Resource allocation within plants: Some theoretical and practical implications for control of plant development

A degree of in-crop management could provide growers with the option to manipulate growth and development in line with ambient weather conditions. Studies presented in this thesis explored this opportunity, and data so far collected support the 'nutrient diversion' hypothesis that internal resource availability and allocation play important roles in regulation of growth partitioning and phenological development. Different levels of defoliation were conducted on maize and cotton plants growing under contrasting water conditions to measure the effect of partial defoliation on their growth and production. In the environment of water stress with low average control yield, defoliation significantly diminished the negative impact caused by water deficit and led to smaller water-deficit-induced decrease of grain yield of maize plants and harvestable product of cotton plants. The relative yield advantage of defoliated plants in the water deficit environment can be attributed to defoliation-induced improvement in water status later in the growth cycle as reflected in measures of photosynthetic rate and stomatal conductance. Early-stage defoliation, removing different parts of maize plants, resulted in varied developmental responses. Removing only the fully exposed leaf blades did not delay the onset of tassel initiation, but tassel initiation and tassel emergence were significantly delayed by either removal of all the shoot tissues above the second ligule or removal of only the expanding leaves at a height just above the soil surface(with the first three or four fully exposed leaves left intact). Continued removal of the expanding leaves delayed tassel initiation further. This indicates the important role that expanding leaves play in control of the transition to reproductive growth. The elongation rate of leaf primordia underwent a gradual decrease as maize plants increased in size with time. The gradual decrease in rate of leaf primordium elongation and the resultant change in shoot apical architecture (described by relative length of leaf primordia) were strongly associated with floral induction. It is proposed that plant internal resource competition lessened the nutrient supply to the shoot apices and, therefore, affected leaf primordium growth and meristem identity simultaneously. The dynamic competition and interdependency among various plant parts were explored using a dynamic model constructed to simulate resource allocation and growth partitioning at the whole plant level.