Population genetic response to microsite ecological stress in wild barley, Hordeum spontaneum

Genetic diversity was studied in six subpopulations (a total of 60 individuals) of wild barley, Hordeum spontaneum , the progenitor of cultivated barley, sampled from six stations located along a transect of 300 m across the two opposing slopes of 'Evolution Canyon', a Mediterranean microsite at Lower Nahal Oren, Mt Carmel. The two opposing slopes are separated by between 100 and 400 m and designated SFS (South-Facing Slope) and NFS (North-Facing Slope) with each having three equidistant test stations. The SFS, which receives up to 300% more solar radiation, is drier, ecologically more heterogeneous, fluctuating, and more stressful than the NFS. Analysis of 12 RAPD primers, representing a total of 51 putative loci, revealed a significant inter- and intraslope variation in RAPD band polymorphism. A significantly higher proportion of polymorphic RAPD loci was found amongst the subpopulations on the SFS (mean P = 0.909) than on the NFS (mean P = 0.682), on the basis of the presence and absence of 22 strong bands. Polymorphism generally increased upwards from the bottom to the top of the SFS (0.636, 0.773, 0.955) and NFS (0.409, 0.500, 0.545), respectively. Gametic phase disequilibria estimates, D, revealed SFS and NFS unique predominant combinations which sharply differentiated the two slopes and indicated that there is differential interslope selection favouring slope-specific multilocus combinations of alleles, or blocks of genes over tens to hundreds of meters. This suggests that selection overrides migration. RAPD polymorphism appears to parallel allozyme diversity which is climatically adaptive and driven by natural selection in the same subpopulations at the microsite.     

RAPD divergence caused by microsite edaphic selection in wild barley

Random amplified polymorphic DNA polymerase chain reaction (RAPDPCR) was used to assess genetic diversity in four subpopulations (86 individuals) of wild barley, Hordeum spontaneum, sampled from Tabigha microsite near the Sea of Galilee, Israel. The microsite consists of two 100 m transects that are topographically separated by 100 m, each equally subdivided into 50 m of basalt and terra rossa soil types. Despite the same macroclimate characterizing the area around the Sea of Galilee, the microsite offers two edaphically different microhabitats, with basalt being a more ecologically heterogeneous and broader-niche than the relatively drier but more homogeneous and narrow-niche terra rossa. Analysis of 118 putative loci revealed significant (P<0.05) genetic differentiation in polymorphism (P0.05) between the two soils across the transects with P being higher in the more heterogeneous basalt (mean P0.05 = 0.902), than in terra rossa (mean P0.05 = 0.820). Gene diversity (He) was higher in basalt (mean He=0.371), than in terra rossa (mean He=0.259). Furthermore, unique alleles were confined to one soil type, either in one or both transects. Rare alleles were observed more frequently in terra rossa than basalt, and in transect II only. Gametic phase disequilibria showed a larger multilocus association of alleles in basalt than terra rossa, and in transect I than II. Spearman rank correlation (r_s) revealed a strong association between specific loci and soil types, and transects. Also, analysis of multilocus organization revealed soil-specific multilocus-genotypes. Therefore, our results suggest an edaphically differentiated genetic structure, which corroborates the niche width-variation hypothesis, and can be explained, in part, by natural selection. This pattern of RAPD diversity is in agreement with allozyme and hordein protein diversities in the same subpopulations studied previously. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Acacia plantations on net photosynthesis, tree species composition, soil enzyme activities, and microclimate on Mt. Makiling

To determine the effectiveness of rehabilitation on improving ecosystem functions, we examined net photosynthetic rate (P _N), tree species composition, soil enzyme activities, and the microclimate (air and soil temperature, relative humidity) of an area on Mt. Makiling that has been rehabilitated and protected from fire for over 12 years. After it was last burned extensively in 1991, restoration was initiated by planting Acacia mangium and Acacia auriculiformis. We selected three areas to study in 2003. Two areas were rehabilitated with A. mangium and A. auriculiformis, and one was still dominated by Imperata cylindrica and Saccharum spontaneum. P _N of A. mangium and A. auriculiformis showed significantly lower values than those of I. cylindrica and S. spontaneum. The Acacia plantations had more naturally regenerated tree species than the grassland. Additionally, more tree species appeared in the A. mangium plantation than in the A. auriculiformis plantation. Ficus spetica was present in all of the study sites. Dehydrogenase and phosphatase activities were significantly higher in soil under the Acacia plantations than under grassland. Grassland showed higher air temperature, relative humidity, and soil temperature as well as a larger variation per hour in these parameters compared to the Acacia plantations. The highest air temperature, relative humidity, and soil temperature were measured in April during the dry season. From the regression analysis, soil temperature was significantly correlated with air temperature. Hence plantations, as a rehabilitation activity for grassland, promote natural regeneration and stabilize the microclimate. This stabilization of the microclimate affects establishment and growth of naturally occurring tree species.     

国内外割手密资源农艺性状表型遗传多样性分析

采用表型性状变异分析和聚类分析,对国内外不同地理来源的456份割手密资源13个性状进行评价,初步了解其遗传多样性特点,为解决种质创新与品种改良遗传基础狭窄问题提供思路。结果表明,456份割手密在株高、叶长、叶宽、锤度等多个性状都表现出了极高的遗传变异,多样性指数介于0.97～7.92之间;对嵌纹病、眼点病的抗病性及对金龟子的抗虫性变异范围广;国内外不同地理来源的割手密群间的遗传变异较大,以云南割手密群体多样性最丰富。聚类分析结果表明,国内外割手密资源聚成三大不同类群,云南独自为一大类,国外割手密被归为第二大类,其他为第三大类。各类群在植株生长特性及锤度方面具有极显著差异。     

Microsatellite diversity associated with ecological factors in Hordeum spontaneum populations in Israel

Microsatellite diversity at 18 loci was analysed in 94 individual plants of 10 wild barley, Hordeum spontaneum (C. Koch) Thell., populations sampled from Israel across a southward transect of increasing aridity. Allelic distribution in populations was not distributed randomly. Estimates of mean gene diversity were highest in stressful arid-hot environments. Sixty-four per cent of the genetic variation was partitioned within populations and 36% between populations. Associations between ecogeographical variables and gene diversity, H(e), were established in nine microsatellite loci. By employing principle component analysis we reduced the number of ecogeographical variables to three principal components including water factors, temperature and geography. At three loci, stepwise multiple regression analysis explained significantly the gene diversity by a single principal component (water factors). Based on these observations it is suggested that simple sequence repeats are not necessarily biologically neutral.     

约旦野生二棱大麦群体籽粒休眠特性的网络分析

本研究以来自约旦的16个野生二棱大麦群体206个基因型为材料,对籽粒不同部分的氮素营养相关性状以及40℃下不同贮藏时间后的萌发率进行了测定,并利用网络相关性技术分析其与起源地生态地理因素之间的相关性。结果表明,来自于不同地区的大麦群体在种子含氮量、壳含氮量、种子可溶性蛋白质含量、单粒重及单壳重上存在明显差异,并且籽粒不同部位含氮量发生分配平衡,种子含氮量较高的群体壳含氮量较低。同时,网络相关性分析证实壳含氮量与籽粒萌发特性呈显著负相关,而壳中潜在抑制萌发的含氮物可能在42d的高温储藏下分解或失活。     

Identification of proteins associated with ion homeostasis and salt tolerance in barley

Identification and characterization of proteins involved in salt tolerance are imperative for revealing its genetic mechanisms. In this study, ionic and proteomic responses of a Tibetan wild barley XZ16 and a well‐known salt‐tolerant barley cv. CM72 were analyzed using inductively coupled plasma‐optical emission spectrometer, 2DE, and MALDI‐TOF/TOF MS techniques to determine salt‐induced differences in element and protein profiles between the two genotypes. In total, 41 differentially expressed proteins were identified in roots and leaves, and they were associated with ion homeostasis, cell redox homeostasis, metabolic process, and photosynthesis. Under salinity stress, calmodulin, Na/K transporters, and H⁺‐ATPases were involved in establishment of ion homeostasis for barley plants. Moreover, ribulose‐1,5‐bisphosphate carboxylase/oxygenase activase and oxygen‐evolving enhancer proteins were significantly upregulated under salinity stress, indicating the great impact of salinity on photosynthesis. In comparison with CM72, XZ16 had greater relative dry weight and lower Na accumulation in the shoots under salinity stress. A higher expression of HvNHX1 in the roots, and some specific proteins responsible for ion homeostasis and cell redox homeostasis, was also found in XZ16 exposed to salt stress. The current results showed that Tibetan wild barley XZ16 and cultivated barley cultivar CM72 differ in the mechanism of salt tolerance.     

The effect of combining scald resistance genes on disease levels, yield and quality traits in barley

Pairwise combinations of genes for resistance to scald in barley were developed using linked isozyme markers to test whether such combinations conferred improved resistance to the pathogen, Rhynchosporium secalis. The resistance genes originally derived from Hordeum vulgare ssp. spontaneum. The combinations were bred into an essentially similar genetic background because the scald-susceptible, Australian barley cultivar Clipper was the recurrent backcross parent in their ancestry. In field tests of the recombinants over 2 years, disease levels were lower in three of six doubly resistant lines than in backcross lines carrying a single resistance gene, which in turn were less diseased than either Clipper or recombinants that lacked the marked resistance genes. All resistant lines significantly outyielded Clipper but did not themselves differ significantly. Lines resistant to scald had significantly higher grain size and grain weight. Gains for malt yield of about 1 % were detected in the higher disease environment. Resistance was not accompanied by any obvious cost in terms of yield or quality. Protection against scald is therefore a significant requirement for new malting barley cultivars in scald-prone areas.