Dao Abdalla, Sanou Jacob, V S Traore Edgar, Gracen Vernon, Danquah Eric Y
Institute of Environment and Agricultural Research (INERA), BP 910, Bobo, Dioulasso, Burkina Faso.
Department of Plant Breeding and Genetics, 520 Bradfield Hall, Cornell University, NY 14850, Ithaca, USA.
Pak J Biol Sci. 2017;20(3):132-139. doi: 10.3923/pjbs.2017.132.139.
In drought-prone environments, direct selection for yield is not adequate because of the variable environment and genotype x environment interaction. Therefore, the use of secondary traits in addition to yield has been suggested. The relative usefulness of secondary traits as indirect selection criteria for maize grain yield is determined by the magnitudes of their genetic variance, heritability and genetic correlation with the grain yield.
Forty eight testcross hybrids derived from lines with different genetic background and geographical origins plus 7 checks were evaluated in both well-watered and water-stressed conditions over two years for grain yield and secondary traits to determine the most appropriate secondary traits and select drought tolerant hybrids.
Study found that broad-sense heritability of grain yield and Ear Per Plant (EPP) increased under drought stress. Ear aspect (EASP) and ear height (EHT) had larger correlation coefficients and direct effect on grain yield but in opposite direction, negative and positive respectively. Traits like, EPP, Tassel Size (TS) and Plant Recovery (PR) contributed to increase yield via EASP by a large negative indirect effect. Under drought stress, EHT had positive and high direct effect and negative indirect effect via plant height on grain yield indicating that the ratio between ear and plant heights (R-EPH) was associated to grain yield.
Path coefficient analysis showed that traits EPP, TS, PR, EASP, R-EPH were important secondary traits in the present experiment. These traits were used in a selection index to classify hybrids according to their performance under drought. The selection procedure included also a Relative Decrease in Yield (RDY) index. Some secondary traits reported as significant selection criteria for selection under drought stress were not finally established in the present study. This is because the relationship between grain and secondary traits can be affected by various factors including germplasm, environment and applied statistical analysis. Therefore, different traits and selection procedure should be applied in the selection process of drought tolerant genotypes for diverse genetic materials and growing conditions.
在易干旱的环境中，由于环境多变以及基因型与环境的相互作用，仅对产量进行直接选择是不够的。因此，有人建议除了产量之外，还应利用次要性状。次要性状作为玉米籽粒产量间接选择标准的相对有用性，取决于其遗传方差、遗传力以及与籽粒产量的遗传相关性大小。
选用48个来自不同遗传背景和地理来源的自交系与测验种组配的杂交种，外加7个对照品种，在两年内分别于充分供水和水分胁迫条件下对籽粒产量和次要性状进行评估，以确定最合适的次要性状并筛选耐旱杂交种。
研究发现，在干旱胁迫下，籽粒产量和单株穗数（EPP）的广义遗传力增加。穗型（EASP）和穗位高（EHT）与籽粒产量的相关系数较大，且对籽粒产量有直接影响，但方向相反，分别为负向和正向。单株穗数、雄穗大小（TS）和植株恢复能力（PR）等性状通过对穗型产生较大的负向间接效应，从而有助于提高产量。在干旱胁迫下，穗位高对籽粒产量有正向且较大的直接效应，同时通过株高对籽粒产量有负向间接效应，这表明穗位高与株高之比（R-EPH）与籽粒产量相关。
通径系数分析表明，在本试验中，单株穗数、雄穗大小、植株恢复能力、穗型、穗位高与株高之比是重要的次要性状。这些性状被用于选择指数中，根据杂交种在干旱条件下的表现进行分类。选择过程还包括产量相对降幅（RDY）指数。本研究最终并未确定一些被报道为干旱胁迫下显著选择标准的次要性状。这是因为籽粒与次要性状之间的关系可能受到多种因素的影响，包括种质、环境和所应用的统计分析方法。因此，对于不同的遗传材料和生长条件，在耐旱基因型的选择过程中应采用不同的性状和选择程序。
