Comparative study of seed germination, phenology, and reproductive fitness in Melilotus sulcatus populations from Israel.

Abstract

Background: Melilotus sulcatus (Fabaceae) is an annual weed species prevalent in the Mediterranean Basin and Asia, characterized by a hard seed coat, indicating physical seed dormancy and long seed-bank longevity. This weed exhibits high phenotypic plasticity, thriving across various climatic regions in Israel. This study investigates seed germination of M. sulcatus populations under different temperatures. Moreover, we have studied the phenology, and reproductive biology of M. sulcatus populations in a common garden experiment. Seeds of M. sulcatus were collected from onion fields at Kibbutz Grofit located in the hyper-arid Southern Arava region, with ~ 30 mm average annual rainfall, and from Kibbutz Yifat, in the Jezreel Valley, where annual rainfall is 450-650 mm. Progeny generations were grown in pollen-proof cages at Newe Ya'ar Research Center also located at the Jezreel Valley.

Results: Differences in seed area and average weight were observed among populations and generations, with field populations producing heavier seeds compared to progeny populations. The optimal temperature (T₀) for seed germination varied among populations, with the highest T₀ recorded for the Grofit field population (23.40℃) collected at the warm site and the lowest for the Yifat field population (17.67℃) collected at the cold site, while the two progeny populations showed similar T₀ values. Phenology and reproductive biology were tested using seeds of the two field populations. Despite the vigorous growth of the Grofit population, there were no significant differences in average final weight (4.59 g for Grofit and 4.23 g for Yifat) and height (51.8 cm for Grofit and 50.3 cm for Yifat) between populations. Grofit progeny plants exhibited a statistically significantly higher number of seeds per pod, combined with larger seed area and average weight.

Conclusions: Overall, our findings underscore the adaptive strategies employed by M. sulcatus populations in response to their environment. Vigorous plant growth, a higher number of seeds per pod, and larger seed area and average weight were observed in individuals from the Grofit population compared to the Yifat population. The greater fitness of Grofit population, originated from hyper-arid conditions, highlights the significant impact of environmental factors on species adaptation.