Published online 22 January 2007
Published in Crop Sci 47:188-192 (2007)
© 2007 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
CROP BREEDING & GENETICS
Genetic Analysis of Triticum compactum L. var. amplissifolium Zhuk. Producing Curved Grain
S. M. S. Tomara,*,
M. K. Menonb,
Vinoda,
M. Sivasamyb and
B. Singha
a Division of Genetics, Indian Agricultural Research Institute, New Delhi-10012, India
b IARI Regional Station, Wellington, The Nilgiris-643231, India
* Corresponding author (smstomar{at}yahoo.co.in)
 |
ABSTRACT
|
|---|
The hexaploid wheat species Triticum aestivum L. ssp compactum var. amplissifolium Zhuk. produces small plump but curved or boat shaped kernels with low thousand kernel weight. The grain number per unit spike length is high. The trait curved grain seems to be rare. The genetic analysis in F2 (T. aestivum cv. NI5439 x T. amplissifolium), BC1 (F1 x NI5439) and F3 generations revealed that the curved grain is governed by a single dominant gene. The gene symbol Cvg is proposed for this trait. The curved nature of the grain could serve as a useful morphological marker. The characters short spike and kernel color are also controlled by a single but independent gene. The number of grains per unit spike length and 1000 kernel weight are presumably governed by more than one gene and both the traits showed some association with the character short spike. The linkage analysis indicated that the character curved grain is linked with short spike length and the distance between these characters is 7.63 Kosambi unit.
Abbreviations: TKW, thousand kernel weight
|
INTRODUCTION
|
|---|
DURING investigations on morphological traits and seed characteristics in diploid, tetraploid and hexaploid wheats, the authors came across two strains of Triticum aestivum L. ssp compactum var. amplissifolium Zhuk. (2n = 6x = 42, genome AABBDD) having small, plump and curved or boat shaped grains with low thousand kernel weight. The curved shape of the grain may serve as a valuable morphological marker in wheat improvement. The botanical free threshing forms of T. compactum is regarded as a genetically more domesticated form than the hulled forms. A single dominant gene on chromosome 2 D differentiates T. aestivum ssp compactum from other hexaploid forms. T. aestivum ssp compactum has been characterized by the genetic formula QQCCSS (Swaminathan and Rao, 1961), having free-threshing, slender grains and compact spike. The variant amplissifolium of club wheat produces curved grains in high number per unit spike length. The curved grain appears to be a rare exception in the genus Triticum and the information on genetic control of this character seems to be lacking. The grains of commercially grown wheats are generally oval shaped, although variation in shape exists among different species. The diploid wheats are usually characterized by long, flat and thin grains pointed at both ends, while tetraploid wheats are generally characterized by larger, plumper, and less pointed grains with the exception of wild emmer which has thin, long, and pointed grains. However, tetraploid wheats T. carthlicum and T. turgidum produce short and plump grains. The grains of hexaploid wheats are relatively still shorter and plumper with the exception of T. macha and T. aestivum ssp spelta, which have longer grains, while T. aestivum ssp sphaerococcum is characterized by spherical grains. This article reports the inheritance of curved grain in T. amplissifolium and its association with spike length, number of grains per spike and thousand kernel weight. Information on genetics of red kernel color and the presence of genes for hybrid necrosis also is included.
|
MATERIALS AND METHODS
|
|---|
The materials used in the study comprised one strain of T. aestivum ssp compactum var. amplissifolium (hereafter referred to as T. amplissifolium) having red curved grains (Fig. 1
) with high grain number (
75) per spike and three T. aestivum testers for hybrid necrosis viz., C 306 (Ne1-carrier), Sonalika (Ne2-carrier) and NI 5439 (non-carrier = ne1ne1). All three testers produce normal shaped, amber, oval and plump grains (= kernels). The seeds of T. amplissifolium were received as WIR accession, most probably from the USSR during 1980 and maintained at the Division of Genetics, Indian Agricultural Research Institute, New Delhi. To test the curvature, a few spikelets from the top, bottom, and middle of spike, were removed before anthesis in amplissifolium. The boat shaped grain is curved at about 35 degrees, where one cheek shows more depression than the other. The curved nature of the kernel is true breeding. An accession of amplissifolium was crossed with all the three testers. To avoid any complication of hybrid lethality a non-carrier parent, NI 5439 was used in the crosses. The F1 hybrid (NI 5439 x T. amplissifolium), F2, BC1 (F1 x NI5439), and F3 generations were studied to determine the number and nature of gene(s) governing seed shape and its association with spike length, grain number per spike, and thousand kernel weight (TKW). The initial cross was made during the winter of 2001–02; the F1 was raised and BC1 seeds were obtained in the off-season summer nursery of 2002. The BC1–F1 and F2 generations were raised during winter season 2002–03 while F3 families were planted in the winter of 2003–04. All the material was raised under normal fertility conditions of the soil. The seeds were placed at 3 to 4 cm depth with a plant-to-plant distance of 10 cm in rows 30 cm apart. The observations were made on matured grains. The segregation patterns for each individual trait were analyzed by the 
2 test to determine the goodness of fit of the observed values with the expected values. Statistical analysis for detection of linkage was performed according to the procedure given by Mather (1951) and the Kosambi unit was computed according to the realistic function, which is commonly used as Kosambi's function (Kosambi, 1944). To test the significance between the means of curved and non-curved grains in the F2 generation, the paired t-test (Youden and Beale, 1934) was applied. The distribution of necrosis genes was also studied in the crosses involving amplissifolium, C 306, and Sonalika, and the genotype was determined on the basis of phenotype.
|
RESULTS AND DISCUSSION
|
|---|
The present study was performed to determine the inheritance of various morphological traits in amplissifolium and linkage relationship between curved seed and spike length. The results are presented in Tables 1
to 4.
View this table:
[in this window]
[in a new window]
|
Table 1. Mode of segregation for spike length, curved grain, seed coat colour, 1000 kernel weight, number of grains per main spike in F2 and BC1 generations.
|
|
View this table:
[in this window]
[in a new window]
|
Table 2. Mean difference in grain number per main spike and 1000 kernel weight in curved and non-curved F2 segregants.
|
|
Grain Shape
The F1 (NI 5439 x T. amplissifolium) produced short spikes containing curved, red grains. Out of 973 plants in the F2 generation, 713 plants produced curved grains while 260 plants produced non-curved grains. The observed frequency of plants producing curved and non-curved grains fit well into the ratio of 3:1 with a nonsignificant 2 value of 1.537. The data indicated that curved grain shape is controlled by a single dominant gene. The observed frequency of 136 curved and 134 non-curved grains in the BC1 generation fit well into the 1:1 ratio, confirming the F2 hypothesis that curved grain is indeed governed by a single dominant gene. Furthermore, a total number of 59 F3 families, each consisting of 30 to 45 plants, were categorized for kernel shape. Seventeen families were true breeding for non-curved grains, 16 families produced curved grains, and the remaining 26 families segregated for curved and non-curved grains. The observed frequency of F3 families fit the 1:2:1 ratio with a 2 value of 0.863, confirming the F2 hypothesis. Most hexaploid wheats produce normal, non-curved grains; curved grain seems to be a rare trait. The gene symbol Cvg is proposed for curved grain in T. amplissifolium.
Spike Length
Spike length in wheat is a complex trait controlled by several genes. The F1 plants produced a short (< 6 cm), compact spike (Fig. 2
) with a higher number of spikelets per unit of length, indicating that short compact spike is a dominant character over long spike. The F2 population segregated into 726 plants with a short spike and 247 plants with a long spike (Table 1). The observed frequency gave an excellent fit into the 3 short spikes: 1 long spike ratio. This confirmed the dominant nature of short spike length. The monogenic inheritance of spike length was further confirmed by analyzing spike length in the BC1 (F1 x NI 5439) and F3 generations. In the BC1 generation, 135 plants produced short spikes and the same number of plants had long spikes thus fitting perfectly into an expected ratio of 1:1 with zero 2 value. Fifty nine F3 families were scored for spike length, of which 16 families produced short spikes, 15 families had long spikes, and 28 families segregated into two classes and were assumed to be heterozygous (Table 3). The observed frequency of F3 families fit well into the ratio of 1 (true breeding for short spike): 2 (segregating): 1 (true breeding for long spike) confirming the monogenic inheritance. It has been reported that a single dominant gene C on chromosome 2D differentiates T. compactum (= T. amplissifolium) from other forms (Swaminathan and Rao, 1961). Four doses of the Q gene (squareheaded) in wheat is known to modify the spike to compactoid nature (Sears, 1954; Muramatsu, 1963). However, its relationship with grain shape has not been studied.
View larger version (136K):
[in this window]
[in a new window]
|
Fig. 2. Spikes of NI 5439(left); F1 between NI5439 and T.amplissifolium (middle) and T. amplissifolium (right).
|
|
Grain Color
Both T. amplissifolium and NI 5439 (r1 r2 r3) are contrasting parents producing red and amber kernel color, respectively. The F1 hybrid produced red kernels indicating dominance over amber color. The F2 segregants of red and amber kernel color fit well into the ratio of 3 red:1 amber indicating that the character red kernel in T. amplissifolium is governed by a single dominant gene. The monogenic inheritance was confirmed by the data recorded in BC1 generation. The F3 seed harvested from F2 individual plants raised from seeds with amber color produced only amber color in the F3 generation. The F3 generation raised from the F2 individuals having red kernel color produced either uniformly red kernel color or segregated into the 3 red: 1 amber ratio. Thus the kernels harvested from those supposedly heterozygous F2 plants gave 3:1 segregation with a high degree of probability (2 = 0.181).
Number of Grains per Main Spike
T. amplissifolium produced on average 75 grains per main spike with a range of 68 to 80 grains, while the number of grains in NI5439 ranged from 44 to 58 with an average of 50 grains per main spike. The grain number per spike in the F1 hybrid ranged from 63 to 78 with an average of 68 grains per main spike. The F1 data indicated that grain number per main spike might be partially dominant. The F2 plants were classified based on 
49 grains and 50 grains per main spike. Out of 973 F2 plants, 708 plants produced 50 grains, while 265 plants produced 49 grains per main spike. The observed frequencies of F2 plants fit a 3:1 ratio with 2 value of 2.592 at 5% level of significance. However, the data for the BC1 (F1 x NI5439) generation did not fit the expected ratio of 1:1 (nonsignificant 2 value = 10.0), indicating that the proposed hypothesis based on F2 data of one dominant gene controlling the production of the number of grains per main spike did not hold true. These results indicate that grain number per main spike is probably governed by more than one gene. The complex locus C may have a major effect on high grain number per main spike, although the genes for high grain number are likely to be dispersed throughout the genome and, therefore, interact in additive manner for high grain number. Therefore the mean grain number in curved and non-curved classes from the F2 generation were compared by the t-test. The table values of t5% and t1% were lower than the calculated value 3.46 and, therefore, the differences in grain number per main spike in the two categories were regarded as significant. These results indicate that the gene(s) governing grain number per main spike may be associated with the genes controlling short spike length and curvature in the grains; the higher grain number per unit spike length in T. amplissifolium is associated with the compactoid nature of the spike.
Thousand Kernel Weight
The short spike of T. amplissifolium produces more grains per unit of spike length, but the mean TKW is around 21 g with a range of 19 to 22 g. On the other hand, the mean TKW of NI 5439 is 46 g. The weight of the F1 kernels was 28.5 g per 1000. The data for TKW were available for 647 F2 plants of which the TKW of 363 plants was < 28 g, while the remaining 284 plants produced a TKW of > 28 g. The observed frequency of F2 plants did not fit into any mono or digenic model of Mendelian ratios. Therefore, the TKW of F2 plants producing curved and non-curved kernels were pooled into two classes, and the t-test was applied to determine if there were any significant differences in grain weight. The calculated t5% value was significantly higher (30.10) than the table value at 
degrees of freedom, indicating significant differences in TKW of curved and non-curved kernels (Table 2). Therefore, there is an association between curved grains and low TKW in T. amplissifolium. The TKW of F2 plants ranged from 18 g to 42 g indicating a skewed variation, with maximum frequency of plants producing 28 g of TKW. The analysis revealed that TKW is quantitatively inherited. Earlier studies have also shown that genetic differences in grain weight among the genotypes is controlled by several genes, which are dispersed in all homeologous groups. Also there are reports that chromosomes 2A, 3A, and 3B significantly decrease the TKW (Kalia and Joshi, 1985). The presence of genes affecting grain weight, have been shown on homeologous group IV and also on chromosomes 5B, 6A, and 6B (Halloran, 1976). Groos et al. (2003) detected three major QTLs on chromosome 2B, 5B, and 7A under varied environments. The present study indicates that this complex locus located in 2D may also reduce the TKW.
Linkage Studies
Linkages were studied between short spike and curved grain versus long spike and normal grains; and red curved grains versus normal amber grain based on the genetic analysis of 973 plants in the F2 generation. Significant 2 values were observed in both cases when the data were subjected to a test of significance. The linkage between the short spike and the curved grain was 7.58 ± 0.14 and the map distance in Kosambi units was 7.63 (Table 4). However, the curved grain shape had no association with kernel color. In a study of a cross between T. compactum x T. aestivum, Paladhi and Bhowal (1986) reported that elliptical ear shape was associated with dwarf stature and short ear head, while Khare et al. (2000) found a linkage between cleavate spike shape with plant height.
Study on Hybrid Necrosis
Hybrid necrosis is the premature gradual death of leaves and leaf sheath, resulting in lethality or semi-lethality of F1 hybrids. It is encountered in certain inter- and intraspecific crosses in wheat. Hybrid necrosis is a well known phenomenon caused by two complementary dominant genes Ne1 and Ne2 (Hermsen, 1963). However, the expression of necrosis in hybrids is variable and depends on a series of multiple alleles existing at these loci. The F1 hybrid plants of the crosses C 306 x T. amplissifolium and Sonalika x T. amplissifolium were apparently healthy and produced well formed seeds. Very weak lethal plants were observed in the F2 and F3 generations of the Sonalika cross, indicating that T. amplissifolium carried a very weak allele of the Ne1 gene. The F2 generation of C 306 x T. amplissifolium produced normal plants thereby eliminating the possibility of T. amplissifolium being a Ne2 carrier. Sarkissian et al. (1971) reported the occurrence of a weaker allele than Ne1w and designated it as Ne1wt which is in accordance with the observation of Hermsen (1963) who also observed similar weaker alleles in some wheat varieties. Weak and very weak alleles of Ne genes are often difficult to detect in F1 hybrids; however, the occurrence of such alleles can be detected in the F2 and subsequent generations. The results of the present study indicate that the strain of T. amplissifolium tested carries Ne1wt. Because of the occurrence of hybrid necrosis which might have influenced the seed shape in the F2 generation, we did not consider the F2 or F3 generations derived from this cross for the genetic analysis of curved grain.
|
CONCLUSIONS
|
|---|
The curved shape of the grain in Triticum aestivum ssp. compactum var. amplissifolium seems to be rare exception among the grains produced by Triticum species. Genetic analysis indicated that the curved grain is controlled by a single dominant gene. The characters number of grains per unit spike length and thousand kernel weight were presumably governed by more than one gene and both traits have some association with the character short spike, which is closely linked to curved grain. The trait curved grain may serve as a useful morphological marker in wheat research.
Received for publication January 27, 2006.
|
REFERENCES
|
|---|
- Groos, C., N. Robert, E. Bervas, and G. Charmet. 2003. Genetic analysis of grain protein-content, grain yield and thousand kernel weight in bread wheat. Theor. Appl. Genet. 106:1032–1040.[Web of Science][Medline]
- Halloran, G.M. 1976. Genetic analysis of hexaploid wheat Triticum aestivum using intervarietal chromosome substitution lines, Protein content and grain weight. Euphytica 25:65–71.[CrossRef]
- Hermsen, J.G.Th. 1963. Sources and distribution of the complementary genes for hybrid necrosis in wheat. Euphytica 12:147–160.
- Kalia, V.C., and B.C. Joshi. 1985. Location of genes on specific chromosomes for quantitative characters in wheat cultivar using intervarietal chromosome substitutions. Indian J. Genet. 45:152–158.
- Khare, D., A.N. Shrivastava, N.D. Raut, and A.S. Timori. 2000. Variation in ear head shape of bread wheat cultivar Lok-1. Seed Research 28:90–92.
- Kosambi, D.D. 1944. The estimation of map distances from recombination values. Ann. Eugen. (London) 12:172–175.
- Mather, K. 1951. The measurement of linkage in heredity. John Wiley & Sons, New York.
- Muramatsu, M. 1963. Dosage effect of the spelt gene q of hexaploid wheat. Genetics 48:469–482.[Free Full Text]
- Paladhi, M.M., and J.G. Bhowal. 1986. Association of ear shape with plant height and ear size in crosses of Triticum sphaerococcum and T. compactum with cultivars of T. aestivum. Indian J. agric. Sci. 56:157–160.
- Sarkissian, N.S., A.A. Mkrtchjian, and G.A. Babadzanjan. 1971. Habit and distribution of necrosis genes in wheat (Triticum aestivum). Biol. J. Armenia 24:19–24.
- Sears, E.R. 1954. The aneuploids of common wheat. Bull. 572. Missouri Agric. Exp. Stn. 572:58.
- Swaminathan, M.S., and M.V.P. Rao. 1961. Macro mutations and sub specific differentiation in Triticum. Wheat Inf. Serv. 13:9–11.
- Youden, W.J., and H.J. Beale. 1934. Contr. Boyce Thompson Inst. 6:437.
TOP
ABSTRACT
INTRODUCTION
