August 19, 2021
Seed stored in genebanks around the world harbors the human history of peppers – a fascinating story of global travel, slave trading, market manipulation, and personal preferences for hot and pungent flavors. A new paper in PNAS chronicles the genetic journey of a highly desirable vegetable.
The great diversity in cultivated peppers is a mirror of human interaction with nature.
In a groundbreaking paper published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) on 18 August 2021, the genetics of more than 10,000 samples of peppers from genebanks around the world were scrutinized by a team of 25 researchers—including World Vegetable Center Genebank Manager Dr. Maarten van Zonneveld and Flagship Leader for Vegetable Diversity and Improvement Dr. Roland Schafleitner—to map genetic relationships of genebank-preserved peppers with human activities such as trade, migration, and invasion.
More than half of the study samples (5,351) came from the WorldVeg Genebank.
The WorldVeg team contributed to the work as part of the HORIZON2020 G2P-SOL project. Funded by the European Commission, G2P-SOL aims to link genetic resources, genomes, and phenotypes of solanaceaous crops (potato, tomato, pepper and eggplant) to enable breeding of pest- and disease-resistant, climate-resilient vegetable varieties.
Data illuminates a globetrotting crop
Besides being vast repositories of seed, genebanks are enormous warehouses of individual data points about the species stored within. The researchers plumbed pepper records from 10 genebanks to find out where each of the 10,038 samples was collected. DNA analysis of the samples showed the genetic links between geographic regions and how pepper plants changed in response to human movement across continents and oceans.
The researchers, led by Dr. Pasquale Tripodi of the Research Centre for Vegetable and Ornamental Crops, Council for Agricultural Research and Economics, Italy, found similar pepper types in Europe and Asia, suggesting that peppers moved along east-west Silk Road trade routes in regions with common day lengths and seasons where the species could flourish. The Ottomans may have been the conduit for the pepper types now preferred from Turkey to Eastern Europe and the Middle East.
The triangular transatlantic slave trade, from Africa to Europe and the Americas during the 16th to 19th centuries, links pepper diversity throughout these continents today.
16th-century Portuguese traders who plied the seas and markets between South America, Europe, Africa and Asia played a double game, the researchers say: They had no interest in introducing pungent pepper fruit types to Europe, because the savory fruit might cut into their lucrative black pepper (Piper nigrum) imports. They did, however, have an incentive to introduce pungent peppers into Asia as a cheap replacement for black pepper.
As the pepper popped up in new locations, the human propensity to fiddle and tweak took over. Personal preferences of farmers (and consumers) for hotter or sweeter fruit of different colors and shapes led to the selection of peppers with those favored traits. Today there are thousands of pepper varieties domesticated from five Capsicum species (C. annumm, C. frutescens, C. chinense, C. baccatum, C. pubescens) spread across temperate and tropical regions of the globe. Generally speaking, East Asia likes its peppers fiery hot; Eastern Europe prefers sweeter, milder fruit; and South and North America revel in all types, from blocky green bell peppers with a sweet, crisp crunch to searingly hot habaneros.
Clearly, pepper is one well-traveled plant. How it contrived to get people to bring it just about everywhere is simple: It’s easy to grow, easy to adapt, easy to preserve or transport in dried form, and only a moderate quantity is needed to add a kick of heat or a mellow warmth to other foods. It’s one of the earliest examples of a globally traded, mass-market, consumer-discretionary good, the researchers say.
Other benefits of the study
In addition to elucidating pepper’s astonishingly full passport, the research found candidates for traits not yet fully exploited, such as the number of pedicels per axil (a small stalk bearing an individual flower growing in the notch between a leaf stalk or branch and the stem or trunk). Breeding for this trait could increase the number of fruit a pepper plant can produce.
The study also turned up 1,618 duplicate accessions among the 10 source genebanks. Accurate classification of germplasm samples is always a challenge, as species can be difficult to differentiate due to interbreeding. The genomics approach researchers employed in this study can be used as a pre-screening method to correct inaccuracies in classification and spot duplicates with a high degree of accuracy.
READ
Global range expansion history of pepper (Capsicum spp.) revealed by over 10,000 genebank accessions. Tripodi P, Rabanus-Wallace MT, Barchi L, et al. Proceedings of the National Academy of Sciences of the United States of America (PNAS) August 24, 2021 118 (34) e2104315118.
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