Abstract
The germination of freshly collected Juniperus polycarpos (K. Koch) seeds is very low and attributed to the large proportion of nonviable seeds in the seed lots. Thus, the aim of this study was to improve seed lot quality by removing nonviable seeds using two flotation techniques: incubation-drying-separation (IDS) and modified specific gravity (MSG) separation. We examined different IDS conditions (the specific incubation time, subsequent drying time and sorting media) for effectively sorting out nonviable seeds; and tested the feasibility of modified SG separation, which involved soaking seeds in water for a certain period before sorting in different concentrations of sucrose solution. Viable seeds were expected to absorb and metabolically bind more water during soaking than dead seeds could, and hence be sorted effectively depending on the viscosity of the sucrose solution. The viability of the seeds that floated or sank was determined in a topographical tetrazolium chloride (TTC) test. For the IDS trial, 7 days incubation followed by 9 h of drying and sedimentation in pure water or 200 g·L−1 sucrose solution identified, respectively, 75 and 82 % of the seeds as viable (sunken) seeds. For the MSG trail, 77 % viable seeds were recovered in the sunken fraction when seeds were soaked for 48 h then immediately sorted in 600 g·L−1 sucrose solution. In both cases, the loss of viable seeds in the discarded floating fraction was only 4 %. The results demonstrate that both IDS and MSG separation techniques substantially improved seed lot viability, but MSG separation is simple and needs no modern seed handling facility, and its efficacy relies on seed mass (due to the initial soaking) and the specific density and viscosity of the flotation medium.
Highlights
IntroductionIn Iran, the species occurs naturally along the southern slopes of the Alborz mountain chain and the northern part of Khorasan at altitudes from 750 to 3400 m above sea level (Korouri et al 2012)
For the modified specific gravity (MSG) trail, 77 % viable seeds were recovered in the sunken fraction when seeds were soaked for 48 h immediately sorted in 600 gÁL-1 sucrose solution
The number of floating seeds ranged from 38 % in pure water (0 gÁL-1) to 55 % in 250 gÁL-1 sucrose solution, whereas the proportion of sunken seeds ranged from 62 % in pure water to 45 % in 250 gÁL-1 sucrose solution (Fig. 3a)
Summary
In Iran, the species occurs naturally along the southern slopes of the Alborz mountain chain and the northern part of Khorasan at altitudes from 750 to 3400 m above sea level (Korouri et al 2012). Over the past several decades, the juniper forests have been greatly degraded by anthropogenic disturbances, coupled with poor natural regeneration and poor growth conditions (low winter temperature, poor soil conditions and summer drought). In Iran, the area of J. polycarpos forest has been reduced from an estimated 1.2 million ha in the early 1970s (Djavanshir 1974) to approximately 0.5 million ha by the early 2000s (Kharazipour et al 2008). In Iran, for instance, commercial harvesting of J. polycarpos has been prohibited since 1989, and protected areas have been established to reduce anthropogenic disturbances. Passive restoration—relying on natural regeneration alone—has been insufficient due to long seed production cycle (seed mast year every 4–8 years) and poor seed lot quality (Ahani et al 2013)
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