The difference in germination in the tested two seasons may be the weather differences in each testing season. Germination was enhanced in distilled water and KNO3 @ 0.1%. The positive influence of priming wheat seed in distilled water is in agreement with the findings of (Tania et al. 2021) and that of KNO3 is in line with the report by (Salehzade et al. 2009). Seeds primed with KNO3 showed improved germination performance, early growth, and vigor index of wheat seedlings (Steiner et al. 2018). However, Salicylic acid @ 0.06% negatively influenced the germination of wheat seed. Similarly, (Tania et al. 2021) reported that wheat seed primed with 2 mM Salicylic acid for 30 minutes performed lower germination compared to the unprimed control under non-saline stress. Mannitol @ 2% resulted in lower and similar germination capacity with unprimed control. Similarly, (Bousba et al. 2021) reported that mannitol reduced germination in durum wheat seed primed with 5g/L compared to the control and the negative effect was higher as the concentration increased. There was no variation in the germination of wheat seed between 12 and 24 hours of soaking time in different media.
Similar to the germination percentage, the vigor index I differences in each year may be due to the weather condition during the testing time or the developmental conditions of the seed on the mother plant. In our result priming the seed could not improve the vigor index I of wheat seed, as unprimed control resulted in a higher vigor index I. Vigor index I was not affected by priming durations between 12 and 24 hours.
Vigorous seedlings observed for seeds primed with KNO3 @ 0.1% for 24 hours (Fig. 1) could be attributed to the fact that the potassium ions might have contributed to root growth. In contrast, the growth of root and shoot lagged in wheat seed primed with Salicylic acid @ 0.06% showing the lowest vigor index II for both priming durations. Mannitol @ 2% also demonstrated a lower vigor index-II at 12 hours of priming time but, a small improvement was shown as the priming time goes from 12 to 24 hours. Wheat vigor index-II was not significantly affected by the interventions of priming treatments. Therefore, priming the wheat seed in distilled water for not more than 24 hours is economical for better vigor index II (Fig. 1).
The longer period of days to heading observed in 2019 may be due to the difference in weather conditions between the two growing seasons. Priming wheat seed did not affect the number of days required to head. There were no differences in days to heading between priming durations (Table 2).
The tallest mean plant height in the 2020 growing season may be due to better rainfall distribution during that season. The plant height of the wheat crop remained the same irrespective of both priming media and priming durations. This indicated that the contributions of different priming media were inconsequential for the plant height of wheat. Previous reports also indicated that seed priming did not affect plant height, number of spikelets, number of grains, and 1000 grain weight of wheat (Farooq et al. 2008). Again priming the wheat for 12 hours or 24 hours could not change the height of the wheat crop.
Maybe due to weather differences the weight of thousand seeds of wheat grown in 2019 was higher compared to 2020. However, any of the priming treatments did not affect the thousand seed weight of wheat seed. Our finding is in agreement with that of (Farooq et al. 2008) who reported that wheat seed priming did not affect plant height, number of spikelets, number of grains, and 1000-grain weight of wheat.
The effect of priming media and priming durations were not significant for the hectoliter weight of wheat seed.
Seeds primed with KNO3 @ 0.1% for 12 hours showed the highest number of spikes per square meter although it has no significant difference with seeds primed with Mannitol @ 2% and distilled water for both 12 and 24 hours, and Salicylic acid @ 0.06% for 24 hours durations. However, the priming duration of KNO3 @ 0.1% media could significantly affect the spikes number. The lowest average spike number was recorded from unprimed seed followed by KNO3 @ 0.1% for 24 hours duration. This indicated that priming the wheat seed with any of the tested priming media improves the number of fertile spikes either by increasing the number of tillers or improving the fertility of tillers. For example, there were 16% more spikes compared to the unprimed control (Table 3).
Nitrogen and K fertilizer increased grain yield significantly by improving the photosynthetic rate and 225-grain health (Bahmaniar and Ranjbar, 2007). The highest mean yield from seed primed with KNO3 @ 0.1% for 12 hours may be due to the contribution of KNO3 to the growth of the wheat plant root system at its early growth stage. Similarly, (Sarlach et al. 2013) reported that 12 hours of wheat seed priming duration in 2.0% KNO3 gave higher grain yield compared to the unprimed control. However, this similar priming media resulted in the lowest mean yield at 24 hours of priming duration may be due to the longer priming duration creating toxicity and deterioration of the seed. There was a 21% yield gap between 12 and 24 hours of priming duration in seed primed with KNO3 @0.1%. Seed primed with KNO3 @ 0.1% for 24 hours resulted in a 19% yield increment as compared to the unprimed control (Table 3). All tested priming media positively enhanced the yield as compared to the unprimed seed for both priming durations (12 and 24 hours), except KNO3 @ 0.1% for 24 hours. Seed priming with water for eight hours gave a 13% grain yield advantage (Harris et al. 2001)