Studies on optimum harvest time for hybrid rice seed.

BACKGROUND: Timely harvest is critical for hybrid rice to achieve maximum seed viability, vigor and yield. However, how to predict the optimum harvest time has been rarely reported so far. RESULTS: The seed vigor of Zhuliangyou 06 (ZLY06) increased and reached the highest level at 20 days after pollination (DAP), when seed moisture content had a lower value, which was maintained until final seed maturation. For Chunyou 84 (CY84), seed vigor, fresh and dry weight had relatively high values at 25 DAP, when seed moisture content reached the lowest value and changed slightly from 25 to 55 DAP. In both hybrid rice varieties, seed glume chlorophyll content declined rapidly from 10 to 30 DAP and remained at a very low level after 35 DAP. Starch content exhibited an increasing trend during seed maturation, while both soluble sugar content and amylase activity decreased significantly at the early stages of seed development. Moreover, correlation analyses showed that seed dry weight, starch content and superoxide dismutase activity were significantly positively correlated with seed vigor. In contrast, chlorophyll content, moisture content, soluble sugar, soluble protein, abscisic acid, gibberellin content, electrical conductivity, catalase and ascorbate peroxidase activities were significantly negatively correlated with seed vigor. Physiological and biochemical parameters were obviously more closely related with seed vigor than with seed germinability during seed development. CONCLUSION: Seed vigor could be better used as a comprehensive factor to predict the optimum seed harvest time. It is suggested that for ZLY06 seeds could be harvested as early as 20 DAP, whereas for CY84 the earliest optimum harvest time was 25 DAP. © 2016 Society of Chemical Industry.

[Effects of combined drought and salinity stress on germination and physiological characteristics of maize (Zea mays).] / 旱-盐复合胁迫对玉米种子萌发和生理特性的影响.

In this study, 15% PEG, 100 mmol·L-1 NaCl and PEG-NaCl mixed solution were employed to respectively simulate the drought (D), salinity (S) and the combined stress (D+S), and effects of these three stresses on the seed germination and the physiological characteristics of seedlings were investigated. The results showed that seed germination, seedling growth and biomass accumulation were significantly inhibited by these three stresses, and the impact of stress ranked as D>D+S>S. The content of reactive oxygen species like H2O2 and O-·2, as well as malondialdehyde (MDA) and membrane permeability were increased under these stresses, meanwhile, proline (Pro), soluble sugar and soluble proteins contents were significantly improved, which were higher in seedlings than in roots with a rank of D>D+S>S. The activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxide (POD), catalase (CAT) and ascorbate peroxide (APX) were also obviously increased. In addition, SOD and APX induced by PEG-NaCl mixed solution were ranked in the middle compared to those induced by their single stress, but POD and CAT were more induced by PEG-NaCl mixed solution than their single stress. It was demonstrated that effect of drought-salinity combined adverse condition on maize seed germination and seedlings physiological characteristics were not simply additive of their single stress, compared with their single stress, drought-salinity combined adverse condition could reduce the effects of drought stress on maize seeding to a certain extent.