Cytoplasmic and cytogenetic relationships among tetraploid Triticum species

Summary The F₁ hybrids from crosses of 59 accessions of wild and cultivated Triticum types including amphidiploids T. boeoticum-Ae. squarrosa, T. timopheevi-Ae. squarrosa, T. timopheevi-T. monococcum, T. boeoticum (4n), T. macha, and T. Zhukovskyi with T. durum Sel. 56-1 and/or T. aestivum were examined for male sterility and chromosome pairing at metaphase I of meiosis in pollen mother cells. Those hybrids which produced male-sterile F₁'s were recurrently backrossed with pollen from T. durum or T. aestivum to study segregation for male sterility and/or to confirm cytoplasmic male sterility.All T. timopheevi and T. araraticum accessions and several T. dicoccoides types, including T. dicoccoides var. nudiglumis from the Turkey-Iran-Iraq area, had male sterility inducing cytoplasm. The chromosome pairing in the F₁ hybrids indicated that all tetraploid Triticum accessions with male sterility inducing cytoplasm had genome AAGG. T. dicoccoides Körn types from the Turkey-Iran-Iraq area had genomes AABB and did not have male sterility inducing cytoplasm. Therefore, T. dicoccoides Körn and the T. timopheevi complex differ from each other cytoplasmically and cytogenetically and occur sympatrically in the Turkey-Iran-Iraq area.Possibly, the cytoplasm of the emmers was not derived from the putative diploid progenitors, T. boeoticum, Ae. speltoides, or Ae. bicornis as indicated by their nucleo-cytoplasmic and cytogenetic relationships with the tetraploid Triticum species. The cytoplasmic differences among Ae. speltoides, T. araraticum and T. timopheevi are of a relatively smaller magnitude than the cytoplasmic differences among T. timopheevi, T. boeoticum, and the emmers. A complete analysis of nucleo-cytoplasmic relationships among Triticum and Aegilops species may indicate the cytoplasmic donor(s) to the two tetraploid Triticum species complexes.Authorized for publication 19 July, 1972 as Paper No 397 in the Journal Series of the North Dakota Agricultural Experiment Stations.     

Location of genes for high grain protein percentage and other quantitative traits in wild wheat Triticum turgidum var. dicoccoides

Summary The genetic control of grain protein percentage (GPP) in the wild tetraploid wheat, Triticum turgidum var. dicoccoides, was determined by crossing four accessions of this taxonomic variety with durum cultivar Inbar, and analyzing the parents, F₁ and F₂ populations. Reciprocal crosses indicated no cytoplasmic effect on GPP. The F₂ variation was continuous in all crosses, showing no transgressive segregation. However, crosses between different accessions of var. dicoccoides showed transgressive segregation indicating the presence of different genes for high GPP in these accessions. Grain protein percentage was mostly codominant with high GPP, showing either no dominance, or a weak dominance. Heritability coefficients (broad sense) ranged from 0.30 to 0.53. Correlation coefficients between GPP and yield components were usually significantly negative, with the exception of the number of spikelets per spike, and in some crosses, grain weight.The number and chromosomal location of genes coding for high GPP were determined by the association between GPP and 27 markers (23 morphological and 4 biochemical markers). For this purpose, the genetic control of these markers, their linkage groups and chromosomal location were studied. At least four loci for high GPP that segregated in the F₂ populations are suggested: one on chromosome arm 1AS, marked by the black glume gene (Bg); one on 1BS, marked by the HMW gliadin locus Gli-B1; one on group 5, marked by the genes for beaked glume (Bkg) and toothed palea (Tp); and one on group 7, marked by the kinky neck gene (Kn). The relationship between GPP and several yield components was studied in a similar manner. In general, loci of markers that correlated positively with high GPP were not correlated with a decrease in yield components. Moreover, several loci of var. dicoccoides were associated with an increase in yield components.The utilization of markers for chromosomal location of genes coding for quantitative traits is compared to the technique of aneuploid analysis, commonly used in wheat. The significance of the above findings for breeding is discussed.     

Genetics of morphological traits in wild wheat,Triticum turgidum var.dicoccoides

Summary The mode of inheritance, linkage groups, and chromosomal location of 23 morphological and 4 biochemical traits were characterized in the wild tetraploid emmer wheat,Triticum turgidum var.dicoccoides. These traits were described and their mode of inheritance was determined by their segregation in four F₂ populations derived from crosses between four var.dicoccoides accessions and a tetraploiddurum cultivar. Linkage groups among the genes encoding for these traits were determined or postulated, and their chromosomal location was deduced by linkage to previously located genes. The genetic control of the following traits was characterized and is first reported here: black keel; hairy leaf sheath; hairy auricles; hairy rachilla; hairy kernel brush; obtuse flag leaf; and curved neck/peduncle. The linkage data indicated that developmentally-related genes tended to occur in clusters.     

Increased grain protein content and its association with agronomic and end-use quality in two hard red spring wheat populations derived from Triticum turgidum L. var. dicoccoides

Suitability of wheat (Triticum aestivum L.) for many food products depends on its unique protein. Elevated grain protein content (GPC) and its quality influences the bread making properties of wheat. The objective of this study was to examine the association of elevated GPC with agronomic and end-use quality in two hard red spring wheat recombinant inbred (RI) populations derived from wild emmer (Triticum turgidum L. var. dicoccoides). The two hard red spring populations (ND683/Bergen and Glupro/Bergen) were developed using a single-seed-descent method. ND683 and ‘Glupro’ are high in GPC (180 g kg^-1), presumably due to the introgression of gene(s) from Triticum turgidum L. var. dicoccoides and ‘Bergen’ is low in GPC (145 g kg^-1). From each of the two populations 12 high- and 12 low-GPC RI lines (F_5:7) were selected for replicated testing at two North Dakota (ND) locations in 1995. In both populations, the high-GPC lines had significantly (p < 0.05) higher values compared to the low-GPC lines for mean GPC and water absorption. Mean grain yield of the high-GPC lines was not significantly different from the low-GPC lines in both populations. In the ND683/Bergen population, the high-GPC lines had significantly (p < 0.05) higher values than the low-GPC lines for mean plant height, days to heading, and flour extraction. GPC was significantly (p < 0.05)and negatively associated with test weight and also significantly (p < 0.01) and positively associated with water absorption in the Glupro/Bergen population. In these populations, results suggested that it may be possible to select lines that combine higher GPC and acceptable yield level, but later in maturity and taller in plant height. This revised version was published online in July 2006 with corrections to the Cover Date.     

Plant nitrogen distribution in wild tetraploid (Triticum turgidum dicoccoides) and hexaploid wheat (Triticum aestivum)

Summary Differences were found in total nitrogen uptake and its pattern of distribution in the main tiller amongst five lines of wild tetraploid wheat (Triticum turgidum dicoccoides) and between it and two hexaploid wheats (Triticum aestivum) under low (48 ppm) and higher (240 ppm) levels of soil nitrogen.Under the low soil nitrogen level the hexaploids had higher amounts of total nitrogen in the main tiller than the dicoccoides lines, but under the higher soil nitrogen level, three of the dicoccoides lines had significantly (P<0.01) higher, and the other two lines, similar amounts as the hexaploids. The total amount of grain nitrogen in the hexaploids was significantly (P<0.01) higher than the five dicoccoides under the low nitrogen soil level but under the higher level, two of the dicoccoides lines had similar amounts as one of the hexaploids (cv. Bencubbin) but significantly (P<0.01) lower than the other (cv. Argentine IX).The efficiency of nitrogen translocation to the grain was significantly (P<0.01) lower in a primitive, compared with four cereal forms of dicoccoides under both low and high levels of soil nitrogen. The cereal forms of dicoccoides, while similar in nitrogen translocation efficiency under low soil nitrogen as the lower translocation efficiency hexaploid (cv. Bencubbin), were significantly (P<0.01) and substantially lower than it under the higher soil nitrogen level.     

A new powdery mildew resistance gene: Introgression from wild emmer into common wheat and RFLP-based mapping

An Israeli accession (TTD140) of wild emmer, Triticum turgidum var. dicoccoides, was found resistant to several races of powdery mildew. Inoculation of the chromosome-arm substitution lines (CASLs) of TTD140, in the background of the Israeli common wheat cultivar ‘Bethlehem’ (BL), with five isolates of powdery mildew revealed that only the line carrying the short arm of chromosome 2B of wild emmer (CASL 2BS) exhibited complete resistance to four of the five isolates. To map and tag the powdery mildew resistance gene, 41 recombinant substitution lines, derived from a cross between BL and CASL 2BS, were used to construct a linkage map at the gene region. The map, which encompasses 69.5 cM of the distal region of chromosome arm 2BS, contains six RFLP markers, a morphological marker (glaucousness inhibitor, W1 ^I), and the powdery mildew resistance gene. Segregation ratios for resistance in F₂ of BL × CASL 2BS and in the recombinant lines, combined with the susceptability of F₁ progeny to all tested isolates, indicate that resistance is controlled by a single recessive allele. This alleleco-segregated with a polymorphic locus detected by the DNA marker Xwg516, 49.4 cM from the terminal marker Xcdo456. The new powdery mildew resistance gene was designated Pm26. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effects of homoeologous group 3 chromosomes on grain colour dependent seed dormancy and brittle rachis in tetraploid wheat

`Langdon' (LDN), a durum wheat (Triticum turgidum L. var. durum) cultivar, and a set of chromosome substitution lines of Langdon, where A or B genome chromosome were replaced with a homologous chromosome of wild emmer wheat, T. turgidum ssp. dicoccoides (DIC), were used to assess the effect of the specific chromosome on seed dormancy in tetraploid wheat. The LDN(DIC 3A) and LDN (DIC 313) lines showed significantly lower seed germination than Langdon. It appears that LDN(DIC 3A) and LDN(DIC 3B) have red grain whose allele were designated as R-A1b and R-B1b, respectively and the rachises of LDN(DIC 3A) and LDN(DIC 3B) were fragile. The alleles for brittle rachis were designated as Br ₂ for LDN(DIC 3A) and Br ₃ for LDN(DIC 3B). From the F₂ of the crosses, Langdon/LDN(DIC 3A) and Langdon/LDN(DIC 3B), Br ₂ was located approximately 44.2 cM from the R-A1b locus and Br ₃ approximately 47.0 cM from the R-B1b locus, respectively. Recombinant inbred chromosomal lines for 3A and 3B were used to assess (1) the linkage relationship between grain colour and fragile rachis, and (2) the effect of grain colour on germination. Estimated distance between R-B1b – Br ₂ was 39.6 cM. For the 3A population, germination percentage of both colour groups was 12.4% for the red grain group and 68.6% for the amber group, respectively. For the 3B population, germination percentage of the red group was 7.3% and that of the amber group was 82.1%. For both populations, differences were statistical significant by t-tests. We considered that seed dormancy of T. turgidum ssp. dicoccoides was dependent on grain colour. It raised the possibility that brittle rachis is due to a paralogous gene set on homoeologous group 3 chromosomes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Transfer of high kernel weight and high protein from wild tetraploid wheat (Triticum turgidum dicoccoides) to bread wheat (T. aestivum) using homologous and homoeologous recombination

Summary Wheat pentaploids were produced by hybridizing a high kernel weight (1000 grain wt=56 g), high protein (25.4%) line of wild tetraploid wheat (Triticum turgidum dicoccoides) as male parent, with the three hexaploids (T. aestivum) — normal Chinese Spring and its two homoeologous pairing mutants, ph _1b and ph ₂. The pentaploids were crossed as female parents to the two commercial hexaploid cultivars Warigal and Barkaee and 42-chromosome stable plants selected from the F₁ of the pentaploid x hexaploid crosses.Mean protein content of certain F₃ lines from all six pentaploid x hexaploid crosses was significantly higher than Chinese Spring and the respective commercial hexaploid parent (p<0.005) indicating high protein had been transferred from the tetraploid to the hexaploid level.Kernel weight amongst certain F₃ lines of the three pentaploids x Barkaee was significantly (p<0.0005) higher than either Chinese Spring or Barkaee, indicating the transfer also of high kernel weight from the tetraploid to the hexaploid level. However kernel weight was not significantly increased over Warigal in any F₃ lines of its crosses with the three pentaploids.High levels of homoeologous chromosome pairing in the ph-mutant pentaploids, plus evidence for significant modification of the composition of high-molecular weight (HMW) glutenin subunits of grain protein in certain F₃ derivatives of the ph-mutant pentaploid x hexaploid, crosses indicates that the ph-mutant-derived lines may possess novel (intergenome) genetic recombination, at least for high protein, and possibly kernel weight.     

Zingiberene-mediated resistance to the South American tomato pinworm derived from Lycopersicon hirsutum var. hirsutum

The Lycopersicon hirsutum var. hirsutum accession PI 127826 is recognized as a good source of resistance to arthropod pests due to the action of the allelochemical zimgiberene, a sesquiterpene present in its glandular trichomes. Five genotypes were selected from the F₂ generation of the interspecific cross Lycopersicon esculentum ‘TOM-556’ × Lycopersicon hirsutum var. hirsutum ‘PI 127826’, based on their low levels (BPX-368-clone#56) or high levels(BPX-368-clone#92, BPX-368-clone#105,BPX-368-clone#179, BPX-368-clone#250) of zingiberene. The five F₂ genotypes were tested for resistance to the South American tomato pinworm Tuta absolutaalong with accession L. esculentum ‘TOM-556’ (pinworm susceptible), and the accessions L. hirsutum var. hirsutum ‘PI 127826’ and L. pennellii ‘LA716’ (resistant). The F₂ clones selected for high foliar zingiberene levels showed lower scores for leaflet lesion type(LLT), percent leaflets attacked (PLA) and overall plant damage (OPD) than the low zingiberene genotypes. The results indicated that zingiberene mediates resistance to the South American pinworm, based on feeding and on ovipositing deterrence, in populations derived from the interspecific cross between Lycopersicon. esculentum and Lycopersicon hirsutum var. hirsutum. Indirect selection for high foliar zingiberene content is suggested as an efficient technique for breeding tomatoes for resistance to the South American tomato pinworm. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

The inheritance and chromosomal location of morphological traits in wild wheat, Triticum turgidum L. ssp. dicoccoides

The homoeologous groups of chromosomes carrying the genes for some morphological traits in wild wheat Triticum turgidum L. ssp. dicoccoides (T. dicoccoides) were determined, but not the actual chromosomes carrying them. The objectives of this study were to investigate the modes of inheritance, and determine the chromosomes carrying some morphological traits in wild emmer (2n = 28; AABB), the progenitor of most cultivated wheats. To investigate the inheritance of morphological traits, crosses were made between T. turgidum L. ssp. durum (T. durum cultivar Chartokhmi (IR10) and T. dicoccoides accessions TA1150 and TA1131. F₂ seeds from each cross were grown in the field and six qualitative characters were investigated. Purple coleoptile, purple auricle, purple culm, hairy auricle, hairy rachilla, and fragility of spike were controlled by single dominant genes. To determine the chromosomal locations, accession TA1131 was crossed with the complete set of LDN D-genome disomic substitution lines. Assessments of F₂ populations showed that chromosomes 7A, 6A, 7B, 5B, 5A and 3B carried genes for purple coleoptile, purple auricle, purple culm, hairy auricle, hairy rachilla and brittle rachis, respectively.     

Inheritance of foliar zingiberene contents and their relationship to trichome densities and whitefly resistance in tomatoes

The sesquiterpene zingiberene, present in leaf glandular trichomes, is reportedly responsible for the high level of arthropod resistance found in Lycopersicon hirsutum var. hirsutum. This paper reports on the inheritance of zingiberene contents and of the various types of glandular trichomes in the interspecific cross L. esculentum × Lycopersicon hirsutum var. hirsutum. Plants of L. esculentum ‘TOM-556’ (= P₁), L. hirsutum var. hirsutum ‘PI-127826’(= P₂), F₁ (P₁ × P₂) and F₂ (P₁ ×P₂) were evaluated for zingiberene contents and densitities of and glandular (types I, IV, VI and VII) trichomes. Broad sense heritabilities were high for all traits studied (0.678, 0.831, 0.996, 0.799 and 0.717 respectively for zingiberene and trichome types I, IV, VI, VII). There were significant positive genetic correlations between zingiberene contents and densities of trichomes types IV, VI and VII. Inheritance of zingiberenecontents can be explained mostly by the action of a single major locus, inwhich the allele from L. hirsutum that conditions high content is incompletely recessive over the allele from L. esculentum. Action of an incompleteley recessive allele in one major locus appears to be evident for densities of trichome types IV, VI and VII, but there is also evidence of the action of other epistatic loci for types IV and VI. F₂ genotypes selected for high zingiberene levels showed higher levels of resistance to the silverleaf whitefly Bemisia argentifolii than L. esculentum ‘TOM-556’, levels that were comparable those found in L. hirsutum var. hirsutum ‘PI-127826’ and other whitefly resistant accessions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hybrids of Bread Wheat (Triticum aestivum) with Thinopyrum scirpeum (4x) and Thinopyrum junceum (6x)

Hybrids were obtained by crossing Thinopyrum scirpeum (4x) and T. junceum (6x) onto Triticum aestivum cv, ‘Chinese Spring’. An average meiotic pairing of 24.44^I+ 5.07^II+ 0.14^IIIin the ‘Chinese Spring’×T. scirpeum hybrid (ABDE₁E²) is attributed to two similar genomes from T. scirpeum (E₁E₂E₃E₄). An average meiotic chromosome pairing in the other hybrid (ABDJ₁J₂E₃) was 31.70^I+ 3.80^II+ 0.90^III and is attributed to autosyndetic pairing between the three genomes of T. junceum.     

Pre-harvest sprouting in bread wheat (Triticum aestivum) as influenced by cytoplasmic male-sterility derived from T. Timopheevi

Summary An investigation into the inheritance of pre-harvest germination (sprouting) in male sterile wheat is described. Sprouting does not occur in material which is hand emasculated prior to anthesis, but is present in cytoplasmic male-sterile lines. Thus sprouting appears to be associated with the interaction between the T. timopheevi cytoplasm and nuclei from T. aestivum. Different T. aestivum nuclei in T. timopheevi cytoplasm produce different sprouting tendencies.     

Morphology,geography and infraspecific taxonomics of Triticum dicoccoides Körn. A retrospective of 80 years of research

Summary Research on the morphology, geography and infraspecific taxonomics of Triticum dicoccoides Körn. performed during the 80 years since its rediscovery by Aaronsohn is reviewed. T. dicoccoides is a vluable genetic resource for the improvement of cultivated wheat. Its intraspecific structure is, however, not known sufficiently. It is evident that T. dicoccoides is subdivided into two morphologically and geographically distinct forms. The intepretations of these forms by various authors are diverse. There is also no consensus concerning their geographical within the general range of T. dicoccoides. It is necessary to carry out a detailed morphological study in order to define their taxonomical rank and specify their ranges. It would be expedient to perform comparative genetic, biochemical and agronomic investigations of the two T. dicoccoides infraspecific types.     

Inheritance of shelf life and other quality traits of tomato fruit estimated from F<Subscript>1</Subscript>’s,F<Subscript>2</Subscript>’s and backcross generations derived from standard cultivar, <Emphasis Type="Italic">nor</Emphasis> homozygote and wild cherry tomato

A tomato cultivar with high quality fruit and a long shelf life is a main goal in tomato breeding and it would be achieved using wild germplasm. The objective of this work was to explore the inheritance for fruit quality traits, especially fruit shelf life, in three tomato crosses using a standard Argentinean cultivar (Ca, cv ‘Caimanta’), a ripening mutant (nor, homozygous for the nor gene) of Solanum lycopersicum, and a wild cherry type (Ce, LA1385 of S. lycopersicum var. cerasiforme). The wild parent had a shorter fruit shelf life than the mutant genotype but higher than Ca. When the Ce genotype was analyzed in hybrid combination, the F₁ (Ca×Ce) was similar to the wild genotype for shelf life whereas the F₁ (nor × Ce) had a longer shelf life. Both F₁ crosses and backcrosses to the cherry type genotype had significantly lower fruit weight than the cultivated genotypes but higher than the cherry type parent. In the F₂ analysis, it was found that the inheritance underlying quality traits is complex since non allelic interactions were detected. A significant additive genetic variance was found for fruit shelf life as well as for other fruit quality traits in each cross. The genetic parameters analyzed by mean values and variances in parental, F₁ and F₂ and backcross generations indicated that the cross between the normal ripening cultivar and LA1385 of S. lycopersicum var. cerasiforme offers the best possibility to obtain long shelf life tomato genotypes with good fruit quality.     

Interspecific hybridization in Gossypium L.: characterization of progenies with different ploidy‐confirmed multigenomic backgrounds

Cytological and molecular investigations were undertaken for parent and progeny derived from a trispecific line [2(Gossypium arboreum × G. anomalum) × G. hirsutum var. BWR], which was crossed with G. hirsutum var. JLH168. Cytomorphological analysis of the F₁ (G. arboreum × G. anomalum), its amphidiploid and progeny from trispecies hybrid showed distorted ploidy segregation with monovalents to hexavalents and high intergenomic (small A₂ and large B₁) allosynthetic chromosome pairing. Microsatellite analysis identified three fragments associated with G. arboreum and G. anomalum and six fragments associated with G. hirsutum in derivates of the trispecies line × G. hirsutum var. JLH168. Inter‐Retrotransposon Amplified Polymorphism (IRAP) analysis revealed fragments of G. arboreum and G. anomalum, only in F₁ and amphidiploid. Chromosomal association and microsatellite analysis of three progeny genotypes (i.e. haploid, hexaploid and tetraploid no. 1) confirmed that they share multigenomic background from the three cotton species (A₂, A_hD_h and B₁ genome). The interspecific hybrid cotton genotypes studied are likely to be useful for the introgression of genes from diploid species to commercial upland cultivars.     

Nearly Total Absence of Homoeologous Pairing in a Hybrid between Tetraploid Hordeum chilense and Triticum aestivum

A hybrid between an induced tetraploid of Hordeum chilense (2n = 28 = H^chH^chH^chH^ch) and Triticum aestivum var. ‘Chinese Spring’ (2n = 42 = AABBDD) has been produced to test gene effects of this wild barley on homoeologous pairing in wheat. Cytological investigations in metaphase I have shown that the hybrid, which is perennial like H. chilense but morphologically more similar to the wheat parent, possesses the expected genome composition H^chH^ch ABD and a stable euploid chromosome number of 2n = 35. Pairing among the homologous H. chilense chromosomes was almost complete. The level of non-homologous chromosome association proved to be lower than the range of pairing known from euhaploids of ‘Chinese Spring’.     

Expression of a Triticum turgidum var. dicoccoides source of Fusarium head blight resistance transferred to synthetic hexaploid wheat

Yield and quality reductions caused by Fusarium head blight (FHB) have spurred spring wheat (Triticum aestivum L.) breeders to identify and develop new sources of host plant resistance. Four wheat synthetic hexaploids (×Aegilotriticum sp.) were developed, each having a quantitative trait locus (QTL), Qfhs.ndsu‐3AS, providing FHB resistance from Triticum turgidum L. var. dicoccoides chromosome 3A. Synthetics were produced by hybridizing a ‘Langdon’‐T. dicoccoides‐ recombinant chromosome 3A substitution line (2n = 4x = 28, AABB with two accessions of T. tauschii (2n= 2x = 14, DD). Synthetics were inoculated and evaluated for FHB resistance in two separate greenhouse seasons. One synthetic, 01NDSWG‐5, exhibited FHB severity ratings of 36% and 32% in the separate seasons, compared with ratings of 9% and 30% for ‘Alsen’, a FHB‐resistant spring cultivar, and ratings of 70% and 96% for ‘McNeal’, a susceptible spring cultivar, respectively. Synthetic × Alsen backcross‐derived lines were produced to initiate combining different sources of FHB resistance.     

Further Studies on the Restoration of Fertility in Triticum durum×T. timopheevi Hybrids

Twenty one F₁ hybrids involving three Triticum durum cultivars and eleven forms of T. timopheevi were backcrossed to their respective durum parents. Backcross fertility (BC₁ grain set) of these sterile hybrids improved with the rise in temperature at the time of pollination. A mean temperature of less than 20 °C results in poor seed set while higher mean temperatures around 24 °C result in increased seed set. It is suggested that a large number of backcross seeds can be produced by pollinating these hybrids late in the season, i.e., after 20th of March in northern India.