Seed germination and seedling vigour
In the present study, standardization of seed priming with different micro-nutrients revealed that seed priming with 0.5% ZnSO
4 recorded higher germination (96%) and vigour index (3811) than control which recorded 84% germination and 2528 of vigour index. Seed priming with 0.5% MnSO
4 was the next best treatment. It recorded higher germination of 11.9% and vigour index of 4.6% over control (Fig 1). The probable reason for higher germination in 0.5% ZnSO
4 primed seeds could be due to greater hydration of colloids, higher viscosity and elasticity of protoplasm, increase in bound water content, lower water deficit, more efficient root system and increased metabolic activity. The increased seedling growth and vigour index observed in this treatment might be due to greater early vigour and higher percentage of germination of the seeds that had reached autotropic stage well in advance than others. ZnSO
4, as a constituent of dehydrogenase enzyme, activator of other enzymes and a constituent for biosynthesis of IAA and amino acid that favored the synthesis of protein. Sulphur in ZnSO
4 also increased the levels of vitamins, biotins and thiamin’s and its coenzymes in seeds and enhanced growth rate of seedlings. These observations were similar to previously reported findings in germination of soybean cultivar LS678 and TGx1835-10E which were influenced by hydropriming and Benzyladenine priming (
Mangena, 2020). Seed priming found effective for reducing emergence time, accomplishing uniform emergence, better allometric attributes and requisite stand in blackgram
(Raja et al., 2019). In general, priming results in metabolic repair of damage during treatment
(Bradford et al., 1990) and better genetic repair like earlier and faster synthesis of DNA, RNA and proteins, which may be the basis for enhanced growth. Seed priming with water and KNO
3 accelerates seed germination and seedling establishment in rapeseed
(Alishavandhi et al., 2014) under both normal and stressful environments.
Growth parameters
Evaluation of production potential of the best performing micronutrient seed priming treatment in combination with
rhizobium coating in blackgram revealed that seeds primed with 0.5% ZnSO
4 and coated with
rhizobium @ 30 g per kg of seeds (T
5) recorded higher field emergence (88%), root length (10.9 cm), shoot length (21.4 cm) and dry matter production (7.24 g/plant) at vegetative stage than control which recorded lower field emergence ( 82% ), root length (9.3 cm), shoot length (16.9 cm) and dry matter production (5.20 g/plant) (Table 1). In pulses, micronutrients play an important role in plant growth and yield. Moreover, the above said treatment contains Zn which is constituent of an enzyme essential for the synthesis of plant hormone indole acetic acid, which is presumed to be capable for stimulating emergence. The root growth was increased due to
Rhizobium treatment. The microorganisms that are used as biofertilizers stimulate plant growth by providing necessary nutrients by their colonization at the rhizosphere/their symbiotic association. The association may also regulate the physiological processes in the ecosystems by involving in the decomposition of organic matter, fixation of atmospheric nitrogen, secretion of growth promoting substances, increasing the availability of mineral nutrients and protecting the plants from pathogen. Seed priming with chemicals play a major role in increasing leaf and stem dry matter and redistribution of dry matter in reproductive parts compared to hydro-priming and control
(Arun et al., 2020). Vazirimehr et al., (2014) reported that seed priming with 1% KNO
3 shorten the time from seed emergence to harvest, improved crop stand and dry matter partitioning to grain in maize. In the present study, the same treatment (T
5) recorded higher plant height (56.3 cm) and a greater number of nodules / plant (38.6) followed by seeds primed with 0.5% MnSO
4 and coated with
rhizobium (T
6) whereas plant height is 55.0 cm and number of nodules/plants is 36.4. Control (T
1) recorded lower plant height of 47.2 cm and lesser number of nodules / plant (29.0) (Table 2). Inoculation of seeds with
Rhizobium recorded a greater number of nodules per plant. The increase in plant height and drymatter production might be due to increased supply of nitrogen due to more nodulation by the
rhizobium inoculation. Seed priming with 100 ppm GA3 for 24 hours increased plant height, number of pods per plant, number of seeds per pod, 1000 seed weight and grain yield in cowpea
(Arun et al., 2020).
Yield and yield attributes
Seed priming techniques exerted a significant effect on seed yield and resultant seed quality. Seeds primed with 0.5% ZnSO
4 and pelleted with
rhizobium culture (T
5) recorded more number of pods/plant (30.1), number of seeds/pod (6.5), pod yield/plant (6.06 g), seed yield/plant (5.18 g), pod yield/ha (1098.64 kg) and seed yield/ha (870.39 kg) followed by T
6 which registered 28.7 number of pods/plant, 6.3 number of seeds/pod, 5.98 g pod yield/plant, 5.12 g seed yield/plant, 1029.20 kg pod yield/ha and 837.04kg seed yield/ha. The same treatment (T
5) recorded higher 100 seed weight (4.77 g) and germination (94%) in the resultant seeds where as it were 4.68g and 93%, respectively in T
6 (Table 2). The increased pod yields due to unaborted reproductive structures could have resulted due to higher photosynthetic activity and adequate vegetative structure to produce more number of reproductive sinks. Poor translocation of metabolites to the reproductive stage may be one of the reasons for lower yield in control. Similar results were also reported in wheat
(Kalpana et al., 2015). In line with the findings in this study, soybean seeds primed with benzyladenine increased number of pods/plant, number of seeds/pod and seed weight compared to hydro-primed seeds (
Mangena, 2020). Seed priming with 5 ppm gibberellic acid enhanced seed quality thereby enhancing crop stand and yield in greengram
(Devi et al., 2021). Similar effects were also highlighted in bittergourd
(Debbarma et al., 2018). The seeds primed with 0.5% ZnSO
4 and coated with
rhizobium in the present study enabled quick emergence and established well in the field with higher population that accounted for higher yield per unit area. Ebrahim Abbasi
Seyahjani et al., (2020) reported that combined inoculation of bean with
rhizobium, pseudomonas and mycorrhizal fungi increases the yield might be due to enhancing the biological activity in the soil, soil characters’ improvements, better root development, improved transport of nutritional elements, enhanced chlorophyll content synthesis and photosynthesis, solubilization of nutrients resulting in higher nutrients uptake
(Menbari et al., 2017). Khandelwal et al., (2012) reported that the inoculation of
rhizobium increased cowpea grain yield by 13.80% compared to control. Similar results were also reported in soybean
(Lingaraju et al., 2016).