AGE 304 — Technology of Breeding Crop: Lecture Note

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Course code: AGE 304 Course title: Technology of Breeding Crop Course credit load: 2 Units Series 1: Concepts, Purposes, and Biological Variation in Crop Breeding • Part 1.1: What is Crop Breeding? o Sub Part 1.1.1: Definition of crop breeding o Sub Part 1.1.2: Historical development of crop breeding o Sub Part 1.1.3: The role of the plant breeder • Part 1.2: Purposes of Crop Breeding o Sub Part 1.2.1: Improving yield and yield stability o Sub Part 1.2.2: Improving quality and resistance o Sub Part 1.2.3: Adaptation to environmental conditions • Part 1.3: Biological Variation in Crop Plants o Sub Part 1.3.1: Sources of genetic variation o Sub Part 1.3.2: Mutation and polyploidy as sources of variation o Sub Part 1.3.3: Phenotypic versus genotypic variation • Part 1.4: Importance of Variation in Breeding Programmes o Sub Part 1.4.1: How breeders exploit variation o Sub Part 1.4.2: Conservation of genetic resources o Sub Part 1.4.3: Genetic erosion and its consequences

Introduction Crop breeding is the science and art of changing the genetic make-up of plants to produce varieties that better serve human needs. Every major food crop grown in Nigeria today is the product of centuries of deliberate or unconscious selection by farmers and, more recently, of systematic scientific breeding programmes. Understanding what crop breeding is, why it is practised, and where the raw material of breeding (biological variation) comes from is the essential starting point for any student of crop improvement. This Series introduces the definition, history, and objectives of crop breeding, the purposes that drive breeding programmes, and the biological variation that makes breeding possible. We begin with the concept of crop breeding and the breeder's role, cover the main breeding objectives, and then examine the sources, types, and importance of variation, concluding with the conservation of genetic resources and the threat of genetic erosion. All subsequent Series build on the foundation established here. Series Learning Outcomes Upon completing this Series, you should be able to: • SLO 1.1 define crop breeding and explain how it differs from crop agronomy (Linked to Part 1.1), • SLO 1.2 describe the historical development of crop breeding from farmer selection to modern scientific breeding (Linked to Part 1.1), • SLO 1.3 state the main purposes of crop breeding programmes and explain the importance of each (Linked to Part 1.2), • SLO 1.4 identify and describe the major sources of genetic variation available to plant breeders (Linked to Part 1.3), • SLO 1.5 explain mutation and polyploidy as sources of variation and give examples relevant to Nigerian crops (Linked to Part 1.3), • SLO 1.6 distinguish between phenotypic and genotypic variation and explain why this distinction matters in breeding (Linked to Part 1.3),

• SLO 1.7 describe how plant breeders exploit variation in a breeding programme (Linked to Part 1.4), and • SLO 1.8 explain the importance of genetic resource conservation and describe the consequences of genetic erosion (Linked to Part 1.4). 1.1 What is Crop Breeding? 1.1.1 Definition of crop breeding Crop breeding is the purposeful manipulation of the genetic composition of plant populations to produce new varieties (cultivars) with improved characteristics that better meet human needs. It combines knowledge from genetics, agronomy, plant pathology, statistics, and molecular biology to develop plants that yield more, resist diseases and pests, tolerate environmental stresses, and produce better-quality products. Crop breeding differs from crop agronomy in that agronomy improves the environment around the plant (soil, water, nutrients) while breeding improves the plant itself at the genetic level. A cultivar (variety) is a plant grouping that has been selected for particular characteristics and can be reproduced with those characteristics maintained. Breeding produces new cultivars through cycles of crossing, selection, and evaluation. The term "variety" is used informally; "cultivar" is the formal term in plant taxonomy. In Nigeria, the National Variety Release Committee (NVRC) under the Federal Ministry of Agriculture must approve new cultivars before they can be commercially released and distributed to farmers. Fill in the blank: Crop breeding is the purposeful manipulation of the ________ composition of plant populations to produce new cultivars with improved characteristics. 1.1.2 Historical development of crop breeding Crop breeding began approximately 10,000 years ago when early farmers in the Fertile Crescent, Mesoamerica, and sub-Saharan Africa began selecting and saving seed from the best plants in their fields. This unconscious selection gradually transformed wild plants into the domesticated

crops we know today: teosinte became maize, wild emmer became wheat, and wild cowpea became the cultivated cowpea dominant in Nigerian agriculture. Key features of domestication (larger seeds, non-shattering seed heads, synchronous maturity) are all the result of unconscious or deliberate selection. Scientific crop breeding began with the rediscovery of Mendel's laws in 1900, which provided the theoretical basis for predicting the outcome of crosses. The 20th century saw the development of hybrid maize in the 1920s to 1940s (doubling yields in the United States), the Green Revolution in the 1960s to 1970s (semi-dwarf wheat and rice varieties that transformed food security in Asia), and more recently marker-assisted selection and genomic selection using molecular tools. In Nigeria, the International Institute of Tropical Agriculture (IITA) in Ibadan has been the leading centre for scientific breeding of tropical food crops since its establishment in 1967. Fill in the blank: Scientific crop breeding began with the rediscovery of ________ laws in 1900, which provided the theoretical basis for predicting the outcome of crosses between parent plants. Figure 1.1: Timeline of the major milestones in the history of crop breeding

1.1.3 The role of the plant breeder The plant breeder is a scientist who designs and manages the programme of crosses, selections, and evaluations that produces new cultivars. Key responsibilities include: defining the breeding objectives based on farmer and market needs; assembling the genetic base (collecting parent materials with the desired traits); making crosses to combine desired traits in one plant; selecting superior individuals or lines from the segregating offspring; evaluating selected lines in multi-location trials; and releasing superior lines as cultivars after meeting national variety release requirements. The breeder must also understand the mating system of the target crop (self-pollinated or cross-pollinated) because it determines which breeding method is appropriate. Close collaboration with agronomists (for yield trial management), plant pathologists (for disease resistance screening), food technologists (for quality evaluation), and extension agents (for feedback on farmer needs) is essential. A breeding programme typically takes 8 to 15 years from the initial cross to the commercial release of a new cultivar, requiring sustained institutional support and funding. Fill in the blank: A breeding programme typically takes ________ to 15 years from the initial cross to the commercial release of a new cultivar, requiring sustained institutional support and funding. Pilot questions 1.1 1. Define crop breeding and explain how it differs from crop agronomy. 2. Define the term cultivar and explain the role of the NVRC in Nigeria. 3. Describe two key milestones in the historical development of crop breeding. 4. State four key responsibilities of a plant breeder. 5. Explain why a breeding programme takes 8 to 15 years to produce a new cultivar.

1.2 Purposes of Crop Breeding 1.2.1 Improving yield and yield stability The primary purpose of most crop breeding programmes is to increase yield: the quantity of marketable product produced per unit area. Yield improvement directly addresses food security by enabling more food to be produced from the same land area. In Nigeria, the yield gap between actual farmer yields and the potential yields demonstrated in research station trials is very large for most food crops (for example, Nigerian farmers average 1 to 1.5 tonnes per hectare of maize against a research station potential of 5 to 8 tonnes per hectare). Breeding for higher yield potential is therefore a critical national priority. Yield stability is equally important: a high-yielding variety that performs well in good seasons but collapses in drought or disease pressure is of limited value to smallholder farmers who cannot risk total crop failure. Breeders therefore select for broad adaptation (performance across many environments) or specific adaptation (high performance in a defined target environment). Yield stability is measured by evaluating varieties across multiple locations and seasons and using statistical tools such as stability analysis to identify varieties that maintain performance despite environmental variation. Fill in the blank: Yield ________ is as important as high yield potential; it measures whether a variety maintains performance across multiple environments and seasons rather than only in favourable conditions. 1.2.2 Improving quality and resistance Quality improvement covers nutritional quality (protein content and amino acid profile in cereals and legumes, oil content and fatty acid profile in oilseed crops, vitamin and mineral content), processing quality (milling recovery, cooking time, taste and texture), and market quality (grain size, colour, and appearance that determine market price). In Nigeria, breeding programmes have developed quality protein maize (QPM) with improved lysine and tryptophan content, high-iron and high-zinc cowpea varieties, and improved oil palm with higher oleic acid content.

Resistance breeding aims to develop cultivars that withstand or tolerate the major biotic

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