Effect of Water Stress on Yield Components in Guar

This study was undertaken to measure the effect of water stress on yield and yield components in guar (Cyamopsis tetragonoloba [L.] Taub.) grown under water-stressed and water-optimal field conditions. Fifteen guar germplasms were grown in irrigated and dryland tests at Lubbock, TX on an Amarillo loam (fine-loamy, mixed thermic Aridic Paleustoll). Plants in each germplasm were hand harvested at maturity and data recorded for number of racemes/plant, pods/plant, seeds/pod, weight/100 seeds and g/seed/plant. We found differences among germplasms for yield components under both dryland and irrigated conditions. Germ-plasms responded statistically the same in both moisture levels. Among three pre-selected cultivars, water use efficiency did not differ statistically. Our analyses indicated that the component of yield most affected by water stress was number of pods/plant. Seed weight, seeds/pod, and racemes/plant each had progressively smaller effects on seed yield.     

Growth Patterns of Early Maturing Maize Cultivars

Growth patterns of two early maturing maize cultivars were analyzed, harvesting shoots twice weekly in 1983. Until the end of leaf expansion the leaf dry matter accumulation was highly synchronized in both hybrids. After a short cessation leaf dry weight accumulation was resumed at low to medium rates during the main part of August, during September losses prevailed. During these two months fluctuations in rates were frequent and synchronisation between genotypes small. For stems no transitory cessation of dry matter accumulation occurred; synchronisation between genotypes and fluctuation in rates were less than observed for leaf dry matter accumulation. Losses in stem dry weight mostly coincided with rapid ear growth. Ear dry weight accumulation steeply increased during the first three weeks of August. Fluctuations in rates were large during the following 30 days of rapid growth. This period ended by a sharp decline in rates. Phosphofructokinase activity of upper leaves was maximum in early July followed by a first minimum shortly before anthesis; thereafter the average activity did not change much. The hybrid with higher initial shoot growth rates had a higher phosphofructokinase activity at the same time.     

Effect of Formative Phase Drought on Different Classes of Shoots, Shoot Mortality, Cane Attributes, Yield and Quality of Four Sugarcane Cultivars

Field experiments were conducted at Coimbatore, India to study the effect of three levels of drought (severe, moderate and no drought) during the formative phase (60–150 days after planting; DAP) of sugarcane on the tillering, the conversion of shoots to millable canes, cane attributes and the quality of different classes of shoots in four sugarcane cultivars (Co 8021, Co 419, Co 8208 and Co 6304)_the different classes of shoots studied were: mother shoots (which emerged 0–30 DAP), early tillers (30–60 DAP), mid‐season tillers (60–150 DAP) and late tillers (150 DAP). The results indicated that drought during the formative phase reduced the total number of shoots and their conversion to millable canes at harvest. Drought also reduced the cane length, number of inter‐nodes and single cane weight of different classes of shootsand the subsequent total cane yield. Irrespective of drought treatments, Co 8021, a high‐tillering, thick‐stalked cultivar, gave the highest cane yield despiteits higher shoot mortality, while Co 8208, a low‐tillering, thin‐stalked cultivar, gave the lowest cane yield despite its lower shoot mortality. Thus a moderate level of shoot mortality is clearly necessary to obtain higher millable canes and subsequently higher cane yield. Mother shoots and early tillers together contributed most of the total number of millable canes (84.5 %) and of the total cane yield at harvest (86.2 %). The contribution of late tillers to the number of millable canes and cane yield was, however, negligible, especially in cultivars Co 6304 and Co 8208. There was a gradual reduction in stalk attributes such as cane length, number of internodes, single cane weight and commercial cane sugar percentage as the physiological age of shoots decreased. This study emphasizes the need for a cultivar with the optimal characteristics of early tillering (like Co 8021 and Co 6304) and maximum conversion to millable canes (like Co 8208) and provides information relevant to breeders making decisions on crossing programmes to produce improved cultivars for drought conditions.     

Generation mean analysis of phosphorus‐use efficiency in freely nodulating soybean crosses grown in low‐phosphorus soil

Freely nodulating soybean genotypes vary in their phosphorus (P) uptake and P‐use efficiency (PUE) in low‐P soils. Understanding the genetic basis of these genotypes’ performance is essential for effective breeding. To study the inheritance of PUE, we conducted crosses using two high‐PUE genotypes, two moderate‐PUE genotypes and two inefficient‐PUE genotypes, and obtained F₁, F_2, BC₁ and BC₂ populations. The inheritance of PUE was evaluated using a randomized complete block design. A generation mean analysis of phenotypic data showed that PUE was heritable, with complex inheritance patterns and the presence of additive, dominance and epistatic gene effects. Seed P, shoot P, root P, P‐incorporation efficiency and PUE were largely quantitatively inherited traits. There were dominance, additive × additive and dominance × dominance gene effects on PUE, grain yield, shoot dry weight, 100‐seed weight, root dry weight and shoot dry matter per unit P for populations grown under low‐P conditions. Dominance effects were generally greater than additive effects on PUE‐related indices. These PUE indices can be used to select P‐efficient soybean genotypes from segregating populations.     

Differential tolerance to Fe and Zn deficiencies in wheat germplasm

Tolerance to Fe deficiency of wheat genotypes exhibiting differential tolerance to Zn deficiency is not known, even though the relationship between Fe nutrition and differential tolerance of wheat genotypes to Zn deficiency has been hypothesised frequently. In the present experiment, eight Triticum aestivum and two T. turigidum L. conv. durum cultivars were grown in nutrient solution deficient in either Znor Fe. Three indices of tolerance to nutrient deficiency were compared: relative [(-nutrient/+nutrient) × 100] shoot growth, shoot dry weight under nutrient deficiency and relative shoot/root dry weight ratio. Genotypes Aroona, Excalibur, Stilleto and Trident were classified as tolerant to both Zn and Fe deficiency, while durum wheats Durati and Yallaroi were sensitive to Zn deficiency and moderate to sensitive to Fe deficiency. Genotypes Excalibur, Stilleto and Trident come from the same breeding programme and have the common parent (line MEC3 =Sonora64//TZPP/YAQUI54) that could have been the donor of the genes for tolerance to Zn deficiency. When Fe-deficient, all wheat genotypes were severely chlorotic but kept producing shoot and root dry matter at a relatively high rate, making the relationship between the relative shoot growth and the relative leaf chlorophyll content poor. This is the first report of wheat genotypes exhibiting multiple tolerance to Zn and Fe deficiencies. This revised version was published online in July 2006 with corrections to the Cover Date.     

品种基因型和温度对马铃薯脱毒试管苗农艺性状的影响

以大西洋、克新1号、青薯168脱毒基础苗为试验材料,采用二因素随机区组设计,研究不同基因型品种、不同温度对马铃薯脱毒基础苗苗鲜重、根鲜重、苗干重、根干重、叶片数、株高、茎粗、根长和根条数影响,培养14d时,测定各性状指标.结果表明,3个不同成熟期基因型品种、3种不同培养温度处理对马铃薯单株平均根鲜重、叶片数、株高影响有显著性交互作用(p＜0.05),其余性状受品种基因型和温度交互作用影响不显著.不同基因型品种对苗干重、根干重、叶片数、根条数农艺性状指标影响显著(p＜0.05),其余性状指标未达显著影响;不同培养温度对马铃薯单株平均苗鲜重、根鲜重、苗干重、根干重、茎粗、根长、根条数(p＜0.05)农艺性状指标有显著性影响(p＜0.01),其余性状指标未达显著影响;3个不同基因型品种所需的适宜培养温度为(23±2)℃,此培养温度时,3个品种基因型的农艺性状表现最好.     

不同小麦基因型孕穗期根系性状与吸氮量的关系

通过水培培养,研究了生产上主栽的不同小麦基因型在充分供氮条件下孕穗期的根系、根系生理活性及根系与地上部干重以及吸氮量之间的关系。结果表明,地上部干重、根干重、根体积、根冠比、根活性及植株吸氮量不同基因型间有显著差异,根总吸收面积、根活跃吸收面积不同基因型间无明显差异;植株吸氮量与地上部干重显著相关,其相关系数达0.634,经进一步相关性分析表明,植株吸氮量的差异和地上部干重的差异主要是由于植株根干重和根体积不同造成的。研究表明,选择根干重和根体积大的小麦品种有利于提高小麦的氮利用效率。     

大豆光谱反射率与地上干物重对数回归分析

摘要：研究目的：从统计学角度分析地上部干物重与叶片反射光谱特征的定量关系;方法：通过对近红外和可见光波段光谱反射率的分析, 确立不同时期大豆地上部干物重的敏感波段,计算出相应的植被指数,并建立植被指数与大豆地上部干物质量预测模型;结果表明：通过RDVI（1005,510nm）植被指数建立对数模型,方程为：y = -295.83Ln(x) - 123.05;结论：此模型能较好的描述大豆合农60光谱反射率与干物重的关系。     

干旱区滴灌模式和种植密度对棉花生长和产量性能的影响

以高产棉花品种新陆早45为材料,自初花至吐絮设置常规滴灌(I500)和有限滴灌(I425) 2种处理,每种滴灌模式下设低(D12)、中(D24)和高(D36)3个种植密度,分析棉花不同生育时期叶面积指数(LAI)、群体生长率(CGR)、棉铃生长率(BGR)、净同化率(NAR)以及产量、灌溉水分利用效率(IWUE)等变化。结果表明,与I500相比,I425将LAI到达顶峰的时间推迟至盛铃期并延缓了盛铃期以后的叶片衰老,显著提高了盛花期至吐絮期NAR,在不显著降低籽棉产量的前提下,提高了IWUE。在I500条件下,LAI、CGR、BGR、NAR、总生物量(TDW)、铃生物量(BDW)、总铃数(BN)、生殖器官与营养器官质量的比例(RVR)均以D24较高,D12最低;I425条件下,上述参数均以D36最高。籽棉产量以I500D24、I425D36较高,IWUE则以I425D36较高。相关分析表明,籽棉产量和IWUE与BN、RVR呈显著正相关,IWUE与NAR呈显著正相关。表明盛花期至盛铃期较快的群体生长速率、较强的物质生产能力以及较多的干物质持续向棉铃的供应,是I425D36提高产量的重要原因。     

Assessment of genetic divergence in salt tolerance of soybean (<Emphasis Type="Italic">Glycine max</Emphasis> L.) genotypes

A large number of soybean (Glycine max L.) genotypes of diverse growth habit and adaptive characters were used in the experiment. Soil salinity-induced changes in nine morpho-physiological characters of 30-day-old seedlings of 170 soybean genotypes were compared in the study. The first and second principal components (PC) of principal component analysis (PCA) results accounted for 97 and 2.5%, respectively, of the total variations of soybean genotypes. The variation for the first PC was composed mainly of relative total dry weight (DW), relative shoot dry weight, as well as petiole dry weight. There were four clusters distinguished in the cluster analysis. The genotypes in cluster IV performed better in respect to relative total dry weight and relative shoot dry weight and hence having salt tolerance. The genotypes clusters III performed very poorly and those of clusters II and I were moderate to poor. D2 analysis indicated that the clusters differed significantly from each other. Discriminant function analysis (DFA) again asserts strongly that more than 92% of the genotypes were correctly assigned to clusters. Both PCA and DFA confirmed that the relative total DW followed by shoot and petiole DW were the major discriminatory variables, and the root DW were the secondary important variables to distinguish genotypes into groups. In this study, multivariate analyses were used in identifying the soybean genotypes of desirable traits for salt tolerance.     

双季稻区长期不同施肥管理对大麦干物质积累及产量的影响

为探明双季稻区不同施肥制度对大麦干物质积累及产量的影响, 以 ‘通 0306’ 和 ‘蒙啤麦 1号’ 为材料, 采用田间小区试验方法, 系统比较研究了 30%有机肥+70%化肥、 60%有机肥+40%化肥和无肥 3种施肥制度对大麦干物质积累及产量的影响。结果表明, 大麦主要生育期, 单株根系、 茎干物质和地上部分干重均表现为 60%有机肥＞30%有机肥＞无肥; 分蘖期至成熟期, 各处理间大麦单株根系和茎干重差异均达显著水平。叶、 穗均表现为 60%有机肥＞30%有机肥＞无肥, 60%有机肥和 30%有机肥处理均显著高于对照。分蘖期到成熟期, 根系干重占总干物质量的比例为无肥＞30%有机肥＞60%有机肥, 穗干重比例为 30%有机肥＞60%有机肥＞无肥; 拔节期到成熟期, 茎的比例均以 60%有机肥处理最高; 叶干物质比例在成熟期为无肥＞60%有机肥＞30%有机肥。大麦主要生育期, 30%有机肥和 60%有机肥处理大麦叶片 SPAD值均显著高于无肥处理; 成熟期, 各处理间差异达显著水平。大麦各生育期, 各处理大麦单株叶面积表现为 60%有机肥＞30%有机肥＞无肥。各施肥处理大麦产量表现为 60%有机肥＞30%有机肥＞无肥, 分别比无肥增产 717.45~721.15 kg/hm²和 756.45~782.05 kg/hm²。说明不同施肥制度大麦干物质积累和产量有各自特征, 有机肥与化肥配施处理植株干物质总量大而且分配合理, 有利于改善产量构成因素, 增加大麦产量。     

棉花耐低钾基因型筛选条件和指标的研究

以2004年我国棉区的主栽品种/组合/品系为主, 收集50个基因型, 在苗期室内液培条件下(低钾浓度和高钾浓度分别为0.02 mmol L^-1和2.50 mmol L^-1)对棉花耐低钾基因型的适宜筛选苗龄和评价指标进行研究, 并与田间缺钾土壤(速效钾含量为59.88 mg kg^-1)的筛选结果进行比较。结果表明, 棉花5叶期幼苗基因型间生物量的变异系数明显高于3叶期, 适宜进行耐低钾基因型筛选。低钾条件下的绝对生物量与相对生物量(0.02/2.50)、吸钾量和钾利用指数(KUI, 单位浓度钾所形成的生物量)极显著(P < 0.01)相关, 相关系数分别为0.7690、0.9522和0.9791。根长、根表面积与整株吸钾量的相关系数分别为0.5201(P < 0.01)和0.3325(P < 0.05)。子叶缺钾斑占子叶总面积的比例(S)在基因型间变化幅度大(变异系数为44.46%)、符合正态分布、与生物量极显著相关(r = –0.4455, P < 0.01), 可作为棉花苗期耐低钾基因型筛选的辅助指标。种子含钾量与棉花幼苗子叶的S值、生物量、钾吸收量和KUI均无相关关系。液培条件下5叶期幼苗的整株生物量与田间条件下产量器官干重极显著相关(r = 0.5091, P < 0.01), 证明苗期室内液培筛选具有可行性, 可作为对大量基因型的初筛方法, 典型基因型需要在田间进行复筛。     

Maize genotypes with deep root systems tolerate salt stress better than those with shallow root systems during early growth

Maize (Zea mays L.) is susceptible to salinity but shows genotypic variation for salt tolerance. How maize genotypes with contrasting root morphological traits respond to salt stress remains unclear. This study assessed genotypic variation in salinity tolerance of 20 maize genotypes with contrasting root systems exposed to NaCl for 10 days (0, 50 mM or 100 mM NaCl, added in four increments every other day from 14 days after transplanting, DAT) in a semi-hydroponic phenotyping system in a temperature-controlled greenhouse. Considerable variation was observed for each of the 12 measured shoot and root traits among the 20 genotypes under NaCl treatments. Salt stress significantly decreased biomass production by up to 54% in shoots and 37% in roots compared with the non-saline control. The 20 genotypes were classified as salt-tolerant (8 genotypes), moderately tolerant (5) and salt-sensitive (7) genotypes based on the mean shoot dry weight ratio (the ratio of shoot dry weight at 100 mM NaCl and non-saline control) ± one standard error. The more salt-tolerant genotypes (such as Jindan52) had less reductions in growth, and lower shoot Na⁺ contents and higher shoot K⁺/Na⁺ ratios under salt stress. The declared salt tolerance was positively correlated with shoot height, shoot dry weight and primary root depth, and negatively correlated with shoot Na⁺ content at 100 mM NaCl. Primary root depth is critical for identifying salt responsiveness in maize plants and could be suggested as a selection criterion for screening salt tolerance of maize during early growth. The selected salt-tolerant genotypes have potentials for cultivation in saline soils and for developing high-yielding salt-tolerant maize hybrids in future breeding programmes.     

水分胁迫及复水对绿洲膜下滴灌辣椒动态生长、产量及水分利用的影响

为了研究水分胁迫对露天膜下滴灌辣椒生长、产量形成和水分利用效率的影响,在辣椒苗期和开花坐果期均分别施加轻度水分胁迫(65%~75%田间持水量)、中度水分胁迫(55%~65%田间持水量)和重度水分胁迫(45%~55%田间持水量),全生育期充分供水处理(75%~85%田间持水量)为对照,分别测定各水分处理辣椒不同生育期末生长指标(株高、茎粗、叶面积指数和单株干物质积累量)以及青果总产量和水分利用效率,并用三次曲线模拟了辣椒各生长指标在全生育期内的动态变化过程。结果表明:三次曲线能够较好地反映不同水分处理下辣椒各生长指标随时间的动态变化。苗期和开花坐果期一定程度水分胁迫能导致辣椒在水分胁迫时段株高、茎粗和叶面积指数显著(P0.05)小于CK组,后期复水后,由于辣椒产生补偿性生长,苗期轻度和中度水分胁迫处理以及开花坐果期轻度水分胁迫处理辣椒,各生长指标增长速率在一定时间内超过CK组,最终辣椒产量和单株结果数均与CK组之间无显著差异(P0.05),且辣椒平均单果重分别比CK组显著高18.48%,22.49%,14.14%。苗期和开花坐果期水分胁迫,均能提高辣椒根冠比和果实干物质分配指数并减少辣椒全生育期灌水量和耗水量,特别是苗期中度水分胁迫处理,在不显著降低产量的情况下,灌水量和耗水量分别比CK组显著低12.36%和11.51%,且水分利用效率、灌溉水利用效率均最高,分别比CK显著高8.61%和9.66%,因此,在苗期施加中度水分胁迫,后期充分灌水是实现绿洲辣椒节水、高产和高效栽培的一种较优灌溉方式。     

不同氮利用效率水稻基因型的根系形态与生理指标的研究

选用氮素利用高效型和低效型具有代表性的12个粳稻品种, 研究了225 kg hm-2施氮条件下根系形态和生理指标的差异及其与氮素利用效率的相互关系。结果表明, 有效分蘖临界叶龄期、拔节期、抽穗期和成熟期, 氮高效型水稻的根干重、根系体积、总吸收表面积、活跃吸收表面积和活跃吸收表面积比均显著或极显著大于氮低效型水稻。有效分蘖临界叶龄期和拔节期, 氮高效类型水稻的根冠比显著大于氮低效型, 而抽穗和成熟期则表现相反趋势。成熟期前, 氮高效型水稻的根系α-NA氧化量极显著大于氮低效型, 而成熟期, 氮高效型中杂交水稻的根系α-NA氧化量略低于个别氮低效型水稻品种。相关性分析表明, 有效分蘖临界叶龄期、拔节期、抽穗期和成熟期, 水稻的根干重、根系体积、根系的α-NA氧化量、总吸收表面积、活跃吸收表面积和活跃吸收表面积比与氮素利用效率呈显著或极显著正相关。有效分蘖临界叶龄期和拔节期, 植株的根冠比与氮素利用效率呈显著正相关, 而抽穗和成熟期则呈极显著负相关。氮高效型水稻在其一生中具有良好的根系形态和保持较强的根系活力, 为植株大量吸收和高效利用氮素奠定了良好基础。同时, 在水稻的生长过程中, 地下部与地上部的合理比例及协调生长也是促进植株高效吸收利用氮素的重要因素。     

Confirmation of a 4BL/5RL Wheat-Rye Chromosome Translocation Line in the Wheat Cultivar ''Viking'' Showing High Copper Efficiency

Populations of 64 taxa of Trifolium were assessed for nitrogen fixation and dry matter production with and without added mineral nitrogen. The number of rhizobia per gram of compost capable of inducing nodulation was tested in 7 species and ranged from 3 to 114, showing interspecific variation for nodulation with indigenous rhizobia. In a sample of 8 species, nitrogen fixation was assessed by acetylene reduction and nodule scoring. There was a good correlation (84 %, P ≤ 0.01) between the two methods, and therefore nodule score was used as a measure of nitrogen fixation in the main assessment. There were large differences between populations in terms of shoot and root dry weight, the shoot: root ratio and nodule score. Added nitrate had a significant effect on all characters, increasing shoot dry weight and the shoot: root ratio and decreasing root dry weight and the nodule score. Results showed the importance of assessing legume germplasm with and without added nitrate in locations where suitable rhizobia for the nodulation of exotic species might not be present.     

Physiological and Growth Responses of Sugarcane Genotypes to Nitrogen Rate on a Sand Soil

Yields of sugarcane (a complex hybrid of Saccharum spp.) in FL, USA, are lower on sand soils than on organic (muck) soils. Nitrogen (N) supply may limit sugarcane growth and yields on these sand soils. A 2‐year pot study was conducted to determine sugarcane genotypic variation in response to N rate on a sand soil. Treatments included four N rates (0, 75, 150 and 225 kg ha^?1) and three sugarcane genotypes (CP 80‐1743, CP 01‐2390 and TCP 87‐3388). Nitrogen fertilizer was equally split and applied at about 55 and 125 days after planting (DAP) for each treatment. During the experiment, the number of nodes and length of the primary stalks and tillers were recorded. Leaf relative chlorophyll (soil plant analysis development (SPAD)) and net photosynthetic rate (Pn) were measured biweekly. All plants were harvested at 183 DAP to measure green leaf area (GLA), shoot biomass accumulation and partitioning, and fertilizer N use efficiency (NUE). Genotypes differed significantly in leaf SPAD, Pn, GLA, and shoot biomass accumulation and partitioning. CP 01‐2390 had the highest leaf Pn and shoot biomass, and CP 80‐1743 had the lowest GLA, shoot biomass and NUE among genotypes. Nitrogen rate affected leaf SPAD, GLA, shoot biomass and NUE, but had much less effect on leaf Pn. Green leaf area and biomass increased with increasing N rates. Our results suggest that a two‐pronged approach, selection of genotypes with high NUE while working to optimize N rates and delivery can improve sugarcane yields on sand soils.     

Variation in Salt Tolerance Among Some Wheat and Triticale Genotypes

The identification of genotypes having potential salt tolerance is an effective approach to solve the problems of saline soils.
Seed germination and seedling establishment are limiting factors in crop production. Seven wheat ( Triticum aestivum L.) and one Triticale (X Triticosecale Wittmak) genotypes were evaluated for salt tolerance at emergence and early seedling growth in solution culture with NaCl salinities up to 300 mM L⁻¹ (electrical conductivity equals 27.6 dS m⁻¹).
Seedling emergence was delayed by increasing NaCl in nutrient media. At 200 mM L⁻¹ NaCl, the emergence percentages of wheat genotypes ranged between 68.7 % and 91.3 % after 7 days and 79.3 % and 98.7 % after 15 days. While at 300 mM L⁻¹, the emergence percentages of the wheat genotypes were 0.0 % after 7 days. After 15 days the emergence percent ranged between 24 % and 72 %. The emergence percent of the Triticale line was 88.7 after 7 days and 89.3 after 15 days at 200 mM L⁻¹, while it was 25.3 % and 84 % after 7 and 15 days, at 300 mM L⁻¹, respectively. Root and shoot dry weight were greatly reduced by increasing NaCl, however, the Triticale line showed less reduction in growth compared to the wheat genotypes. K⁺, Ca²⁺ and Mg²⁺ were decreased with increasing salinity levels while Na⁺ content was decreased in the shoot tissues of wheat and Triticale genotypes.     

磷肥用量对滨海盐土油菜光合性状和干物质生产的影响

为研究盐分土壤条件下磷肥对油菜光合性状和干物质生产的影响效应,以甘蓝型常规油菜品种‘宁油20号’为供试品种,设置不同磷肥用量处理,测定不同生育期叶面积、叶片净光合速率以及干物重。结果表明,0~120 kg/hm²磷肥用量范围内,随着磷肥用量的增加,苗期和初花期叶面积指数、干物质积累量逐渐增加,成熟期籽粒产量及干物质积累量也逐渐增加。不施磷肥和30 kg/hm²磷肥用量处理籽粒含油率较低,在磷肥用量达到60 kg/hm²时再增加磷肥用量籽粒含油率无显著变化。苗期叶片净光合速率随磷肥用量的变化趋势与干物重变化一致,当磷肥用量达到60 kg/hm²时进一步增加磷肥用量,初花期叶片净光合速率无显著变化。     

Root characteristic system improves drought tolerance in orchardgrass

Plant genotypes with higher drought tolerance through improved root characteristics are poorly studied in orchardgrass. In the current research, 30 orchardgrass genotypes were polycrossed and the resulting half‐sib families evaluated under both normal and water stress environments. Under water stress conditions, values for most root traits decreased at 0–30 cm soil depth, while at 30–60 cm depths, the root length (RL), root area (RA), root volume, percentage of root dry weight (RDW) and the ratio of root to shoot were increased. We identified drought‐tolerant genotypes with a high combining ability for root characteristics and a high yield potential. High estimates of heritability as well as genetic variation for root traits indicated that phenotypic selection would be successful in order to achieve genetic progress. Indirect selection to improve dry matter yield was most efficient when selecting for RL and RDW under water stress conditions. Significant associations between a drought tolerance index and RL, RA and root volume confirmed the importance of these traits in conferring drought tolerance of orchardgrass.