Abdel-Ghani Adel H, Parzies Heiko K, Omary Ayed, Geiger Hartwig H
Institute of Plant Breeding, Seed Science, and Population Genetics, University of Hohenheim, Stuttgart, Germany.
Theor Appl Genet. 2004 Aug;109(3):588-95. doi: 10.1007/s00122-004-1657-1. Epub 2004 Apr 9.
The results of previous studies conducted at the University of Hohenheim and the International Center for Agricultural Research in the Dry Areas (ICARDA) indicated that the yielding ability and stability of barley (Hordeum vulgare L.) could be improved in environments with drought stress by increasing the level of heterozygosity. This would require increasing the outbreeding rate of locally adapted breeding materials. As a first step, we estimated the outcrossing rate of 12 barley landraces (Hordeum vulgare ssp. vulgare, in short H. vulgare) and 13 sympatrically occurring populations of its wild progenitor [Hordeum vulgare ssp. spontaneum (C. Koch), in short H. spontaneum] collected from semi-arid localities in Jordan during the 1999/2000 growing season. In each H. vulgare or H. spontaneum population 28-48 spikes were sampled, and up to six offspring (seeds) per spike (called a family) were used for PCR analyses. Collection sites covered high-low transects for rainfall and altitude in order to detect possible environmental effects on the outcrossing rate. Four microsatellite markers located on different chromosomes were used to genotype the samples for estimating the outcrossing rate. Low season-specific multilocus outcrossing rates (tm) were found in both cultivated and wild barley, ranging among populations from 0-1.8% with a mean of 0.34%. Outcrossing rates based on inbreeding equilibrium (te), indicating outcrossing averaged across years, were two- to threefold higher than the season-specific estimates. Under high rainfall conditions somewhat higher--though not significantly higher--outcrossing rates were observed in H. spontaneum than in H. vulgare. The season-specific outcrossing rate in H. spontaneum was positively correlated (r = 0.67, P = 0.01) with average annual precipitation and negatively correlated (r = 0.59, P = 0.05) with monthly average temperature during flowering. The results suggest that outcrossing may vary considerably among seasons and that high precipitation and cool temperatures during flowering tend to enhance outcrossing. The rather low levels of outcrossing detected indicate that increased vigour due to heterozygosity has not been a major fitness advantage in the evolution and domestication of H. spontaneum and H. vulgare, respectively. Stable seed production to secure survival under extreme heat and drought stress may have been more important. Cleistogamy may be considered as an effective mechanism to warrant pollination even in drought-stunted plants with non-extruding spikes.
霍恩海姆大学和国际干旱地区农业研究中心（ICARDA）此前开展的研究结果表明，在干旱胁迫环境下，通过提高杂合度水平，可以改善大麦（Hordeum vulgare L.）的产量能力和稳定性。这需要提高本地适应性育种材料的异交率。作为第一步，我们估算了12个大麦地方品种（Hordeum vulgare ssp. vulgare，简称H. vulgare）及其野生祖先13个同域分布种群[Hordeum vulgare ssp. spontaneum (C. Koch)，简称H. spontaneum]的异交率，这些样本于1999/2000生长季从约旦的半干旱地区采集。在每个H. vulgare或H. spontaneum种群中，采集了28 - 48个穗，每个穗最多选取6个后代（种子）（称为一个家系）用于PCR分析。采集地点覆盖了降雨和海拔的高低梯度区域，以检测对异交率可能产生的环境影响。使用位于不同染色体上的4个微卫星标记对样本进行基因分型，以估算异交率。在栽培大麦和野生大麦中均发现了较低的季节特异性多位点异交率（tm），种群间范围为0 - 1.8%，平均为0.34%。基于近交平衡的异交率（te），即多年平均异交率，比季节特异性估算值高出两到三倍。在高降雨条件下观察到，H. spontaneum的异交率略高——但不显著高于——H. vulgare。H. spontaneum的季节特异性异交率与年平均降水量呈正相关（r = 0.67，P = 0.01），与开花期月平均温度呈负相关（r = 0.59，P = 0.05）。结果表明，异交率在不同季节可能有很大差异，开花期的高降水量和凉爽温度倾向于促进异交。检测到的较低异交水平表明，杂合性带来的活力增加在H. spontaneum和H. vulgare的进化及驯化过程中并非主要的适应性优势。在极端高温和干旱胁迫下确保生存的稳定种子生产可能更为重要。即使在穗不伸出的干旱发育不良植株中，闭花受精也可被视为保证授粉的一种有效机制。
