ABSTRACT
Crop yield is determined by plant growth and partitioning of bio mass to marketable parts of plants. Both growth and partitioning are affected by developmental stages of crops. Knowledge of physiologi cal processes of growth, development, and partitioning into yield components is necessary for a basic understanding of maximizing crop yield. It is important first to define growth. Growth refers to biomass accumulation and can be measured by
leaf area, shoot, root, and total weights, or plant height, and these can be used to compare within cultivars or between cultivar means (McCauley, 1990). The term growth also applies to quantitative changes that oc cur during development and may be defined as an irreversible change in the size of cells, organs, or whole organisms (Wareing and Phillips, 1981). Wilhelm and McMaster (1995) defined growth simply as irre versible increases in physical dimension of individuals or organs with time. Therefore, examples of growth are irreversible lengthening of leaf blade tissue or increases in leaf area. In agriculture, where the purpose of most enterprises is to convert solar energy into dry matter, an equally useful definition of growth is increased dry weight. Growth is affected by environmental factors such as climate, soil, and plants themselves. Growth is sometimes confused with development. These two terms are interrelated but different. Plant development may be defined as the sequence of ontogenetic
events, involving both growth and differentiation, leading to changes in function and morphology (Landsberg, 1977). Development is gen erally measured over time between various physiological stages. De velopment includes processes of organ initiation (morphogenesis)
but extends to differentiation and ultimately includes processes of se nescence. The process by which plants, organs, or cells pass through various identifiable stages during their life cycles can be considered a functional definition of development. Phyllochrons (interval between similar growth stages of successive leaves on the same culm) have been used extensively to describe and understand development of grasses (Wilhelm and McMaster, 1995). Development may be af fected slightly by factors influencing growth but is more closely re lated to heat unit accumulation (Stansel, 1975). Growth and develop ment in crop plants do not proceed at constant or fixed rates through time. They are modified by environmental factors such as tempera ture, light intensity and duration, nutrition, and cultural practices. Therefore, calendar date is not suitable as quantitative descriptions for developmental stages of plants. Many attempts have been made to define precise and easily applicable methods for describing each im portant period and stage during cereal development. The scales used to assess development of cereals have been described by Landes and Porter (1989). These authors identified 23 scales, which are separated into those that codify external development of plants and those that describe events at apical meristems. Similarly, growth stages of le gumes such as soybean and common bean have also been described (Fageria, 1992).
