Exploring Pollination Biology in Southwestern China

This is the sixth in a series of posts reviewing the 17 articles found in the October 2014 Special Issue of American Journal of Botany, Speaking of Food: Connecting Basic and Applied Science.

Insect Pollination and Self-Incompatibility in Edible and/or Medicinal Crops in Southwestern China, a Global Hotspot of Diversity by Zong-Xin Ren, Hong Wang, Peter Bernhardt, and De-Zhu Li

We rely on pollinators to pollinate at least 75% of our food crops, which is why any talk of pollinator decline tends to make us nervous. It is also why research involving pollinators and pollination is so important. Despite all we know, there is still so much to learn. The authors of this study, recognizing that “there are large gaps in the study of the pollination of economically important and traditionally grown species in China,” set out to help close these gaps. Their research not only has the potential to benefit agricultural communities in China, but also adds to our growing understanding of pollination biology – a science that has become increasingly important in an age of human population growth and shifting climates.

The incredibly diverse Chinese flora includes at least 31,000 plant species. Three hundred of the 1500 species of worldwide cultivated crop plants “originated and/or were domesticated and/or underwent differentiation in China.” Southwestern China has a particularly large amount of botanical diversity and is considered a biodiversity hotspot. In this study concerning agricultural pollination, researchers chose to focus on Yunnan, a province in southwestern China. They chose this region due to its high level of current and historical agriculture and because it is “one of the last refuges of the eastern Asian honeybee, Apis cerana, in China.” They narrowed their research down to 11 species that are important for their culinary and/or medicinal use, some of them having widespread use and others having more local, cultural use. Depending on the species, conclusions were drawn either from available literature, from field studies, or both.

Eastern Asian Honeybee (Apis cerana) on Citrus limonia flowers (photo credit: www.eol.org)

Eastern Asian Honeybee (Apis cerana) on Citrus limonia flowers (photo credit: www.eol.org)

A review of the literature revealed information about each plant’s breeding system, the pollinators involved, ethnobotanical details, and other things. No information was available on the breeding system or pollinators of Panax notoginseng, “one of the most highly valued Chinese medicinal herbs.” Five species were found to be self-compatible (Angelica sinensis, Amomum tsao-ko, Brassica napus, B. campestris, and Gastrodia elata) and four were found to be self-incompatible (Camellia oleifera, Dendrobium catenatum, Fagopyrum esculentum, and Paris plyphylla var. yunnanensis). Codonopsis subglobosa was somewhere in the middle. The authors were intrigued by the persistent self-incompatibility in these domesticated plants (some more recently domesticated than others), noting that “both traditional and modern agricultural practices in China could not always overcome ancestral self-incompatibility mechanisms.” A running theme seemed to be that, if able to produce fruit or seed when hand-pollinated or without the aid of pollinators, the plants consistently performed better when insect pollinated. One of the most interesting findings was that Gastrodia elata, Dendrobium catenatum, and Paris plyphylla var. yunnanensis “persist in cultivation only through hand-pollination.”

Camellia oleifera, tea-oil plant, is pollinated by two native solitary bee species. It is avoided by native and introduced honeybees because its nectar contains substances that are toxic to worker bees, including caffeine, raffinose, stachyose, and galactose. Fagopyrum esculentum, common buchwheat, is native to southern China and was likely first domesticated there. It is pollinated by a variety of insects; however, its main pollinator in worldwide cultivation is the European honeybee, Apis mellifera. In China, evidence suggests that when pollinated by native pollinators, buckwheat produces higher yields and larger fruits. Codonopsis subglobosa is an undomesticated but cultivated perennial vine endemic to southwestern China, the roots of which are used as a substitute for ginseng. It can self-pollinate without a vector, but cross-pollination by wasps yields more seeds. Pollination by “hunting wasps” is rare, and C. subglobosa is not the only plant in the area pollinated by them. If the “evolution of hunting wasp pollination systems has evolved repeatedly in unrelated species native to southwestern China,” this region may be a “center for the convergent evolution of hunting wasp pollination.”

Common Buckwheat, Fagopyrum esculentum (photo credit: Wikimedia commons)

Common Buckwheat, Fagopyrum esculentum (photo credit: wikimedia commons)

Beekeeping has been a major part of agriculture in China for centuries. However, the introduction of the European honeybee has caused a significant decline in both wild and managed populations of native honeybees, despite native honeybees being “better adapted to more diffuse nectar resources” than the introduced honeybee. The decline in keeping and managing native honeybees is complicated and involves much more than just the introduction of the European honeybee. Along with the debate about what is best for agriculture in China, is the concern about what introducing non-native pollinators could mean for native flora and fauna. The authors conclude that there is “urgent need for new pollination management policies in China.”

This article ends with suggestions about how to improve and expand pollination biology research in China in order to fill gaps in knowledge, improve agricultural production, and protect and conserve native biodiversity. China is an ideal candidate for such research for several reasons: it has areas like southwestern China that are very species rich, it has a long history of agriculture, and it has numerous unique crops that are specific to Chinese culture. China also has a large and growing population, so improvements that can lead to more sustainable agricultural production will be greatly beneficial in the long run.