The Composition and nutritional value of legumes in relationship to crop improvement by breeding

I 982 acid content of legume seeds, in a diet which has sufficient of these amino acids supplied from other sources, is relatively unimportant.Generally speaking, legumes are used as high-protein crops that play a secondary role to cereal or root crops which are higher yielding and supply much of the energy requirement in a diet.Legumes have the advantage of fixing nitrogen and so often lead to soil improvement, and in developed countries they play an important role as a break crop.Soya bean and peanuts are often grown as a cash crop for oil or, in the former case, used as animal feed and it is important to distinguish whether their ultimate role is direct human consumption or animal feed.Many legumes, of course, are important forage crops but this aspect was not to be dealt with in this paper.Before embarking on a breeding programme for crop improvement, the plant breeder wishes to know ( I ) the importance of a character for improvement; (2) does sufficient variation for this character exist in the breeding materials available to him; (3) are there suitable screening methods?-these must be fast, simple, inexpensive and sensitive; (4) lastly, it is a help if something is known about the inheritance of the character.In considering grain legumes as a source of food for humans, I focus on their high protein content.The primary objective in that respect is to obtain the maximum stable protein yield per area of ground.For some geographic areas there is also a need to improve the sulphur amino acid composition of the legume protein since cysteine and methionine are the fist limiting amino acids nutritionally, i.e. areas where a large part of the protein of the diet is obtained from a legume, the diet over all, may be first limiting in sulphur amino acids especially for young children, nursing mothers, the sick etc.Legumes often contain anti-metabolites and even toxic substances.This problem, except in specific instances, is of less significance because, either the varieties commonly consumed have been selected to contain relatively small amounts of these substances, or, the food is cooked or processed so as to eliminate or inactivate them (this doesn't apply if used as an animal feed).Furthermore, there is an increasing body of evidence that some of these substances play a protective role (Gatehouse et al. 1979), e.g. in insect or fungal resistance, and if this is the case their removal could cause problems in the field.Sufficient variation exists for the main components in legume seeds since oil concentrations vary from I to more than 40'Y0, carbohydrate from 2-3 to 60Y0 and protein from about 15 to 50% of the dry weight.Manipulation of the proportion of these components, however, may not be accomplished easily since the different combinations of the major components are each associated with a complex biochemical machinery about which we know very little, e.g.what is the biological regulation whereby soya beans are oil seeds while broad beans mainly store starch.With respect to individual classes of constituents, relatively little variation in the sulphur amino acid content of different legume varieties has so far been reported, but considerable variation exists in the content of anti-metabolites.For example, there are Phaseolus varieties which contain no lectin, whereas others have