eChapters

Reproduction

Since the life of an individual plant is limited in duration, it has developed certain mechanism by which it can reproduce itself inorder to continue the perpetuation of the species and also to multiply in number. Mode of reproduction determine the genetic constitution of crop plants, that is, whether the plants normally homozygous or heterozygous. A knowledge of the mode of reproduction of crop plants is also important for making artificial hybrids. The various modes of reproduction found in crop plants may be broadly grouped into the following two categories : (i) Asexual and (2) Sexual.

Asexual Reproduction

Heterosis breeding systems depend upon the reproduction system of plants, whether the plant is propagated asexually or sexually. Therefore, before development of hybrids, information regarding type of flower, flowering habits and floral biology is required in hybridization programme (emasculation and pollination). In a sexual reproduction, plants develop from vegetative parts of plants (vegetative propagation) or may develop from unfertilized gametes, ovular tissues, and modified cells (apomixes). Vegetative reproduction includes plant regeneration from underground stems such as tubers in potato, bulbs in onion and garlic, underground tubers such as sweet potato, corms in yams, and rhizomes in ginger and turmeric. In certain cases, aerial parts are used for propagation as stem cuttings in tapioca, sweet potato, watercress, and drumstick, root suckers in curry leaf and globe artichoke and turfts in chive. In apomixes, sexual reproduction or gamete fusion is replaced with other form of asexual reproduction. In this case, embryo develops without fertilization. Apomixis may be of different types: (1) Apogamy—where embryo develops from a gametic cell of embryo sac other than egg cell. Apogamy may be haploid or diploid. Diploid apogamy has been reported in onion. (2) Polyembryony—where more than one embryo develops from a seed, resulting in more than one seedling. In this case, embryos usually develop from nucellus integuments, or chalaza in addition to normal syngametic embryo. (3) Parthenogensis where embryo develops from an unfertilized egg. This may be at haploid or diploid level. Sometimes, embryo development take place from unfertilized egg of a diploid plant. This is called haploid parthenogenesis. It originates in plants due to environmental effects, especially due to effects of high or low temperature, use of foreign pollen, application of chemicals, and use of irradiated pollen. Haploids parthenogenesis produces haploids.

The capacity to reproduce is one of the most important characteristics of all living beings. Reproduction is a process of producing offspring and is aimed to preserve individual species. This is known for self-perpetuation. There are several modes of reproduction, which vary from species to species, in available conditions. All the reproductive methods of plants are broadly classified into two types, i.e., (i) asexual reproduction (apomixis) and (ii) sexual reproduction (amphimixis). In asexual reproduction, the new individuals are produced by any means other than the fusion of sex gametes. In sexual reproduction, the gametes from male (androecium) and female organs (gynoecium) of the flower are fused to produce a zygote (Schranz et al., 2005; Rodrigues et al., 2008). Amphmixis and apomixis are the two sides of same coin (Curtis and Grossniklaus, 2007).

Reproductive processes have profound influence on the ultimate economics of livestock production. Regularity in reproductive functions guarantees a profitable return to the farmers. Reproductive efficiency is paramount to the success of goat husbandry. Disruption of one or another of the reproductive processes in male and female results in decreased reproductive efficiency and hence is of concern to the animal production strategies. Reproductive performance or efficiency depends on many hormonal, genotypic and environmental factors. Environmental stress can drastically reduce reproductive efficiency. Goats are the most prolific of all domesticated ruminants under tropical and subtropical conditions. Goats are genetically endowed with good reproductive efficiency in the sense that goats can breed three times in two years and many breeds give birth to twin and triplets.

Age at puberty in male and female goat

Puberty is the time when the reproduction first becomes possible and is characterized by the release of germ cells and sexual maturity. Age at puberty depends primarily on the growth rate of the kid which in turn depends on its quality and quantity of the feed offered.

Age at puberty in males has been variously defined as the age at which the complete separation of the penis occurs from the sheath, or the age of 1st appearance of spermatozoa in the seminiferous tubules or the availability of the first ejaculate. Although animals develop sex play much earlier than their ability to reproduce,considerable variation can exist between the age at puberty determined in different ways as it evident from the study of Elwishy and Elsawaf (1971) in male Damascus goats. The separation of the penis occurs at a mean age of 242.9 days while first ejaculate could be obtained only at the age of 509.2 days. Age at puberty varies with different breeds, plane of nutrition, presence of females etc. The endocrine development usually precedes the testicular development and androgen production is usually high prior to the actual onset of puberty.

Breeding of Heifers

    ·    Regardless of age, puberty is reached when a heifer weighs approximately 40% of her mature body weight.
 
    ·    Breeding however, is recommended when a heifer has reached 60% of her expected mature body weight. This is normally achieved when the heifer is 14 to 16 months old.
 
    ·    Smaller breeds may be bred one or two months earlier than large breeds because they mature faster.
 
    ·    Heifers in good condition and gaining weight at breeding time generally show more definite signs of estrus and have improved conception rates over heifers in poor condition and/or losing weight.
 
    ·    Over-conditioned or fat heifers have been reported to require more services per conception than heifers of normal size and weight.

Introduction

In India 70 to 75 per cent of the indigenous cattle and buffaloes are designated as non-descript that is they do not come under any well defined breed. Among the animals of defined breed also, less than 5-10 per cent of the population can be considered as elite and used for the production of breeding stock. Average productivity of cross-bred and desi cows is 2141 kg/lactation & 634 kg /lactation, respectively, which is still very low. The average productivity of buffaloes is 1355 kg/lactation only.

Pineapple is a monocarpic perennial herb. Each stem flowers only once and dies after fruiting, similar to bananas, before a side shoot takes over. After the pineapple plant reaches a certain size, natural inflorescence initiation (flowering) occurs in response to decreasing day length and temperature (Bartholomew, 2003). Flowering of Smooth Cayenne pineapples grown under an 8-hour day length was encouraged by a night temperature of 20°C, whereas f lowering was delayed by temperatures of 15 and 20°C, and totally inhibited by 30°C.Flower initiation usually starts in November and lasts through the winter. Flowering in nature is highly irregular, and some plants can fail to produce fruit. Thus, growth regulators such as ethylene (25-50 ppm) and NAA (25 ppm) are used in industrial practise to force plants to bloom. The numerous radish-purple sessile flowers are spirally arranged on the axis, each with a pointed bract. To explain the emergence of developing inflorescence, this stage is also known as the red bud stage. The spike-like inflorescence contains 100 to 200 florets. The petals are white at the base and bluish-purple above the calyx at anthesis. They are ligulae form in shape, about 1.6 cm long and 5 mm wide, and are about 1.6 cm long and 5 mm wide (Collins, 1960).The outer f lower petals are very close together, allowing only small insects to reach the f lower; they have 14 to 20 locules, resulting in a capacity of 6000 to 7000 seeds per 150 floret fruit. After pollination, fruits with 2000 to 3000 seeds are not uncommon (Collins, 1960).

Abstract

The breeding potential of Ompok bimaculatus is declining day by day due to decrease of rainfall and increase of atmospheric temperature. As a result, the population of Ompok bimaculatus is significantly reducing in the fresh water bodies of Tripura.
 
The results of reproductive biology of O. bimaculatus were based on the fish samples collected from different locations of some rivers and Hurijala wetland of Tripura. Total weight of the sampled fish varied from 22 g to 171.50 g and the females had a greater weight and length than males. Total length of the males varied from 16.50 cm to 29.50 cm, while the females ranged from 17.0 cm to 33.0 cm. Female dominance over male was observed in the species. The ratio of males to females was 1:1.58. Significant correlation exists between fish length and weight in both males (R² = 0.943) and females (R² = 0.827).

Knowledge on fish reproductive biology is extremely important to understand various issues relating to reproduction and fishery management. Reproductive success in aquaculture systems depends to a greater extent on our knowledge about sexual differentiation, gonad structure, gametogenesis, spawning, larval metamorphosis, etc for successful captive breeding of a fish species. This chapter therefore, contains information on secondary sexual characters, sex-ratio, gonad structure, gonadal maturity, fecundity and embryonic development of striped murrel.

2.1 Secondary Sexual Characters

The sexes are separate in striped murrel however differentiation of sex is not easy when fish is immature. The differentiations in sexes become distinct with advancement of maturity during spawning season. On attaining full maturity, a good fecund mature female could be easily distinguished with having bulged belly originating nearing the site of pectoral fins and extends near to the vent.

Maintenance of optimum fertility and reproductive goals is very important for profitable and economically viable cattle rearing. It is highly desired and essential for the farmers to maintain the high reproductive efficiency in cows so that the losses incurred on infertility are reduced to the maximum extent through good managemental practices and following scientific guidelines properly.

Reproductive problems in bovine dairy farms can significantly impact the productivity and sustainability of the cattle and buffalo industry. Challenges such as diminished conception rates, delayed age at first calving, prolonged calving intervals, and higher embryonic losses have comprehensive implications, resulting in economic setbacks and impeding genetic advancements. These intricate problems are attributed to a combination of factors encompassing deficient reproductive management strategies, inadequate nutritional provisions, suboptimal breeding methodologies, the prevalence of infectious diseases, and the impact of environmental stressors. Inadequate management of the estrus cycle and mistimed insemination practices underscore the significance of effective reproductive management. Poor nutritional support can detrimentally affect the onset of puberty, compromise the quality of oocytes and embryos, and usher in an overall decline in reproductive performance. The presence of infectious diseases not only intensifies difficulties in achieving successful conception but also amplifies the rates of embryonic as well as pregnancy loss.

Additionally, environmental stressors, particularly heat stress, can disrupt estrus patterns, impede oocyte development, and hinder embryo growth. Consequently, addressing these complex reproductive issues necessitates a comprehensive and multifaceted approach. This approach entails the implementation of sound reproductive management protocols to ensure precise monitoring of estrus cycles and timely insemination practices through proper record-keeping. Furthermore, optimizing nutritional provisions tailored to distinct reproductive stages enhances ovarian function, augments oocyte quality, and promotes healthy embryo development. Rigorous biosecurity measures, including strict quarantine practices and adherence to vaccination regimens, play a pivotal role in disease prevention and control within the farm environment. Moreover, the integration of advanced reproductive technologies, such as ultrasonography and embryo transfer, offers avenues for early pregnancy detection and facilitates selective breeding to enhance genetic progress. By amalgamating these strategies, a concerted effort can be made to enhance reproductive efficiency, safeguard herd health, and ultimately support the overall productivity and sustainability of the cattle and buffalo industries.

Reproductive development determines flowering, pollination, fruit set, fruit growth, maturation, and ultimately horticultural productivity. This chapter introduces the physiological processes controlling flowering and reproductive development and explains the influence of environmental factors and plant hormones. Major plant growth regulators such as auxins, gibberellins, cytokinins, ethylene, and abscisic acid are considered in relation to horticultural applications. PGRs can influence rooting, flowering, fruit set, fruit size, thinning, ripening, dormancy, and senescence when used appropriately. The chapter emphasizes crop-specific concentration, timing, method of application, and environmental conditions, highlighting the importance of responsible PGR use for improving yield, quality, and marketability.

The reproductive physiology of finfish and shellfish involves the complex biological systems that regulate their breeding and spawning cycles. In aquaculture, a sound understanding of these systems is critical for effective hatchery operations, seed production, and broodstock management. Reproductive success in both groups is influenced by hormonal signals, environmental cues, and genetic traits. In finfish, reproduction is typically seasonal and sensitive to external factors such as light cycles (photoperiod), water temperature, diet, and overall water quality. Central to their reproductive regulation is the hypothalamus-pituitarygonadal (HPG) axis. The hypothalamus secretes Gonadotropin-Releasing Hormone (GnRH), which prompts the pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones drive the formation of gametes—oocytes in females and sperm in males. Oogenesis involves yolk formation and final maturation of eggs, while spermatogenesis includes sperm cell development and release. Spawning can be natural or artificially induced using hormonal treatments like human chorionic gonadotropin (hCG), Ovaprim, or carp pituitary extract.
In shellfish, including mollusks and crustaceans, reproductive strategies vary widely. Mollusks may have separate sexes or be hermaphrodites, and they typically respond to environmental changes such as shifts in temperature or salinity. For instance, in oysters, gametes develop within the gonads and spawning can be initiated using methods like thermal changes or chemical stimuli such as serotonin. Crustaceans, like shrimp and crabs, rely on the brain-eyestalkgonad axis. Here, the X-organ–sinus gland complex in the eyestalk secretes gonad-inhibiting hormone (GIH), which slows down reproductive development. To promote spawning in shrimp like Penaeus monodon and Penaeus vannamei, eyestalk ablation is often used to remove this inhibition. Technological advancements have allowed for greater control over the reproductive cycles of aquatic species. Techniques such as hormonal manipulation

Reproductive is fundamental property of living beings. While lower animals reproduce by simple methods, the higher animals attain greater degree of animals reproduce by complexities in the reproductive functions. Basic units (Gonads) of males and females are testis and ovaries respectively. The gonads of each sex perform dual roles:

• Formation of gametes (sperms by testis and ovum by the ovaries)
• Production of hormones.

Role of Hormones in Reproduction

Most of the aquatic organisms spend much of their lives and energies for reproduction. The young ones mature, develop sperms or eggs, spawn, and then recover to repeat the breeding cycle that continues till their death. In a majority of fish species males and females are separate individuals, fertilization is external and large number of eggs are produced (on an annual basis, its fecundity) which develop, hatch and mostly grow without parental care. The sperm and eggs are usually produced in such quantities that they represent a large expenditure of energy. The spawning process may be preceded by migrations or nest building, and followed by care of the young. Thus the success of any fish is ultimately determined by the ability of its members to reproduce successfully in a fluctuating environment and thereby to maintain viable populations.  As each fish species occurs under an unique set of ecological conditions, it has an unique reproductive strategy with varied anatomical, physiological, behavioral and bioenergetics adaptations. Unlike the finfishes, in shellfishes sexes are separate. The shellfishes use various signals to attract the opposite sex.

Insects show sexual Dimorphism i.e., the sexes are usually separate and are dioecious. Male reproductive system produces sperms, stores them and delivers them i.e., spermatozoa. It also produces the seminal fluid, which provides a suitable environment to the sperms and nourishes them. Male reproductive system also situmilates are the female for oviposition. The female reproductive system produces and stores eggs provide nutrition to them for embryonic development, recieves and stores the sperms, is a site of fertilization. Female reproductive system also deposite eggs and may provide additional protection to the embryos. The reproductive system of both male and female insect’s bearis a gononpore, which is an opening of a pair of gonads. Both the gonads open into the gonopore by a median duct. For the secondry sexual purposes, e.g., formation of spermatophore and egg-case or ootheca, some accessory glands are associated with the reproductive system.

Gametogenesis

Male Gametogenesis: Male gametogenesis is the formation of male gametes and it occurs in the anthers. The end products of meiosis in higher plants are four microspores. Two mitotic divisions occur in microspores. The first division produces a tube nucleus and a generative nucleus. The second mitotic division occurs only in the generative nucleus resulting into production of two sperm cells (Fig. 3.1). The microspore is haploid (n) and develops into pollen grain in the anther, and the pollen grain further develops into a pollen tube on the stigma and in the style. The pollen tube, when it reaches the embryo sac is the fully developed male gametophyte and is trinucleate, two sperm cells and one tube nucleus.

10.1. Introduction

During last few decades dairy animal production has been intensified several folds, along with this reproductive problems have also increased. For efficient dairy animal production, the cow should show regular reproductive activities like cyclic breeding activity, pregnancy at appropriate time, give birth of a live healthy calf and again pregnant after sometimes. If any of these activities are inadequate, then it substantially affects the profitability of the farm. There is an ample scope of improvement of these reproductive setbacks through traditional breeding, feeding and management. However, reproductive problems can be minimized by the use of recently developed reproductive techniques. It not only minimizes reproductive problems, but also improves the reproductive efficiency of the dairy herd and better exploitation of the genetic potential of high merit animals.

Failure to accurately diagnose ovarian function is said to be one of the reason for poor reproductive efficiency in this species. The information regarding ovarian function can be gathered either by observing the reproductive behavior of the animal, status of reproductive hormones or palpation of ovaries per rectum for the presence of cyclic or pathological structures. However, due to poor expression of estrus signs behavioral observations poorly reflect the accurate information about ovarian function in buffaloes. Similarly, palpation per rectum does not provide reliable diagnosis since the CL is frequently embedded deep in the ovarian stroma of buffalo ovary and findings vary due to its subjective nature. Furthermore, measurement of hormones requires sophisticated laboratory procedures/ instruments for making a correct diagnosis. Therefore, real time ultrasonic examination is a better alternative to ascertain reproductive status of buffaloes and for devising suitable strategies to optimize fertility of this species (Sharma, 2003). However, it is important to mention that information gained from ultrasound must be used in conjunction with reproductive history of the animal, palpation of genital tract, and other diagnostic procedures rather than in isolation.

The metabolic rate of reptiles is lower than for mammals and birds, and consequently the k constant in determining energy expenditure, nutritional requirements and even calculating allometric drug doses are related to the equation: Basal Metabolic Rate (BMR) = K(Wkg0.75) = Kcal/day, where K is the energy constant = 10 in reptiles and Wkg is the animalís weight in kilograms.