Aims Phase I

Interim Report Phase I

Aims and planned studies Phase II

Scientists:

Prof. H. Stützel
K. Schuhmacher
S. Thanisawanyangkura
Dr. V. Kleinhenz
(finished)

last update:
January 2008

The formation of light intercepting green surface is one of the most important, but also least understood physiological processes. As a consequence, the choice of plant density and planting geometry in relation to cultivar type, fertilisation and up-leading has so far been performed on an empirical basis only. Optimisation of canopy composition on the basis of functional relationships allows the adaptive response to expected variation of environmental and cropping variables. Processes to be considered for optimisation comprise canopy light interception and the resulting dry matter production, dry matter partitioning (leaf area formation, fruit growth) as well as the effects of canopy structure on microclimate and thus the incidence of pests and diseases. Important factors of these processes to be considered are genotype, plant density, plant distribution, greenhouse architecture (project 8), and pest and disease incidence (projects 1 and 4). In a combined experimental and modelling program these factors will be quantified experimentally and taken to parameterise the model which will then be used to derive optimal canopy structures by scenario simulations.


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During the first experimental period, the effects of plant density and planting arrangement on canopy structure, light interception, biomass production and partitioning, and yield were evaluated. Moreover, the interactions between these growth-related factors and the greenhouse microclimate were studied.

Results revealed that raising crop density by increasing the number of plants and/or the number of plant stems per unit greenhouse area resulted in a proportional biomass increase per unit greenhouse area. Light interception increased in parallel indicating that at the plant densities used in this experiment (2.1 and 4.2 plants m^-2) competition for radiation is not a major limitation to yield in protected cultivation in the humid tropics.

Production of vegetative, i.e., stem and leaf, biomass was generally not much affected by season, but marketable yield was. When flowering and fruit setting occurred during the cooler season, subsequent fruit enlargement proceeded well even during the hot season, resulting in a balanced source-sink relationship. However, when flowering and fruit setting took place during the hot season, fruit enlargement and, therefore, marketable yield remained marginal. Since most of the fruits produced under the latter conditions were parthenocarpic, it is likely that high temperatures negatively affected pollination and subsequently fruit enlargement. The restrictions in biomass partitioning into generative plant organs revealed that tropical tomato production is “sink limited” during the greater part of the year. Crop responses to lack of sink strength were deformed leaves standing at acute angles of elevation. Furthermore, accelerated growth of auxiliary shoots expressed the plants’ effort to distribute accumulated (i.e., excessive) assimilates towards vegetative plant parts.

High crop density with large transpiring leaf area per unit greenhouse area reduced greenhouse air temperature below ambient temperature. In turn, lower air temperature apparently contributed to improved pollination and fruit development.

Possible measures to improve tomato production under protected cultivation in the humid tropics include decreasing greenhouse air temperature by maximizing crop density and thereby facilitate pollination, as well as applying growth regulators at appropriate amounts and concentrations to improve enlargement of parthenocarpic fruits.


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The overall project goal is to analyze the bottlenecks to the productivity of tomatoes under hot and humid conditions in topical lowlands, to derive solutions and evaluate them. The major problems are due to biotic and abiotic stresses affecting primary productivity as well as growth and development of inflorescences and fruits. These stresses are distributed heterogeneously over time and space: Photosynthetic capacity of leaves declines with age, light interception and photosynthesis is dependent on leaf position, and fungal diseases like Pseudocercospora fuligena are developing from the lower leaves. Also, fruit production is reduced 3-4 months after transplanting which coincides with the period of maximum canopy development (see section 2.1). The aims are therefore twofold: Firstly, the dry matter production processes will be analysed on the leaf level and coupled with the canopy structure model in order to quantify the effects of removal, shading and disease infestation of individual leaves in a canopy. Secondly, the reasons for poor fruit production observed in the previous experiments will be explored and possible measures to improve fruit set and fruit growth will be analysed.

Specifically, the project aims to:

	quantify leaf photosynthesis and respiration as dependent on leaf protein content, radiation and temperature
	identify genotypic differences in temperature dependence of photosynthetic and respiration parameters
	analyze the relationships between C-metabolism (photosynthesis/respiration) and generative growth and development (inflorescence formation, pollen viability, fruit set)
	analyze the effects of various measures to improve fruit set on vegetative and generative plant parameters
	integrate the processes of canopy formation (from phase I), photosynthesis, respiration and fruit set into a whole-crop model
	analyze the effects of removal and disease infestation of specific leaves with respect to whole-plant productivity