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To the best of our knowledge, this is first report on the association of Rahnella aquatilis with rice and also the application of a mathematical model to evaluate the effect of PSBs on rice growth.

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The purposes of this study were to evaluate the phosphate solubilization activity of bacteria isolated from the rhizosphere of rice paddy soil in northern Iran, and to study the effect of temperature, NaCl and pH on the growth of these isolates by modeling. Three of the most effective strains from a total of 300 isolates were identified and a phylogenetic analysis was carried out by 16S rDNA sequencing. The isolates were identified as Pantoea ananatis (M36), Rahnella aquatilis (M100) and Enterobacter sp. (M183). These isolates showed multiple plant growth-promoting attributes such as phosphate solubilization activity and indole-3-acetic acid (IAA) production. The M36, M100 and M183 isolates were able to solubilize 172, 263 and 254 µg ml(-1) of Ca3(PO4)2 after 5 days of growth at 28 °C and pH 7.5, and to produce 8.0, 2.0 and 3.0 μg ml(-1) of IAA when supplemented with L-tryptophan (1 mg ml(-1)) for 72 h, at 28 °C and pH 7.0, respectively. The solubilization of insoluble phosphate was associated with a drop in the pH of the culture medium and there was an inverse relationship between pH and solubilized P (r = -0.98, P < 0.0952). There were no significant differences among isolates in terms of acidity tolerance based on their confidence limits as assessed by segmented model analysis and all isolates were able to grow at pH 4.3-11 (with optimum at 7.0-7.5). Based on a sigmoidal trend of a three-parameter logistic model, the salt concentration required for 50 % inhibition was 8.15, 6.30 and 8.23 % NaCl for M36, M100 and M183 isolates, respectively. Moreover, the minimum and maximum growth temperatures estimated by the segmented model were 5.0 and 42.75 °C for M36, 12.76 and 40.32 °C for M100, and 10.63 and 43.66 °C for M183. The three selected isolates could be deployed as inoculants to promote plant growth in an agricultural environment.

Seed germination has been modeled extensively using hydrothermal time (HTT) models. Generally, a normal distribution for base water potential w b(g) and a linear upward shift in w b(g) with increasing temperature were used within these models to relate variation in w b(g) to the variation in time to germination of a given fraction of seeds. However, little research has tested these assumptions. Therefore, the main purpose of this study was to test the assumption of normality in the distribution of w b(g) by germinating zucchini (Cucurbita pepo L.) seed with nondormant seed across a range of constant w at sub-and supra-optimal temperatures. Zucchini seeds were incubated at six constant temperature regimes (15, 20, 25, 30, 35, and 37°C) at each of the following osmotic potentials (0, -0.15, -0.30, -0.45, and -0.60 MPa). Results indicate that when incorporated into an HTT model, the Weibull distribution (R 2 = 0.85; RMSE = 11.89) more accurately described w b(g) and germination course over sub-and supra-optimal temperatures than HTT based on a normal distribution (R 2 = 0.77; RMSE = 14.80). According to these models, base temperature and base water potential for the 50th percentile (w b(50) ) were estimated at 9.38°C for both models and -1.27 and -1.31 MPa by the normal and Weibull distribution, respectively. Given the flexibility of the Weibull distribution this model not only provides a useful method for predicting germination but also a means for determining the distribution of w b(g) .

Mavi K., 2010. The relationship between seed coat color and seed quality in watermelon Crimson sweet. Hort. Sci. (Prague), 37: 62-69. This work was carried out to determine the relationship between seed coat color and seed quality in Crimson sweet watermelon. Seed lots (1, 2, 3, and 4) were prepared taking into consideration seed coat colors in fresh seeds with naked eye. The color parameters of these prepared seed lots were determined using Minolta colorimeter. To determine quality differences between the seed lots, standard germination test, seed weight, water uptake ratio, mean germination time, emergence percentage, mean emergence time, seedling fresh weight, seedling dry weight and electrical conductivity values were determined. The seed weight (57.22 mg), germination percentage (86.5%), emergence percentage (77.5% total and 76.5% normal), seedling fresh weight (978.7 mg), and dry weight (64.7 mg) of the brown seed lot (Lot 1) were markedly higher than lots having lighter seed coat (2, 3, and 4). On the other hand the mean emergence time (7.7 days) and electrical conductivity value (128.8 µS/cm g in 24 h) of the brown seed lot (Lot 1) were lower than lots having lighter seed coat (2, 3, and 4). The obtained data indicated that seed quality differences can be determined according to the seed coat color of Crimson sweet seeds. It was found that seed lot 1 had higher seed vigor and viability than seed lots 2, 3, and 4. Color parameters b*, C*, L*, and H°, determined by Minolta colorimeter, showed significant correlation with seeds quality parameters.

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