INFLUENCE OF DROUGHT ON SEEDLING DEVELOPMENT IN DIFFERENT CORN GENOTYPES ( Zea mays L . )

Assuming that drought affects corn seed performance, such conditions were simulated in this study in order to examine their effects on seedling geminability and length in several corn genotypes. The study showed that the tested seeds tolerated the stress conditions up to a certain point. The studied genotypes differed in level of resistance to the stress conditions. Salt concentrations were determined, which were capable of negatively affecting seed germinability and seedling growth.

The aim of this study was to assess the effects of drought on seed germinability of several corn hybrids under laboratory conditions.Effects of these stress factors on seedling growth (hypocotyl and radicle) were observed.Observations were made on the level of individual corn genotypes.

Effect of drought
Drought affects all stages of plant growth and development including germination (H a d a s , 1976).Drought poses problems in most food-producing regions.That is why this problem has been studied by numerous researchers and in a large number of crops such as tomato (T a y l o r et al., 1982), rice (S i n g h and S i n g h , 1983), wheat (K e r e p e s i and G a l i b a , 2000), various grass mixtures (E m m e r i c h and H a r d e g r e e , (1990,1991,1993), etc.
The problem of drought in corn has been extensively studied by P a r m a r and M o o r e , (1965), H e y d e c k e r , (1977) and V a n der V e n t e r , (1988).Numerous authors have found that drought negatively affects seed germinability in various crops as well the growth of the radicle and hypocotyl in seedlings.Polyethylene glycol (PEG) has been used in laboratory studies for simulation of drought conditions.

Material and Method
Experiments were conducted in National Laboratory for Seed Testing in Novi Sad.They included corn hybrids from different maturity groups (NS 300, NS 420, ZP 599, NS 640, ZP 680 and ZP 704).
Three tests were applied: the standard method of seed germinability testing, effect of polyethylene glycol on seedling germinability and length and the effect of high salinity in the substrate on the germinability and length of corn seedlings.
The tests were conducted in accordance with Handbook of Vigour Test Methods (ISTA, 1995), which provides details of these tests.
Polyethylene glycol application (osmotic stress) -Seeds were incubated on filter paper in petri dishes at 25 o C. Filter paper was previously treated with polyethylene glycol, with the molecular mass of 6000, differing in the osmotic potential: -0.1 MPa, -0.3 MPa, -0.6 MPa, -0.9 MPa.Filter paper treated with distilled water served as control.Germinability and seedling length were assessed 7 days after treatment.The tests were done in 4 replications, 50 seeds per replication.The obtained data were procesed by the analysis of variance for the two-factorial trial (H a d ž i v u k o v i ć , 1991).Statistical analyses were performed with the MSTAT computer program.

Osmotic stress -PEG application
The results of these tests showed that seed germination LSD 0.05 was 3.074; for root lenght was LSD 0.05 = 0.430 and for seedling length was LSD 0.05 = 0.142.
The tests showed that the hybrid NS 300 exhibited lowest germinabilities with all PEG concentrations except the highest one (Graphs 1.2 and 3).The same effects were observed for seedling length.Highest germinability values were found for the ZP hybrids, highest radicle lengths for the NS hybrids.As regards the hypocotyl, the hybrids NS 300 and ZP 680 had shortest ones with all PEG concentrations and the hybrid NS 420 had the longest one.A comparison of the above results indicated that the development of the aboveground seedling part was more sensitive to increased PEG concentrations than the radicle development.
The hybrid NS 300 was most sensitive to increased PEG concentrations, i.e. to the occurrence of drought at the time of planting.Conversely, the hybrids NS 420 and NS 640 exhibited the highest resistance.
P a r m a r and M o o r e , (1965), H e y d e c k e r , (1977) and V a n der V e n t e r , (1988) obtained similar results for corn.T a y l o r et al., (1982), S i n g h and S i n g h , (1983), Bhat and S r i n i v a s a R a o , (1987) and E m m e r i c h and H a r d e g r e e , (1990,1991,1993) obtained similar results for seed germinability in various plant species.
Negative effects of drought on the growth of the primary root and hypocotyl were reported by P a r m a r and M o o r e , (1965) and D e and K a r, (1994).These authors showed that the seeds treated with a PEG solution with a low osmotic potential caused significant reductions in the lengths of radicles and hypocotyls, while a solution with a high osmotic potential completely interrupted the formation of hypocotyls.

C o n c l u s i o n
The study involving PEG applications indicated that corn seed is sensitive to abiotic stresses occurring under natural conditions.
Drought tended to reduce corn seed viability.Negative effects were also evident regarding seedling growth and development.
The osmotic potential at which seed quality parameters dropped down was 0.1 MPa.
NS 300 was most sensitive to drought.ZP 599 and ZP 680 were less sensitive than the previous hybrid.NS 420, NS 640 and ZP 704 were most resistant to drought.
It was characteristic of the hybrid ZP 677 that it exhibited average values for almost all traits under study.