Agriculture Reference
In-Depth Information
4000
3500
3000
2500
2000
1500
1000
500
0
3593
3115
3491
3103
2986
2593
Yield in ZT (kg/ha)
Yield in CT (kg/ha)
DBW17
HD2967
PBW550
Wheat varieties
FIGURE 5.4
Genotype × tillage interaction in wheat varieties.
through the development and cultivation of varieties with slightly longer duration
(PBW343, UP2338, WH542, HD2733, and DBW17) against the previous predomi-
nating varieties such as HD2329. The longer duration of the crop, however, increased
the incidence of terminal heat stress and, therefore, led to the recommendation of
wheat seeding in last week of October or the first week of November in states such
as Punjab and Haryana. Early planting without taking into consideration the vernal-
ization base of the cultivars, however, in October, generally many times results in
stunted growth, poor tillering, early flowering, and drastic reduction in yields. Thus,
heat stresses in early and late planted wheat crop adversely affect grain yields for dif-
ferent reasons. CA is known to help in early planting, and increase cropping intensity
by reducing the turnover time between the crops.
It has been pointed out in preceding sections that heat stresses in early-planted as
well as late-season-planted wheat adversely affect grain yields, although with differ-
ent routes. In most of south Asia, wheat and barley crops are exposed to drought and
heat during late reproductive and grain-filling phases. Therefore, crop intensification
strategies to breed for earliness to prevent terminal heat and moisture stress can be
effective for stabilizing crop yield and increasing food production. In cereals, crop
duration may largely depend on vernalization requirements, photoperiod and tem-
perature responses, and presence of genes for earliness per se (Herndl et al. 2008).
The knowledge about the major genes influencing vernalization and photoperiod has
made phenological manipulations rather easy for breeders (Slafer and Whitechurch
2001) despite sketchy knowledge about earliness genes and their interactions with
temperature. In the past, phenological manipulations in wheat and barley have con-
tributed significantly toward yield gains. It is believed that if the duration of stem
elongation can be increased, it may result in more grains per spike and harvest index
(Miralles et al. 2000; González et al. 2003), without additional need for crop water
demands. An extended stem elongation period can be achieved by selecting for
slightly higher sensitivity to photoperiod (Slafer et al. 2005). The duration of floret
primordial differentiation can be extended through selecting for mild vernalization
requirements in spring wheat. In winter wheat, the transition from a vegetative to a
generative (reproductive) stage is conditioned by a “vernalization” process—a long
