Are ordinal rating scales better than percent ratings? a statistical and “psychological” view

Cytoplasmic male sterility (CMS) is considered an efficient genetic tool in pearl millet hybrid breeding. Of the several CMS sources available in pearl millet, A₁ is the only CMS widely exploited to produce commercial hybrids in India. To explore the possibility of using alternate CMS sources, we studied the cytoplasmic effects of different CMS sources on agronomic characters in pearl millet. Five CMS (A) lines representing A₁, A₂, A₃, A₄ and A₅ cytoplasms, their respective maintainer (B) lines and eight restorer (R) lines were used to generate 40 A × R and B × R experimental crosses. The experimental material was evaluated at two different locations in India. Analysis of combining ability and heterosis revealed that A₄ and A₅ cytoplasms had desirable effects for earliness. The A₅ CMS was found to be particularly promising, as compared to other CMS sources for improving grain yield. The study also indicated that the cytoplasmic effects on general combining ability (GCA) for various agronomic characters were largely non-significant. However, cytoplasmic effects on specific combining ability and heterosis were found to be modulated by cytoplasmic-nuclear interactions and influenced by the environmental conditions. The study also demonstrated the advantage of utilizing diverse male-sterile and restorer combinations in maximizing the productivity as well as for genetic and cytoplasmic diversification of hybrids in pearl millet.     

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.     

Stability of male-sterile sources and fertility restoration of their hybrids in pearl millet

Genetic background has a significant effect on the expression of cytoplasmic-nuclear male sterility (CMS) in pearl millet (Pennisetum glaucum (L.) R. Br.). Therefore, a reliable characterization of CMS sources requires the use of near-isonuclear lines and their hybrids. We used this approach to characterize five CMS sources (A₁, A₂, A₃, A_v, and A₄). Male sterility of 81A₄ was the most stable, followed by 81A₁ and 81A_v, indicating the relative merits of these CMS sources in breeding stable male-sterile lines. Male-sterile lines 81A₂ and 81A₃ were highly unstable, indicating their minimal value. Differential male fertility restoration patterns of hybrids made on 81A_V and 81A₄ suggest that the A_v and A₄ cytoplasms represent CMS systems that are different from each other and from A₁, A₂ and A₃. An evaluation of topcross hybrids of 15 diverse populations made on 81A₁ and 81A₄ showed that each population had restorers and maintainers of both cytoplasms and that the frequency of maintainers of A₄ was as high as, or higher than, that of the A₁ cytoplasm. Thus, use of the A₄ cytoplasm can substantially increase the probability of breeding stable male-sterile lines based on inbreds developed from diverse genetic backgrounds, and also provide the opportunity for breeding restorers from each of these diverse genetic sources.     

Relative susceptibility of different male-sterile cytoplasms in sorghum to shoot fly, <Emphasis Type="Italic">Atherigona soccata</Emphasis>

Summary The shoot fly, Atherigona soccata is an important pest of sorghum, and host plant resistance is one of the most effective components for managing this pest. Most of the hybrids grown in India based on milo cytoplasm (A₁ cytoplasm) are highly susceptible to shoot fly. Therefore, the present studies were undertaken to evaluate different male-sterile cytoplasms (CMS) for their relative susceptibility to sorghum shoot fly. Oviposition and deadheart formation were significantly lower on the maintainer lines as compared to the corresponding male-sterile lines. Among the cytoplasms tested, A₄M cytoplasm showed antixenosis for oviposition and suffered lower deadheart formation than the other cytoplasms tested. The A₄G₁ and A₄M cytoplasms suffered lower deadhearts in tillers than the other cytoplasms. Recovery following shoot fly damage in A₄M, A₃, and A₂ cytoplasms was better than in the other cytoplasms tested. The larval and pupal periods were longer and male and female pupal weights lower in A₄M and A₄VzM CMS backgrounds compared to the other CMS systems. Fecundity and antibiosis indices on CMS lines were lower than on the B-lines. The A₄M cytoplasm was found to be relatively resistant to sorghum shoot fly, and can be exploited for developing shoot fly-resistant hybrids for sustainable crop production in future.     

A new cytoplasmic-nuclear male sterility system in pearl millet

Among the cytoplasmic-nuclear male sterility (CMS) systems reported in pearl millet, Pennisetum glaucum (L.) R. Br., the A_m= A₄ system produces the highest frequency of male-sterile hybrids. A CMS source identified in a large-seeded gene pool (LSGP) was compared with the A₄ system. Seven diverse restorer lines of the A4 system produced hybrids with 81A4 that were all fertile (pollen-shedding score 4 and 68–89% selfed seedset). In contrast, all the hybrids of these inbreds made with the isonuclear line with the LSGP cytoplasm were sterile (pollen-shedding score 1 and 0–3% selfed seedset). Topcross hybrids of four diverse composites made with 81A4 had 10–35% plants that had good fertility (> 50% selfed seedset). In comparison, no plant of any topcross hybrid with the isonuclear line having LSGP cytoplasm exceeded 20% selfed seedset, and it was rare for a plant to exceed even 10% selfed seedset. These differential fertility restoration patterns of hybrids indicate that the LSGP cytoplasm represents a CMS system that is different from the A4 and, by implication, from all those reported to date. This new CMS system is designated A₅.     

Characterization of the A4 cytoplasmic male-sterile lines of sorghum using RFLP of mtDNA

Three sorghum cytoplasmic male sterile lines CSV4 A(V), CSV4 A(G₁) and CSV4 A(M), grouped as A₄, were compared with a milo (A₁) and two other non-milo (A₂ and A₃) cytoplasms for their RFLP patterns of mitochondrial DNA (mtDNA). A 9.7 kb clone from pearl millet mtDNA discriminated each of the three A₄ entries whereas other maize and pearl millet mtDNA clones used could not distinguish this group completely. The molecular differences within the A₄ cytoplasmic group offer some explanation for the inconsistency in the fertility restoration behaviour of these A₄ lines obtained with a definite set of testers in the field. This revised version was published online in July 2006 with corrections to the Cover Date.     

Smut severity of pearl millet hybrids with male sterile and fertile cytoplasm

Summary Effect of A₁ male sterile cytoplasm on smut severity in pearl millet (Pennisetum glaucum (L.) R.Br.) was studied by comparing 35 pairs of F₁ hybrids, each pair carrying male sterile and normal cytoplasm. Mean smut severity was not significantly different in the hybrids carrying male sterile or normal cytoplasm. This suggests that in pearl millet male sterile cytoplasm is not associated with higher smut susceptibility. Partitioning of variance into different components showed that pollinators, A/B line pairs and their interaction primarily influenced smut severity of hybrids. Smut susceptibility might be attributed to effects of cytoplasm × nuclear interactions.     

Maternal inheritance of male sterility in the progeny of a natural hybrid between Cajanus lineatus and C. cajan

Adoption of pigeonpea hybrids in central and southern India is showing high impact with on‐farm yield advantages of >30%. The hybrid pigeonpea technology, the first in any legume crop, is based on a cytoplasmic‐nuclear male‐sterility (CMS) system. For a long‐term sustainability of hybrid programme, it is imperative that both nuclear diversity and cytoplasmic diversity are maintained among hybrid parents. In this context, a continuous search for new CMS‐inducing cytoplasms is necessary. This paper reports detection of maternal inheritance of male sterility in the progeny derived from a natural hybrid between a wild relative [Cajanus lineatus (W. & A.) Maesen comb. nov.] of pigeonpea and an unknown pigeonpea [Cajanus cajan (L.) Millsp.] genotype. In the present study, the male sterility was maintained up to BC₇F₁ generation by an advanced breeding pigeonpea line ICPL 99044. This male sterility inducing cytoplasm of C. lineatus was tagged as A₆. In future, this CMS genetic stock can be used to develop a range of new pigeonpea hybrids with high yield and adaptation.     

Influence of Male Sterile Cytoplasms on the Physico-Chemical Grain Quality Traits in Hybrid Rice (Oryza Sativa L.)

Summary Possible unfavourable influence of sterility inducing cytoplasm on physico-chemical grain quality traits in rice hybrids is one of the important concerns hindering the large-scale adoption of hybrid rice technology. Produce from 23 pairs of CMS line × restorer (AF₁) and maintainer line × restorer (BF₁) cross combinations carrying different cyto-sterile sources (WA, ARC, Mutagenized IR 62829B and Kalinga I) was compared for various grain and cooking quality traits. The milling recovery in rice hybrids was not influenced by the sterile cytoplasm. For kernel dimensions before and after cooking there were both favourable and unfavourable cytoplasmic effects, which varied in magnitude depending upon the sterile cytoplasm and parental combinations. Similar results were obtained for kernel elongation and gelatinization temperature. The most widely used WA cytoplasm had minimum instances of unfavourable influence. In general, the cytoplasmic influence was found to be highly cross-specific and depended on the nuclear background of CMS line and fertility restorer. Availability of alloplasmic CMS lines carrying different cyto-sterile sources in the same nuclear background would help in ascertaining the cytoplasmic influence in a more comprehensive manner.     

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.     

Cytoplasmic differentiation using near-isonuclear polycytoplasmic male sterile lines in pearl millet

Summary Five near-isonuclear polycytoplasmic versions of 81A₁ and two of Pb 402A₃ male sterile lines of pearl millet (Pennisetum typhoides), along with their corresponding maintainer lines (81B and Pb 402B) were studied for 14 agronomic and two disease traits, and for isozymes of peroxidase in anthers and leaves for assessing cytoplasmic differences. Significant differences among isonuclear polycytoplasmic lines of both 81A₁ and Pb 402A₃, having the same genome and variable cytoplasms, were observed for several agronomic traits. Banding pattern of peroxidase isozymes revealed clear cut differences among cytoplasms. The results provide evidence for the influence of cytoplasmic factors on the phenotypic expression of nuclear genes.     

A Test of the 'Tall-Dwarf" Hypothesis in Pearl Millet, Pennisetum glaucum (L.) R. Br.

Positive height-grain yield relationships exist for many cereals, but cannot be fully used in breeding because of lodging and harvestability problems in tall cultivars. Law et al. (1978) proposed a “tall-dwarf” hypothesis for wheat, in which the positive effects of minor height genes could be exploited by selecting for them in a major dwarfing gene background. The applicability of this hypothesis to pearl millet was tested by crossing a set of dwarf S₁ progenies (from a single population) which varied in height onto two male-sterile lines. Mean (by S₁ pollinator) hybrid grain yield was closely related to mean hybrid height (r²= 0.60) over a range of mean yields of 3.0–3.9 t ha^?1 and a range of mean heights of 126–165 cm. The effect of height was expressed as an increase in grain number in one cross and as an increase in grain mass in the other, indicating the importance of background genetic effects on yield-height relationships in dwarf hybrids. The concept of “tall-dwarfs” appears to be applicable to pearl millet.     

Feasibility of breeding male-sterile populations for use in developing interpopulation hybrids of pearl millet

Inter‐population hybrids of pearl millet, Pennisetum glaucum (L.) R. Br., have a substantial grain yield advantage over open‐pollinated varieties that makes them an appropriate and economically viable proposition for many African agricultural situations, provided that stable male‐sterile populations can be developed for use as seed parents. The objective of this research was to examine the feasibility of breeding stable male‐sterile populations, using the d₂ dwarf version of Nigerian Composite NCD₂ and the A₄ cytoplasmic‐nuclear male sterility system as a test case. Results showed that two cycles of recurrent selection for sterility maintenance ability led to the development of a fully effective maintainer version of NCD₂. There was no significant difference between the original C₀ cycle bulk and the C₃ cycle bulk (developed from the third and final cycle of recurrent selection) for grain yield and other agronomic traits. The male‐sterile population at the third backcross stage, developed from the maintainer version of NCD₂, had as high a level of stable male sterility as the A¹ system commercial inbred male‐sterile line 841A₁. Thus, it is concluded that with the use of the A₄ cytoplasmic male‐sterile system, it would be possible rapidly to develop a maintainer version of any population without detrimental effects on grain yield and agronomic traits. Male sterility of populations developed from these maintainers will be highly stable, paving the way for their effective utilization as seed parents in breeding inter‐population hybrids.     

Moricandia arvensis cytoplasm based system of cytoplasmic male sterility in Brassica juncea: Reappraisal of fertility restoration and agronomic potential

Cytoplasmic male sterility (CMS) system based on the cytoplasm from Moricandia arvensis (mori) was investigated for fertility restoration and agronomic potential. Fertility restorer gene for mori CMS was introgressed from cytoplasm donor species as all the evaluated Brassica juncea genotypes (155) acted as sterility maintainers. The allosyndetic pairing between M^a and the A/B genome chromosomes in the monosomic addition plants (2n= 18II + 1M^a) facilitated the gene introgression. Partial fertility restoration (43–52% pollen grain stainability) in F₁ hybrids and absence of segregation for male sterility in F₂ progenies suggested gametophytic control of fertility restoration. The pollen fertility in the F₁ hybrids was, however, sufficient to ensure complete seed set upon bag selfing. Introgression from M. arvensis also helped in correction of chlorosis associated with mori cytoplasm in CMS and fertile alloplasmic B. juncea plants. Yield evaluation of thirty F₁ hybrids having the same nuclear genotype but varied male sterilizing cytoplasms (mori, oxy, lyr, refined ogu), in comparison to respective euplasmic hand bred control hybrids, allowed an estimate of yield penalty associated with different CMS systems. It ranged from 1.8% to 61.6%. Hybrids based on cytoplasmically refined ogu were most productive followed by those based on cytoplasmically refined mori CMS. The male sterility systems emanating from somatic hybridization were found superior than those developed from sexual hybridization.     

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.     

Heterosis in landrace-based topcross hybrids of pearl millet across arid environments

This study quantified the magnitude of heterosis in pearl millet (Pennisetum glaucum) topcross hybrids produced by crossing 16 diverse landraces and three high yielding open-pollinating varieties on two homozygous male-sterile lines. Hybrids and pollinators were grown in 12 year ×;location combinations in India that were grouped into three zones. Genetic components of variance quantifying the differences among these hybrids were estimated. The hybrids showed a conspicuous heterosis for grain yield, earliness and biomass yield but not for straw yield. The level and direction of heterosis for time to flowering depended strongly on the earliness of the male-sterile line. In the terminal drought stress zone hybrids made on the early maturing male-sterile line 843A had the highest level of heterosis for grain yield (88%). This was partly due to escape from terminal stress. In the other two zones the heterosis for grain yield was on average 30%. Heterosis for biomass yield and biomass yield per day was on average also positive in all three zones. For all traits, except time to flowering and biomass yield per day, pollinator effects were the only significant source of variation. Differences between hybrids were mostly caused by additive genetic effects. Significant amount of heterosis observed in landrace-based topcross hybrids for grain yield and other productivity-related traits suggested that substantial improvement in pearl millet productivity in and environments can be obtained by topcrossing locally adapted landraces on suitable male-sterile lines. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification and characterization of new sources of cytoplasmic male sterility in rice

Search for male sterility-inducing cytoplasm in wild species of the genus Oryza was attempted with a view to diversify the base of the cytoplasmic genetic male sterility system currently used in the development of commercial rice hybrids. A total of 132 interspecific crosses were made involving accessions of four wild and two cultivated species, all belonging to the A genome. Wild accessions possessing sterility-inducing cytoplasms were identified following reciprocal and sterile F₂ backcross methods. Sterile segregants were pursued through substitution backcrosses to develop cytoplasmic male-sterile (CMS) lines. CMS lines were developed with the cytoplasm of either O. rufipogon (VNI) or O. nivara (DRW 21018, DRW 21001, DRW 21039, DRW 21030 and RPW 21111). Based on shape, staining, and abortive pattern of pollen and also on type of interaction with a set of restorers and maintainers for known cytoplasmic male steriles of WA source (V 20A), the newly-developed CMS lines were grouped into four classes. Of these, RPMS 1 and RPMS 2 showed gametophytic male sterility with a restorer reaction different from WA cytoplasmic male-sterile stocks.     

抗丝黑穗病、抗败育高粱A2细胞质雄性不育系A2Sx3197的选育

A₁Tx3197曾经是我国广泛应用的高粱细胞质雄性不育系,20世纪70年代末,由于高粱丝黑穗病病菌生理小种分化,该不育系以及用其配制的杂交种逐渐失去了对高粱丝黑穗病菌的抗性。同时该不育系小花败育日渐严重,制种产量极低,甚至造成绝收。为了改良A₁Tx3197的抗病性及抗败育性,本研究利用A₂保持系在A₁位点含有A₁育性恢复基因MS₁MS₁和在A₁细胞质背景下表现恢复的特点,以不育系A₁Tx3197为轮回亲本,以含有抗丝黑穗病、抗败育基因的BV₄为供体,通过杂交和多代回交,得到含有双抗基因的A₂类型细胞质雄性不育的保持系BSx3197(MS₁ms₁ms₂ms₂),在该材料自交的同时,用其对A₂细胞质雄性不育系进行细胞核代换,经过多代回交和自交,最终育成了抗丝黑穗病、抗败育的A₂细胞质雄性不育系A₂Sx3197和保持系BSx3197(MS₁MS₁ms₂ms₂)。结果表明,新选育的不育系A₂Sx3197在A₁和A₅细胞质背景下表现恢复,在A₂、A₃、A₄、A₆和9E细胞质背景下表现不育,丝黑穗平均发病率为0~0.8%,败育率为0~8.4%,抗丝黑穗病性、抗败育性明显优于被改良不育系,接近或达到抗原供体BV₄水平;而在抽穗期、株高、穗长、穗宽、千粒重、穗粒重、粒色、壳色、穗形、穗型等主要性状方面与A₁Tx3197差异不显著。     

Effect of wild Helianthus cytoplasms on agronomic and oil characteristics of cultivated sunflower (Helianthus annuus L.)

Sunflower (Helianthus annuus L.) productions reliance on a single source of cytoplasmic male sterility, PET1, derived from H. petiolaris Nutt., makes the crop genetically vulnerable. Twenty diverse cytoplasmic substitution lines from annual and perennial wild species were compared with the inbred line HA89 over four environments. Pairwise comparisons of alloplasmic male fertile (MF) with euplasmic MF lines suggested that cytoplasm of perennial H. angustifolius increased lodging while perennial cytoplasms of H. mollis, H. grosseserratus, and H. divaricatus reduced head size and consequently reduced yield and will need to be used with caution. Lines having annual species, cytoplasms had no effects on agronomic traits. Comparisons of CMS HA 89 with 10 CMS lines suggested yield‐reducing cytoplasmic effects of perennial H. maximiliani and annual H. annuus PI 413178 and PI 413024. Cytoplasmic effects on oil percentage and fatty acid composition were minimal and should not be of concern for sunflower breeders. In general, most cytoplasms of wild annual Helianthus species accommodate cultivated nuclear genes without drastic adverse interactions, and are potential sources of cytoplasmic diversity for sunflower breeding.     

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.