THE BIOLOGY OF MANGO (MANGIFERA INDICA) FLOWERS IN SINDH-PAKISTAN
Mango (mangifera indica) belong to Anacardiceae family. Other members of same family are cashew, pistachio, Ambrella or spondioscyheres (South East Asia), Banno or mangifera verticillata (South East Asia), Hog plum (spondias mombin) from tropical Central America, Jamacian plum (Spondias purpurca) and kumini (mengifera curdera). Mango cultivars in Pakistan are: Anwar Ratol, Bengan Pali, Chausa, Dashehari, Lanngra, Siroli, Sindhri, Suvarnareka, and Zafran.
In the year 1994-95 the area under mango production production was 88,300 hectares, while in that Sindh was 38,700 hectares. The mango production in Pakistan was 833,700 tonnes, while in Sindh its production was 285,300 tonnes.
Polyembryyonic and monoembryonic mango are two distinct types they are separated on the basis of reproduction and their respective centres of diversity: the first from South East Asia and the second from India. The first is tropical and the seocnd sub-tropical.
Mango is a tropical and sub-tropical tree, it can reach up to the height of 30-90 feet. Its leaves are oblong-lanceolate to elliptical, 6-16 inches long, variable in breadth, glabrous deep green, the margin undulate, apex acute, petiole 1-4 inch long swollen at the base. Tree is ever green.
In Hyderabad Sindh (25°-36’N) and 68°-30’E flowering takes place from 10th January to 1st March for various cultivars. Shoot containing 35 leaves, when ringed below the 20th leaf from terminal and terminal bud removed, inflorescence will initiate form the most distal lateral buds. This show that auxin causing inflorescence comes form leaves. Time of ringing for Sindh varieties harvested in June and early July is about end of August after the first vegetative flush is over.
50% of fruit if thinned does not affect number of fruits at harvest, but size is increased and thereby the yield. There is no fruit set in heavy type of panicles of the varieties of Dashehari, Chausa and Langra. Mature tree can attain 30 m height and can survive more than 100 years.
Mango having vigorous tap root and abundant surface feeder roots.
The Mendelian genetics to crop breeding, optimisation of agronomic and horticulture field practices and successful management of insect, pest and diseases planting of regular bearing cultivars, more suitable field practices including irrigation management, control of flowering, fertilisation and use of agri-chemicals help in increasing the mango production in many folds.
Fruit is fleshy drupe, containing edible mesocarp of varying thickness. It is resinous the cultivars are different in shape, size and colour. Fruit colour at maturity is genotype-dependent. The excarpis thick and glandular. The mesocarp can be fibrous or fibre-free with various flavours. The endocarp is woody, thick and fibrous.
The biology of mango (mangifera indica) flowers in Sindh-Pakistan.
Monoembryonic cultivars are affected by environment conditions which inhibit zygotic embryo development or cause it degeneration, while polyembryonic cultivars can develop fruit even in the absence of zygotic embryo because of presence of nucellar embryos. In case of monoembryonic cultivars around 99% perfect flowers and young fruits drop. This could be due to nutrition deficiency in embroys development, degeneration of embryo or its embryo sac, ethylene production with high peroxidase activity with high rate of fruit abscission, while in polyembryonic cultivars show low peroxidase activity.
The mango inflorescence is borne on terminal pyramidal panicle which is glabours or pubescent, are foot are more in length. There are 1000-2000 flowers per panicle each 5-7 mm diameter and only 0.1 to 0.5% may mature to fruit. The inflorescence is rigid and erect is widely branched with densely flowered. Before panicle reach in to its full length flowers start to open. The flowers are small, monoecious and polygamous. Both male and perfect flowers are found within single inflorescence. The pistil abort male flowers. It can be controlled by spray of Ethephon at 400-600 ppm + surfactant at full bloom spray or by control of harmonic deficiency removed by 2-4-D at 25 ppm once or NAA at 25 ppm thrice or planofix or chlorofiinoxi accetic acid at 25 ppm spray thrice reduce fruit drop at mustard, pea and marble stage. When pendicle is of short length (as Langra) its fruit does not fall. Flowers occurs on the same panicle, sepals ovate-oblong, concave, petals twice as long as the sepals ovate, 3-5 ridged, the ridges orange, disk fleshy, five-lobed, stamins 1-fertile, 4 reduced to staminodes of various prominence, ovary glabrous.
There are 4-5 petals that are oblong to avoid to lanceolate and also thinly pubescent. The floral disc is 4-5 lobed fleshy and large, located above the base of the petals. There are 5 large fleshy nectaries that form 5-lobed receptacle. There are 4-5 stamens. In which 1-2 are fertile the remaing are sterile staminodes that are surrounded by small gland. The 2-3 smaller filments arise from the lobes of the nectaries. The stamens are central. Flowers are cross-pollinated by flies and insects.
The pollen grain are tricolpate almost the same size. Fruit a drupe 2-6 inches or more in length, usually compressed laterally greenish, yellowish or reddish in colour, the epicarp forms the skin, mesocarp is fleshy and endocarp is bony forming shell of stone.
Mangoes produce panicle usually 10-60 cm long with 1000-6000 flowers, polygamous, with male, female and hermaphrodite flower on the same panicle.
Maximum flowers open around 9-10 am stigma is receptive before flowers open and remain active about 72 hours after anthesis. Various flies, insects and thrips help in pollination. In mango 27/20°C reduces night respiration and stimulates flowering. For mango 30 days chill is maximum but some flower in 4 chilly days. Night temperature around 10-12°C and dry conditions promote flowering. Flowers reach full blooms within 25-30 days after initiation. The number of perfect flowers rage 1.25 to 81.0%. Late season and those inside the canopy are perfect flowers. Percentage of perfect flowers is higher in the apical rather than central or basal zone of flower panicle. Late flowers have 11.8% of perfect flowers as compared to 6% in early flowers. Highest fruit set is on late emerging panicles.
The photoperiodism and thermoperidosim play important role in controlling the flowers. Time of flower bud differentiation in mango, coincides with beginning of short days in Ocotber/November in Sindh. Pruning to open-up canopy facilities better light penetration, increases flowers and yields. Low temperature of 10-15°C promote growth check and enhance flower initiation but low temperature of 5°C can result into totally male flower inflorescence.
Flowering date is more closely related to degree hours below 18°C, than to the date of last vegetative flush. The flower bud differentiation depend upon the ‘On’ and ‘Off’ year phase of tree rather than the original and cessation of growth of shoots. The shoot that were de-blossomed, defruited and tipped, gave very poor flowering in the following ‘off’ year.
Flower buds are generally barne on terminal buds of shoots is absolutely essential. Contrary to common belief our observation shows that cultivar Sindhri flushes four times a year. The non fruit bearing shoots flush in April and subsequent flushes occur in July to October. The next season flowering in maximum in April flush, followed by August flush. If flush occur in October it produces least flowers July and September flushes are intermediate. In Langra and Dasehri mango only 3-35% flowers are pollinated due to lack of pollinators. Pollination depend upon many factors like: weather, wind, rain, pollen tube growth, temperatures below 16°C which inhibit pollen tube germination and cultivar and many varieties are self-incompatible.
The factors which effect on flowering are: soil and air temperature, relative humidity, saturation deficiency, dew point, continentally, temperature variability after bud swelling, quality and quantity of sun-light, optimum combination of climatic factors, soil moisture, and other unknown environmental factors, which govern, the time extent of flowering.
Climatic factors affect the flowering and cropping pattern of crops in two ways: Frost, high temperature, with low humidity and hail storm, either damage the fruit buds, blossoms and fruits directly or create conditions (cloudy weather and rain during flowering) which affect the fruit set. Mango growth ceases at 12°C and ripening date is connected with heat-sum as well as level of moisture in the soil.
Environment for flowering.
These are as under:
a) Water stress or chill stress: Water stress used an alternative to winter chilling can easily be achieved in dry winter areas by stopping irrigation in autumn and early winter, prior to flowering. Prolonged rainfall before and during blossoming can reduce fruit set.
b) Stopping irrigation: Stoping irrigation proceeding flowering for 2-3 months help to induce heavy bloom, but with-holding irrigation causes severe fruit drop from mustard size to maturation.
c) Ringing and girdling: Girdling response to flowering depends on width of cut, narrow cuts heal in short term and produce no response, whereas wider cuts can kill tree by starvation, if they do not heal in time. Girdling has increased flowering and upto 10 fruits per cluster can be produced.
Effect of low temperature during flowering.
Low temperature of minus 0.5 to 1.5°C (29-31°F) or lower can cause damage to flower or growth flush. Flowers are more tender can be damaged, even above freezing temperatures up to above 4.5°C or (40°F). Baganpali flowers are damaged even at 10°C. At mean temperature of 18.3°C (65°F) or below, mangoes do not show any growth and flowering may be delayed. If after flowering average temperature remains like 18.3°C (65°F) or in range where growth rate is low, the fruit will mature proportionately late. This occurs about twice in every 10 years in Sindh and harvest is delayed by about fortnight.
The early flush of panicles which emerges under colder conditions show low percentage of perfect flowers and high incidence of malformation in comparison to late-emerged panicles which experience warmer environment during the period of development. The malformed panicles usually consist of unopened buds which are usually males.
The correlation studies indicate that there is positive correlation between the presence of sear and floral malformation.
Mango flowering as influenced by foliar feeding of urea at 4% plus NAA, 120 ppm induced early flowering and reduced flowering duration. Growth regulators cycloheximide ethephon, dermen etc., cause abscission of apical panicles and thereby release darmant buds, but these will produce inflorescence when weather is cool, other-wise will produce vegetative growth.
Physical methods of flower induction are:
• Water stress.
• Low temperature.
• Atmospheric stress, high vapour pressure.
• Stem or trunk girdling.
With use of deltamethrin there is increased fruit set as compared with other methods. Decis-D contains dimethoate which will reduce pollinator population.
Regulation of flower initiation by photoperiod.
Plants are classified as short day, long day or day neutral in term of their flowering response to photoperiod. Mango are day neutral plant, meaning that they are not induced to flower by either long or short photoperiods.
Growth and Development.
The flowering process has been investigated based on two physiological theories - the plant nutrition theory (C-N) and theory based on the production of specific flowering hormones by leaves. When the percentage of hermaphrodite flowers below a certain minimum level (below 4%), the productivity of mango is affected. Trees of particular variety have higher age, contain more percentage of hermaphrodite flowers per panicle than trees of lower age.
The methods of flower induction.
These methods are:
• Shading, reduces flowering by delaying flower bud initiation. Reducing shading will induce flowering.
• Shoot decapitation can induce flowering in alternating varieties. Timing has to be 6-8 weeks before actual flowering. Probably 15th - 31st December for late flowering, 15th - 30th November for the early and 1st - 15th December for mid season varieties, can give good results.
• Exposing roots can induce flowering, but the consequences of this stress are not known. Cutting down 12-19mm roots some meters from trunk, about 6 weeks before anticipated date of flowering, can tigger flowering.
• Girdling can increase flowering to clusters. Time for girdling to reduce flowering is end August in Sindh after new flush has matured.
• Early emerging panicles produce male flowers. Removal of them by dormex at 0.5% or other chemicals before 10th January can increase yield 5-10 times, but the climate has to be cool right up to second flush, which may be adverse to heavy flowering and yield may be less.
Single zygotic embryo found in monoembryonic mangoes while one or more embryos which are usually but not always zygotes in polyembryonic cultivars. Adventitious embryos develop from the nucellus, a maternal tissue surrounding the embryo sac. Adventitious embryos can also originate by direct budding from the cotyledons and hypocotyls of other nucellar embryos. If progenies of monoembryonic mango hybridized with polyembryonic cultivars show that monoembrony is a dominant trait. The number of adventitious embryos is influenced by many factors like environmental factors, nutrition, and weather conditions during flowering and fruit set. Zygotic seedlings is different than the nucellar seedling as ‘off-type’ in nursery.
Seeds and polyembryony.
The mango seed is large and flat, ovoid oblong surrounded by fibrous endocarp at maturity. The testa is thin and papery. The seed are not labyrinthine. Certain polyembryonic cultivars can produce seeds with adventitious nucellar embryo only. Mango seeds are considered to be recalcitrant, and can not survive for more than few days or weeks in storage at ambient temperature.
In Sindh 25-30% fruit falls down in the month of May and this June is caused by changes in connecting walls between layers of cells in fruit stem or also abscission layer. These changes are controlled by hormones, which are controlled by other factors.
In mango the malformation are two types - vegetative and floral. The floral make the tree unproductive. The malformed panicles show:
(a) Suppression of apical dominance.
(b) Only production of male flowers.
(c) Presence of inhibitors.
(d) High temperature response.
NAA is used to increase perfect flower, improve fruiting in malformed panicles. Deblossoming treatment at bud burst improve fruit set. It means the tree can with flower single spray of NAA (200 ppm) during October, followed by deblossoming treatment at bud burst stage during December and January. This way yield of mango tree increases by 5-20 times compare to the untreated tree.
The malformation considered physiological viral, carological and fungal but the etiology is still not understood. Due to presence of unknown substance, malformed panicles mostly produce male flowers.
Mango malformation has to be shown to be sap transmitted indicating the involvement of a virus as a causal agent of the disease.
Much research is required to completely understand the biology of mango (mangifera indica) flowers, its environmental, biological and genetic influence on flower and improve these situations with the help of genetic engineering and biotechhnology, which bring high yielding crops and better returns to the farmers.
Aauthor: Farzana Panhwar (Mrs)
Address: 157-C, Unit No.2, Latifabad, Hyderabad
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