Agriculture Reference
In-Depth Information
3.2.5 EFFECT ON CHILLING REQUIREMENTS
Most deciduous fruit trees need sufficient accumulated chilling, or ver-
nalization to break winter dormancy Inadequate chillingdue to enhanced
greenhouse warming may result in prolonged dormancy, leading to re-
duced fruit quality and yield. The low warming scenario is less than 1 °C
is unlikely to affect the vernalization of high-chill fruit (Apple, walnut,
apricot almond, cherry varieties), and if warming scenario exceeds 1.5 °C
and would significantly increase the risk of prolonged dormancy for both
stone-fruit and pome-fruit. Japanese plums have a CR of between 500-
800, while European cultivars have a CR in excess of 1,000 h. Periods of
mild weather can upset the accumulated CR requiring further periods of
cold weather to achieve sufficient hours. Mild winters may result in de-
layed or irregular flowering, reduced fruit set and an extended flowering
period. The CR is a major concern in the marginal temperate area of North
Western Himalayas where fruit trees with a low CR have to be grown.
Therefore in some areas, it is impossible to grow cherries. For example,
sweet cherry requires the accumulation of 1000 chill units at 3.8 °C in or-
der to complete or 'break' dormancy. If chilling is inadequate, the develop-
ment and/or the later expansion of leaf and flower buds may be impaired.
Problems have already been experienced with poor cropping of blackcur-
rant after mild winters and the same might happen with raspberry, apple
and other fruits as winter temperatures continue to increase.
3.2.6 EFFECT ON POLLINATION
Climate change during the past eight years has played a critical role in
apple pollination failure. There are rains during the flowering season,
which affect pollination by wind and insects. Low temperatures also ad-
versely affect fruit set in apple. At present these Delicious group of culti-
vars mainly Starking Delicious and Red Delicious constitute nearly 80%
of apple trees. Although India ranks 10thin world production of apple,
yet the decreasing trend in productivity of its orchards, in the last decade
due to changing climate scenario has caused a serious concern to the fruit
growers and planners of the country.
More than 70% of orchards have less than 20% pollinizer proportion,
whereas a minimum of 30-33% is required in our agroclimatic conditions
