🌽 Crossing Techniques in Maize
Crossing and pollination techniques used in maize breeding and hybridization.
This lesson covers core principles and exam-focused points from this topic in plant breeding.
Maize (Zea mays) (2n = 20) , Family : Poaceae
Maize is predominantly cross pollinated. Wind pollination (Anemophily) is the general
rule. Pollination by insects also takes place to certain extent. The following are the adaptations
for cross pollination, i.e., Monoecious inflorescence, unisexual flower, differences in the time of
maturity of the male and female inflorescences, silk receptive on entire length and abundant
pollen production. It has protoandry and the tassel anthsis extends 2-14 days. Pollen viability
remains for 24 hours. Anthesis of female spekelets starts after the completion of tassel opening
and extends uo to 2-5 days. The stigma is receptive throughout its length for 14 days.
Selfing
Bag the tassel before anthesis with a paper cover. Bagging of tassels should be done in
the previous day evening to avoid contamination from foreign pollen. Cut the tip of the cob
before the silks emerge and cover with a paper cover. After 3-4 days, the silks will emerge in the
form of a ‘saving brush’ in which the silks will be of same height and stand erect. Remove the
cover of the tassel containing pollen and insert it over the cob after removing the cob-cover. The
inserted cover is then tied.
Crossing technique
Female parent
a. Detassel
b. Cut the tip of the cob before the silks emerge and cover with a butter paper cover.
Male parent
a. Cover the tassel before anthesis begins or as soon as the tassel emerges.
When the silks emerges in the female parent in the form of a brush, pollination is done by
transferring the freshly shed pollen cover form the male parent and inserting it over the cob of
the female parent after removing the cover from the cob.
The details like date of pollination, parentage and breeding programme to be carried out are
clearly written by water proof pencil. The date or pollination will be one day later than the date
of tasselling. Pollination should be completed within one week of silk emergence. Isolation
distance for maize = 400M.
Sorghum ( Sorghum bicolor ) (2n = 20) Family – Poaceae
Sorghum is normally self-pollinated but some florets are protogyny resulting in cross
pollination averaging about 6%. So, it is classified as often cross- pollinated. The amount of
natural cross pollination varies from 0.6 to 50 per cent in different varieties and places. The
cross pollination is more in loose panicles than in compact ones. Anthesis starts from tip to
downwards at the rate of 2-5 cm per day and completes within 7-10 days. Anthesis time 3-6 am.
The pollen grains are viable only for short period and stigma is receptive for 8-16 hours.
Selfing
Head bagging becomes efficient for selfing the ear heads. Once the decision to bag heads
has been made, all heads in a row should be covered. If a head has already begun to flower, the
flowering portion should be cut off. During head bagging, boot leaf of the plant is usually
removed prior to placing the bag.
Emasculation
Hand emasculation
Only a part of the panicle is emasculated and the remaining panicle is clipped away.
During clipping, flowered tip and the lower panicle branches are removed. About 50 florets
which would normally flower the following day are selected for emasculation. The needle is
inserted at the middle of the floret and moved across the glumes. The needle is rotated at 900
and three anthers are lifted out. The emasculate panicle is covered by a suitable paper bag.
Hot water method
In this method, in the panicle flowered tip and lower panicle branches are removed.
About 50 florets (in clusters of two or three) are immersed in hot water at 480C for 10 minutes.
Plastic bag/ mass emasculation technique
In this method, sorghum panicle is covered with plastic bag. This creates high humidity
inside the bag. Under such humidity, the florets open, the anthers emerge but shed no pollen.
The anthers are knocked free of head by tapping. In this method, some selfing occurs.
Therefore, marker genes are needed to identify the plants arising form selfed seed.
On a dry morning when pollen shedding is occurring between 6 and 7 A.M., the hand
pollination may begin around 9.30 A.M. In rainy days, the operation may be started at 11.30 –
12.30 A.M. The pollen is collected in paper bags. Sorghum pollen kept in bags is viable for 10
20 minutes. For collection, appropriate heads may be selected and bagged in the previous night
itself.
The selected male parent panicle will be covered with brown paper bag the previous day
evening before dehiscence of anthers. Next day the pollen will be collected by tapping the bag.
The collected pollen will be dusted on to the emasculated head and covered with butter paper bag
labeled properly. Dusting of pollen is done for two to three days continuously.
Cumbu / Pearl Millet ( Pennisetum glacum ) (2n = 14) Family – Poaceae
Cumbu (Bajra) is naturally cross pollinated (Allogamous). Wind is the chief agent of
pollination (anemophily).Adaptations for cross pollination is Protogyny. Anthesis commence
from 1/3rd of the apex of spike and proceeds both ways. Stigma emerges first and anthesis is
over within 2-3 days. This is followed by the first male phase in which the anthers from the
perfect florets emerge out. On the fifth day of anthesis the 2nd male phase begins in which
anthers from the staminate florets emerge. Anthesis time 8 pm -2 am.
Selfing
To ensure selfing, spikes may be bagged before emergence of the stigmas. As the spike
elongates it may be necessary to adjust the bag to cover the lower most spikelets. Another
procedure is to enclose within a bag two full spikes from the same plant, one day (or) 2 days
older than the other and ready to shed pollen as the stigmas are emerging form the younger spike.
Crossing
Emasculation in Cumbu is laborious and difficult due to the small size of the flowers and
the late maturity of the anthers when compared to the stigma. About four-fifths of the upper
portion of the spike is removed an the rest is bagged before the styles appear to prevent
contamination. Flowers are pollinated by dusting them with fresh pollen obtained from the
desired male plant or by shaking a spike which is shedding pollen over the exposed stigmas.
Controlled cross pollination
Pearl millet does not require emasculation for making crosses. The female line will be
covered before stigma emergence with butter paper bag. Without removing butter paper bag we
can see emergence of stigma. After most of the stigma have emerged. Pollen from desired male
parent is collected and dusted on to the female line. Pollination is usually made in the morning.
Care should be taken to cover pollen parent previous day with butter paper bag. The crossed
heads are labeled.
Another method is instead of removing the selfing bag of female and dusting, the top of the
cover clipped of desired male parent inflorescence in the process of pollen bursting is inserted to
bursh the stigma. Then the clipped top of the bag is folded and stapled. The crossed heads can be
collected after 30-35 days.
Small Millets
Ragi/ Finger millet (Eleusine coracana) (2n:36) Family: Poaceae
In this crop self pollination is the general rule. The inflorescence takes 7-8 days to
complete anthesis. Time of anthesis 1 am – 5am. In each spike the order of opening is from the
top to bottom. In each spikelet the opening of the floret is from the base to top and one floret in
each spikelet opens a day.
Selfing, emasculation and pollination techniques
Selfing
The panicle before commencing anthesis is covered with paper cover and retained till the
blooming is over.
Crossing
Emasculation and crossing are tedious. However, both hand emasculation and hot water
treatments are followed. Hand emasculation is done in the evening and pollination is done very
early in the morning i.e., before 6 a.m. Hot water technique of emasculation of florets is also
successful. Hot water treatment at 520C for 2 minutes was the best as judged from the
percentage of hybrid seed-set. Then the spikelets are pollinated early in the morning.
Approach Method or contact method
The inflorescence to be opened will be selected and cut with long stalk from the male
parent. This is brought to the emasculated flower. The male flower as a whole will be tied round
with female flower. Then they are covered with butter paper bag. The cut end of the male
inflorescence will be immersed in water kept in a bottle. Natural cross pollination takes place in
2 to 5 days. Marker genes are utilized for identifying the hybrid seedlings in the nursery plot.
60-90% seed set is recorded in both methods.
Summary Cheat Sheet
Quick Recall Points
- This lesson focuses on key plant breeding concepts, terminology, and exam-relevant applications.
- Review major definitions, classifications, and method-wise distinctions from the sections above.
- Revise tables and examples from this lesson for fast pre-exam recall.
Exam Traps
- Do not confuse similarly named breeding methods without checking their core selection logic.
- Pay attention to crop-specific examples because the same principle can behave differently by species.
References
1 source • [1]
References
Standard Plant Breeding Class Notes (GPBR211)
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