Populations of Medicago minima (L.) Bart. in Iran: High Morphological Variability Irrelevant to ITS Sequences and Geographical Proximity

Medicago minima (L.) Bartal. has received little agricultural development to date, while having potentially useful traits compared to other “medics”, e.g., annual species of section Spirocarpos. However, the range of variation in M. minima requires further studies. This research assessed the diversity of the pod morphological traits of 13 populations in the southwest, west, northwest, and north of Iran. In addition, variation in nuclear ribosomal Internal Transcribed Spacer (nrITS, ITS 1+5.8s+ITS 2) was evaluated. No geographical patterns of variation in the pod traits were found. The molecular phylogenetic assessments of 7 populations indicated low variability, thus being grouped into a well-supported monophyletic clade (99% Bootstrap support/1.00 Posterior Probability (PP)). Nevertheless, the pod morphological traits exhibited significant variations, most notably in Glandular Hairs (GH), with a coefficient variation of 58%. For breeding and possibly conservation purposes, the following populations demonstrated potentially useful characteristics: (1) Baghcheh population with the highest number of seeds per pod (4.6) and angle of spine insertion (2.87◦); (2) Khoramabad population with a higher number of spines on the middle coil (65.27); and (3) Sarvabad population with the greatest fruit length (3.71 mm), fruit diameter (4.17 mm), Seed Length Trait (SLT) (2.37 mm), and Seed Width Trait (SWT) (1.35 mm). In qualitative traits, Khoramabad, Baghcheh, Marivan, and Paveh populations had higher scores, particularly for glandular pubescence and Simple Hairs (SH) on their pods. Results of the correlation analysis were often null or negative; however, altitude indicated a positive relationship with glandular pubescence and SH. No obvious correlations were found between pod morphology and ITS variation and geographical proximity.