EFFECTS OF N-FORM AND SALINE PRIMING ON GERMINATION AND VEGETATIVE GROWTH OF GALIA-TYPE MELON (CUCUMIS MELO L. CV. PRIMAL) UNDER SALINITY

Abstract

Seed priming has become a common strategy for seed treatment which increases rate, percentage and uniformity of germination or emergence, especially under unfavourable environmental conditions. The most frequently used seed priming techniques involve polyethylene glycol (PEG), sodium chloride (NaCl), or potassium nitrate (KNO3). However, for the emergence or growth in conditions of high salinity it becomes necessary to improve on these techniques. Seeds of muskmelon were primed in darkness at 25 °C for four days, in solutions with 150 mM of different N-form salts (NH4NO3; KNO3; (NH4)2SO4) and NaCl. Seeds were then rinsed and dried at 25 °C, and finally germinated in three levels of salinity (0.5; 2.5 and 5.0 dS m) for 38 hours. Germination and growth of the protused radicle were monitored each hour to determine the Germination Index (GI) and rates of germination and growth. All salt solutions except (NH4)2SO4) resulted in an improved germination rate, radicle growth and Germination Index. Seeds primed with NH4NO3 and KNO3 had greater resistance to higher salinity levels in germination solution, while better GI and rates of germination and growth compared to the control; (NH4)2SO4 and NaCl primed treatments. Detrimental effect on total seed germination was observed only on (NH4)2SO4 primed seeds. INTRODUCTION Muskmelon is a moderately sensitive crop to salinity (Ayers and Westcott, 1985) that requires the application the technological and biological strategies (Cuartero, 2003), such as seed conditioning to reduce the less seedlings. This conditioning technique (priming) has accelerated germination, emergence, and growth of seedling. (Cuartero and Fernandez, 1999). The main priming techniques are osmotic (Buitink et al., 2000) and matric (Meredy et al., 2000) used for increasing the germination rate and uniformity of seedlings. All these substances were assayed with sodium chloride (Cayuela et al, 1996; Oliveira et al., 1998; Svritepe et al., 1999; Akinci et al., 1999; Svritepe et al. 2003); polyethylene glycol (PEG) (Buitink et al., 2000), or fertilizers, specially the potassium nitrate (Kang et al, 1996; Bradford et al., 1988; Nacimiento and West, 1999) at different concentrations, for varying lengths of time and with or without oxygenation and darkness. With respect to sodium chloride primed seeds, Cayuela et al., (1996) concluded that greatest tolerance to dependence on osmotic adjustment, is that if allows the roots to contain greater quantities of sodium, chloride, sugars and organic acids as compared to non primed seeds. Bloom et al (2003) reported that the growth of the root in maize seedlings is influenced by the nitrogen form – NO3 or NH4 -, and redox potential of the solution. The NH4 favors faster cellular division in the apical meristem of the root, whereas NO3 has a more important osmotic role. Proc. VII IS on Prot. Cult. Mild Winter Climates Eds. D.J. Cantliffe, P.J. Stoffella & N. Shaw Acta Hort. 659, ISHS 2004 254 MATERIALS AND METHODS Seeds of Galia type melon (Cucumis melo L. cv. Primal) were primed with nitrogen commercial fertilizers KNO3, NH4NO3 and (NH4)2SO4 and with NaCl at 150 mM for four days at 25° C in darkness. After priming, seeds were washed in water for 3 minutes, then rinsed in distilled water (Sivritepe et al., 2003). Finally they were dried at 25 °C for two days. All seeds were germinated at three levels of salinity (0.5, 2.5 and 5.0 dS m1 EC). In order to measure the growth of the radicle, germination was conducted on polyethylene rizotrones (16*8 cm), composed of a fibre-glass mesh and a 3 mm thick glass cover in order to measure the growth of the radicle. Experimental design consisted of three replicates of 5 seeds in two random blocks Number of germinated seeds and length of radicle were measured hourly for 38 hours by means of digital photography. Germination Index (GI) and percentage were calculated at 38 hours to determine the effect of priming treatment and saline concentration. Average growth rate (AGR) and average germination rate (AGeR) were calculated from the beginning of germination of the control treatment (27 hours) to the end of the experiment (38 hours). All the data were analysed by Statgraphics Plus 4.1 © package using multifactorial ANOVA and LSD test. RESULTS AND DISCUSSION Priming At 38 hours, the main effect of priming treatments was the differences in length of radicle rather than in germination percentage. Control and NH4NO3, KNO3 and NaCl priming treatments had over 80 % germination. Nevertheless, (NH4)2SO4 priming treatment only reached slightly above 50 % germination. Only NH4NO3 and KNO3 priming treatments surpassed 90 % germination at the end of the experiment (Table 1) which indicates that the nitrogenous form priming (NH4, NO3 or a combination of the two) significantly affected the response obtained. NH4NO3 and KNO3 priming promotes greater radicle length than control and (NH4)2SO4 treatments (threefold and twofold respectively). As a consequence of these results, NH4NO3 reached the highest GI and AGR as compared to the control treatment. However, from 27 to 38 hours, NH4NO3 had the lowest AGeR (Table 1), due to the fact that at 27 hours its germination percentage was 60%, in comparison to 40% for KNO3 and 4.4% for (NH4) 2SO4 All priming treatments attained a higher GI at all salinity levels as compared to the control; with the exception of (NH4)2SO4 which was lower (Table 2). NH4NO3 had the highest GI value at 5.0 dS m EC (Table 2). These results indicate two effects of priming: First, the physiological activity of the NH4 is related to cellular division in the apex of the root, while NO3 stimulates root growth and development in low osmotic conditions. (Bloom et al. 2003). Second, osmotic potential of solution has a negative effect on germination processes and radicle growth. At the same mM concentration applied during priming, the osmotic potential obtained by (NH4)2SO4 was twice that of other priming treatments; since at values over -1.0 MPa, Nascimiento, (2003) obtained a decrease in the germination percentage in KNO3 primed melon seeds. The results obtained with NH4NO3 agree with those of Kronzucker et al. (1999), with respect to synergic action of the NH4 and NO3. This has also been determined in several other species, such as corn, wheat and rice. Muhlestein et al (1999) indicates that an NH4:NO3 proportion of 30:70 is more suitable for most crops than NO3 alone. However, when the NH4 proportion exceeds 50%, production is negatively affected. Variation in germination and growth of the radicle from 21 to 38 hours due to priming is presented (Fig. 1 and 2). The results indicate that there is a differential response of the primed as compared