Maize (Zeamays) is one of the most important cereal crop in the world grown over an area of 132 Mha with a production of 570m.t. It is the crop with the highest productivity.
Maize is serving as staple food for vulnerable segment of the population and it rank first in importance as feed crop and also important source of raw material used in numerous industrial materials.
Classification maize kernels Dent corn : It is characterized by a depression or dent in the crown of the seed. The starch at the sides of the seeds is corneous while the soft starch extends to the narrow base or tip Flint corn: The seeds of flint maize are hard and smooth and contain little soft starch Sweet corn: Contain is sweetish starch and is characterize by a translucent, horney appearance when immature, and a wrinkled condition when dry.
Flour corn: Flour soft maize as kernels , which are compose entirely of soft starch Pop corn: The grains unusually small pointed and contain an even higher per cent of hard starch than flint maize Pod maize: It is an unusual type of maize each kernel of which enclosed within the lemma and palea which are well develop Waxy maize: Waxy maize is so named because of the some what waxy appearance of the kernels
Floral biology The monoecious corn plant has female flowers that develop on the side of the plant and emerge from the leaf node. The inflorescence is unisexual and monoecious. Staminateinflorescence is terminal and known as tassel and pistillate is axillary and called as cob
Hybrids Open pollinated varieties Synthetics Composites
Hybrid seed production Hybrid seed of maize may generally be produced from following different cross combinations Single cross hybrid: (AXB) e.g. DMH-2(CI-4 X KDMI-10) NAH-2049(147-F2#89 X MAI-105) (Nithyashree) Double cross: (AXB) X (CXD) e.g. Deccan (CM 104 x CM 105) x (CM 202 x CM 201) Ganga-1 (CM 101 x CM 102) x (CM 200 x CM 202) Three way cross: (AXB) X C e.g. Ganga -5 (CM 202 x CM 111) x CM 500 Double top cross : (AXB) X Composite e.g. Ganga safed, Histarch, Ganga 4.
Factors affecting hybrid maize seed production
Maize hybrids vary considerably in respect of plant height, Panicle size, the amount of pollen produced and duration of pollen availability.
Single cross hybrid : 4:2 Double cross : 6:2 Three way cross: 6:2 Non-synchronization of flowering:
Good seed set in seed parent can be achieved by chronological adjustment of pollen shedding and silking respectively.
Prolongation of effective flowering period, planting design, efficient alteration of rows planting ratio, staggered planting are some of measures which are effectively used to ensure maximum synchronization and good seed set.
Genetic drift: It is recognised as a important factor affecting quality of seed. The danger of genetic change in respect of cross pollinated crops like maize is prominent. Detasselling: Removal of male inflorescence from the monoecious crop. The time taken for shedding of pollen from the tassel in 1-2 days after emergence. Hence the tassel should be removed before the shedding of pollen.
Hold the stem below the boot leaf in left hand and the base of
the tassel in right hand and pull it in a single pull.
No part should be left on the plant as it causes contamination.
It should be uniform process done daily in the morning in a
Donot break the top leaves as the field may be reduced due
to the earning of source material to accumulate in sink (seed) as removal of one leaf course 1.5% loss 2 leaves 5.9% loss and three leaves 14% loss in yield.
Detassel only after the entire tassel has come out and immature detasseling may lead to reduced yield and contamination.
Mark the male rows with marker to avoid mistake in detasseling.
Look out for shedders (shedding tassel) in female rows as they may cause contamination.
After pulling out the tassel drop it there itself and buried in soil. Otherwise late emerging pollen from detasseled tassel may cause contamination.
Donot carry the tassel through the field as any fall of pollen may lead to contamination.
Donot practice, improper, immature and incomplete detasseling.
Improper detasseling: a portion of the tassel is remaining in the plant while detasseling.
Immature detasseling: carrying out detasseling work when the tassel is within the leaves.
Incomplete detasseling: the tassel is remaining in lower or unseen or unaccounted in within the whole of leaves.
Shedding tassel: either full or part of tassel remain in female line after detasseling and shedding pollen which may contaminate the genetic purity of the crop.
Mechanical admixtures: These can be avoided taking due precaution at harvesting, seed setting, bagging and storing operations etc. Rouging: Based on distinct and diagnostic characters furnished by the breeder, rouging has to be performed in seedling stage flowering stage and at the time of harvesting (Plant and Ear Characters). Physiological maturity of the crop: The crop should be harvested at proper stage of maturity to minimize qualitative & quantitative losses. The symptoms of physiological maturity are the degeneration, formation of dunken layer, moisture content of seed 35% and cob sheath turn straw yellow colour.
Harvest seed crop: the seed crop should be harvested when moisture content falls to 20-25% and harvest the male row first and remove from the field and then harvest the female rows. Post harvest operation : Cobs sorting: Remove sheath and check for kernel colour, shank colour , disease cobs, kernel arrangement etc. Shelling : moisture content 15 % and mechanical cob shellers and also manual rubbing against stone are used. Improper shelling leads to 48 % damage to kernel, growth of storage fungi and also pericarp damage, to identify the pericarp damage a crack on the pericarp and also by ferrichloride test or Tz test.
Maize is grown in wide range of climatic conditions.
About 85% of the total acreage under maize is grown during monsoon because of the fact that the crop stops growing if the night temperature falls below 15.60 C or 600 F.
Maize crop needs more than 50% of its total water requirements in about 30 to 35 days after tasseling and inadequate soil moisture at seed filling stage results in a poor yield of shriveled seeds.
Maize needs bright sunny days for its accelerated photosynthetic activity and rapid growth of plants.
Prolonged cloudy period is harmful for the crop but an intermittent sunlight and cloud of rain is the most ideal for its growth.
Soil Deep fertile soils rich in organic matter well-drained soils are the most preferred ones however maize can be grown on variety of soils. Soil should be medium textured with good water holding capacity. The pH should be between 6.5 to 7.
Seed source Certified or foundation seeds are to be procured from the approved certified agencies
Seed rate and Spacing A plant population density of 50-55 thousands/ha is ideal to attain maximum yield. Hybrids: Female 10kg/ha Male 4 kg/ha Spacing : 60 - 75cm row spacing and plant to plant 25 -30cm.
Micronutrients : If deficiency is found, apply 20 kg of zinc sulphate / ha , boron @ 5kg /ha and Fe @12.5 kg/ha
Table 1: Plant height, number of days taken for 50% flowering and number of barren plants (without cob) as influenced by spacing and fertilizer levels in African tall fodder maize. Channakeshava B.C (1998)
Methods of planting and Earthingup Sowing depth (3-5cm) must be uniform to get a uniform emergence. The planting may be done as follows Planting on the ridge Planting in furrows Planting on flat bed with no earthing up Planting on flat bed. Earthing up after 40-45 days of days of planting
Isolation Distance Field standards for isolation For Foundation single crosses and hybrid of certified class
Isolation distance Isolation distance depends on seed yield of the lines and size of the plot. The required minimum isolation distance is 200 m in certified seed production from the contaminant source. Four pollen parent border rows in the field is to be inspected four ha or less in size. The isolation distance may be decreased by 5 m for each increment in 2 ha in size of the plot to a maximum of 16 ha. Here the isolation distance may be further decreased by 12.5 m for each additional border rows to a maximum of 16 pollen parent border rows.
Border rows Borders rows must be planted in the seed field or adjacent to it, but in no case separated by more than five meters from the field. Borders rows must be planted all along and opposite to the contaminating maize. There should be a reasonable stand of border row, i.e., there must not be gapes in the border rows. Border rows must have been planted using the seed rate and spacing adopted for the seed crop. The area planted under the border rows is taken into consideration while modifying the isolation distance.
Contd.. natural barriers such as tall thick trees, buildings…etc between in the seed and contaminating fields shall not be a substitute to border rows. Border rows must be planted with seed used for planting male rows in the seed field. Seed saved from male rows of the previous production of the same cross can not be used for planting of border or for planting with isolation distance.
Rouging: It is the process of removal of voluntary plants, off-types, other crop plants, pollen shedders, and objectionable weed plants from the seed field before either of the crops comes to flowering.
Field Inspections First inspection: The field should be inspected to verify that it is properly isolated and free of volunteer plants. Second inspection: During the vegetative growth phase. Isolation should be checked, along with the presence of disease, insect pests, or weed infestations. At this stage, off-type and disease plants may be rouged. Third inspection: made just prior to and during flowering. At this time the maize seed field is most susceptible to genetic contamination from windblown pollen coming from off-type plants within the field or other maize varieties in surrounding fields. Plants that are off-type or diseased, along with harmful weeds, must be removed at this time. Fourth inspection : A pre-harvest or harvest inspection may be conducted as the crop reaches maturity and the seed has lost a significant portion of its moisture content.
Shoot fly and cob borer are the important insects.
Control measures: Spray Mancozeb 2.5g/lit or Dithane M-45 spray can be taken (0.4%) as soon as first symptoms are observed and it can be repeated at 10 days interval till flowering.
Hybrids like Deccan, Ganga-5, Deccan Hybrid Makka-103 and DHM - 1 which are resistant to rot disease to minimize the disease intensity
Harvesting: Harvest when the husk completely turns into straw colour. Methods of harvesting: Male lines are harvested first followed by female lines. Threshing:Dehusking - The husks are removed manually, Cob sorting - Remove non filled, diseased cobs and cobs having kernel colour variation. Shelling: The cobs are shelled either mechanically or manually at 15-18% moisture content. Drying: Seeds are dried to 12% moisture content. Grading: Grade the seeds using 18/64" (7.28 mm) sieve. Seed treatment: Treat the seeds either with captan or thiram 75% W.P. @ 70 g/100 kg. Yield: 2.5 to 3.6 tonnes / ha
Storage Seeds stored in high density polythene bag (700 gauge) and poly lined gunny bag with reduced moisture of 8 per cent retained seed quality parameters upto 15 months compared to seeds stored in cloth bag and gunny bag.