The present study elucidates the effect of matrix priming with vermicompost (VCP) on germination and seedling emergence of two onion seed lots under drought, salt and temperature stress conditions. Seeds treated with water was considered as hydropriming (HP) and untreated (NP) seeds were taken as control. Treated and untreated seeds were exposed to different levels of drought (10 and 15% PEG), salt (50 and 100 mM NaCl) and temperature (30 and 35°C) stresses. Priming with vermicompost improved the performance of onion seed as indicated by higher germination and seedling growth under stress conditions. Catalase, superoxide dismutase and ascorbate peroxidase activities were found to be significantly (P < 0.05) higher in the vermicompost treated seeds than hydroprimed and untreated seeds.

Abiotic stresses are serious problems that hinder crop production. Seed germination and seedling development are stages which are sensitive to abiotic stress. Seed priming improves the performance of seeds/seedlings and provides faster and synchronized emergence under stress conditions. The present study aimed to investigate the effect of priming with biostimulants, vermicompost (5%), karrikinolide (10 -7 M) and seaweed (5%) using the solid matrix method (5 days, dark, 15 °C , 2:1:3, seed:vermiculite:organic solution, w:w:w) on germination and seedling quality of carrot seeds under abiotic stress conditions. Biostimulants were used alone and in double and triple combinations. Drought stress was simulated by PEG-6000 (-0.3 MPa), salinity by using NaCl at 100mM, and high temperature by 30 °C . Dry control and distilled water treated were used as controls. Priming treatment with biostimulants improved performance of seeds and seedlings, though not always significantly (p=0.05). Seaweed alone and its combination with karrikinolide showed the best performance for all the parameters. The germination percentage for dry control of carrot seeds were 37, 63 and 72% in salt, drought and high temperature stresses while distilled water treated seeds had values of 74, 79 and 77%, respectively. Seeds treated with seaweed+ karrikinolide and seaweed alone had 80 and 89% germination. The same treatments stimulated seedling emergence from 57% to 84-88%, 25 to 69-76%, 71 to 85-87% under drought, salt and high temperature stress, respectively. Seedling criteria, seedling height, fresh weight, dry weight and root fresh weight were also higher with these treatments in all stress conditions. Catalase activity of treated seeds was higher for seaweed (0.400 EUg -1 seed) and seaweed karrikinolide (0.411 EUg -1 seed) treated seeds than for both controls (non-primed: 0.299, distilled water: 0.239 EUg -1 seed). Biostimulants have potential as seed priming agents to enhance seed quality in carrots.

Ethanol release was tested in relation to seed vigour measured by seedling emergence and controlled deterioration tolerance in radish, pepper, watermelon, aubergine, leek and onion seed lots. Ethanol release, measured with six lots from each species after four and eight hours at 40&deg;C and 30% seed moisture, was highly negatively correlated with controlled deterioration tolerance (45&deg;C, 48 hours, 20% seed moisture) in radish (r = 0.05, P &lt; 0.05), with seedling emergence in watermelon (r = 0.99, P < 0.01) and to both traits in pepper (r = 0.87 to 0.94, P &lt; 0.05), but not with any variable for aubergine and leek. One single case was significant between ethanol release after eight hours and controlled deterioration for onion seeds. Results indicate that there is a relationship between ethanol release and seed vigour, but this appears to be species dependent.

The work was carried out to test the seed vigour test to correlate seedling emergence potential of rocket seed lots in the field conditions. Standard laboratory germination percentages of the 12 seed lots were ranged between 87 and 93%. Radicle emergence (2 mm) percentages after 18 (RE18h), 24 (RE24h), 36 (RE36h) and 48 (RE48h) during standard germination test, accelerated ageing test (AA, 45 °C, 100% RH, 24h, 48h), electrical conductivity (20 °C, 40 ml, 50 seeds) of 8h, 16h and 24h readings were used as vigour tests. Seeds were sown in two occasions in the field and vigour test results were correlated with seedling emergence percentages. Even though all seed vigour tests were significantly correlated with emergence at various levels EC24h and RE24h showed the highest correlation (p<0.001) with seedling emergence percentages in both sowing times. Correlation values were 0.824 and 0.844 in EC24h, 0.860 and 0.874 in RE24h.The lowest correlations were seen in standard laboratory germination test as 0.640 and 0.654 (p<0.05). Results indicated that EC24h and RE24h are practical and fast vigour tests that can be related to seedling emergence potential in rocket seed lots.

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