چكيده لاتين :
Introduction: Johnsongrass (Sorghum halepense (L.) PERS) is one of the most controversial and
problematic weed. It damages more than 30 different crops over 53 different countries. S. halepense (L.) is a
perennial weed reproducing by seed and rhizome. Since it produces many seeds and rhizomes, it is difficult to
control. A weed germination plays an important role in attaining a proper establishment in a typical agroecosystem
and its trend is adjusted by some environmental factors such as light, temperature, salinity, pH and
soil moisture. Considering the pattern of germination and emergence of weed species, it will be expected to
provide the comprehensive information to develop weed management strategies in the future. Thus, the main
purpose of current research was to evaluate the breaking methods of the seed dormancy. In addition, the effects
of several environmental factors comprising constant and alternative temperature, light, salinity, drought stress,
and burial depth on germination and seedling emergence of Johnsongrass were assessed.
Materials and Methods: Seeds of Johnsongrass (S. halepense L.) were collected in June 2013 from plants
located at the farmlands of the agriculture research in Zarghan, Fars province. The breaking dormancy consisted
five different experimental treatments: (l) six levels of scarification with 95-98% sulfuric acid (4, 8, 15, 30, 45,
and 60 minutes), (2) soaked seeds in the water for 48, 72, and 96 hours, (3) heated up seeds in a 95- 98 boiling
water for two and five minutes, (4) chilled seeds in 3 ·c for 15, 30, 45, and 60 days, and (5) stored seeds in 3 and
12 months after harvesting, compared with control treatment. 25 seeds were transferred into the incubators to
identity a suitable temperature and light regime for subsequent experiments of germination which was
determined under two modes of alternative day/night temperatures ( 15/5, 20/l 0, 25/15, 30/20, and 35/25 ·q and
constant temperature over day/night (5, 10, 15, 20, 25, 30, 35, 40, and 45 ·q. The salt and osmotic potentials
were applied in 0 (control), -1, -3, -5, -7, -9 and -11 levels for the experiment seeds to survey the stress of salt
and drought on seed germination and compare both stresses on it. NaCI was applied based on the Van! Hoff
method to establish the salt stress and PEG 6000 was exploited according to the Michel method to affect osmotic
potentials and create drought stress. In the burial depth experiment, a number of 30 seeds, for 30 days, were laid
in the depth of 0, 0.5, I, 2, 3, 4, 6, and 8 em in the plastic vases with 15 em diameters. All experiments were
conducted twice in the form of randomized complete-block design with four replications. Each replication was
arranged on a different shelf of growth chamber and considered as a single block in the laboratory experiments.
The data of the replicated experiments were pooled for analysis, since the time interaction and treatment was
statistically insignificant. A functional three-parameter logistic model was fitted to the germination values (%)
obtained at different concentrations of NaCI or osmotic potential. A sigmoidal decay curve was also fitted to
show the seedling emergence (%)values at different burial depths.
Results and Discussion: Various treatments of breaking dormancy was influenced seed germination
differently. This is worth to mention that sulti.tric acid treatments of 30, 45, 60, 15 and 4 minutes carried out in
the five most dominant percentages on the seeds germination which in 30 and 45 minutes sulfuric acid
scarification, germination was recorded more than 95o/o, sulfuric add treatments had therefore significant effect
on germination rather than other treatment. Compared with control in the issue of germination percentage, all
sulfuric acid treatments and chilling for 45 days were higher than control. Moreover, boiling could not induce
breaking of dormancy. According to the results, germination was prevented or declined owing to the hard seed
coat and weed thus remained stable in seed bank. No statistically significant difference was observed when
germination percentages were compared with temperature-light regime interaction (both in constant and
alternative) or light regime alone (light/dark and dark), but the influence of both temperature modes (constant
and alternative) on the rate of germination was significant. In other words, the germination percentages were
identical in light/dark and dark regimes while by increasing the temperature (in both temperature modes), the
final germination percentage raised in both light regimes. In both light regimes, at 25/15, 30/20, and 35/25 'C
(day/night), germination was recorded more than 95o/o. Moreover, the maximum and minimum germination
percentages in light/ dark regime were recorded in alternative temperature obtained for 30/25 ·c (99.5%) and
15/5 ·c (35.5 %), respectively. Over the range of 25-45 ·c, the germination rate was also more than 90%. In
addition, the maximum and minimum germination percentage in light/ dark regime were found in 25 ·c (99%)
and 5 ·c (0%), respectively. Johnsongrass seeds were not influenced by light. Therefore, these seeds were not
photoblastie species and the germination percentage cannot be handled through light and temperature has greater
importance relative to light. The statistical analysis revealed that by increasing the salinity, the germination
percentage was significantly decreased. The germination percentage was 99% for control (maximum), 19% for -
I I osmotic potential (minimum), and Xso for -9.62 osmotic potential. The pace of germination followed
aforementioned trend, 0.21 seed/h for control and 0.0004 for -II osmotic potential. These findings imply that
Johnsongrass seeds are resistant to the salinity stress which is crucial for drylands and semi-arid climates.
The results of drought stress were almost identical to that of salinity. The germination percentage was 99%
for control (maximum), 0% for -II osmotic potential (minimum), and Xso for -9.13 osmotic potential. The
deeper the seedling planted, the fewer emergence occurred. The emergence at the surface of the soil (zero depth)
was 83.33% and in depth of3 em was 100%. The minimum emergence (18.35%) was observed in depth of8 em.
With an increase in 3 em burial-depth, the seedling emergence decreased to 81.65%. According to the fitted
signooid model, the depth causing a decrease for the maximum 50% seedling emergence was 5.86 em implying
that tillage more than 6 em can reduce germination and emergence of this species and is beneficial for its
management. The decrease in seedling emergence by increasing buried depths may be linked to the seed energy.
Conclusions: The results indicated that Johnsongrass hard seed can tolerate several environmental factors
e.g. boiling, soaking, prolonged harvesting and partly chilling. Further, light intervention solely cannot break the
dormancy. The species can withstand inappropriate high and low temperature conditions and germinates more
than 90% once the condition particularly in terms of temperature becomes suitable. In addition, the deeper the
depth, the lesser the seedling emergence was. Consequently, one of the best methods of controlling this weed is
to till the field over 6 em.
