Agriculture Reference
In-Depth Information
.org/ag/save-and-grow/pdfs/factsheets/en/SG-crops.pdf).
Several researchers have
indicated that conservation agricultural (CA) practices like zero-tillage and residue
retention change the crop production environment significantly (Kuhlman and Steffey
1982; Nyvall 1982; Triplett and Van Doren 1985), and therefore the genotypic require-
ments under CA are different from the normal tilled production environment (Duvick
1990; Trethowan et al. 2005; Joshi et al. 2007; Yadav et al. 2012). Trethwon et al.
(2012) reported significantly higher yield in Berkut × Krichauff population of wheat
under zero tillage at Nairobi on two soil types largely because of better availability
of water and more days to flower under CA practices. Verhulst et al. (2011) found that
water infiltration was significantly improved when tillage was reduced and crop resi-
dues are retained. CA practices modulate soil temperature depending on crop grow-
ing seasons (mulching keeps the soils cool in summer season and warm in winters)
and maintain soil moisture for a longer period. This has a significant influence on
crop growth and may also effect disease development. A number of necrotrophic
fungal pathogens attacking different parts of crop plants use crop residue retained on
surface as a substrate for survival during the off-season and to infect the succeeding
crop (Forcella et al. 1994; Bianco 1998; Nazareno et al. 1993). Use of host resis-
tance through plant breeding has been highly rewarding against specialized patho-
gens because of availability of major genes with large effect within the crop species.
However, broad-spectrum host resistance to pathogens like
Pythium
is either lacking
or limited within host species. Progress through plant breeding against disease under
CA has been comparatively slow largely because of the reluctance of plant breeders
to select their genetic stocks under zero-till conditions. In Brazil, where CA has been
highly successful, disease control has been recognized as a major weak point (Scopel
et al. 2004). In Australia, root diseases caused by
Rhizoctonia solani
, nematodes, and
Pseudomonas
bacteria (Watt et al. 2005, 2006) are reportedly favored in undisturbed
soils. The slow growth of wheat during its early stage has been linked to inhibitory
Pseudomonas
on the root tips of wheat in no-till soils. In sandy soil with light tex-
ture,
Rhizoctonia
remains a significant problem for no-till cropping (Kirkegaard et al.
2011). Special breeding programs have been established to develop disease-resistant
varieties for zero-till condition in soybean, rice, wheat, cotton, and maize. Residue
mulch is often considered as the major culprit for increased disease problems under
no-till systems. Long-term crop rotation combined with use of moderately resistant
cultivars and judicious use of inorganic and organic pesticides may help in breaking
the disease and pest cycles (Bolliger et al. 2006).
5.6.3 u
SE
of
l
andracES
for
r
iSk
m
anagEmEnt
and
y
iEld
m
aximization
In times when our awareness for genetic diversity is growing, large corporations
typically rely on releasing few high-yielding, genetically homogenous varieties. This
encourages farmers to displace traditional varieties on small farms. However, the
fact that large numbers of traditional landraces of maize are still being grown in the
tribal belts, in the belly of central India and elsewhere, seems to prove that poorly
endowed farmers try to spread their risks in manners that improve their livelihoods
and food security. Cultivating landraces with specific traits is a vital gene pool for
the high-tech plant breeders who need such traits (earliness in maturity, grain color,
