Improving Light Interception by Selecting Morphological Leaf Phenotypes: A Case Study Using a Semi-Leafless Pea Mutant 1999-01-2102

Among the species which are considered suitable candidates for life support programs, legumes would be highly valued because of their high protein content and their capacity to fix N₂ under symbiotic conditions. The legume, Pisum sativum, has a short life-cycle (48 days), is easily cultivated, does not required any special seed treatment to germinate, and all parts of its shoot are edible, all of which make peas a possible candidate crop for life support programs. In conventional pea cultivars, the leaf has a compound structure with over 95% of the laminar surface provided by leaflets and stipules. In the semi-leafless pea mutants, where the “afila” mutation is present, all leaflets are replaced by tendril complexes. Although it was originally assumed that such a dramatic reduction in the laminar surface would significantly affect the gas exchange and plant growth potential of the plant, current data clearly show that the morphological mutation “afila” does not markedly affect the net carbon exchange rate or reproductive capacity of the pea plant. The efficiency of semi-leafless phenotype appears to be due to the high level of light penetration within the canopy and the large surface area of tendrils. On a surface area or chlorophyll basis, the tendrils have similar photosynthesis, respiration and transpiration rates to their laminar counterparts (stipules and leaflets). On a whole plant basis, the reduction in photosynthetic laminar surface produces a more open canopy with less mutual shading and more opportunity for air movement at high planting densities. Furthermore, lodging plants within the growth chambers were not observed with semi-leafless phenotypes. Taken together, the data underscore the value of genetically manipulating plant morphology to improve light penetration within a dense canopy.