White lupin ( Lupinus albus L.)

Abstract

White lupin ( Lupinus albus L.) is an annual legume traditionally cultivated around the Mediterranean and along the Nile valley where it is used for human consumption, green manuring and as forage. The composition of the grain and especially the high protein content makes white lupin highly suitable for ruminant diets as a protein-rich product in intensive farming systems. The absence of anti-nutritional factors makes possible a direct on-farm use of white lupin in self-sustained systems. Being mainly self-pollinating, commercial varieties are pure lines bred through pedigree selection. The major diseases are Pleiochaeta setosa for which selection among autumn-sown genotypes was effective, Uromyces lupinicolus causing early defoliation under warm and dry summers and Colletotrichum gloeosporioides (anthracnose). Anthracnose is a major threat because this seed-borne disease induces an early plant death through stem breakage. No genetic resistance is presently available. More breeding effort should be devoted to this disease in the future. Frost tolerance of the autumn-sown crops depends on the root size, the state of the apex and the hardening ability of the vegetative organs. Major improvements were achieved through earlier sowing and through selection of winter hardy genotypes with marked vernalization requirements. The susceptibility of white lupin to high pH and free lime expressed by iron deficiency is due to the root functioning with nutrient uptake under normal conditions enhanced by citric acid secretion. The recent identification of lime- and high pH-tolerant populations offers new possibilities for breeding and for physiological study. The elaboration of the lupin mainstem is described (leaf primordia production and vernalization) and the relationship between mainstem and branches is analyzed. The indeterminate growth habit due to the production of successive branch levels induces late maturation, allows high potential biomass production, but may lead to poor seed yields because of low harvest index. Poor yield stability seems inherent to the indeterminacy. In the autumn-sown background, determinacy under monogenic recessive control strongly modifies the branch structure, separates the vegetative growth and the reproductive growth and results in better yield stability. Determinate cultivars yield well under early sowing conditions because they produce greater biomass, but may then suffer from lodging. Introduction of dwarfism significantly reduces internode length and favors dry matter allocation to the pods. Breeding is now oriented towards the selection of dwarf determinate varieties. Development of molecular biology and transformation techniques offers new prospects in white lupin breeding.