Differences between wheat genotypes in damage from freezing temperatures during reproductive growth

Cereal crops in the reproductive stage of growth are considerably more susceptible to injury from freezing temperatures than during their vegetative growth stage in the fall. While damage resulting from spring-freeze events has been documented, information on genotypic differences in tolerance to spring-freezes is scarce. Ninety wheat genotypes were subjected to a simulated spring-freeze at the mid-boot growth stage under controlled conditions. Spring-freeze tolerance was evaluated as the number of seeds per head at maturity after plants were frozen at −6 °C. Plants that froze, as confirmed by infrared (IR) thermography, died shortly after thawing and consequently the heads did not mature. Only in plants that had no visible freezing (super-cooled) were heads able to reach maturity and produce seeds. In plants that super-cooled four genotypes had significantly higher seed counts after being exposed to freezing than three with the lowest. In addition, significant differences between genotypes were found in whole plant survival among those that had frozen. Genotypes with high whole-plant freezing survival were not necessarily the same as the super-cooled plants with the highest seed counts. Spring-freeze tolerance was not correlated with maturity suggesting that improvement in freezing tolerance could be selected for without affecting heading date. Spring-freeze tolerance was not correlated with freezing tolerance of genotypes of plants in a vegetative state, either under non-acclimated or cold-acclimated conditions indicating that vegetative freezing tolerance is not a good predictor of spring-freeze tolerance.     

无花果果实果汁的冻结特点及影响因素分析

运用热镀锡膜铜-康铜热电偶测温方法测定了无花果果实在不同空气介质温度下不同部位的冻结曲线,对无花果果实与汁液的冻结特点作了比较,并对冰点温度与可溶性固形物含量的关系进行了探讨。结果表明:无花果果实的冻结曲线有3种形式,典型的形式具有过冷点、初始冰点、平衡冰点、终止冰点等关键特征点。空气介质温度越低,冻结速率越快,果实不同部位的温度梯度曲线差异越显著;果实不同部位的过冷点和冰点温度及其出现的时间顺序存在差异;与无花果果实相比,果汁更容易冻结;无花果果实的可溶性固形物含量为13.8%~20.9%,冰点温度为-2.4~-3.0℃,果汁的可溶性固形物含量为14%~23%,冰点温度为-2.1~-3.3℃。无花果果实、果汁冰点温度与可溶性固形物含量呈现一定的负相关性,也与其他因素有关。     

麦二叉蚜过冷却能力和低温存活率研究

为弄清麦二叉蚜耐寒性,研究分析了1龄若蚜和无翅成蚜的过冷却能力和低温存活率,结果发现：麦二叉蚜1龄若蚜的过冷点和结冰点分别为-26.7±0.68℃和-26.3±0.70℃,均显著低于无翅成蚜的过冷点(-22.8±3.85℃)和结冰点(-19.3±3.80℃),且1龄若蚜的过冷却点和结冰点波动范围较小,分别在-27.7～-24.7℃和-27.5～-24.4℃之间,而无翅成蚜的过冷却点和结冰点波动范围较大,分别在-26.7～-14.2℃和-24.7～-11.6℃之间。与此同时,低温存活率结果发现,1龄若蚜80%死亡率的温度是10℃左右,无翅成蚜80%死亡率的温度是-9℃左右,表明麦二叉蚜耐寒性较强,而且1～龄若蚜的耐寒能力较无翅成蚜强。     

冰核细菌对液体食品过冷却点的影响

于 2 2℃下在KB培养基上培养冰核活性细菌 (Xanthomonascampestris菌株XcIN 1) ,对数生长期离心获得的细胞冰核活性最强。该细胞在 - 3℃时能够起到冰核的作用使纯水结冰。把冰核细菌与液体食品 (如蔗糖、蛋清、牛奶、番茄汁、苹果汁、橘汁、梨汁、酱油、豆酱和食醋 )混合 ,观察其对过冷却点的影响。结果是 ,加入冰核菌使液体食品的过冷却点提高了 0 .3～ 3.7℃ ,表明在冷冻食品工业中应用细菌冰核可以节约能源并提高效率     

大猿叶虫抗寒与越冬能力的研究

研究了大猿叶虫成虫的过冷却点、低温生存能力和越冬情况。结果表明:大猿叶虫成虫的过冷却点在越冬前期降低,后期升高,1月份降至最低值-22.3℃。Lt50和Lt95均随温度的降低而缩短。越冬后期,成虫的死亡率达24.6%。     

不同地区松突圆蚧耐寒性的研究

为探讨松突圆蚧(Hemiberlesia pitysophila)对低温的地理适应能力,2007年测定并比较了广东信宜和福建漳州、泉州和长乐4个地区冬季松突圆蚧雌成虫的过冷却点和信宜、泉州、长乐3地区各虫态的低温暴露死亡率。结果表明:4个地区松突圆蚧雌成虫的过冷却点具有显著差异(P0.05),福建长乐的平均过冷却点最低,为-15.71℃,广东信宜的平均过冷却点最高,为-13.68℃,总体呈现随纬度升高而逐渐降低的趋势。在各种低温暴露下,广东信宜松突圆蚧种群的死亡率均明显高于福建泉州和长乐种群;尤其在-10℃时,前者的死亡率达85.97%,而后二者分别仅为37.58%和56.65%。松突圆蚧各地、各虫态的低温暴露死亡率变化规律均服从改进的双变量逻辑斯谛曲线模型(P0.01),但广东信宜各虫态和种群的致死中有效伤害低温累积(SLIT50)均明显高于福建泉州和长乐。因此认为:随分布纬度上升,松突圆蚧耐寒性存在逐步增强的趋势。     

亚洲玉米螟化性与抗寒能力的关系

过冷却点分析表明：一、二化性越冬代玉米螟抗寒能力有明显差异，一化性玉米螟的抗寒能力强于二化性玉米螟。公主岭一化性玉米螟的过冷却点为-24.27℃，敦化一化性玉米螟为-23.09℃；公主岭二化性玉米螟为-20.89℃，白城二化性玉米螟为-18.40℃。一化性越冬代玉米螟的过冷却点比二化性越冬代玉米螟的过冷却点低4℃左右，相同化性的地理种群之间略有差异。在越冬不同阶段抽样调查得出，一化性玉米螟的越冬死亡率低于二化性15%左右。     

杜鹃属的抗寒性

杜鹃属按其抗低温的能力可分为极抗寒、抗寒、不完全抗寒与敏感四个组,就杜鹃各器官与组织而言,抗低温能力依营养芽、叶和皮层最强,木质部与花原基最弱。杜鹃属在抗寒性上的明显差异与其地理分布密切相关,这一特点显示出抗寒性的自然选择与气候的变异方式相应发生。认为“冰洞”作用,“超冷”能力是抗寒杜鹃花芽和木质部薄壁细胞藉以回避冰冻的机制。     

美国白蛾Hyphantria cunea(Drury)越冬蛹的抗寒性研究

基于为控制美国白蛾Hyphantria cunea(Drury)对桑树和柞树的的危害提供理论依据,测定了美国白蛾越冬蛹不同时期的过冷却点和含水量。结果显示,越冬蛹的过冷却点以2月份最低,为(-27.07±0.38)℃,11、12月份最高,分别为(-20.38±2.26)℃和(-22.99±4.03)℃;含水量以11、3月最高,分别为67.03%和65.07%,1月份开始下降,2月份降至最低30.76%,3月份又增加到45.95%。含水量的变化与过冷却点的变化趋势相似,含水量的下降降低了越冬蛹的过冷却点,可增强其抗寒能力。