Báo cáo lâm nghiệp: "Influence of the moisture content of forest tree its response to different viability tests pollen on"

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Influence of the moisture content of forest tree pollen on its response to different viability tests M. Bonnet-Masimbert 2 J. Webber 1 Research Branch, British Columbia Ministry of Forests, Victoria, Canada, and 2 INRA, Station dAm6lioration des Arbres Forestiers, Ardon, 45160 Olivet, France Introduction atmosphere (humidity, temperature and exposure time) on in vitro viability shown. are response, Pollen management has become an integral part of intensive tree impro- vement, especially for facilitating breeding programs and improving both orchard Materials and Methods yields and genetic efficiency. To handle pollen successfully, particularly its storage, drying to moisture contents of less than Procedures for testing in vitro viability have 10% is required (Webber, 1987; and been described by Charpentier and Bonnet- unpublished data). However, in certain Masimbert (1983) and Webber (1987). The angiosperms, dehydration can have a effect of 2 relative humidities (70 and 100% RH) detrimental effect on pollen germination and 3 temperatures (10, 20 and 30°C) on and vigor which is only restored by rehy- rehydration of Douglas fir (Pseudotsuga men- ziesii) pollen and their effects on germination dration (Shivanna and Heslop-Harrison, and conductivity over 9 exposure times (0, 3, 6, 1981 ). 16, 24, 48, 72, 96 and 120 h) were tested. The The of reduction this 70% RH was generated by controlling wet- in cause bulb/dry-bulb temperatures using a water bath germination and viability with dehydration (T1) and an incubator (T2). The 100% RH was is not fully understood but loss of created by saturating air in a closed container membrane integrity may be involved maintained at the incubator temperature T2. (Shivanna and Heslop-Harrison, 1981).. ) Germination of Douglas fir pollen was Certainly, it is a principal factor in the loss assessed for class 1 grains (defined as elon- of vigor in corn (Kerhoas, et al., 1987). gation more than twice the original diameter of the grain) after 48 h of incubation and In this paper, data from previous expressed as a percentage of the total number experiments are summarized to show the of pollen grains observed. Conductivity was factors affecting reactivation of pollen determined using 25 mg of pollen in 7.5 ml of vigor, and data from recent tests, which ultra-pure H and measured after 1 h at 25°C 0 2 (cold leachate). demonstrate the effect of rehydration
Results at 30°C), suggesting that mem- ticularly brane reorganization was incomplete. RH, membranes ap- at 100% However, Correlation analysis for Douglas fir pollen early and conductivity to stabilize peared values remained relatively stable, at least up to 72 h, after which deterioration TableI summarizes the correlation coef- apparent (again, more prominent at was ficients between 3 in vitro assays (res- 30°C). piration, conductivity and germination) and Of particular interest was the differential percent filled seeds per cone (% Fspc) for response by pollen lots (data not shown). Douglas fir pollen. It is apparent that Our best lot, determined by assay re- respiration is less sensitive to the moisture sponse, remained stable and showed the However, hydration content state. or least deterioration in conductivity over and most conductivity certainly germina- time when compared to our poorest lot. It tion sensitive, showing significant are very is also interesting to note that conductivity improvement inc correlation coefficients values at 10°C were unaffected by expo- with either increasing initial moisture sure time and, in fact, at 100% RH content (MC) hydration state. or actually (lower conductivity improved values indicate more stable membranes). Hydration effects assay responses of on Values for 20°C showed an intermediate Douglas fir pollen response. Germination results led to similar con- clusions. In addition to an ageing effect, Fig. 1 shows the average response of 3 which was accelerated by 30°C and Douglas fir pollen lots to conductivity and 100°C RH, there was also a shock effect germination tests after hydration in 2 which was prevalent in the early stages of humidities at 10, 20 and 30°C. At 70% hydration and most severe for 30°C. It RH, average MC was about 11%, was less severe for 10°C and not ob- whereas, at 100% RH, MC increased to served at all for 20°C. Again, the poorest about 48%. Conductivity was affected by lot seemed to be more sensitive than the both humidity and temperature. At 70% RH, conductivity values increased (par- best one. a Data from unpublished results. b Hydration of pollen at 100% RH for 16 h at 25’C.
Conclusion also apparent that the germination response is highly variable, suggesting that the source of this variation should be Correlating the response of a particular determined. pollen lot to in vivo fertility is largely dependent upon its moisture content. Data collected from this and previous Since most lots in storage are dehydrated suggest that prehydrating Douglas fir tests to less than 10% MC, prehydration usually pollen before in vivo testing is essential improves the viability response. This is and that current procedures (100% RH/16 6 particularly true for germination and con- h/20°C) are still acceptable. In white ductivity but apparently not for respiration. spruce (Picea ,glauca), however, these the effects of hydration on hydration conditions did improve the Regarding correlation between germination and yield results from pollen hydrated germination, at 70% RH suggest that membranes may but had little or even negative effects on other assay responses (Webber, un- be fully reactivated compared to 100%. However, the negative impact of 30°C (at published data). Work must continue to evaluate the effect of hydration on viability 70% RH) is observed immediately and responses for all species and, in par- affects the poorer lots more. Hydration at ticular, investigate the effect of hydra- 10°C appears to be best for stabilizing tion at low temperature on in vivo fertili- and, indeed, improving pollen membranes ty (Mellerowicz and Bonnet-Masimbert, conductivity), but germination (lower good as for 20°C. It is results 1986). are not as
Mellerowicz E. & Bonnet-Masimbert M. (1986) References Importance de la teneur en eau du pollen pour la rdalisation de croisements contr6l6s chez le & Bonnet-Masimbert M. (1983) Charpentier J.P. Douglas. Ann. Sci. For. 43, 179-188 Influence d’une r6hydratation pr6alable sur la Shivanna K.R. & Hesiop-Harrison J. (1981) germination in vitro du pollen de Douglas Membrane state and pollen viability. Ann. Bot. (Pseudotsuga menziesii) aprbs conservation. 17, 759-770 Ann. Sci. For. 40, 309-317 7 Webber J.E. (1987) Increasing seed yield and Kerhoas C., Gay G. & Dumas C. (1987) A genetic efficiency in Douglas fir seed orchards multidisciplinary approach to the study of the through pollen management. For. EcoL Ma- plasma membrane of Zea mays pollen during 8 nage. 19, 209-218 controlled dehydration. Planta 171,1-1 0