Floral Biology & Plant Breeding objective of tea

1. About Floral Biology

Floral biology has important practical implications, in addition to its scientific relevance, given that flower characteristics and bloom affect fruit characteristics and yield. Yield derives from fruit quality (e.g. weight) and quantity (i.e. number), which, in turns, depend on flower quantity and quality: flowers must be suitable to become fruits, and then must be pollinated and fertilized, and must set fruits, which must then grow. Not all flowers can do all of this: some flowers, for instance, have aborted ovaries which are partially developed or absent at bloom, depending on when the abortion occurred. Even when still present, these aborted ovaries are not capable of becoming fruits. Normal pistils, may not be pollinated or fertilized, but also fertilized ovaries may drop after some growth, resulting in fruit drop.

Angiosperm flowers are the most advanced and structurally intricate in the Plant Kingdom. Their multiple components each have one or more specialized functions, most importantly the female and male generative organs, the pistil (gynoecium) and the anthers (androecium) respectively. Other floral organs also contribute to the success of the reproductive process. The sepals (calyx) protect the flower in bud, and in some species contribute to the floral display and even photosynthesis. The petals (corolla) are usually the main component of the floral display, which in animal-pollinated flowers provide visual and olfactory attraction.

2.     Flower Structure

Flowers are the reproductive structures produced by plants which belong to the group known as Angiosperms, or 'Flowering Plants'.  This group includes an enormous variety of different plants ranging from buttercups and orchids to oak trees and grasses. There are about 250,000 known species.

A flower is basically made up of four concentric rings of structures. There is an outer ring of modified leaves called sepals. These provide protection to the flower before it opens and are usually green. This outer ring is known as the calyx.

Inside the sepals is another ring of modified leaves called petals which are often brightly colored. This layer is known as the corolla.

Within the corolla are one or more stamens containing pollen, which are the male reproductive structures.

In the very centre of the flower are the female reproductive organs.

2.1   Idealized Flower Structure

2.2     The Basic Flower Parts

The flower consists of many different parts. Some of the most important parts being separated into both male and female parts.

2.2.1 Male Parts

·         Stamen

This is the male part of the flower. It is made up of the filament and anther, it is the pollen producing part of the plant. The number of stamen is usually the same as the number of petals.

·         Anther

This is the part of the stamen that produces and contains pollen. It is usually on top of a long stalk that looks like a fine hair.

·         Filament

This is the fine hair-like stalk that the anther sits on top of.

2.2.2 Female Parts

·         Pistil

This is the female part of the flower. It is made up of the stigma, style, and ovary. Each pistil is constructed of one to many rolled leaflike structures.

·         Stigma

One of the female parts of the flower. It is the sticky bulb that you see in the center of the flowers, it is the part of the pistil of a flower which receives the pollen grains and on which they germinate.

·         Style

Another female part of the flower. This is the long stalk that the stigma sits on top of.

·         Ovary

The part of the plant, usually at the bottom of the flower, that has the seeds inside and turns into the fruit that we eat. The ovary contains ovules.

·         Ovule

The part of the ovary that becomes the seeds.

2.2.3 Other Important Parts of a Flower

·         Petal

The colorful, often bright part of the flower. They attract pollinators and are usually the reason why we buy and enjoy flowers.

·         Sepal

The parts that look like little green leaves that cover the outside of a flower bud to protect the flower before it opens.

2.3     Flower Types

1.         Imperfect Flower

A flower that has either all male parts or all female parts, but not both in the same flower. Examples: cucumbers, pumpkin, and melons.

2.         Perfect Flower

A flower that has both the male parts and female parts in the same flower. Examples: roses, lilies, and dandelion.
4.  Pollination & Fertilization

     4.1     Definition:

The transfer of pollen grains from the anther to the stigma of a flower.

4.2     Types of pollination

Two types of pollination

1.      Self-pollination

2.      Cross-pollination

ü  Self-pollination

Transfer of pollen grains within one flower:

• One flower
• Pollen grains from the anther are transferred onto the stigma

ü  Cross-pollination

Transfer of pollen grains from one flower to another:

• Two similar flowers
• Pollen grains from the anther of one flower are transferred onto the stigma of the other flower

4.3     Agents of pollination

• Plants generally do not transfer the pollen from one flower to another by themselves.
• Although a few plants do have self-pollination – pollen from flower’s anther pollinating its own stigma.
• These plants need agents of pollination to help them.

Agents of pollination

Ø  Insects (bees)

• Pollen will stick to parts of insects’ bodies, e.g. pollen “bags” situated on the legs of bees

Ø  Other animals (birds and bats)

• These animals are usually nectar-drinking animals like sunbirds. (birds)
• These animals are usually nectar-drinking animals like nectar-feeding bats. (bats)

Ø  Wind

• Pollen tends to be smaller and lighter in order to be carried by the wind.

4.4     Fertilization

• When the male sex cells join with the female sex cells within the ovule.
• The resulting embryo then develops into a seed.
• Unfertilised ovules cannot become seeds.
• Fertilised ovules become seeds.

5. Self-incompatibility

5.1     What is Self-incompatibility – Definition?

Self-incompatibility is a general name for all those genetic mechanisms in flowering plants / angiosperms, which prevent selfing. It is phenomenon with which a plant with functional pollen fails to set seed when self pollinated. It is incompatibility between the pollen and the stigmas of the same plant.

5.2     General features of Self-incompatibility

§  Prevents selfing and promotes outbreeding so increases the probability of new gene combinations

§  Causes may be morphological, physiological, genetically or biochemical

§  Normal seed set on cross pollination

§  May operate at any stage between pollination and fertilization

§  Reduces homozygosity

§  In plants, self-incompatibility is often inherited by a single gene with different alleles in the species population

6.     Tea Floral Biology

6.1     Introduction

A comprehensive knowledge on reproductive traits is a prerequisite in utilizing the existing tea germplasm effectively for crop improvement to develop superior planting material for grower acceptance and market profitability. The Sri Lankan tea germplasm was characterized based on

ü  Reproductive traits viz

ü  Floral morphology

ü  Pollen biology

ü  Stigma receptivity  

ü  Phenology of flowering and fruit set

The variability in floral morphology, especially the style morphological features, formed phenotypic clines rather than distinct groups. Studies on pollen biology and stigma receptivity revealed significant variability and asynchrony that could result unequal reproductive success among the genotypes. Four distinct patterns were predictable among the genotypes based on flower and fruit abundance and the time of flowering and fruit set.

Three well marked flowering periods occurred in February to April, July and in November. Nonetheless, major flowering period coincided February and March in all the genotypes allowing free crossing between the different genotypes. Profuse mature fruit crop was obtained in February to May. Approximately 26% success was achieved in tea controlled hybridization programmes. Fruits carry two seeds on average and became mature in 8–9 months after pollination. Zygotic development in tea takes more than 1 month after pollination and early embryonic development continued for 4 months after pollination. The indexing of the morpho-physiological diversity and the phenological calendars of flowering and fruit set made available in the study are of significant importance in effective utilization of the tea germplasm for crop improvement.

Flower Part	China	Assam	Cambod
Ovary	Densely hairy three locules	Three locules	3-4 or sometime 5 locules
Style	3-4,free for the greater part of length	3,united to the greater part of length	3,free up to one third

6.2     Tea flower growth stages

The flower growth of tea was divided into 5 different stages as described below picture

Stage I. Sepals separated and their ends just started to go away from each other.

Stage II. Ends of sepals completely separated from each other.

Stage III. Petals started to split.

Stage IV. Half opened flower.

Stage V. Full bloom.

7.     Objectives of Plant Breeding in tea

The prime aim of tea breeding is to improve the characteristics of plants that they become more useful automatically and economically. Some of the objectives may be summarized as follows.

1. Higher Yield

2. Improved Quality

3. Disease and Pest Resistance

4. Maturity Duration

5. Agronomic Characters

6. Photo and Thermo Insensitivity

7. Synchronous Maturity

8. Non-Shattering Characteristics

9. Determinate Growth Habit

10. Dormancy

11. Varieties for a New Season

12. Moisture Stress and Salt Tolerance

13. Elimination of Toxic Substance

14. Wider Adaptability

15. Useful for Mechanical Cultivation

8.     Discussion

ü  The development of flowers from the bud to full bloom takes usually about 24–28 days, varying between different cultivars.

ü  Flower development follows initially cell division slow growth phase followed by rapid cell expansion phase. In case of tea, the petals and flower size was 38–44% of the full bloom size which results from cell elongation.

ü  Mean fresh weight of tea flowers at different developmental stages was statistically the same in initial developmental stages. An increase in the fresh weight of the flowers was observed from stage 4 to stage 5. The moisture percentage in different stages of tea flowers was highest in full bloom stage.

ü  The amount of protein per unit dry weight was highest in the youngest stage and lowest in the later stages of flower development.

ü  Tea flowers contain similar nutrients as tea leaves.

ü  Flavan-3-ols recorded highest levels at the stage 3 where petals started to split and all the five catechins showed the similar trend. Epigallocatechin (EGC) recorded the highest content in stage 3 of flower development followed by epigallocatechin gallate (EGCG). Epicatechin gallate (ECG) recorded highest levels at stage 5 full bloom of flower development. The individual catechins as well as total catechin levels were highest in the stage 3 of flower development excepting ECG which recorded higher levels at stage 5. This decrease in levels of total catechin and individual catechins could be due to the flower expansion at stage 4 and stage 5.

9    References

ü  Ausin, I., et al. (2005). "Environmental regulation of flowering". Int J Dev Biol

ü  Balasooriya J (1996) Effect of altitude on shoot development of clonal tea with special reference to clonal selection and harvesting intervals. Sri Lank.

ü  Anonymous (2001, 2002) Reports of the Agronomy Division, Annual Reports, 2001 & 2002. The Tea Research Institute of Sri Lanka, Talawakelle, Sri Lanka.

ü  Robin Joshi, Poonam, Ashu Gulati (2011).” Biochemical attributes of tea flowers (Camellia sinensis)”. India.

ü  W.A. Janendra M. De CostaI, A. Janaki MohottiII,  Madawala A. Wijeratne (2007),( Ecophysiology of tea). Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Sri Lanka

ü  http://leavingbio.net/vegetativepropagation.htm

ü  http://www.familymanagement.com/holidays/flowers/flower_anatomy.html

ü  http://www.countrysideinfo.co.uk/flower.htm