Effect of Phaeosphaeria nodorum-induced seed shrivelling on subsequent wheat emergence and plant growth

Summary The bread wheat cultivars Pasqua and Katepwa, and durum wheat cultivars Kyle and D8257 were used to test the effects of sowing Phaeosphaeria nodorum-shrivelled seed. In a controlled environment, emergence, tillering, and dry weight of seedlings were compared at two sowing depths. Emergence, tillering and plant dry weights were also determined in field plots in 1992 and 1993, as were yield and thousand kernel weight (TKW) in plants inoculated with P. nodorum. Under controlled conditions the level of shrivelling did not affect emergence at depths of 25 mm and, except for Katepwa, 50 mm. Deeper seeding reduced emergence regardless of the level of shrivelling. Seeding depth did not affect dry weight of roots and shoots and the effect on tillering was inconsistent in the two years. Dry root weight was positively correlated with original seed size and decreased with level of shrivelling. In the field, seedling emergence of severely shrivelled seed was significantly lower in Katepwa and Pasqua. Tillers per plant appeared to increase with increased level of shrivelling, but was significant only for D8257 in one year. Dry tiller weight was inversely related to tillering and decreased consistently with level of shrivelling. Excepting Pasqua, in one year, yield and TKW did not differ between plots originating from plump or shrivelled seed. Inoculation with P. nodorum caused a significant reduction in TKW and yield in all cultivars but Kyle. Seed shrivelled due to P. nodorum was in general found to be as suitable as plump seed for growing a wheat crop.     

Reduced Tillering Spring Wheats for Heavy Textured Soils in a Semi-arid Mediterranean Environment

Low tillering lines of spring wheat ( Triticum aestivum L.), were evaluated for their ability to conform to a high yielding ideotype in a dryland environment with spring drought. The ideotype was based on a concept of saving water as a result of reduced canopy development before anthesis; this should improve moisture supply for grain filling, thus reducing the effect of drought.
Five genotypes were compared under two nitrogen (N) levels, and at similar plant densities, at a site in the drier wheatbelt area of southwestern Australia. The genotypes formed three tillering groups based on the maximum number of culms produced: a free tillering group (G1), which included the standard cultivar Gamenya , with 4.3 culms per plant, an intermediate tillering group (G2) with 3.2 culms per plant, and a low ullenng group (G3) with 2.4 culms per plant.
Leaf area indices (LAI) were strongly affected by N but this was not reflected in total water use and biological yield. However, water was prematurely depleted before anthesis as a result of rapid early leaf development in response to N, and this reduced grain yield. Reduced tillering produced no significant increase in gram yield over the controls; fewer tillers per plant failed to suppress LAI development and water-use before anthesis because of a compensating increase in LAI; this resulted from a greater leaf size in the reduced tillering lines. Hence the low tillering lines did not fully conform to the requirements of the ideotype.
The development of low tillering lines is seen as a significant advance towards the ideotype; with yields comparable to commercial cultivars grown in the region, their performance indicates a potential for substantially higher yields if compensating increases in leaf development can be suppressed.     

The differential responses of chrysanthemum cultivars to light and temperature

Summary Chysanthemum cultivars were grown in 4 experiments in the greenhouse and in the phytotron. The growing conditions in the greenhouse varied from 14 C, 60 J cm² day^-1 to 17 C. 431 J cm² day^-1, those in the phytotron from 12 to 455 J cm^-2 day^-1 at a temperature of either 14 or 20 C.Most cultivars responded differentially to light and/or temperature, but this was only measurable when large differences in light and/or temperature were imposed. Reducing the light level in a greenhouse by 50% does not bring out cultivar×light interactions. Such interactions may be pronounced however when the performance in summer is compared with that in winter. This is also reflected in the correlation coefficients. The correlations between summer and winter performance for number of flowers per stem and the number of days to flowering are non-significant, those for the 7 other traits measured were all significant.The occurrence of interactions does not preclude the possibility of breeding cultivars adapted to a wide range of light and temperature conditions. Appropriate selection procedures are discussed.     

Indirect selection for grain protein and grain yield in winter wheat

Summary The efficiency of the honeycomb selection procedure in selecting outstanding genotypes was observed at two interplant distances (d), i.e. d=100 cm, low density, representing noncompetitive conditions and d=15 cm, high density, representing presence of interplant competition. Progress due to selection among the plants grown with and without competition was established by comparison of the plot performance of offspring from selected plants with that of offspring from plants taken at random. The relation between selection intensity and response to selection was observed to detect a possible negative correlation between competing and yielding ability.So far, the results obtained do not yet allow to make a choice between selection of individual plants in presence or in absence of interplant competition. No significant correlation between single plant yield and plot yield was found at any of the two densities. However, response to selection for yield was higher when selecting at low density supporting Fasoulas' preference for selecting single plants in absence of competition. These results must be taken with caution since seed quality and a biassed sample of random plants exerted an important effect on the obtained response to selection.     

三种栽植方式下不同株型和化感特性水稻对无芒稗的干扰控制作用

以直播、小苗移栽和大苗移栽3种栽植方式为主处理,接种和不接种稗草为裂区处理,17份不同株型和化感特性水稻材料为再裂区处理,设计了对无芒稗干扰控制田间试验。结果表明,直播和小苗移栽对无芒稗株高、分蘖和干重有较好的抑制作用,优势株型和化感特性水稻对无芒稗具有较好的干扰控制作用。在30株 m^-2无芒稗的竞争干扰下,3种栽植方式间水稻产量差异不显著,杂草竞争干扰使水稻减产21.73%,化感作用水稻吓一跳、IR644-1-63-1-1、谷梅2号对稗草竞争力强,仍具一定产量水平。无芒稗竞争干扰对直播水稻株高、分蘖和植株干重影响大,与移栽水稻的差异显著。杂草干扰对供试水稻材料的农艺性状产生不同影响,水稻化感种质吓一跳中期分蘖强、植株高、干重大。无芒稗竞争干扰对成熟水稻株高无影响,但对分蘖、植株茎秆和穗干重差异显著。杂草竞争对3种种植方式的水稻千粒重无显著影响,但单株谷粒重以大苗移栽显著大于直播,移栽水稻的穗型较大,每穗总颖花数、每穗实粒数和结实率显著大于直播水稻。化感作用水稻谷梅2号、IR644-1-63-1-1、TN1和PI312777每穗颖花数不高、每穗实粒数少,化感作用水稻吓一跳每穗颖花数不高,但结实率高。水稻材料中早27、早籼浙207、早籼浙101、中早22等拥有较高的千粒重,化感作用水稻谷梅2号的千粒重显著高于IR644-1-63-1-1、TN1和PI312777。早籼浙101、早籼浙207和中早22等拥有较高的单株谷粒重,化感作用水稻中156的单株谷粒重显著高于谷梅2号、吓一跳、IR644-1-63-1-1、TN1和PI312777。     

Role of chromosome 3A in stomatal resistance of winter wheat

Summary Leaf stomatal resistance, through transpiration and photosynthesis control, constitutes a major factor of productivity and adaptation in wheat. The aim of the investigations reported here was to identify chromosomal effects on the expression of the maximum stomatal resistance, determined under optimum conditions of irradiance and water supply. Leaf stomatal resistance was measured, on wheat grown in pots under natural and well-watered conditions, using a LI-COR LI-6200 portable photosynthesis system under a saturating light>1400 mol m^-1 s^-2. Reciprocal sets of chromosome substitution lines between two hard red winter wheat cultivars, Wichita and Cheyenne, were used to identify the chromosomes involved in the expression of this trait. The two parental cultivars were significantly different for the parameter investigated. Chromosome 3A appeared to be involved in the expression of the stomatal resistance value under optimum conditions. Taking into account the relationships previously established between this parameter and some agronomic traits, chromosome 3A might be involved directly in productivity-determining processes or in the adaptation to water conditions, in wheat.     

Wurzelsystem, Biomasseproduktion, Bestockung und Ertragsbildung von vier Winterweizensorten in einem System mit geringer Betriebsmittelzufuhr von außen

Rooting patterns, biomass production, tillering, and yield formation of four winter wheat cultivars in a low external input system Growth conditions of winter wheat in agricultural low external input systems, e.g. ecological agriculture differ from those in conventional agriculture with regard to nutrient flow, impact of diseases, and weed competition. Knowledge of the dynamics of yield formation of winter wheat cultivars is very important for further development of such systems. During two growing seasons root growth, above ground biomass production, tillering, and yield formation were studied with four winter wheat cultivars of different periods of release at two ecologically managed farms in Northern Hessia. The results can be summarized as follows: – In general, plant breeding did not lead to a reduced development of root systems or above ground biomass production in winter wheat (Stöppler et al. 1989 a). Modern wheat varieties develop an extensive root system in greater depth, which means better drought resistance. – Not only root length densities, total root length, characteristics of tillering, and yield formation showed clear genotypic differences between the winter wheat cultivars, but also the development of root systems and above ground biomass production. – Winter wheat cultivars with a high plant density seem to have a retarded root growth after tillering due to intra-plant-competition and late root growth during grain filling, whereas cultivars with a high ear weight develop an extensive root system before the grain filling period. At the beginning of this period, a great root length per culm seems to be most important to achieve a high ear weight. The results indicate that those cultivars with poor to medium tillering and high ear weight are very well adapted to the reduced nutrient flow in low external input systems of farming. –In low external input systems, a satisfactory wheat crop need be established before tillering.     

钵苗机插密度对不同穗型水稻品种产量、株型和抗倒伏能力的影响

选用3种穗型水稻品种,设置3种钵苗机插密度,以毯苗机插为对照(CK),系统研究钵苗机插不同密度对水稻产量及其构成、穗部性状、冠层叶系配置、茎秆物理特性和抗倒伏的影响,旨在探明水稻钵苗机插配套不同穗型品种适宜栽插规格及其增产特点;同时,阐明钵苗机插不同密度下水稻株型特征和抗倒伏特性。结果表明:(1)3种钵苗机插密度处理下,大穗型品种产量随密度降低呈先增后降的变化趋势,但均显著高于CK;中、小穗型品种产量有随着密度降低而下降的趋势。不同穗型品种穗数随着密度降低而显著减少,每穗粒数显著增加,结实率和千粒重无明显变化规律。(2)钵苗机插下不同穗型水稻品种的穗长、着粒密度、单穗重、一次枝梗数、二次枝梗数、一次枝梗粒数和二次枝梗粒数均随密度降低而增加,且高于CK;一、二次枝梗数比值和一、二次枝梗粒数比值随密度降低而呈下降趋势。(3)钵苗机插下不同穗型水稻品种的上三叶的叶长、叶宽、叶基角、披垂度和比叶重随着密度降低而呈增加趋势;且上三叶的叶长、叶宽和比叶重高于CK。(4)随着密度降低,不同穗型品种钵苗机插水稻基部N1、N2、N3节间长度减少,茎秆粗度、茎壁厚度和节间干重增加,穗下节间长、秆长、株高、重心高增加,而相对重心高有减小趋势。(5)不同穗型品种钵苗机插水稻基部节间N1、N2、N3抗折力和弯曲力矩随着密度降低而增加,倒伏指数呈下降趋势,且低于CK。说明水稻钵苗机插配套大穗型品种宜适当降低密度,增加每穗粒数以获高产;中穗型品种需兼顾穗数和每穗粒数,提高群体颖花量而增产;小穗型品种依靠穗数而提高产量。水稻钵苗机插降低密度能改善穗部性状和增加上三叶的叶面积,但增大了叶基角和披垂度,同时利于缩短基部节间长度,增加基部节间粗度、茎壁厚度和充实度,从而提高抗折力,降低倒伏指数。     

杂交籼稻机械化种植的分蘖特性

为探明不同播期杂交籼稻机械化种植的分蘖特性及其与产量的关系, 以F优498为材料, 采用二因素裂区设计, 研究了早播与迟播2个处理下机直播、机插、手插3种种植方式的杂交籼稻分蘖发生与成穗特点及各分蘖穗的穗部性状。结果表明: (1) 一次分蘖群对产量贡献大且稳定, 均在58.67%~63.82%之间; 主茎对产量贡献率以机直播最高, 手插最低; 机插和手插二次分蘖群占产量比例均显著高于机直播。(2) 不同种植方式分蘖发生与成穗规律不同, 机直播与机插分蘖发生均属一次高峰型, 手插属二次高峰型。机直播分蘖发生早而快, 一次分蘖群发生在主茎第1~第8叶位, 其中第1~第4叶位分蘖成穗率较高, 二次分蘖成穗以第1、第2叶位为主。机插分蘖发生晚、起点低, 但比较集中, 一次分蘖群以3/0~8/0发生为主, 3/0~6/0分蘖成穗率较高, 二次分蘖群成穗以第3~第5叶位为主。手插秧田与本田均发生分蘖, 分蘖发生叶位数多, 持续时间长, 一次分蘖群发生在主茎第1、第2、第4~第8叶位, 其中第1、第2、第4、第5和第6叶位成穗率较高, 二次分蘖群发生与成穗主要在第1、第2叶位。分蘖成穗叶位数和产量均随播期延迟而减少。(3) 3种种植方式的主茎及中低叶位一次分蘖枝梗数和每穗粒数多, 粒大, 单穗重高; 高叶位一次分蘖和二次分蘖枝梗数和穗粒均较少, 稻穗小。机直播优势叶位为第1~第4叶位, 机插为第3~第6叶位, 手插为第1、第2、第4、第5和第6叶位, 对产量贡献率分别达70.51%、73.83%和76.81%。优势叶位分蘖发生与成穗率高, 稻穗大, 对产量贡献率高, 应优化农艺措施挖掘其增产潜力。     

The effect of interplant distance on the effectiveness of honeycomb selection. II. Results of the second selection cycle

Summary For a second consecutive generation, the efficiency of the honeycomb selection procedure was observed at low and at high density, i.e. interplant distance being 100 cm and 15 cm respectively. Progress due to selection was determined for each of the two plant densities applied by comparing the performance of offspring from selected plants with that of offspring from plants taken at random. The relation between selection intensity and selection response was observed to study the relation between competing and yielding ability in presence and in absence of interplant competition.Compared to results obtained in a previous generation, it is now dared to be more positive about the perspectives of selection in absence of interplant competition. It is tentatively concluded that single plant selection for yield at wide spacing gives a higher progress and allows a better identification of outstanding genotypes. However, the superiority of selection at low density is not confirmed neither by any estimator of a quantitative genetic parameter nor by the correlation between single plant yield and plot yield of their offspring. The disturbing factors found already in the former generation, namely variation in seed quality and a biased sample of random plants, exerted a less important role in the estimation of the progress. Nevertheless, it is believed that only when they can be reduced more reliable results can be achieved.     

稀植对大豆生长、结荚特征及产量的影响

以铁丰29大豆为试材,研究了不同栽培密度对大豆生长、结荚特征及产量的影响。采用两种行距40,60cm,四种株距15,20,25,30 cm共8种栽培密度进行了大豆的田间栽培,调查了不同栽培密度条件下产量及相关指标。结果表明：60cm行距条件下大豆的株高、结荚高度明显高于40cm行距的处理;行距和株距对主茎节数的影响无明显的规律性,对有效分枝数、百粒重也无明显影响;株行距为40cm×30cm时,单株荚数、有效荚数、单株粒数、产量显著高于其它处理;大豆品种铁丰29最适宜栽培密度株行距为40cm×30cm,合理的栽培密度是夺取大豆高产的关键措施。     

Constitutive expression of Cry proteins in roots and border cells of transgenic cotton

Transgenic cotton plants expressing Cry1Ac and Cry2Ab, from the soil bacterium Bacillus thuringiensis (Bt), provide effective control of certain lepidopteran pests, however, little is known about the proteins below ground expression. We used ELISA to quantify in vitro expression of the Cry1Ac and Cry2Ab proteins in mucilage, root border cells and root tips in five transgenic cultivars of cotton compared to conventional cultivar Sicot 189. Expression of Cry proteins in roots and border cells of the transgenic cotton cultivars was constitutive and at detectable levels, with Cry1Ac and Cry2Ab protein expression ranging from <20 ppb to >100 pbb. To determine if genetically modified cotton demonstrated simple differences in properties of the root, when compared to an elite parental line (cv. Sicot 189), we enumerated border cells on seedling radicles. Border cell counts of 14 cultivars ranged from 0.2 to 1.1 × 10⁴ cells per root tip with an average of 5 × 10³ border cells. Border cell production in the transgenic cultivars was generally similar to that of both donor and elite parents, the exception being the cultivar Sicot 189, which had substantially more border cells than all of its transgenic derivatives. Comparison of border cell number with varietal disease resistance ranking found a limited relationship (r ² = 0.65, n = 7) between border cell numbers and the commercial resistance rank against Fusarium wilt of cotton. The implications of differences in cotton cultivar border cell number and root tip expression of Cry proteins for plant–microbe interactions in the rhizosphere and the soil ecosystem are yet to be resolved.     

Effect on leaf photosynthetic rate by leaf blast for rice cultivars with different types and levels of resistance

Summary The effect of an inoculation with Pyricularia oryzae (isolate P06-6) on net leaf photosynthetic rate of rice (Oryza sativa) was studied with four cultivars. Measurements were taken on the sixth leaf of the main culm of plants in the early tillering stage. On cultivars CO39, IR50 and IR64 a susceptible infection type developed, but a clear difference in relative infection efficiency of the cultivars was observed. The highest number of lesions developed on leaves of CO39, whereas the lowest number was found on leaves of IR64. For all three cultivars the effect of a single lesion on the reduction in net leaf photosynthetic rate was found to be equal to a reduction in leaf area of three times the area occupied by the visible lesion. On IR68, a cultivar with complete resistance, brown specks of pinpoint size appeared without any effect on net leaf photosynthetic rate.     

播种方式与种植密度互作对大穗型小麦品种产量和氮素利用率的调控效应

为探明实现冬小麦进一步增产增效的调控途径,于2015—2016年和2016—2017年连续两个生长季,选用大穗型品种泰农18,设置2种播种方式(宽幅播种和常规条播)和7个种植密度(130×10~4、200×10~4、270×10~4、340×10~4、410×10~4、480×10~4和550×10~4株hm~(–2)),研究了播种方式与种植密度互作对大穗型小麦品种产量和氮素利用率的调控效应。结果表明,与常规条播相比,宽幅播种配合增密能够有效缓解单位面积穗数增加与单穗粒重降低、氮素吸收效率提高与氮素内在利用效率下降之间的矛盾,通过增加单位面积穗数和氮素吸收效率协同提高籽粒产量和氮素利用率。宽幅播种条件下获得最高产量和氮素利用率的密度为410×10~4株hm~(–2),显著高于常规条播条件下的最优密度(340×10~4株hm~(–2)),且其增产增效幅度亦显著高于常规条播。综上所述,宽幅播种配合合理密植具有进一步协同提高大穗型小麦品种产量和氮素利用率的潜力。在本试验条件下,宽幅播种(苗带宽8～10cm)与410×10~4株hm~(–2)密度相匹配是大穗型小麦品种泰农18获得更高产高效的最优组合。     

Effects of inoculum density and temperature on three components of leaf rust resistance controlled by Lr34 in wheat

Summary Different inoculum densities had negligible effects on latent period, uredinium density and uredinium size measured on flag leaves of adult RL6058 (Thatcher^*6/PI58548[Lr34]) plants kept at low (17.5°C) post-infection temperatures in a glasshouse. In a qualitative assessment of rust severity at higher (24.6°C) temperatures, all three components of resistance indicated a susceptible flag leaf response on RL6058. In the latter environment, precise estimations of receptivity to different inoculum densities showed that adult RL6058 plants supported significantly less pustules than the leaf rust-susceptible cultivar Thatcher. In tillering plants, statistically equal numbers of uredinia developed on RL6058 and Thatcher in all paired temperature-inoculum density combinations. Growth stage-related susceptibility, and higher temperatures conducive to a shorter latent period and larger uredinia, could result in high terminal severities of Puccinia recondita f. sp. tritici on wheat genotypes containing Lr34. The reduction in receptivity associated with this gene may contribute, however, to delayed disease increase on cultivars or lines with monogenic Lr34 resistance.     

Genetic variation for nitrogen use efficiency in winter wheat (Triticum aestivum L.)

Summary The new European Common Agricultural Policy and environmental considerations are certainly to change agricultural practices toward low input cultivation systems. Nitrogen is one of the main inputs of winter wheat in northern France and it contributes highly to phreatic water pollution. A research programme has then been set up in order to study whether it is possible to breed for winter wheat cultivars using more efficiently N fertilisers. Less nitrogen would be applied, decreasing pollution risks and operational costs. It has been shown that a large variation exists for N related traits and for the resistance against N deficiency. On the one hand the cv Arche is very resistant to N deficiency, its yield on low N conditions (with no N fertiliser) is on average 89% of its yield on high N conditions (with a high N application). On the other hand, cv Récital is very susceptible to N deficiency as this same percentage is only 61%. A study on 10 hybrids showed that heterosis for grain yield was higher at low N level than at high N level. This was due to a higher number of grains per m².     

Relationship between cold resistance,heading traits and ear primordia development of wheat cultivars

Summary For breeding early heading wheat cultivars with resistance to frost damage which are well adapted to dry areas of West Asia and North Africa, the relationships between winter hardiness, ear primordia development and heading traits, i.e. veernalization requirement, photoperiodic response and narrow-sense earliness, were assessed using a total of 30 genotypes of wheat (Triticum aestivum L.) grown in an experiment in Syria. The results of artificial freezing tests indicated that cultivars with good winter hardiness were to be found only in the winter wheat cultivars which required 50 or more days of vernalization treatment. These winter wheat cultivars did not initiate internode elongation without vernalization even at 95 days after planting. Thus their ear primordia were still underground and were protected from frost injury at this stage. Photoperiodic response and narrow-sense earliness were not associated with winter hardiness and earliness of internode elongation, but were related to the number of days to heading after planting. This indicated the possibility for breeding early heading cultivars with winter hardiness and tiller frost avoidance by combining high vernalization requirement, short narrow-sense earliness and neutral response to photoperiod.     

Ontogenetic analysis of yield components and yield stability of durum wheat in water-limited environments

Summary One main reason for the slow improvement of durum wheat in water-limited environments is the lack of clear understanding of the interrelationships among yield components and their compensatory changes under low and erratic moisture availability. Five cultivars, varying in many physiological attributes, were tested under different drought-stress conditions in field and greenhouse experiments. The cause-effect relationships of duration of vegetative period, duration of grain-filling period, number of spikes per m², kernels per spike, kernel weight and grain yield per m² were assessed. Furthermore, yield stability was evaluated. Yield reduction was largest under mid-season stress (58%), followed by terminal stress (30%) and early stress (22%). Cultivar Po was very sensitive to terminal stress.Path-coefficient analysis revealed a complex pattern of relationships among the six variables. An increase in vegetative period reduced the grain-filling period under all conditions. It increased number of kernels per spike under non-stress conditions. The direct effect of spikes per m² on grain yield was significantly positive. However, more spikes per m² resulted in fewer kernels per spike and a low kernel weight and, as a result, a negative relationship with grain yield under early stress. Grain-filling period had a strong influence on grain yield via kernel weight. Kernels per spike had the largest direct effect on grain yield. However, it was negatively correlated with kernel weight, especially under terminal stress. Grain yield heavily depended on kernels per spike under early stress and grain-filling period and kernels per spike under terminal stress.Variation in drought susceptibility index among cultivars was significant under early and terminal stress conditions, but not under mid-stress conditions. Yield potential and stability were not correlated for the different drought-stress conditions.Longer grain-filling period, increased number of kernels per spike and limited spike number per m² can be used as selection criteria for sustainable yield in water-limited environments.     

Evidence for a ‘uniculm effect’ in spring wheat (Triticum aestivum L.) in a mediterranean environment

Summary The concept of the uniculm habit as an important feature of a wheat ideotype for a mediterranean environment was evaluated under field conditions. A uniculm plant produces a single shoot and when sown in a stand exemplifies a non-tillering crop with a fixed density of shoots throughout the growing season. Yield and harvest index of normal tillering spring wheat was compared with that of the same crop surgically detillered throughout the growing season to a constant density of 2 shoots per plant. The use of a biculm, whilst retaining the uniculm principle of a fixed density of shoots throughout the growing season, permitted comparison on a single crop sowing at normal field density.The control plots followed the usual pattern of tillering for the region attaining a maximum of about 4.0 shoots per plant by early spring. Shoot number declined to 2.3 and 2.6 per plant by maturity in 1978 and 1979, respectively.Detillered plots outyielded the controls by 14 per cent in 1978 (2.05 v. 1.80 tonnes ha^-1) and 22 per cent in 1979 (1.84 v. 1.51 tonnes ha^-1). Harvest indices were 0.39 v. 0.35 in 1978 and 0.30 v. 0.24 in 1979 for detillered and control plots, respectively.Higher leaf area indices and better water relations after anthesis in biculm stands indicated more efficient water use when shoot population was controlled at near optimum level. Irrigation at anthesis reduced the difference in yield between detillered and control plots.Although the uniculm principle was demonstrated with biculms in practice control of shoot number will require the use of genetic uniculms.     

播期和密度对云南冬播燕麦主要经济性状及产量的影响

为探知云南冬燕麦的适宜播期和种植密度,以白燕15号、坝莜6号和远杂2号3个不同生育期的燕麦品种为材料,采用单因素随机区组设计,研究了3个播期和3个种植密度对云南冬播燕麦主要经济性状和产量的影响。结果表明：播期对白燕15号和坝莜6号两品种的主穗小穗数、穗轮层数影响显著(p﹤0.05),对3个供试材料其余的经济性状影响不显著(p﹥0.05);密度对3个供试材料的单株分蘖数和单株有效分蘖数影响显著(p﹤0.05),对其余的经济性状影响不显著(p﹥0.05)。产量结果显示：白燕15号适宜播期为10月29日,密度为64万株.hm-2;坝莜6号适宜播期为10月14日,密度为64万株.hm-2;远杂2号宜适宜播期为10月14日,密度为48万株.hm-2。