Agriculture Reference
In-Depth Information
5.2.1.2
REPRODUCTIVE GROWTH
Studies under controlled conditions have shown, of the different weather
variables, temperature exerts an important influence on different com-
ponents of reproductive phenology starting right from flowering (Bruce
Schaffer et al.
,
1994). They opined that mango gets affected when tem-
perature falls below 0 °C hence low temperature factor more than others
defines the range of its cultivation. A period of stress generally precedes
flowering, which occurs following stress relief, and temperature, partic-
ularly in the subtropics provides the strong environmental stimulus for
flower induction, the threshold being cultivar-specific. On the contrary,
dry period preceding flowering appears necessary for satisfactory flow-
ering in the tropics highlighting the role of drought stress to be the key
environmental cue. Studies of Pongsomboon (1991) showed that no flow-
ering occurred in trees held at 30/20 °C at either soil temperatures, while
at 15/10 °C air or 12.5 °C soil temperature, all the trees had flowered after
16 weeks but only 40 percent trees flowered when soil temperatures were
held at 25 °C. These results suggested that '
root signals
' probably played
significant role in induction of flowering in mango. Similar indications
from the work of Ravishankar (1987) on Alphonso (alternate bearer) and
Totapuri (regular bearer) strengthens this view. Export of cytokinins from
roots impacting reproductive morphogenetic responses of shoots under the
influence of temperature cannot be ruled out as high temperatures pro-
vided increased vegetative bias in mango (Whiley et al., 1989). The fact
that foliar gibberellins applications suppressed flowering in mango despite
trees being grown in inductive conditions (Kachru et al., 1971) empha-
sizes that interpolations of promoters and inhibitors under the influence of
high soil temperatures perhaps play crucial role in coordinating shoot-root
communication (Ravishankar, 1987) ultimately determining the flowering
responses in mango whichhowever needs further investigation as major
focus of research so far in mango focused on signals and responses gener-
ated in shoots (Chacko, 1991; Ravishankar, 1987).
Issarakraisila et al. (1992), reported that mean temperature of 12-
15 °C sustained panicle growth in mangoes of the subtropics. Singh et al.
(1965) found temperature dependency of male and hermaphrodite flowers
dynamics of the panicles. Their study indicated that late emerging panicles
of '
Dashehari
' had seven times the percentage of perfect flowers as com-
pared to early emerging panicles on the same trees with mean maximum/
