The foliage of mature tomato plants typically consists of leaves that are initiated from the apical meristem (referred to as main or “true” leaves) or from axillary meristems (referred to as axillary leaves or “suckers”) (Decoteau, 1990). The initiation of main leaves in tomato is regulated by environmental factors such as temperature (Paul, 1984a, 1984b) and light (Hussey, 1963). Axillary leaf initiation and growth in tomato appears to be more precocious than for the main leaves (Decoteau, 1990; Tucker, 1977), and the factors involved in regulating axillary initiation and growth are not well understood.
Leaf area distribution in a tomato canopy is important for maximizing plant photosynthetic capacity (Wolk et al., 1983) and protecting developing fruit from excessive exposure to solar radiation (Andegoroye and Jolliffe, 1983). Removal or loss of main leaves or decapitation (or removal of the apical bud) enhances the growth of axillary leaves (Decoteau, 1990), whereas the removal or loss of axillary leaves has a lesser effect on the growth of the main leaves (Aung and Kelly, 1966; Decoteau, 1990).
The relative amount of axillary leaves to main leaves appears to exert an influence on subsequent tomato fruit production. A large number of axillary leaves present on the plant during the vegetative growth phase often delays initiation of the reproductive phase. In addition, the resulting fruit are smaller than those produced from tomato plants that had many of their axillary leaves removed (Decoteau, 1990).
Various cultural practices and environmental factors have profound effects on crop development resulting in modified overall canopy structure and appearance. In commercial tomato production, polyethylene (plastic) mulches are often used to increase yields (Jones et al., 1977; Kasperbauer and Hunt, 1998; Orzolek et al., 2000; Wien and Minotti, 1987), enhance fruit quality (Wien and Minotti, 1987), and reduce weed pressure (Smith, 1968). The beneficial effects attributed to the use of plastic mulch appear directly related to changes in plant microclimate (Decoteau, 2005; Decoteau et al., 1986; Kasperbauer and Hunt, 1998). We have previously reported that mulch surface color can influence tomato plant growth (Decoteau et al., 1988; Fortnum et al., 2000) and fruit yield (Decoteau et al., 1989; Fortnum et al., 1997). For example, plants grown over white mulch were shorter and branched earlier than plants grown over black mulch and overall canopy structure appeared different (Decoteau et al., 1988).
Dry or fresh plant weight (biomass) and amount of foliage (leaf area) are commonly used measurements for documenting differences in plant development among experimental mulch color treatments (Decoteau et al., 1988; Fortnum et al., 2000). These growth measurements often do not account for biomass distribution differences that may be occurring among plant parts at individual nodes that contribute to overall shape and structure of the crop canopy. The objective of this study was to document the influence of polyethylene mulch surface color on leaf area distribution as measured at two sampling periods: an early sampling period with relatively young plants that had been in the mulch treatment for 22 d and a late sampling period with relatively mature plants that had been in the mulch treatments for 50 d.
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