Internal fruit rot of capsicum (VG17012)
What’s it all about?
Beginning in late 2019, this investment is investigating the causes behind internal fruit rot in capsicums and developing management techniques for growers to both prevent infection and minimise the risk of sending damaged fruit to market. Ultimately, this project aims to deliver capsicum growers with an integrated disease management strategy to control internal rot, as well as developing a predictive model that will help growers identify crops at risk and diagnose infection early.
Internal fruit rot can be a significant issue for capsicum growers, as although infection occurs during flowering, the disease can remain latent in the fruit until it starts to ripen. Once capsicums are harvested, development can accelerate, with fungal growth spreading into the seed and the edible flesh. As the disease cannot be detected externally, infected fruit can be sent to market resulting in waste and loss of consumer confidence. Several different fungi can cause the disease, including species of Fusarium and Alternaria, however it is unclear which are the primary organisms that are responsible for this disease in Australia.
Project progress continues despite flooding and travel restrictions impacting project activities.
Modelling work in Bowen and Bundaberg has been moved to 2022 to verify whether models developed over the 2021-22 summer in NSW are widely applicable.
A new trial is underway at the Richmond lowlands site. Staggered plantings over a 12-week period are being used to model the relationship between the risk of internal mould and environmental conditions during flowering and fruit maturation.
A trial testing the effects of fungicides and chelated calcium is planned for the same site. A range of fungicide combinations will be tested, utilising different groups and modes of action. The effects of application with a normal backpack sprayer will be compared to a fogger, with the aim of increasing penetration into downward pointing flowers.
Fruit from these crops will be assessed to determine whether cold storage immediately after harvest can significantly reduce postharvest development of internal mould.
Since the last update, the project has progressed, with outputs from the initial, detailed literature review condensed into a format suitable for sharing with growers and supply chain members.
The team also isolated four fungal species from infected capsicum fruit, with three identified as Alternaria alternata, A. tenuissima and Fusarium oxysporum. Although the fourth species (possibly F. semitectum) was not re-isolated, this may have been due to a different spore type produced in culture. This species is now being re-tested.
Samples of brown and black seeds were also analysed, as they can appear to resemble the early stages of internal mould and be rejected retailers. With no fungi cultured from any sample, this is likely a physiological condition.
A trial was conducted to examine the effectiveness of NIR grading with capsicum fruit sourced from farms at Bowen, Gumlu and Bundaberg. The grader successfully detected and removed fruit with internal mould. However, dark / black seeds resulted in many otherwise good quality fruit being rejected.
Evidence from the grading trial suggested that cv. Shadowfax had a low rate of internal mould and fewer fruit with dark seeds compared with other varieties. Growers and wholesalers have also suggested that pointed, rather than blocky shaped, fruit are far less susceptible to internal mould. Variety trials have been planted at Stanthorpe and Richmond NSW to examine varietal differences to susceptibility for internal mould.
The project’s activities were presented at a well-attended webinar on 2 September 2020. With a high level of industry interest, a second webinar is planned. Variety trial results will be published once available.
Initial work has focused on isolating and identifying the organism(s) responsible for causing the disease. Infected flowers and fruit have been collected from around Sydney as well as Warwick and Bundaberg in Queensland. A number of different Fusarium and Alternaria species have been isolated and cultured.
Four of the strains found so far are now being inoculated onto flowers of four different varieties of capsicum plants. The fruit will be allowed to develop to full (red) maturity, then assessed for presence of internal rots.
- Read article Exploring the internal issues affecting capsicums which details some early results from the project, found in the Winter 2020 edition of the Vegetables Australia magazine, p 58-59.
- Learn more about the internal rot of capsicums in the Autumn edition of the Soilless Australia magazine p 9, published by Protected Cropping Association (PCA).
This project is a strategic levy investment in the Hort Innovation Vegetable Fund