Agriculture Reference
In-Depth Information
Drought avoidance
to drought at different growth stages. These
effects indicate that water management should
be cultivar dependent when water supply is
limited. Due to the importance of relative drought
tolerance to growers, many national organiza-
tions note the cultivars that are more tolerant to
drought than other cultivars. In the UK, potato
cultivars are ranked on a scale of drought toler-
ance that is based on ware yield under field con-
ditions (Harris, 1992).
Several plant traits can help in dealing with
drought. For example, cultivars with deep root
systems allow water absorption from lower soil
layers. In addition, stomata sensitive to water
deficits reduce transpiration, osmotic adaptation
helps to maintain turgor and assists recovery
when potato plants are exposed to an adequate
water supply.
The synchronization of crop growth and devel-
opment with water supply is a successful strat-
egy for escaping from the adverse effects of
drought (Rockström, 2003; Blum, 2009). Plants
that complete their growing cycle before or at
the onset of drought are drought-avoiding or
drought-escaping plants, since they are seldom
severely stressed (Turner and Kramer, 1980).
Consequently, early crop maturation may be bet-
ter suited to regions where growth is limited by
environmental constraints such as high temper-
atures and limited water availability.
A potato model (Haverkort and Kooman,
1997) suggested that early-maturing potatoes
are sensitive to early-season transient drought
but escape late-season drought and have a better
harvest index when compared to late-maturing
cultivars. Stark
et al
. (2013) noted that the early-
maturing cultivar, Russet Norkotah, was the least
sensitive to drought, particularly to late-season
drought, as compared to later-maturing cultivars.
Under Mediterranean growing conditions, early-
maturing potato cultivars had smaller yield losses
when compared to later-maturing cultivars that
experienced increasing temperatures and evapor-
ation demand during late spring and early summer
(Levy, 1986). Drought avoidance requires breed-
ing and selecting potato plants for specific growing
sites that are based on the harmonization of plant
development with growing conditions and water
supply (Levy
et al
., 2013).
7.2
Potato Roots
Potato plants growing from tubers produce branch-
ing fibrous roots from adventitious roots associated
with above- and belowground shoots (Cutter,
1978; Kratzke and Palta, 1985). The potato plant
is shallow rooted and exhibits inhibition of root
growth by soil strength levels above
1
MPa.
Currently, a major cause of drought sensitiv-
ity is a result of the limited ability of potato roots to
transport water efficiently to stems and leaves
(Chaves
et al
., 2003). Essential factors for coping
with drought stress include superior root archi-
tecture that allows potato roots to grow in high-
strength soils with efficient water extraction and
transport (Taylor
et al
., 1983; Iwama and Yama-
guchi, 2006; Iwama, 2008; Tardieu, 2012).
Increased efficiency for extracting soil water will
require major changes to features such as root growth
rate, external morphology, and internal structure
(Clarke
et al
., 2003; Boyer
et al
., 2010; Jaramillo
et al
., 2013). The root system will also need to pos-
sess increased water transport efficiency in order to
avoid, or significantly delay, the effects of drought
stress (Burton, 1981; Levy
et al
., 2013).
Drought tolerance
Potatoes require a well-managed water supply to
secure yield and quality. However, in many
major potato production regions, potatoes are
exposed to sporadic droughts due to short-term
hot and dry spells, an irregular rainy season, or
improperly delivered irrigation. Hence, moder-
ate drought tolerance in potato is useful to help
cope with seasonal droughts. For example, Stark
et al
. (2013) reported a differential response of
six potato cultivars to seasonal drought pat-
terns, while Lynch and Tai (1989) observed sig-
nificant differences in tuber yields among eight
cultivars exposed to water deficit. Both reports
showed that potato cultivars varied in their response
Stolons and tubers
Lateral shoot buds under the soil surface often
develop into diageotrophic stems called stolons.
