Agriculture Reference
In-Depth Information
responsiveness, which simply means newer
breeds do not benefi t from elevated CO 2 as much
as older breeds (Ainsworth et al. 2008 ). The sim-
ple agronomic measures such as mixing varieties
reduced rice blast severity by 94 % and increased
yield by 89 %.
Following crop rotation increases biodiversity.
Crop residues are often host of pathogens and
alternating crops will prevent the infection from
the residues to the host crop.
Ecologically based pest management (EBPM)
considers belowground and aboveground habitat
management equally important. A “healthy” soil,
with optimal physical, chemical, biological prop-
erties, increases plant resistance to diseases
(Altieri et al. 2005 ). Excess of nitrogen can
increase the severity of certain diseases.
8.10.5 Transgenic Disease-Resistant
Varieties
Fig. 8.5 Yellow plants on the left are nontransgenic papaya
severely infected with ringspot virus; plants on right are
transgenic 'Rainbow' papaya resistant to ringspot virus
Transgenic ring spot virus-resistant papaya has
been genetically engineered to contain a virus
gene that encodes for the production of the coat
protein of the virus. As a major component of
viruses, the coat protein's primary function is to
protect viral genetic information. Expression of
this gene in the resulting papaya line renders the
plants resistant to the virus (Fig. 8.5 ).
The transgenic plum called C5 (variety Honey
Sweet) expresses a plum pox virus coat protein,
the plant produces the coat protein mRNA , and it
is processed by a system called posttranscrip-
tional gene silencing (PTGS), which functions
like the plant's immune system and is mechanis-
tically similar to RNAi (Hily et al. 2004 ). C5 pro-
vides a unique source of germplasm for future
breeding programs worldwide (Fig. 8.6 ).
Approaches that have been used to produce
transgenic sweet potato include expression of
viral replicase genes, anti-sense RNAs, and viral
coat protein genes. Transgenic sweet potato is
resistant to feathery mottle virus (FMV) and has
the potential of increasing yields of sweet potato
roots and foliage.
Exploitation of the plant immune system
against cassava mosaic disease by expression of
hairpin RNA homologous to viral sequences has
proven effective to generate virus-resistant cas-
sava (Yadav et al. 2011 ).
Specifi cally in summer squash, coat protein-
mediated resistance is used against viruses.
Transgenic summer squash plants (CZW3,
Liberator III, and Destiny III) with resistance to
three viruses (cucumber mosaic virus, zucchini
yellow mosaic virus, and watermelon mosaic
virus 2) produce as many or more marketable
fruit than nontransgenic squash. A Cornell
University study found that transgenic squash
with resistance to three viruses produced a
50-fold increase in marketable yield over non-
transgenic varieties (Fuchs et al. 1998 ).
The GM potato variety Desiree has been trans-
formed with an R or resistance gene (Rpi-vnt1.1)
along with its native promoter and terminator
intact, using GMO technology. The R-gene con-
fers the GM potato line with resistance to the late
blight fungus.
The RNA interference (RNAi) gene was intro-
duced in pinto bean ( Phaseolus vulgaris ). This
GM bean is resistant to the golden mosaic virus.
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