Crop Improvement and the Accumulation and Partitioning of Biomass and Nitrogen in Lentil

sion problems are increasingly severe (Küsmenoğlu and Muehlbauer, 1998). Domestication and subsequent genetic enhancement in lentil (Lens Individual lentil plants are typically short with slender culinaris Medik.) have involved changes in plant structure and DM stems and so crop stands produce small amounts of distribution. These changes were examined using a ‘‘genetic gradient’’ comprising three representatives each of Lens orientalis (Boiss.) probiomass relative to cereals. For example, in independent genitors, landraces, pre-1980 cultivars, and modern germplasm. All work done at comparable latitudes, five modern culti12 genotypes were sown at Pullman, WA, in 1996 and 1997, and at vars of winter wheat (Triticum aestivum L.) grown at Reading, UK, in 1997. The biomass (all genotypes) and N concentraCambridge, UK, averaged 7.8 Mg straw ha21 (Austin tion (four genotypes) of above-ground tissues were measured at 50% et al., 1989), whereas six lentil cultivars grown over three flowering (leaf and stem) and at reproductive maturity (leaf, stem, seasons in Pullman, WA, produced just 1.4 to 3.3 Mg pod wall and seed). The progenitors produced meager biomass (averresidue ha21 (McPhee et al., 1997). In these latter experiaging 0.72 Mg ha21) and poor HI (0.19), and consequently small seed ments, ‘Brewer’, the most widely grown lentil cultivar yields (0.11 Mg ha21). Productive landraces had substantially higher in the Palouse, produced 1.7 to 2.3 Mg residue ha21. A biomass (3.52 Mg ha21), improved HI (0.34), and larger seed yields (1.13 Mg ha21). Biomass and seed yield were increased further by further contrast with cereals is that lentil residues are the selection of cultivars (5.11 and 1.32 Mg ha21, respectively). The easily fragmented during harvesting and tillage. Consedevelopment of modern germplasm by hybridization further increased quently, as much as 85% of the residue may be blown seed yields (1.95 Mg ha21). Consistent seed yield improvements have away and/or will decay rapidly rather than remaining not been associated with consistent increases in HI. Instead a strong, as fragments in the surface layers of the soil where they positive correlation between seed yield and biomass has persisted. are needed to help restrict erosion (McPhee et al., 1997). NHI increased more rapidly than HI and is unlikely to increase further The difficulties experienced in meeting USDA Natural in the future. Future seed yield improvement will therefore depend Resources Conservation Service requirements for suron increased N accumulation. Reliance on N2 fixation must be supface residues, and thus in maintaining eligibility for fedported by increased photosynthetic capacity and therefore by vegetaeral support, have consequently focused attention on tive biomass. An advantageous correlation between seed yield and biomass production and management in traditional lenresidue production seems likely to persist as crop improvement continues. til–wheat cropping systems in the Palouse. Throughout the past century cereal breeders have sought to increase grain yield primarily through the selection of traits which reduce the incidence of lodging, T SEEDS OF LENTIL are an important proteinand hence which permit cereal crops to benefit from and carbohydrate-rich food in many developing reincreased applications of N fertilizer and assured supgions and are becoming increasingly popular in develplies of water (Austin et al., 1980; Hay, 1995). The incoroped countries where they are perceived as a healthy poration of dwarfing genes in the 1960s increased grain component of the diet (Savage, 1991). Lentil seed yields yield potential dramatically while reducing straw proare small relative to those of cereals: the world average duction substantially. For example, when cultivars of in 1996 was just 0.83 Mg ha21, i.e., about one-third that English barley (Hordeum vulgare L.) released in 1900 of wheat (2.54 Mg ha21) (FAO, 1997). Despite the tradior 1980 were compared under uniform growing conditional use of lentil straw as feed, primarily for sheep tions the older ones yielded 4.5 Mg grain ha21 compared and goats in the Middle East, biomass production has with 7 Mg grain ha21 for the modern cultivars (Hay, not been a conscious selection target for lentil breeders 1995). Increased seed yield was almost entirely acuntil the last 20 yr (Erskine, 1983; Erskine et al., 1999). counted for by increased harvest index (HI; the ratio of However, the increasing need for organic residues to the dry weight of grain to that of above-ground biomass) help restrict soil erosion has stimulated interest in the from 0.36 to 0.48. In contrast with cereals, lentil cultivars breeding of lentils for biomass production (Whitehead et al., 1998; Erskine et al., 1999). Nowhere is the need released prior to 1980 were mostly selections from germfor residue production greater than on the slopes of the plasm rather than the products of hybridization (Hawtin Palouse region of Washington and Idaho, USA, where et al., 1980). More recently, breeding programs have about 90 000 Mg of lentils are produced annually (USA successfully produced improved genotypes from lentil Dry Pea and Lentil Council, 1996) and where soil erohybridization and selection. However, there is cause for concern that the already poor residue productivity of this grain legume crop could be further depressed if, S.J. Whitehead, R.J. Summerfield, R.H. Ellis, and T.R. Wheeler, Plant as in cereals, improved seed yields are sought through Environment Laboratory, Dep. of Agriculture, The Univ. of Reading, Cutbush Lane, Shinfield, Reading, RG6 9AD, UK, and F.J. Muehlbauer and C.J. Coyne, USDA-ARS, Washington State Univ., 303W Abbreviations: DM, dry matter; FAO, Food and Agriculture OrganiJohnson Hall, Pullman, WA 99164-6434. Received 22 Dec. 1998. *Corzation of the United Nations; HI, harvest index, the ratio of seed dry responding author ([email protected]). weight to above-ground biomass; NHI, nitrogen harvest index, the proportion of N in above-ground tissue which is found in mature seed. Published in Crop Sci. 40:110–120 (2000).