Breadfruit Disease Identification and Varietal Resistance in Hawai‘i

Objective 1: Catalog Breadfruit Diseases.

A total of 511 samples were received from 42 different growers across the state, with 468 samples yielding identification of likely causal agents (Table 1). The resolution was inadequate to explore spatial or temporal patterns to the diseases, but the extensive documentation of the symptoms and likely causal agents provided important knowledge about how prevalent and potentially damaging the different diseases were.

Objective 2: Varietal Resistance to Disease.

No infection establishment was observed for Colletotrichum in any treatment. It is possible that this is not an infectious agent, or perhaps the method of inoculation was insufficient. Given the commonality of symptoms that we isolated Colletotrichum from and the consistency from which Colletotrichum was the sole potential pathogen associated with the symptoms, we believe that Colletotrichum is a pathogen associated with fruit and leaf anthracnose despite not seeing results from inoculation. Further investigation and trials are needed here, as the symptoms we associated with Colletotrichum were among the most prevalent across the state. Fusarium demonstrated low levels of infection for seedlings only, with no symptoms established on inoculated fruit. Although Fusarium was associated with some fruit spotting in the field, it was selected for testing due to its prevalence in stem rot and leaf withering. Similar symptoms were observed and re-isolated from the inoculation trial, confirming its pathogenicity. All varieties had relatively low incident of take, with ‘Otea’ and ‘Puou’ varieties having the highest incidences. Finally, Phytophthora showed establishment on all varieties for both seedling and fruit, with incidence ranging from 5% to 95%. Clear varietal differences were apparent, with ‘Maafala’ and ‘Otea’ varieties demonstrating lower susceptibility, and ‘Puou’ demonstrating very high susceptibility. These findings further support field observations of a large phytophthora outbreak that occurred in Waiahole Valley in 2018, where all the ‘Puou’ trees in the valley died, ‘Maoli’ exhibited extreme fruit loss but no tree dieback, and ‘Maafala’ exhibited reduced levels of both fruit and tree losses. These results contradict current knowledge that suggests smooth skinned varieties are less susceptible than rough-skinned varieties, as ‘Fiti’, a very smooth skinned variety, demonstrated relatively high susceptibility.

Objective 3: Develop Technical Factsheet and other publications.

The extension publication includes (1) the history of breadfruit disease outbreaks globally, (2) a description of known breadfruit pathogens, description of their symptoms, and an assessment of their threat, and (3) chemical, biological, and cultural methods of managing diseases in breadfruit production. As an appendix, the publication includes a Technical Factsheet that summarizes identification and management of the most common and/or threatening breadfruit diseases in Hawai’i. The publication is currently in press with the College of Tropical Agriculture and Human Resources, hopefully to be officially released in the next 1-2 months. Drafts of this document have been distributed to growers as requested and during outreach, and an “in-press” version of the documents are included as an appendix to this report.

Objective 4: Conduct 2 on-farm workshops.

The on-farm workshop was held at “Ulu Bros” farm on Maui Island May 15^th, 2021. The location is part of a 400-acre agricultural parks, and includes 6 farms with breadfruit. This workshop was attended by 18 participants, one of which was a breadfruit processor. We were able to tour three farms in the agricultural park and observe disease incidence in the field, highlight the various diseases and management techniques, and allow for farmer-to-farmer sharing of issues and solutions in terms of breadfruit diseases. This workshop was conducted by PI Lincoln, as Co-PI Isele resigned from his position due to personal reasons. An electronic version of the Western SARE evaluation tool, compiled in Google Forms, was disseminated to workshop participants after the fact. 

An overview of this work and dissemination of the draft extension publication was also presented at the Hawai’i ‘Ulu Producers annual membership meeting on June 17^th, 2021, with representatives from 85 breadfruit farms in attendance. This was not so much a workshop, as it was a brief summary of the work conducted and a dissemination of the draft extension publication and technical factsheet. At this meeting a contact list was generated for farmers interested in a breadfruit disease workshop once concerns of COVID abate.

Finally, an extension video on breadfruit disease and management was produced in partnership with the Hawai’i ‘Ulu Producers Cooperative. A seven-minute script was devised that condenses the findings of this project into an easily digestible format, and directs viewers to the permanent home for the associated written publications.  The footage for the video was shot in June 2021, and the approved extension video is expected to be released in October 2021.

During the project period, we also conducted a four-part virtual series on breadfruit in partnership with Kahumana Farms, and presented virtually on breadfruit orchard management at the Hawai’i Tropical Fruit Growers Association’s annual conference.