Volume 39, No. 2, 2018

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(pp. 105-115)
Effects of Dormancy-Breaking Treatments on Kelussia odoratissima Seed Germination
J. Tabatabaeian*, A. Kadkhodaee and J. Razmjoo
Mountain celery is a native medicinal plant of Iran, and an endangered species due to overuse and climate changes. Seeds of this species have high dormancy levels, which must be broken for domestication. Thus, this study was carried out in 2016 to determine the most effective treatment for stimulating germination of mountain celery seeds.

A factorial experiment based on a completely randomized design with four replications was used.  Effects of stratification (4 °C for 0, 4 and 8 wk), 500 ppm solutions of gibberellin (GA3), benzyl adenine (BA), naphthalene acetic acid (NAA), indole butyric acid (IBA), and their combinations (GA3+IBA, GA3+NAA, GA3+BA, IBA+NAA, IBA+BA, NAA+BA, GA3+IBA+NAA, GA3+IBA+BA, GA3+NAA+BA, IBA+NAA+BA and GA3+IBA+NAA+BA) were tested. Stratification and hormonal treatments alone increased percentage germination and germination parameters, namely germination rate, mean germination time and radicle length. On average, the highest percentage germination, germination rate and radicle length were obtained upon treatments with GA3, BA and GA3+ IBA+BA, after eight weeks of stratification at 4 °C, suggesting that seeds of this species exhibit physiological dormancy. GA3, BA and GA3+IBA+BA after eight weeks of stratification at 4 °C were the most effective treatments. There were no synergistic effects among hormonal treatments.
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(pp. 117-127)
Presence of Epichloë Fungus in the Endosperm-Side of the Seed Predicts the Symbiotic Status of the Seedling
P.E. Gundel*, A.C. Ueno, M. Panteix and L.J. Iannone
Some important forage grasses of the genera Festuca and Lolium establish persistent symbiotic associations with vertically-transmitted fungal endophytes (genus Epichloë). In certain cases, the fungus causes livestock diseases due to fungal toxins that accumulate in the plant biomass. Killing the fungus in the seed is a possibility for getting rid of the problem.

However, since the symbiosis is mutualistic, the inoculation of elite cultivars with non-toxic but still beneficial endophytes is a current breeding strategy. Additionally, the symbiosis has become a model system to study in ecology and evolution, where the manipulation of the symbiotic status of plants is critical for the experiments. In this study, we confirmed that testing for the endophyte’s presence or absence in the endosperm-side of the seed was a reliable predictor of the symbiotic status of the seedling. We built on this previously proposed concept by (i) estimating the high correspondence between the infection status in one side of the seed (either + or −) and the infection status of the other side, and (ii) demonstrating that cutting the seed in two halves did not affect seed germination, normal seedling growth, nor the endophyte transmission to the seedling. We also showed that cutting the seed reduced seedling size, an impact that increased with endophyte presence provided the fungus was alive. The strengths and weaknesses of the technique, as well as its potential use in other species, are discussed.
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(pp. 129-142)
Sub-Optimal Temperature Effects on Hybrid Corn Seed and Seedling Performance
Omar N. Ali, J. Bryan Whittenton, J. Joseph Williams, Fabian Watts and W. Brien Henry*
Corn is a versatile crop grown over a range of agro-climatic zones. If producers adopt early planting to avoid high temperature and drought under rain fed systems, cold temperatures may negatively affect corn yield. The objectives of this study were to determine germination and root development variability among 20 commercially available corn hybrids subjected to cold temperatures.

Experiments were conducted by imposing low temperatures treatments during seed germination. Seeds for these trials were obtained from two industry-leading seed companies in 2015 and 2016, and standard germination assays confirmed all seed germinated at or near 100% under optimal conditions. To evaluate cold germination and root elongation, seeds from each treatment were placed in rolled moistened seed germination paper and exposed to either 10, 8.6 or 7.2 °C temperatures for 14 d, then transferred to 20 °C for 7 d. Corn hybrids varied significantly in seed germination and root traits under cold temperatures, and in a corresponding field emergence trial. Some hybrids significantly surpassed others in seed germination traits, germinating earlier as well as having longer radicle lengths.  Our data suggested that significant variability existed in emergence and vigor at cold temperatures for commercially available hybrids. Producers who plant early should consider seed company ratings for cool season vigor and select a hybrid that performs optimally at cool temperatures.
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(pp. 143-154)
Soybean Seed Germination Response to In Vitro Osmotic Stress
Chathurika Wijewardana, Firas A. Alsajri and K. Raja Reddy*
Seed germination is considered the most crucial stage for seedling establishment, and success at this stage is dependent on moisture availability in the soil. An experiment was conducted to evaluate in vitro seed germination responses using two soybean cultivars, Asgrow AG 5332 and Progeny P 5333RY, with different growth habits.

Seeds were subjected to six levels (0.0, −0.1, −0.3, −0.5, −0.7, and −0.9 MPa) of polyethylene glycol (PEG-8000) treatments at 25°C. Four replicates of 100 stratified seeds were germinated and monitored at 4-h intervals from incubation. Maximum seed germination and seed germination rate were derived from time-series seed germination data at different osmotic potentials. Maximum osmotic potential when seed germination was zero and maximum osmotic potential when seed germination rate was zero were then derived by fitting linear and quadratic regression models of seed germination parameters as a function of osmotic potential. Maximum seed germination and seed germination rate decreased with decreasing osmotic potential for both cultivars. A significant decline in cumulative percentage germination was recorded after −0.3 MPa osmotic potential and no seed germinated at −0.9 MPa for both cultivars, suggesting that −0.3 MPa was the threshold value for good germination of soybean seed, and −0.9 MPa was the lowest osmotic potential for soybean seed germination. The soybean cultivar Progeny P5333RY was more tolerant to PEG stress and germinated more rapidly compared to Asgrow AG5332 under osmotic stress. The identified cultivar-specific algorithms could be used in modeling seed germination under variable moisture conditions among soybean cultivars.
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(pp. 155-171)
Radicle Length in Agar is a Reliable Predictor of Seed Vigor
R. Baalbaki*, S.A. Chaharsoughi, V. Le and S. Koonse
Radicle emergence and development are commonly used parameters for evaluating seed vigor. This research investigated germination behavior and radicle elongation in agar of different concentrations, as predictors of seed vigor.

Early radicle elongation under two agar concentrations (0.65 and 0.75%), using lettuce and broccoli seed samples with known differences in vigor, was evaluated and compared to germination parameters based on radicle emergence counts. Of the three evaluated germination parameters,
time to 50% germination, mean germination time, and AUC (a parameter that combines germination capacity, speed and uniformity information), only AUC could consistently reflect the small differences in vigor between the samples, regardless of agar concentration. Differences in radicle elongation rates were indicative of differences in vigor, especially at the higher agar concentration. The magnitude of the difference in radicle length between high and low vigor seeds was wider in 0.75% agars, mainly due to reduced
elongation rates of the lower vigor sample. The differential radicle elongation rates, revealed by testing in different agar concentrations, were a reliable indicator of even small differences in seed vigor, and could form the basis of a new simple and practical vigor test.
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