The effect of root interference on root and shoot morphology and growth in a simplified intercrop of tomato (Lycopersicon esculentum Mill.) and cucumber (Cucumus sativus L).

Abstract

A simplified intercropping system was set up in a glasshouse using recirculating nutrient solution culture. Two factorial experiments were conducted in order to assess physiological effects of interspecific and intraspecific root interference in limited root space. In Experiment I combinations of three species of plants (Lycopersicon esculentum Mill., cv. Eurovite; Cucumus sativus L., cv. Hybrid No.2; Phaseolus vulgaris L., cv. Mangere Pole) were used, while paired combinations of only two species were used in Experiment II (Tomato and Cucumber; cvs as above). Each plant was trained as a single main stem where possible and shoot systems spaced equidistance in an attempt to keep the shoot environment uniform.

In experiment I different root volumes were allocated to various treatments. Comparisons were made between pairs of plants with root systems intermingling in the one pot with an available root space of 5.0 1, and the same paired species growing in the one pot but with roots in separate compartments of a range of volumes (1.0 1, 2.5 1 and 4.0 1).

In the second experiment, all treatments involved pairs of plants with root systems intermingling in the one pot. The available root space was either 1.5 1 or 3.0 1.

In both experiments, comparisons were made for each of the above treatments on flowering and deflorated plants.

Weekly measurements of stem length and leaf number were made for all plants and dry weights of roots, stems, leaves and fruits were measured in both experiments. Further, in the second experiment, leaf area, root length and root number were also measured when plants were harvested.

Considerable differences existed between the species in terms of root morphology and gross size, shoot characteristics and growth rates.

Yet despite these differences, interspecific root interference effects could not be clearly distinguished from intraspecific root interference effects.

When root systems mixed in a volume of 5.0 1, plant growth attributes were similar to when root systems were individually allocated 2.5 1.

Inconsistent and complex interactions were observed between the flowering status of plants, available root space and associate species in the pairs, with removal of flowers having a greater influence than other treatments. Difficulties in maintaining a uniform shoot environment could have contributed to these complexities.

Various effects observed, such as leaf epinasty, and reduced growth rates coinciding with flower initiation even on deflorated plants, and reduced growth on root confined plants when nutrients and water were non-limiting, possibly indicated the complex involvement of various growth regulating substances.

While no benefits of intercropping were observed in these experiments, the interactions observed emphasized the complex nature of a mixed species study. When two plants root systems intermingled it was not possible to separate, or distinguish individual plant root systems, even when different species were involved.