PRINCIPLES OF CROP PRODUCTIONABT-320(3 CREDIT HOURS)) LECTURE 4 LECTURE-WISE COURSE BREAKUP MATING SYSTEMS IN SEXUALLY REPRODUCING PLANTS BIOMETRICAL GENETICS AND PLANT BREEDING FACTORS AFFECTING CROP PRODUCTION
MATING SYSTEMS IN SEXUALLY REPRODUCING PLANTS Three mating systems: • Random mating • Inbreeding • Outbreeding Can be seen in sexually reproducing populations. Accordingly, the genetic structure of the populations will also be different.
RANDOM MATING This is the condition in which each male gamete is likely to get equal chance to fertilize a female gamete. This phenomenon is called panmixis. The only factor that acts in the process of fertilization is chance. Under such conditions, the population will be a balanced group of the different genotypes and phenotypes possible, distributed according to theoretical ratios of probability.
INBREEDING Inbreeding is the phenomenon in which gametes from the same genetic source (gametes from the same genetic structure) get higher chance to mate at the time of fertilization. Many crop plants naturally promote inbreeding (e.g., rice, wheat and pulses). Inbreeding results in the improvement of homozygosity in plant populations. Self-pollination (autogamy) promotes inbreeding. There are several mechanisms in nature that accomplish autogamy including bisexuality, homogamy and cleistogamy.
BISEXUALITY This is the condition in which both the male (androecium) and female (gynoecium) reproductive structures are produced by the same flower. Bisexuality promotes self-pollination. Capsicum, pulses, are the examples of bisexual flowers.
HOMOGAMY This is the condition in which both the male and female reproductive parts of a bisexual flower mature simultaneously. The androecium and gynoecium mature at the same time to promote self-pollination. In such flowers, mostly pollination takes place before the opening of flower.
CLEISTOGAMY In some cases the flowers never open and pollination takes place in the bud condition. This is called cleistogamy. As a result of this, chance of cross-pollination is eliminated. Arachis hypogea is an example.
OUTBREEDING Outbreeding is the phenomenon in which gametes from different parental sources get higher chance to unite at the time of fertilization. There are many crop plants which show cross pollination (allogamy). E.g., coconut, maize, sunflower and pearl millet. The following mechanisms are involved to promote cross-pollination in such plants: • Monosexuality • Dichogamy • Heterostyly
MONOSEXUALITY This is the condition in which male and female flowers are separate. Both the types of flowers may be seen on the same plant (monoecy, e.g., coconut) or on different plants (dioecy, e.g., papaya).
DICHOGAMY In many bisexual flowers, androecium and gynoecium mature at different times so as to promote cross-pollination. This phenomenon is called dichogamy. It may be of two types: protandry in which androecium (male reproductive organ) matures first and protogyny (female reproductive organ) in which gynoecium matures first. Both protogynous and protandrous varieties of walnut have been reported.
HETEROSTYLY This is a condition in which two or more types of styles are seen in some plants. Accordingly, different types of staminal filaments are also seen. In flowers with long styles, short staminal filaments are seen, whereas in flowers with short styles long staminal filaments are present. Primrose shows heterostyly.
BIOMETRICAL GENETICS AND PLANT BREEDING FACTORS INVOLVED IN AN EXPERIMENT Experiments related to the screening of plants are conducted either in net houses or green houses under controlled conditions or in the open field under technical supervision. When a field experiment is designed, many factors like soil heterogenerity, replications, border effect and randomization are taken into consideration. • Replication • Randomization • Local Control
REPLICATION The most important factor in the conduct of an experiment is the replication of the treatments. The repeated application of the treatments under investigation is known as replication. It is possible to calculate an estimate of error of the experiment from replicated trials. Experimental error gets reduced with the increase in the number of replications. But, in practice, an optimum number is to be fixed for each type of experiments. The number of replications will depend on the degree of accuracy required, availability of land and the quantity of seeds available.
RANDOMIZATION Random allocation of treatments to various plots is necessary for an objective comparison between treatments. By randomization, better estimate of the average impact of environmental factors on the outcomes becomes possible.
LOCAL CONTROL This is the grouping of homogenous experimental units into blocks and the study of within block variations. The variations within block are caused by soil heterogeneity and other local effects. One such effect is known as border effect. It is the harmful or useful effect enjoyed by border lines of the experimental plants. To avoid border effect, separate border rows of plants are grown surrounding the experimental plots.
FACTORS AFFECTING CROP PRODUCTION Agricultural production, including food and other crops and livestock husbandry, is determined by the interaction of farmers with: • natural resources - biophysical framework of soils, water, temperature, flora and fauna; • traditional practices; • government policies (e.g. land tenure, marketing, animal welfare, labour relations); • international trade agreements; • public opinion and concerns; • environmental fluctuations.