Genotypic variation in specific leaf area for genetic improvement of early vigour in wheat

Rapid leaf area development early in the season has potential to increase weed competitiveness, water use efficiency and grain yield of winter cereals. Greater early vigour, defined here as an increase in seedling leaf area, is partly associated with a larger specific leaf area (SLA). Selection in a breeding program for greater SLA should contribute to genetic increases in early vigour. However, little is known of factors influencing genotypic variation for SLA of seedling leaves. Random sets of wheat and barley genotypes were: evaluated in field, glasshouse and outdoor tray studies for seedling characteristics including SLA, plant biomass and leaf area. Glasshouse-grown plants produced significantly (P < 0.01) higher SLA (308 cm(2) g(-1)) than outdoor (272 cm(2) g(-1)) plants. Genotypic differences for SLA were large, ranging between 276 and 335 cm(2) g(-1) for wheat genotypes Stiletto and Tobari 'S', respectively. Broad-sense heritability on a genotype-mean basis varied from 51 to 68%, depending on environment type. Genotype x year interaction was smallest and heritability largest for outdoor (seedling tray and field) environments indicating the need for progeny evaluation in the field, or after preliminary evaluation in trays grown outdoors. Genetic correlations for SLA and leaf area were strongest for plants evaluated outdoors (r(g) = 0.60-0.96, P < 0.05) while the genetic correlation for leaf I width and SLA was significantly (P < 0.01) different from zero in all environments (r(g) = 0.45-0.86). Significant (P < 0.05) genetic variance was observed for SLA in two segregating wheat populations evaluated over 2 years. Genotypic variation in SLA was under additive genetic control with small to moderate narrow-sense heritability (h(2) = 51% on a single-plant basis). The higher heritability for leaf I width and its strong genetic correlation with SLA and leaf area indicates the value of leaf width in integrating genotypic variation for SLA toward selection of greater early vigour in wheat. (C) 2004 Elsevier B.V. All rights reserved.