The Pollen Viability Of Different Pumpkin Inbred Lines Under Low Temperature And The Relation Between It And The Chilling Tolerance

The breeding selection of high chilling tolerance variety is the new emphasis of pumpkin breeding at present following the pumpkin cultivation area enlarging in Protected Field . Pollen is one of the genetic materials, there is high meaning in practice for its character of germination under low temperature to the breeding of chilling tolerance. The experiment is to discriminate the different inbred lines(variety) by the pumpkin pollen germinability under the different flowering temperature(FT) and germination temperature(GT), and analysis the correlation with other chilling tolerance index identifying pumpkin, for finding the index to identify the chilling tolerance of different pumpkin(variety) lines by means of pollen low temperature germination., and offer the foundation to screening the chilling tolerance of pumpkin and select the crossing parent.1 Using the method of liquid culture medium, the pollen germination rate of 14 pumpkin inbred lines were mensurated under the different flowering temperature(FT) and germination temperature(GT). The result showed that:①the pollen germinability was going down following the falling of FT and GT, Pollen germination rate is above 48% under normal GT24℃, about 31% under GT15℃, about 18% under CT12℃, the germination rate under GT9℃is fearfully low, approaching zero, all the influence of FT and GT is high significant, but, the effect of the GT is bigger, the interaction between FT and GT is not significant.②The different of the pollen germination rate of different lines is high significant under the combination between FT(15℃,12℃,9℃) and GT(24℃,18℃,15℃,12℃,9℃) excepting FT 15℃/ GT 24℃.③Cultured under FT9℃/ GT12℃,the F value of variance analysis and the coefficient of variation is the biggest, the variance is the biggest for the pollen germinability of different lines, and the cole tolerance identied by liquid culture medium is consistent on the whole, so that, the proper temperature is FT9℃/GT12℃,which will be used to identify the chilling tolerance of different pumpkin lines(variety) by method of pollen germination. The germination of chilling tolerance above 25%, the middle chilling tolerance is about 10-25%, the non-chilling tolerance is under 10%.2 Using the method of TTC, the pollen coloration rate of 14 inbred lines were mensurated under the different flowering temperature(FT) and coloration temperature(CT). The result showed that:①The suitable coloration concentration of TTC is 0.1%.The suitable coloration time is 40min,50min,60min,90min and great 90 min。②the pollen coloration rate was going down following the falling of FT and CT, Pollen coloration rate is above 49% under normal CT24℃, about 30% under CT15℃, about 18% under CT12℃, the coloration rate under CT9℃is fearfully low, approaching zero, all the influence of FT and CT is high significant, but, the effect of the CT is bigger, the interaction between FT and CT is not significant. The difference of the pollen coloration rate of different lines is high significant under the low combination temperature.③Cultured under FT9℃/ CT12℃, the F value of variance analysis and the coefficient of variation is the biggest, the variance is the biggest for the pollen coloration of different lines, so that, the proper temperature is FT9℃/CT12℃,which will be used to identify the coloration difference of different pumpkin lines(variety) by means of pollen coloration. But the coorelation between this method and chilling tolerance of vavieties is not stable, it is not better than the method of pollen liquid medium.3 The seedling of fourteen inbred lines is treated in light incubator under 5℃low temperature. Following the time increasing, the difference of chilling injury index is enlarged, and it decreases after the biggest in 7d. Treated 7d, Sel-M and Sz's chilling injury is light, their chilling tolerance is better; F-2,31-6,S17,S25,23-4G,Q-1,31-10 and 15-1's chilling injury is in the middle; 20-3,23-1G,F-1 and 14-9's chilling injury is heavy. This is in accord with the result in field. So the chilling injury index of 7d is the proper temperature to identify the chilling tolerance of different pumpkin inbred lines(varieties). But this method will need too long time, about 16d.4 The seeds of 14 inbred lines germinate under 24℃,18℃,15℃and 13℃, the result indicates that the difference of germination rate and germination index is not significant under normol temperature 24℃by variance analysis,the difference is significant or high significant following temperature falling from 18℃to 13℃, and the difference is the biggest at 13℃. 13℃can identify the germinability of difference pumpkin inbred lines(varieties). The F value of germination index, the coefficient of variation and the correlation coefficient absolute value with inbred`s chilling tolerance are all bigger than the correspondence value of germination rate, the germination index under 13℃can display the difference better than the germination rate by multiple comparison, and it is in accord with the chilling tolerance in field. So, it is good to identify the chilling tolerance of different pumpkin inbred lines(varieties) with the seed's germination index under 13℃. But the coorelation with chilling tolerance is lower than the coorelation identified by pollen liquie culture medium method, and it need too long time, about 16d.5 It is found that the pollen germinabiliy mensured by liquid medium under low temperature is correlated high significantly with the chilling tolerance identified by chilling injury index, the correlation is the biggest under the FT9℃/GT12℃; And it is correlated high significantly or significantly with the chilling tolerance identified by seed germination index under low temperature, the correlation is also the biggest under the FT9℃/GT12℃; So, the low temperature FT9℃/GT12℃is the proper temperature index to cultivate the pumpkin pollen for identifying the chilling tolerance of different inbred lines(varieties), and it is comparatively reliable. The method of TTC could identify the chilling tolerance under FT9℃/GT12℃, but it is not stable.Otherwise, the chilling tolerance identitied with pollen is the chilling tolerance of the Adult-plant with fruit,which is more suit to the need of chilling tolerance breeding than the prophase's chilling tolerance identified by the method of seeds germination index and seedings chilling injury index, and the use of pollen method is much less, time is need only 1d(but other two method need 13-16d), and the result is more stable; so, the method of pollen liquid culture medium is a better method to identify the chilling tolerance of different pumpkin inbred lines(vavieties) than other method.6 Six inbred lines with the different grade of chilling tolerance were diallelly crossed by the method of GriffingⅣ, the chilling tolerance combining ability of 15 cross combination and superstandard were analyzed, the result showed:①Superstandard analysis. The combinations which have superstandard are in turn SZ×Sel-M,SZ×31-6,Sel-M×31-6,Sel-M×14-9,SZ×S25,SZ×14-9 under FT9℃/GT12℃and FT12℃/GT12℃, the combined chilling-tolerance advantage of parants Sz and Sel-M is the biggest;②The variance analysis of combining ability. g.c.a and s.c.a is significant or high significant under FT9℃/ GT12℃and FT12℃/GT12℃. It shows that the additive genes effect and the non-additive genes effect are all great effect to the pumpkin chilling tolerance, the additive effect is the bigger.③Under FT9℃/GT12℃and FT12℃/GT12℃, the s.c.a of cross combination Sz×Sel-M,S25×14-9,31-6×20-3 are all high, but the g.c.a of patents 31-6, 20-3 and14-9 is negative, the combination S25×14-9 and 31-6×20-3 are not suit to chilling tolerance advantage cross combination, but the combination Sz×Sel-M has not only the high s.c.a, but the partents Sz and Sel-M have the high g.c.a, so, parents Sz and Sel-M are the better chilling tolerance parents selection. So, the parents` selection of chilling tolerance in pumpkin ought to consider by total combining ability. It could obtain the better combination that selectes the combination of high s.c.a after the parents` selection of high g.c.a.