Determination of the chromosome and its arm carrying the Ne₁-locus of Triticum aestivum L., Chinese Spring and the Ne₁-expressivity

A. C. ZEVEN

Institute of Plant Breeding (I.v.P.), Wageningen, The Netherlands

Summary

The Ne₁^w-locus of Chinese Spring was located on chromosome 5B^L. It was found that the expressivity of three Ne₁^w-alleles of Chinese Spring is similar to one Ne₁^m-allele.

Introduction

The complementary genes Ne₁ and Ne₂ cause hybrid necrosis. The degree of necrosis depends on the nature and the dosage of the Ne-alleles and on the environment (HERMSEN 1962, 1963b). Three alleles of Ne₁ (Ne₁^w, Ne₁^m, and Ne₁^s) and five alleles of Ne₂ (Ne₂^w, Ne₂^mw, Ne₂^m, Ne₂^ms and Ne₂^s) have been distinguished (HERMSEN 1963b).

Wheat varieties can be classified according to their Ne-genotype. Up to now about 597 Ne₁-, 654 Ne₂- and 1262 non-carriers have been identified (ZEVEN 1971).

The Ne₁^m-locus of Prelude is on 5B and the Ne₂^s-locus of Kharkov on 2B (TSUNEWAKI 1960). It is interesting to note that both loci are on chromosomes of the B genome.

Chinese Spring carries an extremely weak Ne₁-allele (HERMSEN 1964a). By using di-iso-5B^L and di-telo-5B^L of Chinese Spring it is possible to determine if chromosome 5B or rather its long arm also carries the Ne₁^w-allele.

Materials and method

Chinese Spring, and its di-iso-5B^L and di-telo-5B^L created by Dr. E. R. SEARS, Columbia, U.S.A., were received from Dr. R. RILEY, Cambridge, U.K.

These three lines and the F₁ (di-iso-5B^L x di-telo-5B^L) were crossed with Touzelle a gros grains (ne₁ne₁Ne₂^sNe₂^s), and the number of green and necrotic plants counted in the F₁'s and F₂'s.

Results

Chinese Spring x Touzelle :

F₁ (Ne₁^wne₁Ne₂^sne₂) remains green, while only the F₂ plants with Ne₁^wNe₁^w Ne₂^sNe₂^s are necrotic. Plants which the have genotypes Ne₁^wNe₁^wNe₂^sne₂, Ne₁^wne₁Ne₂^sNe₂^s and Ne₁^wne₁Ne₂^sne₂ do not show necrosis symptoms.

Chinese Spring di-iso-5B^L x Touzelle :

The F₁ plants remained green. In one F₂ 24 green and 5 necrotic plants and in a second F₂ 27 green and 6 necrotic plants were counted. This is in total 51 green : 11 necrotic plants.

Chinese Spring (di-iso-5B^L x di-telo-5B^L) F₁ x Touzelle:

Only two F₁'s were grown. One consisted of 6 green and one necrotic plants and the other of 6 green plants only, which makes a total of 12 green : 1 necrotic plants.

Discussion

Localisation : If a chromosome other than 5B carries the Ne₁^w-locus of Chinese Spring the F₂ would have segregated into 15 green : 1 necrotic. In the F₂ (Chinese Spring diiso-5B^L x Touzelle) our results deviate significantly from a 15 : 1 ratio (chi²=13.80, P< 0.0001) so Ne₁^w-locus is not a chromosome other than 5B.

As necrosis was observed, the Ne₁^w-locus was present and hence must be on 5B. This is interesting because Ne₁^m of Prelude also is on 5B (see above). Furthermore as in the crosses only the long arm of 5B is involved the Ne₁^w-locus of Chinese Spring must be on this arm.

Dosage effect :

The expected Ne-genotypes and their necrotic experssion in the F₂ (Chinese Spring di-iso-5B^L x Touzelle) are shown in Table 1. The frequencies of these genotypes are not given because they are hard to predict.

The genotypes Ne₁^wNe₁^wNe₁^wNe₁^wNe₂^sne₂ is also given as necrotic, because of the observation of one necrotic plant in the F₁ (di-iso-5B^L x di-telo-5B^L) x Touzelle. This necrotic plant must have had the genotype Ne₁^wNe₁^wNe₁^wNe₂^sne₂ as plants with Ne₁^wNe₁^wNe₂^sne₂ are green. In crosses of varieties with stronger Ne₁-alleles (Ne₁^w of some Italian varieties, Ne₁^m and Ne₁^s) with Ne₂^s-carrying varieties the F₁'s (Ne₁ne₁Ne₂^sne₂) are necrotic. The degree of necrosis observed in the necrotic plants of the F₂ (Chinese Spring di-iso-5B^L x Touzelle) (genotype Ne₁^wNe₁^wNe₁^wNe₁^wNe₂^sne₂) is similar to that of an Ne₁^mne₁Ne₂^sne₂-necrotic plants. This would suggest that the expressivity of four Ne₁^w-alleles of Chinese Spring is about equal to that of one Ne₁^m-allele, while the expressivity of two Chinese Spring-alleles is less than one of an Ne₁^w-allele of an Italian variety.

Acknowledgements

I am indebted to Dr. R. RILEY for providing me with seeds of Chinese Spring and its di-iso-5B^L and di-telo-5B^L and to Dr. J. G. Th. HERMSEN for advice.

Literature Cited

HERMSEN, J. G. Th. 1962. Bastaard-necrose by tarwe. Versl. Landb.k. Onderzoek no. 68. 5. Wageningen. 129 pp.

HERMSEN, J. G. Th. 1963a. Hybrid necrosis as a problem for the wheat breeder. Euphytica 12: 1-16.

HERMSEN, J. G. Th. 1963b. Sources and distribution of the complementary genes for hybrid necrosis in wheat. Euphytica 12: 147-160.

TSUNEWAKI, K. 1960. Monosomic and conventional gene analysis in common wheat III. Lethality. Japan. J. Genetics 35: 71-75.

ZEVEN, A. C. 1971. Fifth supplementary list of wheat varieties classified according to their genotype for hybrid necrosis and geographical distribution of Ne-genes. Euphytica 20: 239-254.

(Received January 5, 1971)