Oxford University Exploration Club

The mountains of Central Asia hide the center of origin of many fruit trees that we cultivate nowadays. Whole forests of apple, apricot and walnut trees that in autumn become of amazing bright orange and red. These forests have been extensively cut in the past and are disappearing -a risk not only for the loss of their beauty, but also because our cultivated varieties have lost most of their resistance to parasites, and are at high risk from possible future diseases, whereas the wild varieties are still resistant. But where are the remaining fruit forests of Central Asia?

The purpose of this expedition is to map the location and study the ecology of the last fruit forests of Central Asia. In particular we will:

• collect data on autumn leaf colour and parasite insects to test the evolutionary hypotheses or the evolution of autumn colours
• collect seeds of wild apples to bring to the UK and to the local researchers for future genetic and ecological analyses.

BACKGROUND

The cultivated varieties of many fruit trees (apple and apricot for example) generally do not have bright autumn colours. The leaves of almost all (94%) the apple cultivars in the National UK collection in Kent, for example, stay green in autumn and do not display any red or yellow colour. Many wild apple species however do have bright autumn colours, and there is evidence that the original, wild varieties of the domestic apple (Malus sieversii) have bright red autumn colours in their area of genetic origin: the mountains of Central Asia, from Uzbekistan to the eastern slopes of the Tien-Shan in China. Apparently, these wild varieties also retain much of the resistance to parasites that has been lost during the process of domestication of fruit trees.

This is very interesting for the theories of the evolution of autumn colours. One of the hypotheses is that autumn colours are warning signals towards parasites, for example aphids, that migrate to the trees in autumn, an idea that the expedition leader (Marco Archetti) started to develop ten years ago, after the initial suggestion of the late W.D. Hamilton, FRS and Professor of

Evolutionary Biology at New College. The other main hypothesis is that the red pigments protect the tree from photoinibition and photooxidation when it is cold, thus allowing the leaves to reabsorb nutrients (especially nitrogen) more efficiently. Understanding the link between leaf colours, plant defenses and susceptibility to parasites is useful not only for evolutionary biology but also for horticulture. Our western cultivated varieties are so genetically uniform and prone to parasites that we risk losing them with the outbreak of a future disease. Germplasm material exists for all the cultivated varieties of fruit trees in Europe and the US, but not for the Central Asian varieties. The national apple collection at the Brogdale Horticultural Center in Faversham (Kent), for example does not have any of the wild varieties of Central Asia, which instead have been extensively collected by the US researchers in the past few years.

While in Europe wild fruit trees grow usually isolated, in Central Asia fruit trees form pure forests – whole forests of apple and apricot trees! – that in autumn become of a variety of incredibly bright orange and red, like, or even more than, the famous autumn colours of New England. These forests are disappearing. They have been cut extensively in the time

of the Soviet Union, and nowadays they continue to be cut by the locals. In southern Kyrgyzstan for example, in the mountains around Jalalabad, because of the lack of fuel (usually provided by Uzbekistan, then discontinued for geopolitical reasons), two years ago the local people had to cut their walnut forest to gather wood for the winter. In Uzbekistan and Kazakhstan apples continue to be cultivated extensively to be sold in the local markets.

But where are the wild forests of apple trees that once covered all the mountains of Central Asia? How different are these trees form the domestic varieties? What is the link between their autumn colours and their resistance to parasites?