Temperature effects on seed germination and expression of seed dormancy in wheat

Because preharvest sprouting decreases quantity and quality of wheat grain, researchers need effective protocols to assess response to preharvest sprouting conditions. The aim of this study was to determine which temperature gives the greatest difference in seed germination and expression of seed dormancy in 10 spring wheat genotypes. The genotypes were grown in the field near Swift Current, Saskatchewan in 2000 in a randomized complete block with four replicates. Seed samples were harvested at approximately 25% moisture content (wet weight basis) and dried to 12% moisture content with minimal after-ripening. Germination was under controlled environment at temperatures of 10, 15, 20 and 30 °C in darkness. A weighted germination index (WGI) was calculated. The analysis of WGI, for each temperature, showed highly significant (p ≤ 0.01) genotype effects on germination. Most genotypes decreased in WGI (increased dormancy) as temperature was increased from 10 to 30 °C. The greatest differences in seed germination tended to be at 15 °C and 20 °C. The level of seed dormancy depended on the genotype and germination temperature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heritability estimates of bread wheat quality traits in the Western Cape province of South Africa

High performance liquid chromatography analysis revealed the presence of five phenolic acids in embryos of triticale caryopses (vanillic, caffeic, p-coumaric, ferulic and sinapic). Free phenolic acids reached the highest level at the early stages of development when germination was the lowest and decreased considerably in embryos at the final stage of grain maturation when germination was the highest. Revealing inverse correlation between the contents of free phenolic acids in developing embryos and intensity of precocious germination may indicate a role of phenolic acids in preventing pre-harvest sprouting in cereals. Total content of phenolic acids in embryos (i.e. free, and liberated from soluble esters and glycosides) increased gradually to 43DAF and decreased at full ripeness, whereas the content of total phenolics fluctuated slightly in embryos during development and ripening of caryopses. Enforced dehydration of unripe triticale caryopses stimulated germination both in embryos and whole grains. During the enforced dehydration treatment, a decrease in total content of both phenolic acids and phenolic compounds in embryos of triticale caryopses at different stages of development and maturation was observed. It should be stressed, that a number of naturally occurring phenolics are known to inhibit the germination of cereal grains. A possible role for phenolics in preventing pre-harvest sprouting and acclimation to dehydration in cereals is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dormancy breaking procedures and the breeding of white-grained wheat with resistance to pre-harvest sprouting

Summary Gibberellic acid, cold (4°C) and a combination of these two treatments were tested for use in breaking dormancy in 27 lines of white-grained wheat with varying levels of resistance to pre-harvest sprouting. Germination increased in all lines treated with gibberellic acid. Dormancy could be broken with 1 M gibberellic acid. Response to cold varied. A combination of gibberellic acid and cold treatment was the most effective. This technique has been found useful in treating seed in a breeding program aimed at producing wheats with resistance to pre-harvest sprouting.     

Utilization of tom thumb source of pre-harvest sprouting tolerance in a wheat breeding programme

Summary Segegating populations of the cross Tordo (a spring white-grained Tom Thumb derivative) and Tr 454-16 (a spring white-grained Sonora-Gabo derivative) were studied for plant height, apparent -amylase synthesis (AAS) and response to gibberellic acid. Means, variances and heritabilities for these characters were computed and their association was studied by computing correlation coefficients. Plant height showed high heritability while AAS and response to GA₃ showed moderate heritability. Plant height was positively correlated with AAS and response to GA₃. The results pointed out the importance of using Tom Thumb as a source of pre-harvest sprouting tolerance in a wheat breeding programme, particularly in areas where wheat breeding is restricted to evolving white-grained cultivars.     

丝氨酸和脯氨酸离体诱导小麦超早抽穗无性变异研究

用丝氨酸和脯氨酸作诱变剂和选择剂,对10个小麦品种的成熟胚和近成熟胚进行离体培养,从97-7的近成熟胚中筛选出优良变异株(抗性-2)。该变异株的后代比亲本抽穗期提早10d左右,且也早于其他早熟品种。     

两淮麦区小麦品种穗发芽敏感性研究

对两淮麦区40年来代表性小麦品种穗发芽敏感性进行了全面研究，主要结果是：（1）黄熟期的培养皿种子发芽、水层纸巾穗发芽、延期收获田间穗发芽调查和α－淀汾酶活性测定等方法对鉴别小麦品种穗发芽敏感性都有显著的效果；（2）经改进的水层纸巾7天穗发芽度试验是简便、有效、功能全面和适用性好的鉴定方法；（3）小麦品种穗发芽敏感性有4种类型：种子深休眠的低敏型、种子浅休眠与其它机制联合作用的低敏型、种子浅休眠的中敏型和无任何保护机制的高敏型；（4）低敏型和中敏型都有红、白皮两类品种，高敏型全是白皮品种；（5）红色种皮除有助于种子休眠外，还有延缓和减轻田间穗发芽的效应；（6）、1980年代以来的小麦品种抗穗发芽性有严重退化趋势，抗性品种只占12．5％，而50－70年代的供试品种有81．8％是抗穗发芽的；（7）就其重要性，抗穗发芽育种的地位不应低于抗病育种，应改善沿淮、淮北小麦品种布局，重视选择推广红皮品种；（8）小麦抗穗发芽育种选择指标─黄熟期7天穗发芽度；高抗＜1．15、中抗＜1．70；（9）推荐红皮品种博爱7023和马场2号、白皮品种丰产3号和百农3217为小麦抗穗发芽鉴定试验的标准品种。     

Gibberellic acid effects on germination and α-amylase activity of winter wheats

Summary Sensitivity to GA in non-Gai genome winter wheat (Triticum aestivum L.) cultivars was investigated to determine magnitude of variation of the trait, its association with other traits, and effects of geographical location of production. -Amylase enzyme activity was measured before and after treatment with gibberellic acid in 18 cultivars grown at one location and in five cultivars grown at six locations. Dye-labeled starch and agar-starch media procedures were used for the first and second experiments, respectively. -Amylase activity differed significantly among the 18 cultivars after germination in water, germination in GA, and in absolute and relative sensitivity to GA. Cultivars that reacted similarly to GA had some common ancestors in their pedigrees, and -amylase activity and sensitivity to GA were significantly negatively associated with seed weight. -Amylase activity differed between tall and semi-dwarf cultivars in the second experiment, but not in the first experiment. The magnitude of variation in -amylase activity and its relationship to preharvest sprouting susceptibility of the cultivars suggested that the trait can be modified to improve seed dormancy. Significant interactions between cultivar responses to GA and geographical location of grain production suggested that selection should be carried out in several environments.Contribution no. 81-162-j, Department of Agronomy, Kansas State University, Manhattan KS 66506, USA.     

Genetic diversity of South African winter wheat cultivars in relation to preharvest sprouting and falling number

The falling number method, which is widely used to estimatealpha-amylase activity in wheat grain, was officially introduced as part of theSouth African grading regulations in 1998. The preceding two seasons hadbeen characterised by abnormally wet conditions during harvest time,especially in the eastern parts of the Free State, resulting in majorpreharvest sprouting problems. Downgrading due to a low falling numberis an intermittent problem in South Africa. In this study South Africanwinter wheat cultivars were screened for their preharvest sproutingresistance in comparison with their inherent falling number. Wheat cultivarsvaried substantially in their ability to withstand moist harvest conditions.The falling number of cultivars which were exposed to optimal conditionsfor preharvest sprouting by using a rain simulator, dropped drastically inmost cases. It is generally accepted that the long-term solution to thisproblem lies in the development of cultivars which are able to tolerate orresist the damaging effects of rain during the period between ripeness ofmaturity and the completion of harvest. By using the data generated fromthis study, it will be possible to select for more tolerant types which can beused in the development of cultivars with an inherently higher fallingnumber.     

杂交水稻种子穗萌遗传效应的研究

 以穗萌抗性水平不一的6个不育系和7个恢复系为亲本材料，采用不完全双列杂交的试验设计，并运用包括胚乳、细胞质和母体植株三套遗传体系的种子遗传模型及估算遗传方差分量和预测遗传效应值的统计分析方法，对杂交水稻种子穗萌特性的遗传效应进行了研究。结果表明，杂交水稻种子的穗发芽率同时受种子直接加性、种子直接显性和母体加性效应的影响，且以种子直接效应为主，不受细胞质和母体显性效应的影响。在选择育种中，田间穗上发芽率以单粒选为好。而穗萌指数同时受制于种子直接遗传效应、母体效应和细胞质效应，但母体植株中只测到显著的母体加性效应。     

白粒小麦穗发芽性状的遗传变异研究

白粒小麦品种群体中存在着高抗穗发芽的材料,水层纸巾穗发芽7天的发芽率为0。穗发芽性状表现为适续性变异,在品种群体和杂种群体都有较大的遗传变异度,GCV(％)=26.9～54.4。且具有母性遗传的特点,广义遗传力较高,h_B~2(％)=80.8～86.9。