Abstract
Soybean seed vigour declines with increase in storage duration, due to ageing, which can be alleviated through seed priming. The objective of this study was to investigate the effects of Humic acid (HA) priming on germination, vigour and seedling performance under laboratory and greenhouse conditions with two soil moisture level [50% and 80% field capacity (FC)]. Seeds stored for 12 months having 60% germination were primed either with 0.2 g/L HA solution or distilled water (hydro-primed) at 25 °C for 1, 3, 5 and 7 h. Non-primed dry seeds were used as control, giving nine treatment combinations. Various germination traits [mean germination time (MGT), final germination percentage (FG%), germination rate index (GRI), seedling emergence percentage (SEP)], mean emergence time (MET), seedling quality traits [seedling vigor index (SVI), shoot length, root length, root volume], antioxidant enzyme activities [catalase (CAT), peroxidase (POD)], lipid peroxidation [malondialdehyde (MDA)] and electrical conductivity (EC) were determined. A germination test in the laboratory was conducted as single factor (nine priming treatments), while the greenhouse experiment was conducted as two factors [2 soil moisture level (50 and 80% FC) and 9 priming treatments]. The results indicated that seeds primed with HA for 5 h was able to reinstate the CAT activities (25%), POD activities (50%) and reduced EC (51%) and MDA content (40%) compared with non-primed seeds, reduced the MET (from 4.3 to 3.5 days), increased FG% (from 62 to 71%), GRI (15.6–21.1) and SEP (from 35 to 54%) and (from 60 to 72%) at 50% FC level and 80% FC level, respectively. A strong negative correlation (r = −0.80 **) was found between MDA content and GRI, while CAT and POD activities had positive correlation with GRI r= 0.67 ** and r = 0.56 **, respectively. Thus, priming with 0.2 g/L HA for 5 h improved the vigour of minimally deteriorated soybean seeds resulting in increased emergence with more uniform field establishment.
Highlights
Seed ageing is considered as one of the primary consequences of seed deterioration during storage
We aimed to investigate the potential of Humic acid (HA) to instate repair via enhancement of antioxidant defense mechanisms and reduction of peroxidation activities of stored soybean seeds, providing a good stand establishment even under stress conditions, for minimally aged soybean seeds
The present study revealed that primed seeds (HA and HP primed for 3 h and 5 h) had reduced amount of MDA content compared with non-primed seeds believed to be attributed to minimization of oxidative damage by improved antioxidant mechanisms and repairing of the membrane damage
Summary
Seed ageing is considered as one of the primary consequences of seed deterioration during storage. De Vitis et al [1] reported that seed deterioration is an inevitable process, even under proper storage conditions. All seeds undergo deterioration during storage, differing in rate depending on initial seed quality [2] and storage environment [3,4]. Tropical in nature, the deterioration is enhanced when seeds are stored under ambient conditions. Several studies have found that lipid peroxidation [4], degradation of enzyme activities [7], disruption of cellular membrane integrity [8] and damage to genetic materials as the foremost roots of seed ageing [9]. Seeds with low vigour may not perform well and result in delayed germination and low seedling quality especially under abiotic stress conditions
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