水稻新质源(CMS-FA)雄性不育恢复基因的遗传研究

发掘水稻新型雄性不育细胞质源CMS-FA,育成系列优质米不育系和系列新质源恢复系,组配成强优势杂交稻组合的基础上研究新质源雄性不育恢复系的恢复基因遗传。采用新质源(CMS-FA)不育系金农1A与恢复系金恢3号杂交获得杂交F₁代种子,种植F₁代,收获自交F₂代种子。用F₁分别与不育系或保持系回交,获得(不育系//不育系/恢复系和不育系/恢复系//保持系)2个测交群体。同时种植P₁、P₂、F₁、F₂、B₁F₁和B₂F₁等群体,考察花粉染色率、套袋结实率和自然结实率,卡平方测验遗传分离适合度。结果表明,不育系与恢复系杂交F₁代正常可育,育性恢复(可育)基因为显性遗传。F₂代分离出可育︰不育适合3︰1,育性恢复(可育)基因为1对显性基因控制。B₁F₁和B₂F₁代2个测交群体的可育︰不育都适合1︰1分离规律,验证了F₂代育性恢复(可育)单基因的遗传模式。暂时确定新质源(CMS-FA)核质互作三系的基因型为不育系S(SS)、保持系F(SS)和恢复系S(FF)。     

Inheritance and mapping of a restorer gene for the rapeseed cytoplasmic male sterile line 681A

A novel cytoplasmic male sterility‐fertility restoration system has been developed in rapeseed (Brassica napus). The cytoplasmic male sterile line 681A was derived from a spontaneous male sterile mutant in a newly released double‐low rapeseed cultivar ‘Xiangyou 13′. The restorer line 714R was identified in the interspecific progeny from a B. napus×B. juncea‐cross. Genetic analysis showed that fertility restoration for 681A cytoplasmic male sterility was controlled by a single dominant nuclear gene which might originate from B. juncea. The RAPD marker S1039_‐520 was found to be linked to the restorer gene in F₂ progeny of 681A × 714R with a recombination frequency of 5.45%.     

大豆质核互作雄性不育系NJCMS3A双亲雄性育性基因的SSR标记

利用大豆质核互作雄性不育系NJMCS3A的质、核供体亲本N21566和N21249构建F₂和BC₁F₁育性分离群体进行雄性育性的遗传分析与基因定位。结果表明, F₁正反交可育,F₂和BC₁F₁的可育株与不育株分离比例经χ²测验分别符合3∶1和1∶1,表明NJCMS3A供体亲本雄性育性由一对基因控制,可育等位基因为显性。该基因可能是NJCMS3A的一个恢复基因。选用793对SSR引物对F₂和BC₁F₁群体分别进行育性基因定位,发现该育性基因位于O连锁群上,在Satt331和Satt477标记之间,与Satt331、CSSR133和Satt477标记距离的次序一致,分别为8.1~10.4 cM、11.4~16.4 cM、13.3~19.2 cM。     

Identification and Inheritance of Fertility Restorer Genes for 'tour' CMS in Rapeseed (Brassica napus L.)

Eighteen genotypes of Brassica napus were crossed to a cytoplasmic male sterile (CMS) line of B. napus BO 15 carrying B. tournefortii cytoplasm (‘tour’ cytoplasm). Fourteen genotypes were found to be stable maintainers of the ‘tour’ CMS. Of the remaining four genotypes, GSL-1 and ‘Asahi-natane’ were found to be heterozygous and ‘Mangun’ and ‘Yudal’ were homozygous for the restorer gene. Analysis of the F₁ and F₂ progenies of (CMS) BO 15 בMangun’ and (CMS) BO 15 בYudal’ showed that fertility restoration is controlled by a single dominant gene. The availability of a number of stable maintainer lines and the simple inheritance pattern of fertility restorer gene makes ‘tour’ CMS a useful system for hybrid seed production in rapeseed.     

Chromosomal location of fertility restoring genes for ‘wild abortive’ cytoplasmic male sterility using primary trisomics in rice

Summary Identification and location of fertility restoring genes facilitates their deployment in a hybrid breeding program involving cytoplasmic male sterility (CMS) system. The study aimed to locate fertility restorer genes of CMSWA system on specific chromosomes of rice using primary trisomics of IR36 (restorer), CMS (IR58025A) and maintainer (IR58025B) lines. Primary trisomic series (Triplo 1 to 12) was crossed as maternal parent with the maintainer line IR58025B. The selected trisomic and disomic F₁ plants were testcrossed as male parents with the CMS line IR58025A. Plants in testcross families derived from disomic F₁ plants (Group I crosses) were all diploid; however, in the testcross families derived from trisomic F₁ plants (Group II crosses), some trisomic plants were observed. Diploid plants in all testcross families were analyzed for pollen fertility using 1% IKI stain. All testeross families from Group I crosses segregated in the ratio of 2 fertile: 1 partially fertile+partially sterile: 1 sterile plants indicating that fertility restoration was controlled by two independent dominant genes: one of the genes was stronger than the other. Testcross families from Group II crosses segregated in 2 fertile: 1 partially fertile+ partially sterile: 1 sterile plants in crosses involving Triplo 1, 4, 5, 6, 8, 9, 11 and 12, but families involving triplo 7 and triplo 10 showed significantly higher X² values, indicating that the two fertility restorer genes were located on chromosome 7 and 10. Stronger restorer gene (Rf-WA-1) was located on chromosome 7 and weaker restorer gene (Rf-WA-2) was located on chromosome 10. These findings should facilitate tagging of these genes with molecular markers with the ultimate aim to practice marker-aided selection for fertility restoration ability.     

Development of cytoplasmic-genic male sterility in safflower

An interspecific cross was made between Carthamaus oxyacantha and the cultivated species C. tinctorius to develop a cytoplasmic‐genic male sterility (CMS) system in safflower. C. oxyacantha was the donor of sterile cytoplasm. The 3: 1 segregation pattern observed in BC₁F₂ suggested single gene control with dominance of male‐fertility over male‐sterility. The information obtained from crossing male sterile X male fertile plants in BC₁F₃ and BC₁F₄ generations showed statistically significant single gene (1: 1) segregation for male sterility vs. male fertility. The results demonstrated that C. tinctorius possesses a nuclear fertility restorer gene and that a single dominant allele restored fertility (Rf) in progeny carrying CMS cytoplasm of C. oxyacantha. Male sterility occurred with the homozygous recessive condition (rfrf) in a sterile C. oxyacantha cytoplasm background and not in the normal cytoplasm of C. tinctorius. The genetic background of different restorer lines of C. tinctorius having normal cytoplasm did not effect fertility restoration. The absence of male sterile plants in C. tinctorius populations ruled out the possibility of genetic male sterility. Normal meiosis in F₁ and BC₁F₂ ruled out a cytogenetic basis for the occurrence of male sterility.     

Genetic and cytological analysis of a new spontaneous male sterility in radish (<Emphasis Type="Italic">Raphanus sativus</Emphasis> L.)

A male sterile plant appeared in the radish breeding program at the Hubei Academy of Agricultural Sciences, Hubei, China. In its progeny, a two-type (half of plants male sterile, the other half male fertile) line 01GAB was established. An F₂ population of 260 plants from a cross of male-sterile 01GAB and a male fertile line 9802H segregated for male fertility in a 3:1 ratio indicating that fertility was restored by a single dominant gene, here designated RsMs. A PCR-based DNA marker specific to the male fertility Rfob gene in 9802H was absent in 01GAB. Linkage analysis placed the RsMs locus 10.7 cM away from the Rfo locus. In an F₂ population of hybrids between 01GAB and male fertile 9802B, a co-dominant DNA marker for the RSultr3.2A (a radish sulfate transporter gene) locus was linked to the RsMs locus at 1.5 cM suggesting that fertility restoration in 01GAB was located in the region with known male sterility restorers in radish. However, no maintainer for the 01GAB source of male sterility has been identified so far. Cytological observations have shown that the abnormalities in male sterile anthers first appeared in tapetum at the tetrad stage, followed by a hypertrophy of the tapetal cells at the vacuolate microspore period. These results suggest that male sterility in 01GAB is likely to be genetic in nature, or it may represent a new type of the cytoplasmic male sterility.     

Genetic linkage between male sterility and non‐spiny trait in safflower (Carthamus tinctorius L.)

Genetic male sterility (GMS) exists naturally in safflower (Carthamus tinctorius L.). In the existing safflower GMS lines, sterile and fertile plants are distinguishable at flowering. This causes delay in fertile plants rouging and reduction in hybrid purity. In this investigation, a cross between a spiny GMS parent 13‐137 and a spiny non‐GMS parent ‘A1’ was effected. One sib cross, SC‐67, producing non‐parental‐type non‐spiny sterile and spiny fertile plants in F₃ was advanced to F₉ through sib crossing between non‐spiny sterile and spiny fertile plants. Mendelian digenic segregation was not observed for non‐spiny trait and male sterility. The results revealed strong linkage between these traits. The linkage was confirmed in F₂ generations of crosses between a non‐spiny marker‐linked GMS line (MGMS) and five elite lines. Male sterility–linked non‐spiny trait could distinguish sterile and fertile plants at elongation stage. The MGMS would be useful in production of pure F₁ hybrid seed and development of elite populations.     

Cytogenetic analysis of cytoplasmic male sterility in wheat line KTP116A and molecular mapping of two thermo-sensitive restoration genes

The cytoplasmic male sterile (CMS) wheat (Triticum aestivum L.) line KTP116A developed at Northwest A&F University, Yangling, China, was sterile at temperatures below 18 °C and fertile at temperatures above 20 °C during Zadok’s growth stages 45–52. The possibility of a two-line system has a promising future for hybrid wheat production. The present study describes morphological differences in pollen abortion behavior at different temperatures, and the genetics of the thermo-sensitive restorer gene(s) in line KTP116A. Cytological observations showed that abnormalities in development of male sterile anthers first appeared at the bi-nucleate stage. Only a few pollen grains go through the second mitosis to produce two sperm cells; most of those became abnormal pollen grains and shell structures without protoplast, confirming that the conversion from sterility to fertility in the CMS line was accompanied by changes in morphology and cytology. A BC₁ population of 198 plants from a cross of male-sterile KTP116A and male fertile F₁ TP116B/WM5-5 was developed to study the genetic control of thermo-sensitive sterility. Chi squared tests on data from back-crossed populations revealed that two recessive genes, designated rfv ₁ ^sp and rfv ₂ , were responsible for sterility of line KTP116A. Sixteen of 712 SSR markers were polymorphic between the parents and bulks. Four SSR markers, viz. Xgwm11, Xgwm18, Xgwm413 and Xbarc137, were linked to thermo-sensitive gene rfv ₁ ^sp on chromosome 1BS of T. spelta, and another four markers were linked to rfv ₂ located on chromosome 2A. This thermo-sensitive male sterile line can be used for production of experimental hybrids in order to test levels of heterosis.     

Analysis of genic male sterility in Brassica oleracea

Summary The male sterility system MS-1 of Brassica oleracea was studied in order to elucidate if nucleo-cytoplasmic interactions determine this system. Crosses of male sterile MS-1 genotypes with heterozygous MS-5 genotypes gave fully fertile F₁ progenies. Selfing of seven F₁ plants resulted in five F₂ populations showing a 9:7 segregation ratio and two a 3:1 ratio for fertile and male sterile plants. Two F₂ progenies deviated from the expected 9:7 or 3:1 segregation ratios for fertile and male sterile plants. Thermosensitivity and distortion of the meiosis are suggested as the causal factors underlying the deviation of the segregation ratios. It was concluded that nuclear factors determine the male sterility in the MS-1 system, because the presence of a nucleocytoplasmic interaction in this system should have given only a 3:1 segregation ratio for fertile and male sterile plants in the F₂ generation.     

Investigation of possible associations between partial fertility restoration and agronomic traits in Triticum aestivum L.

Summary Many conventional hard red spring wheat (Triticum aestivum L. em Thell) lines, including several North Dakota cultivars, carry a gene (or genes) which restore partial male fertility to male sterile plants with Triticum timopheevi Zhuk. cytoplasm. Since this gene has no fertility restoration function in T. aestivum cytoplasm, the postulation can be made that it is being retained in conventional lines because of pleiotropic effects, favorable linkages or chance. The research reported in this paper examined these possibilities. Forty F₆ lines, derived from a single F₂ plant which was heterozygous for a gene (or genes) for partial fertility restoration, were evaluated for two years in a yield trial planted at Fargo, North Dakota. The 40 lines were testcrossed to a male sterile line having T. timopheevi cytoplasm, and the mean seed set of testcrosses was used as a measure of a line's fertility restoration potential. Twenty-seven lines had the gene for partial fertility, and 13 lines apparently lacked this gene. The 40 lines differed for heading date, anther extrusion, plant height, grain yield, 200-kernel weight, test weight, and grain protein percentage. However, comparisons of lines having the restorer gene with those lacking the gene did not provide any obvious explanation for the retention of the partial fertility restorer gene in the breeding stocks of the North Dakota conventional hard red spring wheat breeding program. The possibility that the restorer gene was linked with genes for resistance to stem rust or leaf rust also was evaluated by testing lines for their reaction to several races of rust. No conclusive association was found.Contribution from the Agric. Exp. Sta., North Dakota State University, Fargo, ND 58105, Journal Article no.     

Chloroplast-DNA variation in the wild and cultivated olives (Olea europaea L.) of Morocco

The male sterile plants that segregated in a BC₅F₂ of `C. sericeus × C. cajan var. TT-5' population were maintained by sib mating. The male sterile plants were crossed with ICPL-85012.Approximately 50% of the F₁ plants were sterile. F₂ plants derived from the fertile F₁ plants did not segregate for male sterility. The reciprocal hybrid i.e. ICPL-85012 × Fertile derivatives from C. sericeus × TT-5, did not express male sterility. However, among the 12 F₂ plant to row progenies, two segregated 25% male sterile plants and remaining 10 did not segregate. The segregation pattern in subsequent progenies revealed that the sterility was under control of a single recessive allele. Studies on the backcross and their BC₁F₂ and BC₁F₃progenies revealed another sterility gene which was found to be dominant in inheritance. This paper shows that what was thought to be cytoplasmic male sterility from C. sericeus cytoplasm is actually a single dominant gene possibly acting in concert with a single recessive gene to mimic cytoplasmic male sterility. This revised version was published online in July 2006 with corrections to the Cover Date.     

小麦花粉致死基因Ki的SSR标记分析

小麦雄性不育主要是通过花粉的败育表现,其不育材料对小麦杂种优势的利用研究具有重要意义和价值,国外研究表明,某些特定普通小麦品种间杂交F₁表现的花粉部分不育现象,受控于核基因组花粉致死基因Ki,为了筛选小麦花粉致死基因Ki的连锁标记,利用现代分子生物学技术通过定位该基因,克隆出花粉致死基因连锁标记片段,为小麦雄性不育种质材料的转育提供有效的选择标记。对小麦花粉致死基因Ki进行了分子标记定位,以‘中国春’和澳大利亚春小麦品种的BC₁F₁代作为定位群体,利用分离群体分组分析法(BSA)对位于小麦6B染色体上85对SSR引物进行多态性筛选,具有多态性的引物再通过BC₁F₁定位群体进行验证,从中筛选出与目的基因连锁的2个SSR标记Xgwm626和Xgpw4138。运用Mapmaker 3.0软件进行连锁分析。结果表明,Xgwm626和Xgpw4138与Ki基因的遗传距离分别为9.2 cM和6.9 cM,且2个SSR标记位于目的基因两侧,并将Ki定位于小麦6BL染色体上。研究结果为Ki基因的分子标记辅助选择和进一步精细定位奠定了基础。     

Genetics of fertility restoration in A2-based cytoplasmic genetic male sterility system in pigeonpea (Cajanus cajan)

The three short duration cytoplasmic genetic male sterility (CGMS) hybrids developed using A₂ (Cajanus scarabeoides) cytoplasm-based male sterile lines (CORG 990047A, CORG 990052A and CORG 7A) and the restorer inbred AK 261322 and their segregating populations (F₂ and BC₁F₁) were subjected to the study of inheritance of fertility restoration in pigeonpea. The fertility restoration was studied based on three different criteria, namely, anther colour, pollen grain fertility and pollen grain morphology and staining. The F₂ and BC₁F₁ populations of the three crosses, namely, CORG 990047A × AK 261322, CORG 990052A × AK 261322 and CORG 7A × AK 261322, segregated in the ratio of 3:1 and 1:1, for anther colour (yellow:pale yellow), pollen grain fertility (fertile:sterile) and for pollen grain morphology and staining. The above study confirmed that the trait fertility restoration was controlled by single dominant gene. This finding can be utilized for the identification of potential restorers, which can be further used in the development of CGMS-based hybrids in pigeonpea.     

Evaluation of three sources of pollen fertility restoration genes and natural outcrossing of cytoplasmic male-sterile wheat

Summary Fertility restoration genes in Triticum aestivum L. in Texas Restorer Composite (TRC), D6301, and four CIMMYT restorer lines were studied, and selection was made for higher fertility in TRC. Mean-while, outcrossing percentages of seed set for 27 spring habit cytoplasmic male sterile (cms) varieties were evaluated for 3 to 5 years at Davis. The winter-habit TRC material did not restore reasonably good fertility, and the response to selection for higher fertility seemed to be slow. This poor fertility could be partly due to its late winter growth habit causing flowering at a period of high temperature and low humidity at Davis. The highest F₁ fertility was 46.6% in the cross cms Ramona x TRC-6, and its F₂ segregated into the ratio of 15 fertile to 1 sterile, with fertility ranging from 3.2 to 100%. Suggested for its improvement was intensive selection in the original TRC material and in the segre-gating F₂ population, followed by intercrossing. D6301 has 2 fertility restoration genes with different strengths which restore fertility up to 45.2% when both genes are heterozygous. D6301 is quite likely heterogeneous for these genes. Four CIMMYT restorer lines, D7464, D7465, D7466, and D7467, had satisfactory F₁ fertility restoration after crossing with cms Ramona 50. In 1975, the fertilities of the F₁'s ranged from 71 to 85% and were over 90% in 1976. The F₂ population of the cross cms Ramona 50 × D7464 segregated into a ratio of 3 fertile to 1 sterile, indicating that D7464 has a single dominant gene for fertility restoration. The F₂'s of crosses cms Ramona 50 × D7465, cms Ramona 50 × D7466, and cms Ramona 50 × D7467 gave a ratio of 15 fertile to 1 sterile, indicating that two gene pairs in these three lines were responsible for the fertility restoration. The best of this group was D7467 which restored fertility fully after being crossed with cms Ramona 50 (T. timopheevi cytoplasm).The early-flowering cms male-sterile varieties had higher outcrossing rates (16 to 38%) than late varieties (6 to 30%) over a 5-year period. This was due to hot and dry weather during the late growing season as well as to the rarity of windborne pollen. In 1970, 1971, 1972, and 1976, the variation among varieties was rather great. Some of them such as Roque 66 and Bajio 67, had consistently high outcrossing rates. This outcrossing ability seemed to be inherited and probably associated with the open-flowering characteristics of each variety.     

A unique introgression from Moricandia arvensis confers male fertility upon two different cytoplasmic male-sterile lines of Brassica juncea

A Brassica juncea line carrying an introgression from Moricandia arvensis restored male fertility to two cytoplasmic male‐sterile (CMS) B. juncea lines carrying either M. arvensis or Diplotaxis catholica cytoplasm. Genetics of fertility restoration was studied in the F₁, F₂, F₃ and backcross generations of the cross between CMS and fertility‐restorer lines. No male‐sterile plants were found in F1‐F₃ generations of the cross between CMS [M. arvensis] B. juncea and the restorer. However, a 1: 1 segregation for male sterility and fertility was observed when the F1 was pollinated with non‐restorer pollen from a euplasmic line. These results clearly show that restoration is mono‐genic and gametophytic. In CMS lines carrying D. catholica cytoplasm, the restorer conferred male fertility to the F1 and showed 3: 1 and 1: 1 segregations for male fertility and sterility in F₂ and BC1 generations, respectively, indicating a monogenic, sporophytic mode of fertility restoration. The results were also supported by pollen stainability in the F1 which was about 65% in M. arvensis‐based CMS and >90% in D. catholica‐based CMS. The above results are discussed in the light of previous molecular studies which showed association between CMS and atpA in both systems.     

YM型小麦温敏雄性不育系不育基因的QTL定位

YM型小麦温敏雄性不育系的不育基因被定位在1Bs染色体片段上, 但已发现的相邻分子标记与该基因的遗传距离较大, 达10 cM以上。为寻找与该基因连锁更紧密的分子标记, 以YM型温敏雄性不育系ATM3314与恢复系中国春杂交的F₂代200株为作图群体, 从1Bs的22个SSR引物中筛选出5个在亲本和F₂代中分离的SSR引物, 构建了1个包含5个标记的1Bs局部遗传连锁图谱。结合F₂代个体的育性调查, 采用复合区间作图法在YM型温敏雄性不育系的1Bs染色体上检测到不育基因的1个主效QTLrfv1-1和1个微效QTLrfv1-2。rfv1-1位于SSR标记Xgwm18和Xwmc406之间, 与两标记的遗传距离分别为6.0 cM和4.6 cM, LOD值为8.80, 加性效应23.87, 显性效应10.44, 可解释表型变异的23.91%; rfv1-2位于Xwmc406和Xbarc8之间, 与两标记的遗传距离分别为4.0 cM和3.4 cM, LOD值为3.10, 加性效应17.59, 显性效应5.99, 可解释表型变异的7.78%。本研究初步定位了YM型小麦温敏雄性不育系1Bs染色体片段上不育基因的QTL, 为进一步准确定位该基因奠定了基础。     

Digenic nature of male sterility in pepper (Capsicum annuum L.)

Summary A cross was made between two nearly isogenic lines differing for male sterility genes, viz. ms₁ms₁Ms₂Ms₂ s Ms₁Ms₁Ms₂ms₂. F₁ plants yielded F₂ populations which segregated either in 3:1 or 9:7 ratios of fertile vs male sterile individuals. Test crosses between male sterile and male fertile sibs in the 9:7 segregating populations provided a few lines in which most of the progenies were male sterile. A 3:1 ratio model of male steriles vs fertiles is suggested and the value of the system is discussed.Contribution A.R.O. Agricultural Research Organization, The Volcani Center, Bet Dagan 50 250, Israel No. 3703-E, 1992 series.     

Characterization of a male sterile mutant from progeny of a transgenic plant containing a leaf senescence-inhibition gene in wheat

A male sterile plant of wheat (Triticum aestivum L.) segregated from progenies of a transgenic family containing the leaf senescence-inhibition gene P _SAG12 -IPT in the genetic background of ??Xinong 1376??, a well adapted winter wheat cultivar. The male sterile plant (named TR1376A) showed no phenotypic changes, except for florets and male organs, compared to its male fertile sibling plants (named TR1376B). The glumes and florets of male sterile TR1376A plants widely opened whereas those of the fertile counterpart TR1376B were closed or opened only briefly at flowing. Anthers of TR1376A were slender and indehiscent, and failed to release pollen. Compared to TR1376B, TR1376A anthers contained greatly reduced amounts of pollen, which was inviable or weakly viable. Ultra-structure studies indicated that cells in the endothecium and middle layers of the anther wall were dissolved or poorly developed in the sterile anthers of TR1376A. Molecular studies showed that the male sterility of TR1376A was caused by a sequence deletion or mutation that occurred in the promoter region of the transgene. F₁ hybrids of TR1376A and TR1376B gave 1:1 segregation of male fertility to sterility, indicating that the male sterility of TR1376A was heritable and controlled by a single dominant gene (named Ms1376). To date, only a few dominant nuclear male sterility genes have been characterized and one of them (Ms2) has been successfully used to improve wheat cultivars through recurrent breeding strategies. The discovery of the Ms1376 gene provides another dominant male sterile source for establishing recurrent breeding systems in wheat.     

SSR and SCAR markers linked to the fertility-restoring gene for a D2-type cytoplasmic male-sterile line in wheat

‘Yi 4060’ is an elite restorer line of a non‐photoperiod‐sensitive D²‐type cytoplasmic male‐sterile (CMS) line of wheat. Random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers were employed to map one major fertility‐restoring gene (D²Rf₁) in ‘Yi 4060′. The sterile and fertile DNA pools were established from individuals in BC₆, based on bulked segregant analysis. One RAPD marker E09, linked to D²Rf₁, was converted to a SCAR marker and designated as E09‐SCAR₈₆₅. The genetic distance between E09‐SCAR₈₆₅ and D²Rf₁ is 9.5 cM. Two SSR markers, Xgwm11 and Xgwm18, were also linked to a D²Rf₁ and co‐segregated with E09‐SCAR₈₆₅. The three molecular markers are useful in marker‐assisted breeding of the elite restorer lines for D² ‐type CMS lines in wheat.