Volume 28, No. 1, 2006

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(pp. 7-21)
Impact of Mechanical Damage to Hybrid Maize Seed from Harvesting and Conditioning
S. Adesola Ajayi,* Gerhard Rühl and Jörg M. Greef
The effect of harvesting and processing operations on the quality of hybrid maize seeds was studied to identify those operations that cause the greatest damage. Three single-cross maize hybrids, ‘Ulla’, ‘Benicia’ and ‘Dea’, differing in their susceptibility to mechanical damage, were subjected to manual and mechanical processing during harvesting to grading.

Following processing, seeds were stored at –20 °C and at ambient temperate room conditions. Standard germination, accelerated aging and two cold tests were performed every four months to assess seed quality over a 15-month storage period. The post-shelling operations of cleaning and grading caused the greatest damage. More than all other operations combined, grading caused the most damage to round seeds, irrespective of the degree of susceptibility. Mechanical damage affected seed storability more than viability and vigor. Flat and large seeds were more tolerant to mechanical damage than round and medium-sized seeds. Seed shape influenced susceptibility to  mechanical damage much more than seed size.
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(pp. 22-35)
Partial Purification and Characterization of Single-Strand-Specific Nucleases from Gram and Pea Seedlings
Zafar Rasheed*
An enzyme that rapidly catalyzed the hydrolysis of denatured DNA was partially purified from germinated gram (Cicer arietinum) seeds and its molecular weight was found to be 45,000. The nuclease was studied for its endonucleolytic activity in comparison to single-strand-specific nuclease from germinated pea (Pisum sativum) seeds.  As with pea seed nuclease, the gram seed nuclease exhibited an affinity towards single-stranded DNA and showed a higher affinity towards depurinated DNA.

The temperature optima of both enzymes fall in the same range (40 °C for heat denatured DNA and 60 °C for native DNA). The nucleases from gram and pea seedlings degraded native DNA in a similar fashion at elevated temperature and exhibited maximum activity at pH 7.5. Both enzymes were affected by the same chemical agents among which Mg2+ and Ca2+ had stimulatory effects. However, Mn2+ and EDTA had no effect, and Zn2+ and 8-hydroxyquinoline were inhibitory on both nucleases. Under high salt concentration, enzymatic activity of both enzymes was inhibited. Native, denatured, alkylated, depurinated and crosslinked DNA were also tested as substrates for nuclease activity with pancreatic DNAase I, which degraded all DNA substrates at approximately equal rates. The degradation of native DNA by gram and pea seed nucleases was only 4 and 5%, respectively, in comparison with that of denatured, alkylated, or depurinated DNA; whereas, crosslinked DNA was not degraded by either gram or pea seed nucleases. These data suggest that the enzyme from germinated gram seeds is a single-strand-specific deoxyribonuclease.
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(pp. 36-46)
Alleviation of Salinity Stress by Seed Invigoration Techniques in Wheat (Triticum aestivum)
Shahzad Maqsood Ahmad Basra, Irfan Afzal,* Shoaib Anwar,
Muhammad Anwar-ul-Haq, Muhammad Shafiq and Kashif Majeed
Crop production faces stringent problems due to increased salinity, but salt tolerance can be induced effectively by pre-sowing seed treatments. This study was conducted to investigate the effects of pre-sowing seed treatments on germination and vigor of wheat (Triticum aestivum) cv. ‘MH-97’ under saline and non-saline conditions.

Seeds were subjected to hydropriming, osmoconditioning, halopriming with CaCl2.2H2O (50 mol m–3) and NaCl (50 mol m–3 ), chilling (–19 °C) or hardening (one cycle) for 12 h. All of the invigoration techniques except osmoconditioning and hardening were effective in alleviating adverse effects of salt stress on wheat at germination. Hydropriming proved to be the most effective followed by halopriming with CaCl2.2H2O,NaCl and chilling treatments as expressed by the final germination percentage, root and shoot dry weight, root and shoot length and root shoot ratio. The concentration of Na+ and K+ increased more in seedlings sown under saline conditions than under non-saline conditions. The Na+ concentration of seedlings was significantly increased by NaCl priming while other treatments had no effect on Na+ or K+ concentration. This study indicated that wheat grown under saline conditions can be improved by pre-sowing seed treatments.
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(pp. 47-57)
Salinity Effect on Ion Content and Relationship Between Ion Leakage, Growth and Salinity in Different Vegetable Seeds
Muhammad Jamil, Eui Shik Rha* and Mi Suk Han
Seeds of three varieties of cabbage (Brassica oleracea var. capitata), cauliflower (Brassica oleracea var. botrytis), canola (Brassica napus), sugar beet (Beta vulgaris), pak-choi (Brassica compestris) and radish (Raphanus sativus) were investigated for their germination percentage, germination rate (1/t50,where t50 is the time to 50% of germination), root and shoot lengths, Na+,Mg2+,Ca2+ and K+ and ratios of K+/Na+, Ca2+/Na+ and Mg2+/Na+ concentrations (ions lost during soaking for 36 h in different NaCl solutions) in four salinity treatments including 0.0 (control), 4.7, 9.4 and 14.1 dS m–1 NaCl.

Linear regression revealed a significant negative relationship between salinity and  germination percentage, germination rate, root length, shoot length and Mg2+, Ca2+ and K+ and ratios of K+/Na+, Ca2+/Na+ and Mg2+/Na+ concentrations. There was a positive relationship between salinity and Na+ concentrations. Multiple regression equations were developed to predict the relationship between chemical factors (ions leached from seeds  due to salinity) and biological parameters (germination percentage, germination rate and root and shoot lengths affected by salt stress). These equations show that Na+ had a significant negative relationship with germination rate, but a significant positive relationship was observed between Mg2+, Ca2+ and K+ and ratios of K+/Na+, Ca2+/Na+ and Mg2+/Na+ concentrations and germination rate. It was shown that root length had a significant negative relationship with Na+, but a significant positive relationship existed with Ca2+, Mg2+, Ca2+ and K+ had a significant negative relationship with shoot length.  A non-significant relationship was found between Na+, Mg2+, Ca2+ and K+ and ratios of K+/Na+, Ca2+/Na+ and Mg2+/Na+ concentrations with germination percentage. These equations provide a simple and rapid method based on chemical analysis and germination tests for determining salt tolerance in different vegetables.
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(pp. 58-63)
Modeling the Temperature Effect on Days to Germinate Some Hypericum Species from Turkey
Cüneyt Çırak,* Mehmet Serhat Odabas¸ Ali Kemal Ayan and Kudret Kevserog˘lu
The ability to predict the number of days for seeds of four Hypericum species (H. perforatum, H. bupleuroides, H. nummularioides and H. pruinatum) to germinate was investigated by using mathematical models based on temperature. 

A model, D = a – (b × T) + (c × T2), was used that previously predicted the time to emergence in relation to temperature for some vegetable crops and was unchanged when applied to the Hypericum spp. In addition to determining optimum seed germination temperature (T0 = –b /2 × c) in the tested species, days to germination was calculated by using coefficients obtained from regression models. Considering the marked interest by many researchers in modeling plant growth and development in recent years, the equations produced in this study may be helpful in this field. Models that predict days to germination or optimum temperatures could be used to adjust for an optimal time for sowing seed in different regions and thereby utilizing the growing season of these regions more productively.
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(pp. 64-70)
Pattern of Fruit and Seed Maturation in Himalayan Maple (Acer caesium)
S. S. Phartyal* and R. C. Thapliyal
Fruit and seed development in Acer caesium is described for trees growing in montane, temperate forests of the western Himalayas of India. Fruits of A. caesium were harvested during 1997 and 1998 at biweekly intervals after anthesis until maturity. Changes in physical characteristics of samaras and the percent seed germination during developmental stages were recorded.

Seeds matured around 210–225 days after anthesis (DAA).With maturation, pericarps and testae turned dark brown in color. This stage coincides with minimum fruit and seed moisture content and maximum germination percentage. Moisture content in both intact samaras and seed (hulled) showed an abrupt decline during the final phase of maturation and stabilized around 12–14% in mature seed. Dry weight accumulation ceased before seed attained physiological maturity. The study revealed that A. caesium seeds underwent a tri-phasic development, that is, growth, reserve accumulation and desiccation.
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(pp. 73-79)
Laboratory Test to Detect the Presence of Small Broomrape (Orobanche minor) in Red Clover
Sabry Elias,* Adriel Garay, Juan Zavala and Stephen Alderman
Small broomrape (Orobanche minor) is an obligate parasitic weed that attacks the roots of a wide range of broadleaf crops, resulting in varying degrees of economic loss. Red clover (Trifolium pratense) is one of the most common host plants that can suffer considerable yield reduction, particularly with heavy Orobanche infestation. The objective of this study was to develop a laboratory test to detect the presence of Orobanche seed in red clover.

The test was based on differences in seed size and density between red clover and broomrape. The recommended procedure for detection of Orobanche in red clover includes two main steps: 1) separation of Orobanche seeds from red clover by screening samples through a round-hole perforation sieve with a hole diameter of 1.04 mm using a seed shaker; and 2) visual examination of the screened portion using a microscope with a 40X magnification to detect the presence of Orobanche seed. Knowledge of seed color, shape, and texture of Orobanche is critical for proper identification. The test can detect the presence of one Orobanche seed in 453 g (1 seed/lb) red clover seed, which is the recommended working sample size for the test.
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(pp. 80-86)
Germination Properties of Some Wild Medicinal Plants from Iran
Mohammad Bannayan,* Farsad Nadjafi,Mehdi Rastgoo and Leila Tabrizi
Germination properties, including germination rate, germination percentage and cardinal temperatures, of eight wild medicinal species from Iran were studied. The seeds of the eight medicinal plants were exposed to germination temperature treatments ranging from of 5 to 35 °C consisting of seven constant and three alternating temperature regimes. A linear model was applied to describe the germination rate-temperature relationship.

The species studied using constant germination temperatures showed the highest germination percentages in the range of 20–30 °C for Nepeta binaludensis and Nepeta crassifolia, 15–20 °C for Zataria multiflora, 20–25 °C for Nepeta glomerulosa,
25–30 °C for Dysphania botrys and 15–30 °C for Thymus kotschyanus, Rubia tinctorum and Achillea millefolium ssp. elburensis. The highest germination percentage and germination rate were observed at alternating temperatures of 20–30 °C for Nepeta binaludensis, 10–20 °C for Zataria multiflora, Thymus kotschyanus, Nepeta glomerulosa and Nepeta crassifolia, and, 10–20, 20–30 °C, for Dysphania botrys. The various species showed clear differences in the temperature requirements of their seed for germination. Both germination percentage and rate were higher at constant than alternating temperatures. The highest base (Tb °C) and optimum temperatures (To °C) were observed in Dysphania botrys, while the highest critical temperature (Tc °C) was recorded for Rubia tinctorum. There was a positive linear relation between temperature at which the highest germination percentage was obtained at To, but this relationship was negative for Tb.
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(pp. 87-92)
Breaking Seed Dormancy of Selinum wallichianum, a Medicinal Plant of the Himalaya
Meena Joshi, R. S. Rawal and Uppeandra Dhar*
Successful propagation of Selinum wallichianum, a high value medicinal plant of the Himalaya, requires development of methods to overcome its seed dormancy. While seeds collected from alpine and subalpine provenances spanning the range of this species were found to be viable, only 46.7% and 24.5%, respectively, of the seeds germinated without any pre-sowing treatment.

Chilling (4o C.) for 14 days improved the germination percentage of seed from both provenances compared to the control.  Also, 100 ppm KNO3 pre-treatment for alpine and 500 ppm for subalpine seeds improved the percent germination significantly over the control. Higher concentrations of KNO3 (> 500 ppm), however, reduced the percent germination of seeds from both provenances. Use of 100 ppm GA3 improved the germination percentage and lowered the mean germination time (MGT) compared to the control for seeds from both provenances. Improved germination responses to chilling treatments corresponds well with natural conditions where S. wallichianum seeds are covered with snow during the winter. Response to chilling and GA3  treatment implies Intermediate Complex Morpho-Physiological Dormancy (MPD) of S. wallichianum seeds.
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