Peas and Beans

PREFACE

Peas and beans represent just a small section of the large family of Fabaceae that contains many hundreds of species, from tall trees to soil-clinging shrubby plants. They have been successful in colonizing many areas of the planet due to their adaptability to grow in a range of conditions from dry hostile semi-deserts to tropical rain forests. However, the main feature that humans have exploited in domesticating those species that could be of most use is their successful symbiotic relationship with soil-borne Rhizobium bacteria that allow the plants to produce their own supply of nitrogen nutrition, thereby extending the range of growing habitats to those soils that are inherently low in natural nutrients.

Of this huge group of plants, varieties of peas and beans have been developed from wild ancestors to provide grain crops that are high in food value. Although not understood by the early cultivators of these crops, the seeds contain some of the highest levels of proteins of all crop plants. It is no wonder that humanity has found that their production has provided a rich source of food that is easily stored once dried and can be used in a wide variety of foodstuffs for humans and their animals.

This book has been written to include the main types of peas and beans now grown on a significant scale and mostly commercially produced in large-area farming systems. Whilst there are several types and species of Pisum, Vicia and Phaseolus worldwide, the chapters herein purposely concentrate on peas as Pisum sativum and beans as Vicia faba and Phaseolus vulgaris and confine the species to those grown in cool temperate regions. Although there is some reference to small-scale subsistence farming of these crops, the contents are mainly restricted to the types of crop and their production on a large scale.

I have based much of the information in this book on my own 40-plus years of working in applied research, specializing in peas and beans and in particular as a plant pathologist and agronomist with the Processors and Growers Research Organisation based near Peterborough in Cambridgeshire. During this time I enjoyed close contact with the scientific community and also commercial growers, food processors, merchants and plant breeders in the UK, Europe and the USA, as well as visiting producers in all of these countries and the Middle East and Australia. The chapters therefore deal with the crops in detail as to the agronomy, crop protection and their use in processed food for humans and livestock, but chapters on breeding and physiology have been assisted greatly by colleagues in other research institutes and universities. There are a number of scientific books written by specialists detailing aspects of physiology, genetics and breeding in depth, and although I have included references to the main areas of development in each section, the chapters have been very much summarized for the purposes of this book.

I have aimed this book towards an audience of practical agronomists, students and others involved in the production of peas and beans, concentrating on aspects of husbandry and means of controlling pests, diseases and disorders. In addition, there are details of the characteristics of the varieties of peas and beans desired by producers to maximize their potential for variety improvement by breeders and to show that there is a big future for these crops in supplying food and refined food fractions of high quality and value for humans and their livestock and in the relatively new art of aquaculture. As the world population increases and developing countries become more demanding for meat and dairy-based food, the importance of peas and beans becomes greater both as an additional vegetable food source and as a source of nutritiously healthy products and reducing the reliance on animal proteins for food or for livestock feed. The continuing demand for vegetable protein that is more sustainable than conventional cereals or oilseed crops and that reduces the risks associated with nitrate leaching and nitrous oxide emission is a key factor in promoting peas and beans in temperate cool-season climates and growing areas. It is hoped that this book will provide a useful background to all engaged in production or research of these valuable legume crops.

The book has been a very long time in preparation but I would not have been able to complete the task without the generous help of colleagues and friends. I am particularly indebted to colleagues at PGRO, namely, Steve Belcher, Becky Howard (née Ward) and Jim Scrimshaw, with whom I worked for many years on a whole range of aspects of research into the production of the crops, and the information that I have been able to include in many parts of the book based on our research and practical experiences. Details included in the chapters covering pea breeding and genetics have been greatly helped by Claire Domoney and Mike Ambrose of the John Innes Centre; and Donal O’Sullivan of the University of Reading has helped with critically reviewing the section on faba bean breeding. A lifetime of working with Phaseolus vulgaris meant that Colin Leakey was the ideal prime contributor to that section along with relevant parts of other chapters. I am grateful to Pietro Iannetta of James Hutton Institute and Claire Domoney, who have provided detail and expanded the section on nitrogen fixation. On husbandry and harvesting, I am grateful to Matthew Hayward of Swaythorpe Growers and to Peter Waldock on aspects of fresh market production as well as Keith Costello, formerly of Princes Foods, for aspects of canning and Steve Marx for his description of the freezing operation.

Last but not least, I thank my editor, Rachael Russell, for her patience in waiting for the final manuscript and my wife Linda for prodding me into getting on with the job.

Anthony J. Biddle

Stamford, UK

2017

1

INTRODUCTION TO PEAS AND BEANS

Amongst the world’s most important non-cereal food crops, peas and beans are probably the most versatile. They provide a source of protein, are easily stored for long periods and can be consumed as processed or whole food by both humans and livestock. Commonly known as pulse crops or grain legumes, they are widely grown in temperate, subtropical and arid climates all over the world. They can be consumed as fresh vegetables or frozen, canned or dehydrated and also can be harvested as dry seed or pulses, which can be milled for use as a flour, or rehydrated and cooked whole. It seems likely that the adoption of legumes as agricultural crops in part reflects the nutritional balance between legumes and cereal seeds as well as the ability of legumes to break cereal rotations. Because of their ability to fix atmospheric nitrogen through their symbiotic relationship with soil-borne bacteria providing them with sufficient nitrogen for growth, the residue enriches the soil nitrogen supply for the following crop. The diversity of locations where peas and beans have been developed in agriculture is reflected in the diversity of species and varieties currently grown. They are found in agricultural systems throughout the world and have been domesticated in South and Central America, the Middle East, China, India and Africa. More recently they have been introduced to Europe and North America and to other temperate regions in Asia and elsewhere.

PEA AND BEAN FAMILIES

The family Fabaceae has been divided into three main subfamilies: Caesalpinioideae, Mimosoideae and Papilionoideae, but recently Caesalpinioideae has been further subdivided into several lineages, including the tribe Cercideae (Group, 2013) which contains a small group of tropical and temperate woody plants with flowers similar to those of Papilionoideae. The subfamily Mimosoideae includes 82 genera and more than 3200 species. Like Caesalpinioideae, Mimosoideae legumes are mainly tropical woody plants but a few temperate species exist. The woody perennial legumes are widespread and many species within this group have the ability to fix atmospheric nitrogen and as such have colonized many areas of the world where soil nutrients are low. They have also been commercially exploited for their timber or for various extracts such as gums and dyes.

The subfamily Papilionoideae (or Faboideae) is the largest group of legumes, consisting of about 650 genera and nearly 19,000 species (Lewis et al., 2005).

As members of the group of large-seeded legumes in the family Fabaceae, peas and beans fall into several distinct taxonomic groups (Fig. 1.1). Among these, three lineages have a number of groups that contain cultivated crops. The most important group economically is Phaseoleae, which includes soybeans (Glycine max), Phaseolus species and cowpea (Vigna unguiculata). The second group, Genisteae, contains Lupinus, of which there are three economically important grain legume species: Lupinus albus (white lupin), Lupinus angustifolium (narrow-leaved lupin) and Lupinus luteus (yellow lupin). The third taxonomic group, Fabeae, contains the so-called cool-season legumes, which include peas (Pisum sativum) and faba beans (Vicia faba) as well as lentils (Lens spp.) and sweet pea (Lathyrus spp.).

This book describes the most commonly grown large-seeded legumes used as food crops throughout the world. The species considered are: Pisum sativum, in the forms of dried peas (combining peas) and as fresh vegetables (vining peas or fresh market peas); Vicia faba, in the dry form as faba beans (or field beans) and the fresh form as broad beans; and Phaseolus vulgaris, in the dry form as dried beans and fresh as dwarf French or green (snap) beans.

Fig. 1.1. Classification of Fabaceae.

PEAS

History

Pisum sativum is the most commonly cultivated species in temperate climates. It is an annual with seeds that can be harvested in the immature state either as whole pods and consumed as mangetout, or as shelled immature peas that can be consumed fresh, quick frozen, canned or bottled. Peas may also be harvested in the dry mature condition and the dried produce stored for later use, or for seed.

In cultivated use, peas range from an indeterminate growth type with long haulm that can be used as a forage crop, or ensiled for animal feed, to a shorthaulmed type with an evenness of maturity of the pods for harvesting on a single occasion, as a vegetable for freezing, canning or for the fresh vegetable market.

Peas probably had their centre of origin in Middle Asia and the central plateau of Ethiopia. By the Bronze Age (c. 3000 BC) they were used by the inhabitants of central Europe and primitive seeds have been found in areas inhabited by Swiss lake dwellers and in caves in central Hungary. Peas were known by the Greeks and Romans and these early types were first mentioned in England after the Norman Conquest (AD 1066).

Fresh peas were popular in the 19th century, when improved varieties were developed by English plant breeders, and in some parts of the world such varieties are called English peas.

Dry-harvested peas were also grown on a wide scale in the 19th century in both Europe and the USA. Dry peas are also grown extensively in more small-scale subsistence systems but the most significant variety development came about by the introduction of mechanical harvesting equipment, firstly (for dry-harvest peas) threshers and latterly the combine harvester and for fresh peas the complete pea harvester known as the viner.

Production

Wet growing conditions can increase the length of haulm and indeterminacy. Botanical determinacy can be achieved by breeding by selection for apical determinacy whereby the flowers and subsequent pods are grouped closely together. Such a type may be more suitable for a single mechanical harvesting operation. There has recently been a further development with modern pea varieties in the production of a stiffer stem, which holds the plant in a more erect position, and ‘afila’ types where the leaflets have been converted to tendrils. The tendrils of afila types tend to twine together and offer mutual support.

Such morphological changes have greatly improved the agronomic characteristics of peas to enable them to be grown in a wide range of geographical areas and have been exploited by large-scale harvesting operations.

Older less determinate types lend themselves to smallscale and garden production where harvesting is carried out by hand and multiple harvests of the same set of plants can be made to extend the productivity cycle.

Vining peas

Of the two main commercial types of peas, those for fresh harvest, freezing or canning (known as vining peas) (Fig. 1.2) are produced in most of the world’s temperate agricultural areas. The main constraints to production are weather, soil type and the availability of processing factories. The largest European producers of vining peas for freezing are the UK with 155,000 t and France with 190,000 t, Belgium with 69,000 t and Spain with 62,000 t produced annually. The USA is also a large producer with around 260,000 t per annum (Fig. 1.3).

Peas harvested fresh as immature pods and seeds are known as garden or fresh peas and are usually harvested by hand. An additional small quantity is grown for whole-pod consumption and the crop is known as mangetout, sugar snaps or snow peas. However, the main production of peas as a ‘fresh’ vegetable is as vining peas, where the pods are mechanically removed from the stems, threshed green in the field and the peas are processed within a few hours of harvest as either frozen or canned peas.

Fig. 1.2. Vining peas.

Fig. 1.3. Major producers of peas for processing (from FAOSTAT, 2013).

Since the development of canning and freezing techniques, peas have been considered an important vegetable for use on their own or in mixed vegetable packs or ‘ready meals’.

In the USA, peas were first brought over by European immigrants in the 16th century. From New England, settlers moving by wagon train brought the crop first to Wisconsin, where the canning industry would begin, and thence to the west, where they are now grown in Idaho, Washington and Oregon as both dried and green peas. The first steps to preserving fresh peas came in 1885 at the Paris Exhibition when a Madame Faure exhibited a hand-operated machine that shelled the peas from their green pods. The principles of this pea viner are still used today in self-propelled pea vining machines that operate in the field and are capable of harvesting many tonnes of peas per day.

The next advance was the development of preservation by canning; and the vegetable canning industry began in the 19th century.

Frozen peas began to be processed in the early 1920s primarily by fish freezers, hence the development of freezing factories in major fishing ports. The major growth in frozen peas was in the 1950s to 1970s with the increase in consumption linked to demands for convenience foods and the ownership of home freezers. The amount of peas grown for canning has declined since the early 1930s and today around 70% of vining peas are destined for quick freezing.

The quantity of peas frozen in recent years has begun to fall as consumption of vegetables has also dropped in developed countries. In the UK the tonnage of frozen peas has fallen from 155,000 t to around 140,000 t over the past 5 years and this trend also appears to be occurring in the USA and Europe.

Harvesting

Pea varieties continue to show improvements through careful breeding. Peas were at first pale in colour and susceptible to poor weather conditions and disease. Modern varieties are very tolerant to disease and are high yielding with generally improved flavour. The plant architecture has been changed in many varieties by reducing the plant height, reducing the vegetative growth by modifying the leaf shape or replacing leaves with tendrils and strengthened stems. A range of types are available to provide a 6–8-week harvest period allowing a continuity of fresh product to the factory for freezing or canning.

Harvesting is now mechanized on a large scale. By the 1950s farm- and factory-owned static viners were present on many farms. The use of these was based on peas being cut in the field, loaded on to a trailer and transported to the farm. The peas were then fed by hand on elevators to the static viners, where the peas were threshed, washed and chilled before transport to the factory. The next development was the introduction of trailed viners, which picked up a cut crop in the field and vined the peas in situ, unloading the vined peas into a trailer before transporting to the factory.

Since then, complete pea harvesters are the main form of harvesting with vined peas being delivered to the factory within 2 h of harvesting. Control of harvesting is now based on the accurate measurement of maturity. In the early 1950s, the Martin pea tenderometer was invented and even today derivatives of the original tenderometer provide the farmer and factory with a robust means of assessing the optimum time of harvesting.

The freezing process has also been modernized, with most of the processes and quality control being carried out automatically. Because of the necessity for a processing factory to operate at maximum efficiency over the 6–8-week harvest period, it is usual to have fixed tonnages of peas delivered over each 24 h period. In order to supply the required amounts, growers in the UK and in some other countries have formed pea cooperatives that may jointly own all the growing and harvesting equipment, organize the programme of seed sowing to allow continuity of supply and work together as a single group in harvesting and transporting to the factories. Currently in the UK there are around 12 pea cooperatives supplying 130,000 t of peas to eight freezing factories and one canning factory throughout the season.

Fresh peas

Production

Fresh peas are harvested as whole pods and are harvested by hand to minimize pod damage. The peas are stripped from the stems in the field and packed in boxes before being transported to the farm or pack house for packing.

Three types of fresh peas are marketed, including the standard garden pea or English pea varieties, where the pods are picked for hand shelling after sale, the sugar snap and the snow peas or mangetout types, which are picked when the seeds have developed but before the pod becomes stringy. Garden or English peas are usually grown on a large scale in fields with no additional support for the stems, in a similar way to vining peas, whereas the other two types may be grown in beds or on the flat. The variety chosen will dictate if they are grown on the flat or if support by some form of wire or trellis system is required. Plants grown on the flat are usually harvested at the same time, whereas crops grown on wire or trellis systems will be harvested over a period of time allowing several harvest dates per crop. Some crops are planted in the autumn and protected by a fleece covering, which is removed the following spring once the frost risk has passed. This system allows an early harvest. A large degree of hand labour is required for these crops but the final product can demand a premium price. Garden peas are more suited to cool temperate climates and can be grown on a range of medium to light soil types, but the whole-podded types are usually grown in areas where the temperature variation is not great and freedom from the risk of frosts or excessive rainfall is guaranteed. Pod quality is essential for achieving customer purchase and pods can be easily damaged by weather extremes. Edible podded varieties are generally more prone to root rot issues than garden peas.

Dry peas (combining peas)

Production

Dry-harvest peas are more commonly grown on a large scale commercially in Europe, particularly in France. Most of these are grown for the animal feed market. By comparison, production in the UK is smaller but the peas are grown for high-quality human consumption and export markets. The USA and Canada together are very large producers of dried peas, again mostly for animal feed though a significant amount is used as food ingredients (Fig. 1.4).

The largest producing country is Canada at 2.5 million tonnes; China and the Russian Federation each average around 1 million tonnes, whilst France, India and the USA each produce 0.5 million tonnes of dry-harvest peas annually (Fig. 1.5).

There are many uses for the dried pea seed,