Matcha is under threat from climate change – can genomics save it? | New Scientist

Climate change is wreaking havoc on matcha, traditional Japanese tea that has become a popular addition to iced lattes and even doughnuts around the world. Japan’s hotter nights and erratic spring temperatures are reducing yields and impacting the plant’s distinct umami flavour. But tea growers are starting to use genomic selection to overcome this, by identifying markers of heat tolerance in the plant’s seedlings.  

Premium tencha, a green tea leaf that grows in shade and is ground into matcha, develops best during Japan’s spring, from March to May. Daytime temperatures ordinarily hover around 20 to 25 Celsius, then dip at night, which help develop the plant’s umami-producing amino acids.  

But spring temperatures in the Kyoto-Uji region, home to Japan’s finest matcha, have risen by roughly 0.6 to 1 Celsius over the past 100 years. Heat also causes tea plants to produce more catechins, defensive compounds that taste bitter. 

“Climate change has altered growing conditions, and conventional cultivars [plants produced by breeding] are not always able to perform adequately under these changing conditions,” says Akiko Ogino at the NARO Institute of Vegetable and Tea Science in Makurazaki, Kagoshima in Japan. 

Another problem is that tea breeding is slow. Breeders cross-pollinate carefully selected parent plants, each carrying different desirable characteristics, such as high yields or some degree of adaptation to warmer conditions.

But because the onset of these traits is complex and controlled by many genes, breeders must raise thousands of seedlings and identify the few that inherited the best combination of characteristics. Traditionally, they cannot judge whether a seedling has those traits until it matures, which can take around 15 years.

Now, genomic selection is accelerating this process, by identifying seedlings that seem to have good heat tolerance at a much earlier stage. This is already being incorporated into Japanese tea breeding programmes, says Takashi Ikka at Shizuoka University Research Institute of Green Science and Technology, Japan, who has co-authored a review on genomic approaches to tea breeding.

But it isn’t a perfect solution. It isn’t always possible to accurately predict a plant’s traits from its DNA and our existing genomic databases are relatively small, says Ikka. “[The] immediate value [of genomic sequencing] is not to replace field evaluation, but to prioritise parents and seedlings, and eliminate less promising candidates, before committing many years to clonal and multi-location trials,” he says. These trials involve growing promising plants at multiple sites over successive seasons to assess yield, flavour, disease resistance and adaptation to different growing conditions.

Japan’s tea cultivar registration system requires breeders evaluate 41 officially defined characteristics before a new one can be released, says Ogino. As a result, developing a cultivar still takes around 25 years.

There’s also a possibility that heat tolerance could affect matcha’s flavour, however, Ogino doesn’t think this is a big risk. “At present, there is no clear evidence that tolerance to high-temperature conditions and bitterness or astringency are strongly linked at the genetic level,” says Ogino. 

Ikka suggests that breeders may be able to select for both heat tolerance and a pleasant taste. “Regarding heat tolerance and flavour quality, I do not see an inevitable biological trade-off between them,” says Ikka. “In principle, breeders should be able to select for both simultaneously.” 

Another possibility is that high temperatures increase catechin production regardless of how tolerant the plant is to heat, all of which will be revealed in time. “New research helps, but in the end, tea farming is still a waiting game,” says George Guttridge-Smith at Kyoto Obubu Tea Farms in Uji.