What was it all about?

This short project, which ran from 2019 to 2020, was a collaboration between Australian and USA researchers to better understand the causes behind splitting and skinning in sweetpotato crops, and how they can be reduced. This project generated new information in relation to nutrients and variety interactions, however further research will need to be conducted to further understand these complex interactions.

Splitting can occur during storage, but in cooler weather the main nematode-resistant sweetpotato cultivar grown in Australia is prone to splitting on-farm at harvest, with reported losses as high as 30 per cent. Meanwhile, other cultivars are susceptible to skinning damage during harvest and post-harvest operations, leading to sunken, darkened areas on the skin surface.

Glasshouse experiment results

Across a range of varieties, the team investigated the effect of nutrients on skin hardening and the rates of splitting and skinning.

In 2019 and 2020, glasshouse experiments were conducted at the Department of Agriculture and Fisheries Bundaberg Research Facility and Louisiana State University Chase Sweetpotato Research Station.  The Australian experiments focused on links between calcium and boron in four varieties. Whereas the US studies assessed the role of nitrogen source (nitrate versus ammonium) and phosphorus availability on the incidence of early storage root splitting in the ‘Georgia Jet’ variety.

The Australian results showed that the omission of boron or calcium had no significant effect on root weight, length, diameter and total number of roots per plant across all four varieties. However, significant differences were identified in individual variety responses. Periderm width values were generally higher in all varieties for experiments conducted during cooler weather than during summer. The US experiments indicated that although ammonium and nitrate forms of nitrogen have roles in sweetpotato splitting, other environmental variables and nutrients are also involved.

This successful international collaboration has ensured the Australian sweetpotato industry is at the forefront of international research. Australian researchers gained skills in controlled nutrient studies, and standardised methodologies now exist between countries. A skinning evaluation tool has been constructed and is now available for use in future research projects.

Recommendations

Suggestions for future research include:

• How calcium and boron impact sweetpotatoes during winter months
• Role of boron and variety in periderm thickness determination
• Nitrate vs. ammonium studies in storage root splitting
• Possible interaction between temperature and splitting associated with nitrate using ‘Georgia Jet’ as the experimental system.