Intra- and inter-population variation in Spinacia turkestanica: Implications for spinach genetic resources sampling

Spinacia turkestanica Iljin is closely related to cultivated spinach (S. oleracea L.) and therefore of interest to genebank curators and plant breeders. In 2008 an expedition was carried out in Tajikistan and Uzbekistan to collect seed samples of S. turkestanica. Eighteen of these accessions and two additional accessions from Turkmenistan were characterized for 21 phenotypic traits and 50 SNP markers to study the distribution of variation within and between populations. Six varieties of cultivated spinach were included in the study as references. In general, S. turkestanica was clearly distinct from the reference varieties for phenotypic and molecular diversity. The main part of the observed diversity in S. turkestanica was distributed within rather than between populations. The populations from Tajikistan and Uzbekistan showed a positive correlation between phenotypic and genotypic distance (r = 0.458, p < 0.001) and between geographic distance and genotypic distance (r = 0.515, p < 0.001). Genetic differentiation was largest between populations from Tajikistan and populations from Uzbekistan, which are separated by the Zarafshan mountains. A resampling study showed that sampling 30–50 plants from each of 5–6 geographically widespread populations is sufficient to capture more than 98 % of the observed SNP alleles and more than 99 % of the observed phenotypic variation within the targeted area in Tajikistan and Uzbekistan. Whether this recommendation also holds for adaptive variation, such as resistance to biotic and abiotic stress, is subject of further study.