**Abstract**

Legumes are the second-largest source of food after cereals, all over the world, and an essential protein source in the vegetarian diet. These crops remain essential to subsistence production as they have the inherent capacity to survive in an adverse ecosystem and require minimum investment for their management. The increasing challenge of feeding a rapidly growing population places excessive pressure on current food production systems, which can no longer be sustained by traditional plant breeding alone. Therefore, modern breeding methods with increased genetic gains are required to meet the food demand of the increasing population. In the past few decades, the efficiency of legume crop breeding programs has increased considerably using novel and multidisciplinary approaches in breeding programs. A multidisciplinary approach combining conventional plant breeding, mutation breeding, plant biotechnology, and molecular breeding is strategically ideal for production of new and improved crop varieties. This chapter focuses on recent advancements in plant biotechnology, related molecular methods, phenomics, and their application in breeding of legume crops.

**Keywords:** molecular marker-assisted backcrossing, molecular markers and genomics, food legume crops, genetic improvement, genomic assisted breeding

## **1. Introduction**

Legumes are present in the diet of millions of people worldwide because these crops are associated with nutrition and health. Along with this, also have economic and environmental benefits. These are safe for consumption, relatively inexpensive, readily available, and the preferred food source after cereals. These crops have the ability of symbiotic nitrogen fixation; as a result, they help in the efficient use of fertilizers, lower emission of greenhouse gases and soil health enhancement. This ability of legumes promotes the inclusion of these crops in cultivation systems, thereby contributing to the diversified system and sustainability [1].

Food legumes are divided into two groups: 1) oil seeds and 2) pulses/ grain legumes. Oil seed legumes have high oil/fat content such as soybean and peanuts and pulses are dry seed legumes with low-fat content used as food (moong, urad, lentil, moth, etc.). Grain legumes are grown in both tropical and temperate regions of the

world and used with cereals as pulse (dal). These are one of the major sources of income for smallholders who practise sustainable farming.

Today, malnutrition is more pronounced in developing countries due to the increasing population, and the most troubling one is caused by protein deficiency. Plant-based protein sources are the most desirable as they are nutritious, cheap, and easily accessible to poor people. Cereal-based diet system is deficient in protein content and essential amino acid lysine. In contrast, legumes contain protein and lysine amino acids, improving the nutritional status of diets based on cereals. Cereal diets containing legumes are considered one of the greatest therapies for protein caloric deficiency in developing nations [2]. In this way, legumes and cereals complement each other, and they must be eaten in a 35:65 ratio for nutritional balance.

In recent years, more people have substituted animal protein with vegetable protein due to increased health awareness and nutrition. With the increasing demand for vegetable protein, research on food properties and the utilization of indigenous food crops like legumes for protein-rich supplements are significantly increased [3]. These crops are also adapted to adverse climatic circumstances and are resistant to insect pests and disease, so they may be cultivated in arid climates with low or irregular rainfall.

In African and Asian countries, the primary contributors to protein and calories are legumes due to their economic and cultural reasons [3, 4]. Even though legumes crops have several benefits so far production is still less in comparison to cereals and vegetables. Cereal crops clearly overshadow these crops. It is necessary to increase awareness, spread the knowledge among the people, and encourage the farmers to grow legume crops along with cereals to increase their production.

#### **1.1 Constraints in genetic improvement of legumes**

Although legumes are a very useful protein source for humans and livestock, the research efforts to increase the productivity of legumes are lesser than the cereals. The poor yield of legumes may be due to growing these crops as subsistence in marginal lands with local varieties that do not tolerate biotic and abiotic stresses. Concerted attempts have been made during recent decades to enhance the yield potential of legumes with conventional methods, but genetic progress is poor compared to cereals [5].

The key challenges facing plant breeders in genetic improvement of legumes are discussed shortly below.

#### **1.2 Genotype and environment interactions**

Crops are largely determined by climatic conditions, and even minor changes from optimal conditions can severely affect plant growth and yield. Differential responses of improved cultivar strains are expected in different environments due to unpredictable climatic factors encountered at various sites and/ or years. G x E interactions then become a big challenge for any crop breeding program as they restrict effectiveness of breeding programs and selection responses. Legume crops show phenotypic instability due to environment (70–80%) and genotype x environment (17–27%) interactions for economically important quantitative traits, resulting in variable yield potential. The genotypic effects contribution is very less that is 1.5–7%. As a result, the environment has a crucial role in the stagnation of legume crop progress [6].
