Validation of a method for screening taro for drought tolerance (Phase 1)

Context

The frequency and severity of droughts, floods and heatwaves, as well as the continued sea level rise as consequences of climate change impact negatively food and agriculture security in vulnerable regions such as the Pacific. One of the most promising mitigation and adaptation strategies to counteract food and agriculture insecurity is to employ drought-tolerant crop cultivars in production systems. Taro is one of the major staples grown in the Pacific, however, no drought-tolerant varieties have been identified in the region and there is currently a large gap of knowledge on the response of taro varieties to drought stress. Therefore, it is essential to screen existing germplasm collections and identify germplasm that is tolerant to drought and promote its use in drought-prone regions. Furthermore, including drought-tolerant varieties in future taro improvement programmes will assist in understanding climate resilient germplasm traits.

The Centre for Pacific Crops and Trees (CePaCT) at the Pacific Community (SPC) hosts the largest collection of taro germplasm in the world (>1100 taro accessions), accounting for 70% of global taro diversity conserved ex situ.

Objectives

The Objective of this project was to validate a method for screening taro for drought tolerance by

1. Conducting experiments within controlled environment greenhouse facilities at CePaCT-SPC in Fiji to provide insights into the types of osmotic stress tolerance used in specific taro genotypes and the best ways to integrate these strategies into climate-smart lines.

2. Following this pilot trial, the phenotyping pipeline will be used to screen other taro varieties conserved at CePaCT to identify a subset that is tolerant to higher levels of osmotic stress and used for potential breeding projects.

Methodology

Targeted taro varieties were from the Fiji Ministry of Agriculture taro field genebank located at Koronivia Research Station (KRS), Nausori. A total of 72 varieties were collected.

These taro varieties were genotyped (non-observable characteristics of an organism (genetic traits)) using the technology DartSeq-LD (a technology used for genotyping, that reduces the complexity of the genome to be sequenced). They were also matched against the existing CePaCT collection of taro. Accessions that were not represented in the CePaCT collection were then included in it.

The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) water stress (drought induction) protocol was evaluated for use with taro with advice from Dr Millicent Smith, Lecturer Crop Physiology, from University of Queensland. The phenotyping strategy included the measurement of water uptake, transpiration, water use efficiency, and biomass accumulation.

A PhenoCam system (time-lapse cameras) using cheap RaspberryPi computers with camera attachments to record images was setup to record the drought trials. The cameras were setup to take regular photos of the taro plants which could later be analysed with image processing pipeline to determine proxies associated with drought stress.

Outcomes

Among the 16 taro varieties screened, the varieties Tausala, Jabeni, Tarova Vula, Matadrala and Sikavi Loa showed the highest water use efficiency. These varieties (except Jabeni) also had lower stress index, suggesting that these lines could potentially have drought resistance.

There needs to be further screening in the field of both drought-tolerant and -susceptible varieties to validate the screenhouse trial results. Also, while the initial PhenoCam system setup was a success and photos were taken, the pipeline for processing the data was not optimised by the end of the project as further validation was needed.

Nonetheless, the capacities gained under this project will guide future similar research at SPC-CePaCT for the Pacific region.