Orchard Management (1+1)

IMPACT OF CLIMATE CHANGE ON FRUIT CROPS

A. Influence of elevated CO₂

• Increase in atmospheric CO₂ is reported not only to improve the yield but also to alter the quality of the produce.
• The quality (carotene, starch and glucose content) starchy fruits increased in elevated CO₂ conditions. Under high CO₂ level, the water use efficiency of crops is reported to increase.
• In coconut, areacanut and cocoa are reported to benefit due to CO₂ concentrations. Studies indicated that the elevated CO₂ (550 and 700 ppm) increased growth of coconut seedling by 20 to 30 %.

B. Influence of Temperature

• Each fruit crop requires a specific temperature range from minimum to maximum within which a crop will survive. What kind of impacts might occur when a crop is planted outside this range?
• Cold waves during December 2002 – January 2003, caused considerable damage to fruit crops like mango, guava and papaya in India.
• Even though elevated CO₂ is expected to cause positive impacts, however, this may be nullified by increased temperature and less water availability and thereby can decrease production under the current level of management.

i. Growth and development: Experimental findings indicate increased leaf production in banana with increase of 1 – 2^oC temperature beyond 25-30^oC thereby, reducing crop duration and increasing production. Occurrence of frost during January has affected mango flowering resulting in crop yield.

ii. Flowering and pollination:

• Weather conditions during flowering, pollination and subsequent fruit growth determine the production quantity and quality.
• It has been reported that mild winter temperatures followed by warmer springs advanced bud burst exposing buds to frost damage in almond and apricot.
• A cool and dry period, generally in winter, that slows or stops vegetative growth is essential in inducing flowering. On the other hand, low temperature (4 to 11^oC), high humidity (> 80 %) and cloudy weather in January delayed panicle emergence, low temperatures during inflorescence development reduce number of perfect flowers.
• The perfect flowers in mango were significantly higher in the temperature regime of around 27 / 13^oC than in a temperature regime of around 21/4^oC.
• In citrus, ultimately winter rains promoted vegetative flushes instead of flowering flushes while, dry spell during flower emergence and fruit set affected flower initiation and aggravated pest (Psylla) incidence.
• Washout pollen grain during flowering has been reported by various workers from different parts of the world.
• During rainy days pollinating insects remain dull and effective pollination cannot occur and affects fruit setting. After continuous moist weather severe attack of mango hopper certain fungi cause heavy shedding of flowers and fruits and often results in crop failure.
• Pre-harvest low light intensity due to cloudy weather reduced content of ascorbic acid and sugar in fruits.
• Heavy rains during harvest period adversely affected production and quality of cashew nuts due to nut germination.
• Extension of monsoon rains beyond October in west coast delays bud break and flowering.
• Entrapment of back radiated heat from the soil by the clouds is attributed for fruit let and flower dropping in mango.
• During prolonged rainless periods, supplemented irrigation should be provided.

iii. Yield:

• Apple productivity declined up to elevation of 1500m amsl to tune of 40 – 50 % due to warmer climate resulting in lack of chilling requirement during winter and warmer summers in lower elevations resulting into shifting of apple production to higher elevation (2700m amsl).
• High temperature and moisture stress resulted in sun burn and cracking in apples, apricot, cherries and litchi, dehydration injury to panicles and low fruit set in mango.

iv. Quality:

• Climate change may alter quality of fruits.
• It may impair quality in terms of colour and different quality parameters which may need appropriate investment for targeted quality of produce.
• In vine grapes anthocyanin development is influenced by difference between day and night temperatures, with high variation (15 – 20^oC) promoting colour development.

v. Pests and diseases:

• Under the changing climatic situations, existing fungal pathogen, bacteria, viruses may cause more damage.
• Some of the minor pests may become major pests in future. Added to these, vector population may increase and new pathogens may emerge.
• Increase in temperature with low RH (< 60 %) reduced leaf spot diseases in banana in the sub humid region.
• Tea mosquito bug populations and damage score in cashew were negatively correlated with minimum temperature (15 – 20^oC), RH (85 – 90 %) and positively with bright sunshine hours (9 -10 hours).
• Bright sunshine hours less than two hours per day triggered incidence of inflorescence blight in cashew.

What are the damages caused by high temperature?

• In summer the leaves, new shoots, branches, flowers and fruits are exposed to sun and high temperature. High temperature is generally more harmful when accompanied by low humidity. This causes excessive transpiration and wilting of leaves and twigs.
• The ability of plants to withstand such condition varies greatly with species; e.g. banana is more sensitive than guava plants.
• Young trees are affected more than old plants.
• High temperature and low humidity is a limiting factor in case of certain fruits like banana.
• Sun burn of leaves, fruits (pineapple) and bark is sometimes a serious factor. Plants planted in a east and south aspect are more affected than in other directions as they are exposed to sunlight for longer time.
• Flowering and fruit set are adversely affected by high temperature as in mango and mandarin. Citrus fruits suffer a production loss when temperatures over 37^oC are experienced

Preventive measures:

• Planting of thick and tall growing wind breaks are required to be planted at the time of orchard establishment.
• Severe pruning of trees be avoided during summer season.
• Adopt protection measure before the commencement of high temperature. White washes the main stem and also small branches and young plant shoots at the beginning of summer season.
• Irrigate properly to have more humidity in the orchard.
• Spread the mulch in the basins of young and old trees. Provide grass cover to fruits as in pineapple.

What are effects of low temperature on plants?

• In the hills and plains of north India frost occurs either during winter or in early spring. Low temperature effects due to freeze and frost occurrence in these area.
• Low temperatures (Freezing) occurring either during the rest period of fruit plants or after wards, cause damage to roots, stems and buds. At lower temperatures, water is withdrawn from protoplasm and ice is formed in the intercellular spaces. If this process proceeds beyond critical limits the protoplasm of the cells disintegrates and dies from loss of water.
• Frost causes damage to the newly opened blossoms of fruit trees, to young growth and newly set plants. Frost occurs when there is sufficient moisture in the air and the temperature of the exposed surfaces fall below 32^oF.
• Important types of injuries due to occurrence of frost observed in fruit plants are (1) Black heart—Inner wood of nursery fruit plants becomes dark; (2) Splitting of bark—this may be extended to trunk and branches; (3) Killing of shoots and young branches— if there is early growth in spring and flowering in fruits like mango, flowers may be killed while in others like citrus and papaya even fruits are injured; (4) Frost damage—evergreen tree are damaged heavily but deciduous fruit trees shed their leaves and not normally damaged. In young fruit plants, the damage is very severe.

Preventive measures:

• Delicate young fruit plants be planted in the inner side of the orchard.
• Wind-breaks should be planted in time on west and north side of the orchard.
• Apply adequate manures and fertilizers to make the plants stronger and more tolerant.
• Plants of frost tolerant varieties be given preference for planting in the new orchard.
• Irrigate orchards regularly during the frost periods.
• Burn dry leaves and twigs in orchards (10 – 12 places in one hectare).
• Cover the trunk with grass. The young plant may be covered on three sides leaving south east side exposed for light and sun.
• Plants quick growing green manuring crop around young plant to provide protection.
• Climate change has been a cause of serious concern if the fruit industry has to grow in the context of country’s overall economic growth, to respond to rural households’ livelihood, country’s nutritional security and poverty alleviation.
• It may take some years to fully experience the devastating effects of climate change on quality fruit production but the time is ripe for the Government, private sector and public to have adequate concern, commitment and accountability to mitigate the effects of climate change.