Effect of source:sink ratios and vegetative melon growth

We evaluated the effect of different source:sink ratios determined through variations of planting density and number of fruits per plant during the vegetative growth of melon plants. Two experiments were carried out in a plastic greenhouse in the 2004/2005 spring-summer season. In one experiment, three planting densities (1.7; 2.4 and 3.0 plants m-2) and two different quantities of fruits per plant (3 and 4) were studied. In the other experiment, two treatments were set: pruning all fruits and keeping 3 fruits plant-1, in order to evaluate the effect of the absence of fruits. From the data of dry and fresh matter and leaf area (LA) 68 days after setting, it was determined dry matter production, distribution to the vegetative parts, leaf area index (LAI), specific leaf area (SLA) and dry-matter content of the stems and leaves. The increase of the planting density did not improve the source strength and had no effect on vegetative growth during periods of the year with high solar radiation. At the end of the cropping period, the relatively low melon planting density LA, in association to a high available solar radiation, avoided an excess of mutual shading among plants; this allowed the penetration of solar radiation inside the vegetative canopy, even at higher planting densities. A new fruit competes more with the remaining fruits than with the vegetative organs. The fruits compete indistinctly with the vegetative aboveground parts. In other words, stem and leaf act as an entity. The melon plant adapts to a low demand of sinks accumulating fotoassimilates in vegetative organs.