Contributors: Wendy Hoashi-Erhardt and Michael Hardigan
Breeding for heat tolerance is a crucial approach to beat the heat and overcome the challenges of high temperatures in agriculture. The heat tolerance of caneberry cultivars varies due to their genetics. In the Pacific Northwest, Michael Hardigan, a research geneticist at the United States Department of Agriculture in Corvallis and Wendy Hoashi-Erhardt, program lead for small fruit plant breeding at the Washington State University’s Puyallup Research and Extension Center, are exploring this aspect of breeding to develop more heat-tolerant varieties. But what is the process of selecting for heat tolerance and what are the factors contributing to the variation in heat tolerance? Researchers Hardigan and Hoashi-Erhardt were able to give some expert insight.
To begin, it is important to understand the term “genotype”. A genotype refers to a unique plant individual. To produce genotypes with specific traits, breeders cross two established genotypes (or parents) with desirable characteristics. Hardigan and Hoashi-Erhardt do this using classic breeding techniques that involve careful cross-pollination between selected parents. Once a new genotype is obtained, it needs to be replicated multiple times through vegetative propagation techniques like tissue culture. This replication is essential for cultivating large quantities of the same genotype and evaluating its performance on a larger scale.
Heat stress significantly affects the growth and productivity of caneberry plants. Looking at high heat tolerant genotypes and understanding the mechanisms underlying heat tolerance, allows breeders to create adapted cultivars or varieties that are better suited to the evolving needs of the industry. “We can create better methods for evaluating heat tolerance,” stated Hoashi-Erhardt when referring to heat tolerance research. Hardigan and Hoashi-Erhardt have utilized high heat events, like the “2021 heat dome”, to evaluate and screen for heat tolerance traits. Identifying genotypes with better plant health and berry quality during and after high temperature events could enhance the resiliency of the caneberry industry and enable production expansion into areas with hotter climates.
As explained by Hardigan, “We see differences in heat tolerance among current genotypes which include altered ripening time, and cuticle thickness.” The cuticle is the outside layer of the fruit. It has been found that earlier ripening can sometimes allow for avoidance of heat stress effects during peak summer temperatures.
Additionally, berry location within the plant canopy can influence heat damage. Raspberry and blackberry fruit that are shielded by foliage are less susceptible to sunburn compared to those directly exposed to the sun.
Plants that are under heat stress can exhibit damage as early as the budding stage, leading to downstream effects on nutrient partitioning and reduce overall yield and berry appearance due to insufficient nutrients. In recent years, Hardigan and Hoashi-Erhardt have observed varying degrees of resilience to heat among different genotypes.
Once heat tolerance is identified, intentional crosses are conducted to generate new caneberry cultivars with higher marketable yields and improved fruit quality. Other important quality traits of importance to the researchers include firmness, color, and machine harvestability. Machine harvestability reduces labor intensive harvesting, particularly for the processed market.
Growers in the industry are innovative and capable of adapting quickly to changes in conditions that improve profitability, sustainability, and fruit quality. However, adaptation can be costly. Once new cultivars have been released, it is hoped that growers will avoid higher costs of horticultural management to adapt to elevated temperatures. Alternatively, they can combine new genetics with horticultural tools to remain cost-competitive and ensure production amid high temperatures.
Public breeders in the Pacific Northwest are actively developing germplasms that are more resilient under high temperatures, despite the process being expensive and time-consuming. Washington and Oregon small fruit genetic diversity is constantly being used to generate new varieties within our valuable public breeding programs to address old and emerging challenges.
For more information you can find the Washington State University Puyallup Small Fruit Breeding and Genetics website on our additional information page.