Agriculture Reference
In-Depth Information
stocks are produced by combining durum wheat cultivars (2n = 4x = 28) with each
diploid thus generating hexaploids that are genomically AABBDD, AABBAA and
AABBBB(SS). All stocks cytologically are expected to be 2n = 6x = 42 and major
genetic resources that provide unique allelic diversity for wheat improvement.
Biotic stresses of significance vary according to location and our major ones
are the three rusts, karnal bunt with upcoming concern prevailing for powdery mil-
dew, barley yellow dwarf and the new emergence of spot blotch (Mujeeb-Kazi et al.
2008b
). Progress to combat these stresses has be driven in tandem with locational
priorities and these dictates have shifted global and national focus among the rusts
to stem rust with the threat of race UG99's spread linked with a local races pres-
ence (Mirza et al.
2010
). Thus diversity for exploitation has extended beyond the
diploid relatives to include tertiary gene pool resources where most notable men-
tion is of the diploid
Thinopyrum bessarabicum
that has the potential to address
multiple stress factors and will be elucidated in an agglomerated manner to embrace
various accessional sources as they relate to the major biotic stresses resistance
management. This communication covers our major biotic stresses, address a few
of international importance using strategies that embrace diverse means of intro-
gressing genes integrating technologies that add to the efficiency of pre-breeding
and breeding to deliver outputs that are expected to form a conduit to food security.
The overall theme is captioned “wide crossing”.
Major credit for motivating research on the course of wide crosses goes to Kruse
1967
,
1969
,
1973
,
1974
following the events of
1891
(Rimpau) and
1904
(Farrar).
Initial impetus was derived from the wheat/barley findings of Kruse
1974
that paved
the way for significant cytogenetical outputs by Islam et al. (
1981
) and followed by
some additional digressions with other
Triticeae
members Sharma and Gill (
1983
),
Mujeeb-Kazi and Kimber (
1985
), Mujeeb-Kazi et al. (
1987
,
1989
), Wang (
1989
),
Jiang et al. (
1994
), Sharma (
1995
). All these reports have centered on “intergeneric
hybridization” and considered complex for realizing alien genetic transfers. Paral-
lel to these efforts since mid-1980s emerged the era of exploiting of close relatives
particularly the diploid wheat progenitor
Aegilops tauschii
(2n = 2x = 14, DD) via
direct crossing (Alonso and Kimber
1984
; Gill and Raupp
1987
) or via bridge cross-
ing (Mujeeb-Kazi and Hettel
1995
; Mujeeb-Kazi et al.
1996a
). Both these strategies
will be highlighted but for handling practical outputs for key biotic stresses only
those at a priority in our perception shall be considered that others could modify
according to their desires.
Wheat Production
The productivity levels across varied environments are separated into the irrigated
and rainfed regimes of cultivation. Stress constraints vary as well and these are
locational holding their specific priority profiles. Often diversity to address a trait
is present in conventional sources but when limitations prevail then unique sources
are tapped. Over the past few decades this emphasis on suing novel genetic resourc-
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