus fl avus (the producer of
afl atoxin) in the weakened crop. Similarly, wheat
scab caused by Fusarium spp. produces myco-
toxin in contaminated grain. Mycotoxin can pro-
duce muscle spasms and vomiting in humans.
The emergence of wheat scab in the Great Plains
may be linked to the increase in temperatures
observed in key agricultural areas of this region
during the past 10 years.
Climate change may lead to more incidence of
insect-transmitted plant diseases through range
expansion and rapid multiplication of insect vec-
tors (Sharma et al. 2010 ). Increased tempera-
tures, particularly in early season, have been
reported to increase the incidence of viral dis-
eases in potato due to early colonization of virus-
bearing aphids, the major vectors for potato
viruses in Northern Europe (Robert et al. 2000 ).
The comprehensive effort to provide a mea-
sure of global crop losses by diseases is made by
Oerke ( 2006 ) (Table 8.1 ). They analyzed data on
pest damage in six important food and cash crops.
The estimate of preharvest loss caused by patho-
gens to the principal food and cash crops is 16 %
of potential production on a global basis.

Both climatic variability and climate change are
the relevant drivers of plant disease epidemics
and are expected to alter the synchrony between
crop phenology and disease patterns. This change
in climatic patterns also affects the spatial distri-
bution of agroecological zones, habitats, and dis-
tribution patterns of plant diseases which can
have signifi cant impacts on food production.
Whatever may be the reason, be it climate
change, global change, or shifts in seasonality,
changes in disease situations have already been
experienced as some minor diseases have become
major diseases in the Indian subcontinent. Current
shift in the disease scenario in India, especially in
rice and wheat, is a case in point. In rice, bacterial
leaf blight ( Xanthomonas oryzae pv. oryzae ) has
become a global biotic threat despite constant
efforts to improve resistance through exploitation of
host R-gene. Sheath blight ( Rhizoctonia solani ) and
tungro virus that were of minor importance, have
emerged as major problems in most of the rice-
growing areas. Spot blotch ( Bipolaris sorokiniana ),
once unknown or of minor importance, has become
a serious problem in wheat. Increasing trend in win-
ter temperature probably provides a favorable situa-
tion to the spot blotch in the Northwestern India
(Duveiller et al. 2007 ). Dry root rot ( Rhizoctonia
bataticola ) in chickpea is becoming more severe in
the rainfed environments due to moisture stress and
higher temperatures (Pandey et al. 2010 ). Excess
moisture on the other hand is favoring some of the
dreaded soilborne diseases caused by Phytophthora ,
Pythium , Rhizoctonia solani , and Sclerotium rolfsii ,
especially in pulses (Sharma et al. 2010 ).
Quantitative analysis of climate change is largely

8.2 Climate Change and Plant

Disease

The global climate change, especially increased
levels of CO 2 and temperature (Pachauri and
Reisinger 2007 ), is thought to infl uence or change
all the elements of a disease triangle, viz., host,
pathogen, and weather factors and their interac-