The choice of disease-resistant and robust varieties forms the basis for integrated and organic fruit production, and this is an important factor for resource-efficient, sustainable and resilient production in all production systems.
Aim of Work Package 3
The combined research activities of Agroscope, the Research Institute of Organic Agriculture FiBL and the cantonal agencies involved brings together a vast amount of information on robustness and resistance to the main plant diseases. This knowledge will serve to identify fruit varieties suitable for growing with reduced crop protection, and which thus provide significant added value compared to the standard varieties. The project phase will see the development of a testing infrastructure and test methods for identifying varieties that produce marketable fruits with reduced use of crop protection products.
Developing a testing network
For many years now, apple varieties have been tested both under conditions that are common in practice and with strategies involving reduced crop protection at Agroscope’s Wädenswil site and at FiBL’s site in Frick. Numerous new international varieties and crossings from Agroscope’s breeding programme have been tested.
Variety testing of the remaining fruit crops has primarily taken place under ideal standard conditions thus far, with the main focus on agronomic suitability for cultivation and fruit quality. As part of the RESO project (Resilient Varieties for Sustainable Swiss Fruit Production), pears, cherries and plums are now also being tested with a reduced-crop-protection method at Agroscope’s testing sites. In Wädenswil, the plot for pear variety testing was divided into two blocks and in 2020 the first trees were planted. Their first fruits have now been harvested. Additional trial plots for cherries and plums are being created at Breitenhof (Canton of Basel Land) to test the suitability of varieties for cultivation with reduced crop protection.
To obtain meaningful results on the performance of a new variety using reduced crop protection, the variety must be tested at several sites and in fairly large blocks. Consequently, further plots are planned at the sites in Flawil (Canton of Sankt Gallen), Frümsen (Sankt Gallen) and Conthey (Valais) in partnership with the cantonal agencies and trees have been ordered for the tests. These trees are currently being raised in nurseries before they can be planted on the new test plots in spring 2024.
Selection of varieties
A wide range of varieties from different maturity groups was selected in consultation with all the project partners involved. This was done by drawing on the knowledge amassed by Agroscope and FiBL from their many years of variety testing, as well as on the experience of advisory services, the commercial sector and production.
For the apple varieties, we mainly selected varieties with Rvi 6 (Vf) scab resistance. This included several slightly more widely known varieties, such as Bonita, Ladina and SQ 159 (Natyra®/MagicStar®). In addition, several brand-new or as yet relatively unknown varieties such as Delcored, WUR 037 (Freya®) and Ipador (Giga®), as well as several advanced breeding numbers were selected.
With pears, besides the more widely known varieties such as CH 201 (Fred®) and Celina (QTee®), novelties and largely unknown varieties such as PremP009 (Piqa® Boo®), Harovin Sundown and Bay 6474 (Alessia®) are being tested.
Resistance breeding for cherries and plums is less advanced than for apples. Strictly speaking, hypersensitivity to sharka in plums is the only resistance here. Although robustness is monitored, given that most of the breeding programmes to date have worked under ideal cultivation conditions, highly susceptible varieties are identified whilst highly robust ones are not. Variety selection for cherries and plums was based on the criteria of relevance, potential, our own observations and genetic diversity.
For purposes of comparison, the respective standard varieties such as Gala or Conference are included in the tests for all fruit species.
Choice of crop protection strategy
A number of issues still need to be clarified when developing strategies for reduced crop protection. For example, site-specific characteristics such as climatic conditions and disease pressure on the plots must be borne in mind. The reduced cop protection strategy will therefore not look the same at each site but will be determined by a group of specialists from among the project partners for each site. We can also draw on extensive experience from trials like Agroscope’s ‘low-input trial’. The reduced-use strategies in the experimental plots should be selected so as to allow variety-specific differences to be identified: in other words, ideally, the most-susceptible variety should exhibit an infestation that is no longer tolerable, while the most robust variety should perform impeccably.
In the practical experimental work, however, it often proves difficult to maintain adequate disease pressure – although testing at several sites increases the likelihood of substantiated statements about the resistance or robustness of a variety being made in future.
Organic crop protection strategy trial at the UFL in Morges
A crop protection strategy trial has been underway in an organic apple orchard in Morges (Canton of Vaud) in conjunction with the project partner Union Fruitière Lémanique (‘Lake Geneva Fruit Union’, UFL) since 2022. The trial is meant to yield findings for future crop protection trials within the RESO project. In the trial, a practice-based organic and a reduced organic crop protection strategy are being tested on the apple varieties Daliclass, Rustica and Ladina. Targeted scab control is carried out in both strategies according to the RIMpro forecast model, with crops in the reduced organic strategy treated only when the risk of infection is very high. Myco-Sin and sulphur are applied for the preventive control of scab, switching in summer to a strategy using Armicarb and sulphur. Prior to the harvest, final treatments with Myco-Sin are applied in both strategies, with Blossom Protect additionally being used in the practice-based organic strategy.
In 2022 the incidence of disease was kept very low with both the practice-based organic and the reduced organic strategy. The occurrence of scab symptoms was largely prevented, with a very slight scab infestation on the fruits on Daliclass occurring only in the reduced organic strategy.
However, the fruits must be of suitable quality not only at the time of harvesting, but also during storage. When investigating the susceptibility of the fruits to storage diseases, no differences were found between the two organic strategies. Varietal differences, however, were observed: storage losses were significantly higher in the late variety Rustica. Further rainfall in the run up to harvesting is likely to have favoured the risk of infection. In 2023 the organic crop protection strategies are being adapted and the final treatments intensified to reduce the occurrence of storage diseases.
Initial findings from the ongoing trials
Agroscope’s pome-fruit variety testing is currently pursuing a strategy in which standard integrated crop protection is applied up to post-flowering, followed by a reduced strategy with Vitisan and Myco-Sin. In recent years, significant pressure from powdery mildew has become entrenched in apples and major variety-specific differences are evident each year. However, particularly in the case of powdery mildew, these differences are not particularly dependent on the crop protection strategy. By contrast, differences between varieties for Marssonina leaf blotch, rain spots and storage diseases are more clearly discernible with the reduced crop protection strategy. Disease pressure has increased in the last two years, especially for Marssonina leaf blotch, and variety-specific differences are now clearly evident. However, further years of experience and comparisons with other sites are needed in order to make reliable statements about the susceptibility or robustness of a new variety in terms of Marssonina. So far, no resistance breakthroughs for the largely Rvi 6 scab-resistant varieties have been observed. With pears, no difference between the strategies have been observed to date in the newly planted pear orchard.
Pome-fruit variety testing has been established at the FiBL for many years now. New national and international breeding numbers and varieties are tested for a test phase of at least four years under organic growing conditions using two different methods: (1) practice-based (with thinning as well as standard crop protection); (2) very extensive (without thinning and with reduced crop protection). The agronomic potential of the varieties can be seen under practice-based conditions, whilst the genetic potential can be seen under extensive conditions. Differences between the two methods can be detected for different varieties, particularly in terms of scab and Marssonina infestation. Resistance breakthroughs in Rvi 6 scab-resistant varieties have already been observed.