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The F1 hybrids
between Sonalika, a Ne2 Ch2m-carrier
(Kochumadhavan et al 1984), and three T. dicoccum varieties,
viz., HW 1016, HW 1017 and Sangli 2-2, exhibited only chlorosis and
it is likely that chlorosis may obscure the expression of necrosis.
Consequently, this type of epistatic gene action caused difficulty in
identifying the genotype of these varieties of T. dicoccum as
to have Ne1 or ne1. When both the complementary gene
systems for hybrid necrosis and hybrid chlorosis operate in
F1 hybrids, the phenotypic expression of one hybrid
weakness over the other or the simultaneous occurrence of both kinds
of hybrid weakness depends on the relative strength of alleles
existing at Ne- and Ch-loci. Therefore, the genes with
respect to necrosis in the varieties, HW 1016, HW 1017 and Sangli
2-2, could not be determined for want of a single-gene tester
(ne2Ne2ch1ch2) for necrosis or a
two-gene tester (ne1Ne2Ch1ch2) for
necrosis and chlorosis with the authors. While the single-gene tester
is extremely rare, the two-gene tester has not yet been established
in polypIoid wheats.
Varieties of T. dicoccum, like other tetraploid species of
wheat, are either Ne1-carriers or non-carriers (Nishikawa
1967; Tsunewaki 1969; Tomar et al unpublished). Ne2-carriers
have not yet been reported in 4x wheats despite the location of this
gene in B genome. Therefore, the Ne2 gene, found
restricted to the western 6x wheats is presumed to have originated by
mutation at the hexaploid level in Europe (Tsunewaki and Kihara
1962).
Hermsen (1966) reported that the Indian emmer wheat Khapli carried
the Ch1 gene. The present study reveals a high
prevalence of Ch1-carriers in T. dicoccum varieties and
this further corroborates the observation of Kochumadhavan et al
(1984) that the gene Ch1 widely occur amongst the
Indian varieties of T. dicoccum.
Acknowledgment
The authors are grateful to Dr. Munshi Singh, Head, Division of
Genetics and Dr. A. M. Michael, Director, IARI, New Delhi for their
keen interest in the study.
References
Hermsen JGTh (1966) Hybrid necrosis and red hybrid chlorosis. Proc:
2nd Int Genet Symp Lund 1963, Hereditas Suppl 2: 439-452.
Hermsen JGTh and Waninge J (1972) Attempts to localize the gene
Ch1 for hybrid chlorosis in wheat. Euphytica 21: 204-208.
Kochumadhavan M, Tomar SMS and Nambisan PNN (1984) Hybrid necrosis
and hybrid chlorosis in Indian varieties of Triticum dicoccum
Schubl. Euphytica 33: 1-6.
Nishikawa K (1967) Identification and distribution of necrosis and
chlorosis genes in tetraploid wheat. Seiken Ziho 19: 37-42.
Tsunewaki K (1960) Monosomic and conventional analysis in common
wheat. III. Lethality. Jpn J Genet 35: 71-75.
Tsunewaki K (1969) Origin and phylogenetic differentiation of common
wheat revealed by comparative gene analysis. Proc III Int Wheat Genet
Symp 71-85.
Tsunewaki K and Kihara H (1961) F1 monosomic analysis of
Triticum macha. Wheat Inf Serv 12: 1-3.
Tsunewaki K and Kihara H (1962) Comparative gene analysis of common
wheat and its ancestral species I. Necrosis. Jap J Genet 37:
474-484.
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