ЭлБиб

CHAPTER 6.

Hybridisation of Immune and Susceptible Varieties.

In this chapter a critical sketch is given of investigations in hybridi

sation of immune and susceptible varieties {works, of Farrer, Biffen,

Nilsson-Ehle, Orton, Heribert NilsSon, Rasmuson, E. Fischer, Salmon).

The author shares the views of N i l s s o n - E h l e on genetical

complicacy of such characters as immunity, and susceptibility and believes

that the simple numeric relations in segregation by crossing of' immune and

susceptible varieties as in В i f f e n ’s experiments (3 : 1, 1 : 2 : 1 ) are

rather an exception than a rule. Especially, the simple relations in Fa of

hybrids are improbable in crossings of different species, where often a great

number of flowers of Fj and Fa arc sterile.

The. author has made many icrossings of «Persian Wheat» absolutely

immune to mildew

(Erysiphc graminis)

, with different species and varieties

of wheat susceptible or immune, but in a lesser degree, to this, fungus,as

well as other crossings of other varieties of wheat, immune and susceptible

to mildew and yellow rust

(Puccinia glumarum).

In the first crossings,,

immunity of «Persian Wheat» proved to be always dominant (in 13 different

combinations, the list, of which is given on page 194).

The process of segregation in F

proved to be rather complicated1).

E. g. in the crossing of «Persian Wheat» with

T. turgidum

var.

lusitanicum

Kcke.N? 3326 from the whole number of 197 plants in F»,.there were:

112plants, absolutely immune (0)

» very resista’nt (1)

» resistant (2)

» feebly resistant (3)

. ,

susceptible like

T. turgidum

(4). 2)

Liike N i l s s o n - E h l e and F a r r e r the author observed in Fa

of hybrids the appearance of plants more susceptible than their parents.

So for instance in the crossing of «Persian .Wheat» with

T. dicoccum

var.

pienurum

AI. were:

97 plants-with the mark of susceptibility to mildew—0

7 »

.» > »

1 »

» » » »

.»

» • 2

» » » »

» . »

The parent form of «Persian Wheat» had at the same time the mark~0.

The parent

T. dicoccum

var.

pienurum

— 1.

*) Plants were grown in pots in a green-house and were artificially and equably

infected with mildew.

5) See Ph. 4. The difference in degrees of susceptibility to mildew of plants of

Fj of the hybrid Triticum pcrsicum Vav. Л* 173X T. turgidum var. lusitanicum Kcke

.N* 3326 under equable conditions of infection in a green house. Some plants observed

to be very susceptible like № 3326; some observed to be absolutely immune like

173. This tlble illustrates at the the same time' the scale of marks of degrees of

susceptibility to mildew. Represented are the leaves of the 2 stage from the top.

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