Combining ability and heterosis as influenced by male-sterility inducing cytoplasms in sorghum [Sorghum bicolor (L.) Moench]

An investigation was carried out to assess the efficiency of A₂ cytoplasmic-nuclear male-sterility (CMS) system in comparison to the widely used A₁ cytoplasm in terms of general combining ability (gca) effects of male-sterile (A-) lines and mean performance, specific combining ability (sca) effects and mid-parent heterosis of hybrids for days to 50% flowering, plant height and grain yield at International Crops Research Institute for the Semi-Arid Tropics, Patancheru, Andhra Pradesh, India in 2001 and 2002 rainy seasons. The material for the study consisted of six pairs of iso-nuclear, allo-plasmic (A₁ and A₂) A-lines and 36 iso-nuclear hybrids produced by crossing these A-lines with three dual restorer (R-) lines. The results revealed that cytoplasm and its first-order interaction with year, R- and A-lines did not appear to contribute to variation in iso-nuclear hybrids for plant height and grain yield. Cytoplasm had limited effect on gca effects of A-lines and on sca effects and mid-parent heterosis of iso-nuclear hybrids for days to 50% flowering, plant height and grain yield. The mean days to 50% flowering, plant height and grain yield of A₂ cytoplasm-based hybrids were comparable with those of widely used A₁ cytoplasm-based hybrids. The relative frequency of the occurrence of the A₁- and A₂-based hybrids with significant sca effects and mid-parent heterosis indicated that A₂ CMS system is as efficient as A₁ with a slight edge over A₁ for commercial exploitation. The implications of these results are discussed in relation to opportunities for broadening not only cytoplasm base but also nuclear genetic base of both the hybrid parents.     

Ergot reaction of pearl millet hybrids affected by fertility restoration and genetic resistance of parental lines

Summary High ergot (Claviceps fusiformis Loveless) susceptibility of pearl millet (Pennisetum glaucum (L.) R. Br.) hybrids has often been associated with the A₁ cytoplasm of male-sterile lines (A-lines). To understand the underlying basis of this association and to examine the prospects of breeding ergot-resistant hybrids, we evaluated 56 hybrids and their 15 parental lines for ergot reaction and selfed seedset for 2 years in disease nurseries at ICRISAT Asia Center. Hybrids were made by crossing seven pollen parents (2 susceptible and 5 resistant) onto two resistant and two susceptible A-lines, and their four corresponding maintainer lines (B-lines). A-lines had no selfed seedset while B-lines had 32–75% selfed seedset. Hybrids of A-lines had significantly less selfed seedset than the hybrids of the corresponding B-lines. The reduced seedset of A-lines and their hybrids, however, was not always accompanied by significantly higher ergot susceptibility. Highly resistant hybrids were obtained where both A-lines and pollen parents were highly resistant, regardless of male fertility levels of the hybrids. Thus, although the A₁ cytoplasm, by its reduction of male fertility, had a large and significant effect in increasing ergot severity of hybrids, the contribution of nuclear genetic factors of female parents was about 1.8 times larger than that of the cytoplasm.Submitted as JA No. 1776 by the International Crops Research Institute for the Semi Arid Tropies.     

Seed parent breeding efficiency of three diverse cytoplasmic-nuclear male-sterility systems in pearl millet

Pearl millet (Pennisetum glaucum (L.) R. Br.) hybrids, grown widely in India and to some extent in the US, are all based on an A₁ CMS source, leaving the pearl millet hybrids vulnerable to potential disease or insect pest epidemics. A comparison of this CMS system with two additional CMS systems (A₄ and A₅) in the present study based on isonuclear A-lines (seed parents) and their isonuclear hybrids showed that A-lines with the A₄ cytoplasm had much fewer pollen shedders and much reduced selfed seed set in visually assessed non-shedding plants as compared to those with the A₁ cytoplasm. A-lines with the A₅ cytoplasm had neither any pollen shedders nor did they set any seed when selfed. This showed that the A₅ CMS system imparts complete and most stable male sterility, followed by the A₄ and A₁ CMS systems. The frequency of maintainers, averaged across a diverse range of 26 populations, was highest for the A₅ CMS system (98%), followed by the A₄ (59%) and the A₁ (34%) system indicating the greatest prospects for genetic diversification of A-lines lies with the A₅ cytoplasm, and the least with the A₁ cytoplasm. Mean grain yield of hybrids with the A₁ cytoplasm was 5% more than the A₄-system hybrids, while there was no difference between the mean grain yield of hybrids based on A₁ and A₅ CMS systems. Based on these results, it is suggested that seed parents breeding efficiency will be the greatest with the A₅ CMS system, followed by the A₄ CMS system, and least with the currently commercial A₁ CMS system.     

四川盆地小麦籽粒的灌浆特性

四川盆地小麦灌浆期长,粒重优势明显,但易受环境影响。2010-2011和2011-2012年连续2个小麦生长季,选用10个品种在3个地点进行灌浆特性研究,以揭示该区域小麦灌浆参数的基因型差异及环境效应。2年平均粒重48.25 g,灌浆分为渐增期(T₁)、快增期(T₂)和缓增期(T₃) 3个阶段,各阶段持续时间为T₃ (16.30 d)>T₁ (13.41 d)>T₂ (12.98 d),其灌浆速率分别为0.618、0.772和2.205 mg grain^-1 d^-1。3个阶段的干物质积累贡献率依次为21.21% (T₁)、58.27% (T₂)和20.53% (T₃),可见快增期结束时可以积累80%左右的干物质量。基因型、地点和年份对除粒重以外的所有灌浆参数均有显著影响,以年份的效应最大。同一年中,粒重、最大灌浆速率、平均灌浆速率、缓增期灌浆速率、渐增期灌浆速率和快增期灌浆速率主要受基因型的影响,而其他参数则以地点效应大于基因型效应。粒重与平均灌浆速率、最大灌浆速率、快增期灌浆速率和缓增期灌浆速率呈极显著正相关。10个参试品种中,川麦42、川育23和川麦56具开花期早、灌浆速率高、灌浆时间长、粒重大等特征。     

Smut reaction of pearl millet hybrids affected by fertility restoration and genetic resistance of parental lines

Summary Pearl millet (Pennisetum glaucum (L.) R. Br.) hybrids based on the A₁ cytoplasmic-nuclear male-sterile (CMS) lines are more susceptible to smut (Tolyposporium penicillariae Bref.) than open-pollinated varieties. Seventy eight pairs of hybrids, made onto male-sterile (A) lines and their counterpart maintainer (B) lines, were evaluated to examine the effects of male sterility and genetic resistance of parental lines on the smut severity of hybrids. The A-line hybrids had higher smut severity and lower selfed seedset than the counterpart B-line hybrids, indicating that it is the CMS-mediated male sterility rather than the A₁ cytoplasm per se that caused greater smut severity of A-line hybrids. However, with the use of resistant parental lines even male-sterile hybrids of A-lines, in several cases, were as resistant as some of the highly resistant male-fertile hybrids of B-lines. It would be possible to produce smut resistant hybrids (< 10% severity) on A-lines, albeit in low frequency, even if only one parent of a hybrid were resistant. However, the probability of producing such hybrids would be higher when both parents were resistant to smut. Thus, improvement in smut resistance of parental lines and fertility restoration ability of pollinators would provide the most effective genetic approach to smut disease management in hybrids.Submitted as JA No 1737 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).     

CHA杂种小麦灌浆优势规律研究

以4个CHA杂种及其亲本和CK为材料, 采用数学模型分析、 相关分析、 通 径分析等方法, 研究了CHA杂种灌浆优势及其动态规律和与气象因子的关系, 结果表明 , (1) 4个CHA 杂种籽粒干物质积累动态过程均存在杂种优势, 最终干物质积累均存在 超亲优势, 最终干物质超亲优势形成过程有灌浆全期形成、 灌浆中后期形成和灌浆后期     

Compensation in grain weight and volume in sorghum is associated with expression of resistance to sorghum midge, Stenodiplosis sorghicola

Sorghum midge, Stenodiplosis sorghicola (Coquillett) is one of the most important pests of grain sorghum worldwide. We studied the inheritance of resistance to sorghum midge and compensation in grain weight and volume in panicles of sorghum hybrids and their parents under uniform infestation (40 midges per panicle for two consecutive days). Sorghum midge damage ranged from 8.2 to 82.4% in the maintainer lines (B-lines) of the females parents (A-lines), and 9.0 to 67% in the male parents (restorer lines). Hybrids involving resistant × resistant parents were highly resistant, while those involving resistant ×susceptible and susceptible × resistant parents showed moderate susceptibility. Susceptible × susceptible hybrids were susceptible. Compensation in (percentage increase) grain weight and volume in midge-infested panicles of midge-resistant parents and their F₁ hybrids was greater than in midge-susceptible parents and hybrids. General combining ability effects for midge damage, and grain weight and volume were significant and negative for the midge-resistant females (ICSA 88019 and ICSA 88020), whereas those for the midge-susceptible females (ICSA 42 and 296A) were significant and positive. However, the reverse was true in case of compensation in grain weight and volume. Inheritance of compensation in grain weight and volume and resistance to sorghum midge is controlled by quantitative gene action with some cytoplasmic effects. Resistance is needed in both parents to realize full potential of midge-resistant hybrids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heterosis in yield,fiber quality,and photosynthesis of okra leaf oriented hybrid cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.)

Leaf shape is an important factor affecting canopy structure, photosynthetic characteristics, and yield. Introducing okra leaf shape is considered an important strategy in cotton heterosis breeding. The objective of the study was to evaluate the heterosis in okra leaf cotton hybrid F₁s, which were developed by crossing two sterile near isolines and three restorer near isolines. A normal leaf check hybrid F₁, Zhongza 29, and four newly developed okra leaf oriented hybrid F₁s, including the super-okra (severely cleft and narrowly lobed leaf), okra (deeply cleft and narrowly lobed leaf), semi-okra (intermediate leaf lobe), and sub-okra (large leaf lobe) hybrids were selected in this experiment. Okra leaf oriented cotton hybrids significantly reduced leaf area index (LAI) (P < 0.0001), thus more light penetrated into the lower canopy. The LAIs for the super-okra and okra hybrids, however, were too small to supply adequate photosynthate, thus resulting in early maturity, short boll filling period, and low yield. As the LAI increases, the semi-okra and sub-okra hybrids showed certain heterosis. The semi-okra hybrid showed 7–12% heterosis over the check hybrid in lint percent, 6–11% in boll weight, 2–147% in canopy light intensity, 1–10% in net photosynthetic rate (Pn), and −3 to 3% in lint yield. As well, all tested okra leaf hybrids improved fiber quality such as micronaire compared with the normal leaf check hybrid. The results suggested that adopting okra leaf parental lines in cotton breeding provided potentials in increasing fiber quality with comparable lint yield.     

Commercial viability of alternative cytoplasmic-nuclear male-sterility systems in pearl millet

Commercial viability of three cytoplasmic-nuclear male sterility (CMS) systems (A₄, A₅ and A_v) as potential alternatives to the most widely used A₁ system in pearl millet (Pennisetum glaucum (L.) R.Br.) was evaluated in terms of stability of complete male sterility of four isonuclear A-lines (81A₁, 81A₄, 81A₅ and 81A_v) and the level and stability of male fertility restoration of their 44 single-cross hybrids. Lines 81A₄ and 81A₅ had no pollen shedders (PS), and there were very low frequency of non-PS plants of these A-lines that had a maximum of 1–5% selfed seedset (SSS). In 81A₁ and 81A_v,there were, albeit low frequency (<1%) of PS plants, and relatively higher frequency of the non-PS plants in these two lines, the more so in 81A_v,had 1–5% and even greater SSS. Some hybrids made on each of the three A-lines (81A₁, 81A₄ and 81A_v) had high and stable male fertility, while others made on the same three A-lines displayed large variation in SSS across the environments, the more so in case of hybrids made on 81A_v. These results indicate that the A₄ CMS system provides a better alternative to the A₁ CMS system, while the A_v system does not. On the basis of highly stable male sterility and the highest frequency of pollinators behaving as maintainers, the A₅ CMS system appeared to be the best for A-line breeding. The commercial viability of this CMS system in breeding R-lines of grain hybrids, however, still remains to be ascertained as no hybrid on it was fully male fertile in any environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Potentialities of heterosis breeding in wheat

Summary Heterosis for yield and yield components were studied in F₁, F₂ and F₃ generations in ten crosses of wheat, Triticum aestivum L., under normal spacing. Eighty and 60% F₁ hybrids exceeded the high parent and standard variety to the extent of 44.3 and 36.4 per cent. respectively. The two best crosses excelled the high parent and the standard variety by a significant margin. The result showed that seed of advanced generations cannot be used for commercial wheat production, Heterosis in yield seems to be reflected through heterosis in spike number and 1000-kernel weight. In general it was found that the greater the genetic difference of the parents with a high yield capacity the better are their hybrids.     

Heterosis,molecular diversity,combining ability and their interrelationships in short duration maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) across the environments

Five inbred lines, 10 single cross maize (Zea mays L.) hybrids and two standard cultivars as check were used to study the combining abilities and heterosis under three environmental conditions. Random amplified polymorphic DNAs (RAPDs) markers were used to study the genetic diversity (GD) and further to analyze relationship of RAPDs based GD with combining ability and heterosis in short duration maize. Spearman’s rank correlation coefficients and linear regressions were analyzed to identify the most important factor determining heterosis and per se performance of the hybrids. Variances due to general combining ability (GCA), specific combining ability (SCA) and their interactions with environment were found to be significant. Twenty random primers generated 179 RAPD fragments. Of these, 102 RAPD fragments were polymorphic. GD was determined using Jaccard’s similarity coefficient, and a dendogram was constructed by UPGMA cluster analysis. The RAPDs based GD exhibited non-significant negative or positive association, non-significant linear regression along with very low coefficient of determination (R ²) with SCA, high and mid parent heterosis (HP and MP) and per se performance of the hybrids. Significant positive correlations and regressions along with high coefficients of determination were recorded for SCA with HP, MP and per se performance of the hybrids. The HP and MP also established significant positive association and linear regression along with high coefficient of determination with per se performance of hybrids whereas the parental mean did not establish any significant correlations with the GD, HPH, MPH and grain yield of F₁s. The present investigation, therefore, did not find any role of RAPDs based GD in determining hybrid heterosis and hybrid performance in short duration sub-tropical maize. The SCA, however, has emerged as the most important factor in determination of heterosis as well as per se performance of the hybrids in short duration maize.     

Line × Tester Analysis Involving Diverse Cytoplasmic Systems in Sorghum

Sorghum hybrids, involving three iso-sterile (A₁, A₂ and A₄) females and a set of five fertility restorers, were evaluated for yield components in both rainy and winter seasons. In general A₂ cytoplasm had larger grain size and higher yield than traditional milo (A₁) cytoplasm and cytoplasm A₄ had an adverse effect of yield and yield components. Cytoplasmic systems also affected plants height, days to bloom and grain size. Restorers IS 12567C, IS 12662C and SPV 650 had desirable general combining ability effects. The cross (A₂T × 398) × IS 12662C had the highest mean yield coupled with positive heterosis and specific combining ability effects, Exploitation of A₂ cytoplasm in Sorghum heterosis breeding is suggested.     

Genetic distance and its association with heterosis in peas

Summary The relationship between the genetic distance of parents and both the heterosis of F₁ hybrids and the variance of F₅ lines was investigated in 72 crosses of pea (Pisum sativum L.). The genetic distance between each pair of parents was estimated, using isozyme (GDi), morphological (GDm) or quantitative (GDq) markers and finally a combination of isozyme and morphological markers (GDi+m). GDm was poorly correlated with the other measures of genetic distance, which in turn were strongly correlated with each other. Genetic distance was moderately correlated with the level of heterosis for yield over midparent in the F₁ generation, with the highest correlation obtained from GDi+m. GD was not significantly correlated with heterosis for yield over the better or best parent but it was significantly correlated with all three measures of heterosis for pods per plant and hundred seed weight. There was no correlation between genetic distance and the level of heterosis for yield and total dry matter in the F₂ generation, but GDi, GDi+m and GDq were predictive for the level of inbreeding depression in grain yield and total dry matter. When parents were high in genetic distance, crosses produced highly transgressive segregants for basal branches per plant, hundred seed weight, harvest index and onset of flowering. Genetic distance between parents was thus a useful measure for predicting a portion of hybrid performance and also of the variance of derived inbred lines. It was concluded that when choosing parents for a cross, consideration should be given to their genetic distance as well as their overall adaptation and their yield. There is considerable potential for optimising choice of parental combinations in the development of improved pea cultivars.     

化杀杂种小麦灌浆规律及粒重优势

对化杀杂种小麦灌浆特性及播期、密度、灌水效应的研究表明，其灌浆规律与常规（亲本）品种相同，籽粒增重遵循慢—快—慢的节律变化，同时具有自己的特性。杂种的快速增重期较对照早１～３天，灌浆速度峰值超对照优势达２４．７１％～４６．３４％，且持续时间长，灌浆速度的峰面宽，因而单粒重比对照高６～１１ｍｇ，但不同部位小穗间的粒重差异依然存在，且较对照大。杂种的灌浆特性与亲本有关，但仍表现出明显的超亲优势。播期、密度、灌水等影响灌浆进程，因而可通过亲本选配、强优势组合筛选及农艺措施调节进一步发挥杂种的粒重优势     

K,V型杂种小麦优势的研究

利用５（Ａ）×２（Ｒ）两组亲本杂交的１０个杂种及其相应的亲本材料，探讨高产条件下Ｋ、Ｖ型小麦的杂种优势。结果表明：单株产量有很强的杂种优势，７个组合超双亲平均值为７．１１％～２５．１％，其中３个为１５．７％～２５．１％，４个组合超标优势２．４％～１８．１％。Ｋ、Ｖ型杂种优势的主要表现是千粒重的增高，其次是穗粒数，有３个组合超双亲平均值。单株穗数的减少对杂种产量有影响，选择多穗亲本，对提高杂种的穗数有效     

Inheritance of yield components and yield in relation to evidence for heterosis in F1 barley hybrids

Summary Yield components and yield were studied in F₁ barley hybrids produced by hand pollination or male sterility. Grain number exhibited only partial dominance but grain weight showed dominance or overdominance and contributed to the heterotic situation particularly in 2×6-row crosses. For the commercial exploitation of heterosis it is essential that hybrids should be found which show greater dominance for high grain number.     

Changes in morphological and physiological traits associated with recurrent selection for grain yield in maize

Summary Experiments were conducted during the growing seasons of 1975 and 1976 to determine changes in morphological and physiological traits associated with recurrent selection for grain yield in maize (Zea mays L.). Four variety hybrids, BSSS(R)CO x BSCB1(R)CO, BSSS(R)C7 x BSCB1(R)C7 [from a reciprocal recurrent selection program involving Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic #1 (BSCB1)], BS12CO x B14A, and BS12C6 x B14A [from a half-sib selection program involving the open-pollinated variety Alph (BS12) and the inbred tester B14A] were grown at 59 300 and 98 800 plants/ha near Ames, Iowa We obtained data on CO₂-exchange rate (an estimate of photosynthetic rate), grain yield, grain-yield components, flowering dates, maturity traits, light interception and use, shelling percentage, harvest index, and various other plant traits.CO₂-exchange rate did not change appreciably with recurrent selection for yield. Grain yield per hectare and per plant were larger for the improved than unimproved hybrids. Grain-yield components did not change significantly with recurrent selection. Kernel weight of BSSS(R)C7 x BSCB1 (R)C7, however, was larger than that of BSSS(R)C0 x BSCB1(R)C0. Pollen-shed-to-silking interval was shorter for the improved than the unimproved hybrids, and grain-filling duration was longer in C7 x C7 than in C₀ x C₀ of the reciprocal recurrent selection program. Furthermore, improved hybrids were characterized by smaller tassels and more upright canopies. Usually, plant traits and leaf-area-related traits were similar for all hybiids.Although dry-matter productivity was similar for all hybrids, those that were improved by recurrent selection produced more grain per unit leaf area and per unit light interception. Also, BS12C6 x B14A was characterized by a higher harvest index than BS12CO x B14A.We concluded that the source (i.e., photosynthetic capacity) was not limiting grain yield in BSSS(R) x BSCB1(R) and BS12. Increased grain yields that resulted from recurrent selection were consequences of longer grain-filling duration for BSSS(R) x BSCB1(R) and increased translocation of photosynthate from source to sink for both BSSS(R) x BSCB1(R) and BS12.Journal Paper J-8953 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project No. 2152.     

The influence of Elymus sibiricus L. genome on the diploidization system of wheat

Summary The meiotic behaviour of five tetraploid wheat strains x Elytricum fertile (2n=42 chromosomes, AABBD(SH) genomes) F₁ hybrids has been analysed. Multivalent associations were observed in the hybrids which could be attributed to Elymus sibiricus L. gene (s) somewhat suppressing the activity of the wheat homoelogous pairing control system. This interaction depends on the wheat genotype. The effect was particularly notable when Triticum turgidum var. salomonis was the wheat parent. The possibility of gene transfer from Elymus to wheat is discussed.     

Heterosis and hybrid performance in topless faba beans (Vicia faba L.)

Parental lines, F₁ and F₂ hybrids from a 7×7-diallel of topless faba beans and eight standard cultivars were grown in single-rows for two years at four sowing dates on a highly fertile loam soil near Göttingen. In grain yield, F₁ hybrids showed 21 to 54% advantage over the higher yielding parent. Compared with the midparental value an average heterosis of 50% was observed for grain yield. Corresponding heterosis mean values ranged from 3 to 37% for yield components and up to 11% for phenological traits. The grain yield of the highest yielding topless F₁ hybrid was equal to that of Alfred, the highest yielding indeterminate standard cultivar. High grain yield in the topless hybrids was closely correlated with high biomass yield, late ripening and tall plants generally having a high number of podded nodes and pods on the main stem. Due to their agronomic advantages, i.e., lower plant length, reduced lodging sensitivity and earlier ripening, efforts at breeding topless hybrids seemed to be worth-while in faba beans. However, their yielding ability must be improved further before they can compete with normal, semi-dwarf and stiff-strawed cultivars.     

Heterosis for yield and other agronomic traits of winter triticale F1 and F2 hybrids

Triticale is generally treated as a self‐pollinating crop and line breeding is practised. Hybrid breeding has been discussed for some time, but there is little information for winter triticale. This study investigated heterosis for eight agronomic traits in F₁ and F₂ hybrids grown together with their parents as drilled plots in three environments. On average, grain yield heterosis was 12.5 dt/ha (a relative 10.5%) compared with the mid‐parent value for F₁ hybrids, and 6.2 dt/ha (5.0%) for F₂ hybrids and withawide range of 4.4–17.1 dt/ha for F₁ hybrids. A positive contribution to the heterosis of yield was made by kernels/spike and 1000‐kernel weight, whereas spikes/m² showed negative heterosis. Hybrid plants in F₁ and F₂ were taller than mid‐parents (8.3 cm and 5.3 cm, respectively), with a tendency to earlier heading. The negative heterosis for falling number in F₁ and F₂ hybrids could be a problem for commercial production of triticale hybrids. By selecting parents for combining ability and the identification of heterotic patterns, grain yield heterosis of 20% appears feasible.