ABSTRACT
Critical growth periods may be defined as stages in a plant’s development when active growth occurs. Plants are generally sensitive to water deficit (WD) during critical growth periods. Plant WD implies that the plant water status is less than the optimum value for growth and development. Plant demand for water is influenced by many factors including the evaporative demand of the aerial environment, soil characteristics, plant characteristics, and growth stage.[1]
Most plants experience WD at some stage during their life cycle. It may occur diurnally when the evaporative demand for water by the atmosphere is greater than the plant’s ability to draw water from the soil, or seasonally as soil moisture is depleted due to transpiration and not renewed.[2] Water deficit typically results in a reduction in transpiration due to stomatal closure. If severe, this may also reduce photosynthetic rate and therefore carbon acquisition. This, in turn, may lead to reduced plant growth and biomass accumulation. The sensitivity of plant growth and the reduction in biomass accumulation during periods of WD are dependent on plant’s developmental stage. Water deficit imposed during periods of active growth will impact upon the growth of the developing organ as cell turgor is required for cell growth.[3] Generally, however, not all organs of a plant undergo active growth at the same time. This results in different organs within the plant having different critical growth periods during the growing season. This difference allows the manipulation of plant WD to target particular plant organs with little carry over influence of WD on other plant parts. This phenomenon is demonstrated in Fig. 1,[4]
where the clear separation of maximum shoot and fruit growth periods are illustrated for peach and pear.
