Performance of organic and conventional crop varieties and species mixtures under stress
by Anoush Miriam Ficiciyan
Date of Examination:2020-05-19
Date of issue:2022-02-24
Advisor:Prof. Dr. Teja Tscharntke
Referee:Prof. Dr. Teja Tscharntke
Referee:Prof. Dr. Stefan Siebert
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Abstract
English
The conservation of agrobiodiversity is considered a priority to ensure the sustainability and sovereignty of food production under changing climatic and socio-economic conditions. In this context, substantial value is placed on the conservation and promotion of plant genetic diversity in the forms of seeds and varieties. The spread of modern, high-yielding crop varieties has led to an increasing loss of traditional and locally adapted varieties. However, access to traditional and locally adapted crop varieties may be crucial for crop cultivation in locations with sub-optimal growing conditions. A high diversity of crop varieties is also of importance for the preservation of agrobiodiversity and associated provisioning, regulating and cultural ecosystem services. In addition, crop diversification through mixed-cropping is a promising strategy to strengthen the resilience of farming systems under changing environmental conditions. However, scientific research on the use of crop varieties and variety mixtures from organic plant breeding, meaning plants conserved and bred without synthetic fertilizers and pesticides, remains especially for vegetable species limited, which may hinder the potential to build more resilient cultivation systems. In this dissertation, I address this knowledge gap from an agroecological perspective. My dissertation addresses the question of whether the cultivation of traditional and locally adapted crop varieties has a positive impact on agrobiodiversity and ecosystem services. In the first part (Chapter TWO), this dissertation focuses in a systematic review on the existing scientific literature on the contributions of traditional varieties (also known as landraces) to provisioning, regulating and cultural ecosystem services with those of modern, high-yielding varieties. The evaluation of 41 publications showed that modern, high-yielding crop varieties are often preferred by farmers worldwide due to their provisioning services (e.g. higher yield) under optimal cultivation conditions. However, performance benefits, such as resistance to pests and diseases, appear to be often decreasing among modern, high-yielding varieties. Traditional crop varieties, on the other hand, often show higher resistance under sub-optimal growing conditions and are considered a trusted source of stable crop yields, especially by small-scale farmers in the global South. Furthermore, due to their cultural characteristics, such as importance for traditional cuisine, traditional crop varieties play a socially formative role in family and cultivation traditions. The value of a crop variety must therefore be considered within the social-ecological context of the farmers, consumers, and cultural communities. It goes beyond performance and economic value and includes the intrinsic value and the cultural relation between the crop variety and people. In the second part (Chapter THREE), the yield performance between hybrid, conventional and organic varieties of tomato and sweet pepper is examined in a cultivation experiment from 2017. Yield, yield stability and fruit quality were tested under optimal irrigation and under drought stress conditions. Performance of both species was negatively affected by the lack of water. The results confirm the expected positive effect of hybrid breeding for performance to some extent, as hybrid varieties delivered higher fruit numbers under both optimal and drought stress conditions. Yield in harvested kilograms and the distribution of marketable and non-marketable fruits were comparable for hybrid, conventional, and organic tomato and sweet pepper varieties. The benefit of the higher yield of the hybrid varieties was mitigated by higher seed costs and the impossibility of reusing the seed. These results call into question the widespread assumption that open-pollinated conventional and organic varieties cannot be regarded as equivalent alternatives to hybrid varieties, especially when considering that organic crop varieties, in contrast to hybrid and conventional varieties, are not restricted for use by private intellectual property rights. The third part (Chapter FOUR) of the dissertation compares the yield performance (yield, yield stability, fruit quality) of eight conventional and eight organic tomato varieties from a cultivation experiment in 2018. These varieties were cultivated either as single plants or in mixed-cropping with a legume, with or without weed stress. The results showed that the organic varieties outperformed the conventional varieties. In mixed-cropping, the organic crop varieties produced higher yields and more fruit of the highest quality than conventional crop varieties. Under weed stress, the organic crop varieties as single plants showed higher fruit weight stability. These results demonstrate the ability of the organic crop varieties to produce good yields under sub-optimal growing conditions. Furthermore, the results justify the maintenance and restoration of a diverse crop variety portfolio for diversified cultivation systems such as mixed-cropping. In summary, the literature review provides for the first time a structured overview of the high importance of traditional crop varieties for regulating and cultural ecosystem services worldwide. Based on this review, I recommend to farmers and growers the seed market supply of a portfolio of crop varieties that is as large and diverse as possible. Since traditional crop varieties are, in many cases, still the more reliable source of stable yields for small- scale farmers, a seed system should be promoted that ensures the availability of these traditional varieties in the long term. The design and execution of the stress tests with crop varieties from different breeding approaches are novel, and provide new insights for the promotion of resilient farming systems. The findings provide evidence that organically-bred crop varieties may be often better suited for mixed-cropping. My crop variety experiments thus should mark the beginning of a series of new experimental studies that should be extended to as many vegetable and cereal species as possible and to a wide range of stress scenarios.
Keywords: Agrobiodiversity; Food sovereignty; Seed commons; Variety diversity; Protection laws; Landraces; Drought stress; Ecosystem services; Genetic diversity; Sustainable vegetable production; Variety comparison; Vegetable breeding; Genetic diversity; Organic breeding; Vegetable diverstiy; Weed stress