NATURAL CROSSING IN WHEAT' 



A Cause of Impurities in Breeding Plots — Belief of Some Agronomists that 

 Hybrids Frequently Revert to the Parental Type 



H. K. Haves 



Minnesota Agricultural Experi)ncnt Station 



SOME difference of opinion exists 

 among plant breeders as to the fre- 

 quency of natural crossing in 

 wheat, some contending that such 

 crosses rarely, if ever, occur, while 

 others ])elieve that natural crosses are 

 comparatively frequent. Piotanists do 

 not all agree regarding this question ; for 

 Robbins- states that durum wheats 

 have the habit of cross pollination, and 

 also states that cross pollination appears 

 to be the rule in hot, dry countries, as in 

 certain parts of India, while in the 

 northern, wet climates close pollination 

 is the rule. On the other hand. Friiwirth 

 cites Kiirnicke as an authority for the 

 statement that self-fertilization is by far 

 more prevalent, but cross pollination is 

 possible in T. vulcjare, T. duniin, T. 

 dicoccunt, and T. spclta.^ 



As this subject is of much importance 

 to wheat breeders, and also of inter- 

 est to crop experts and farmers who 

 are desirous of producing pure seed, a 

 note as to the frequency of natural 

 crossing at University Farm may be of 

 some general interest. For a fairly 

 complete sinnmary of literature on this 

 subject the reader is referred to a litera- 

 ture review by Pope (previous citation). 



FREQUENCY OF NATURAL CROSSES AT 

 UNIVERSITY FARM 



The evidence here given is believed to 

 be about as comjiletc as circiunstantial 

 evidence can be. In order to appreciate 

 it, a knowledge is necessary of the be- 



havior in crosses of a few simple dif- 

 ferential wheat characters. These facts 

 are well known by wheat breeders who 

 have made artificial crosses. 



Varieties commonly grown in the 

 Northwest may be placed in two 

 groups : 



Group 1. — The so-called awnles.s^ 

 wheats, as Marquis and the Bluesteni 

 varieties. These have very short awns 

 on the upper spikelets. 



Group 2. — Bearded sorts, such as 

 Preston, Arnautka, Kubanka, and 

 'J'urkey (winter). 



Crosses between such bearded and 

 awnless varieties give heads with inter- 

 mediate awns on the tip of the head, 

 and shorter awns on some spikelets 

 from the middle to upper part of the 

 head. In Fo ^ ratio of 1 awnless, 2 Fj 

 types to 1 bearded is generally obtained. 

 There is some difficulty in separating a 

 homozygous awnless from an Fj be- 

 tween awnless and bearded, but the sep- 

 aration is very easy between an Fj and 

 the bearded sort. 



A cross between a hairy chaffed va- 

 riety, as P)luestem. and a smooth chaff, 

 as Marquis, has hairy chaff' in Fj and in 

 !''., ?) hairy to 1 smooth is the expected 

 result. A hairy chaffed plant in a row 

 of Marquis or other smooth chaffed 

 variety is therefore easily determined. 



Indications of natural crossing were 

 observed in 1916 and 1917 in the nur- 

 sery wheat plots at University Farm, 

 and the conclusion was drawn that nat- 



1 Published with the approval of the Director as Paper Xo. 1.^7 of the Journal 

 Series of the Minnesota Agricultural Experiment Station. 



2 Robbins. W. W. The Botany of Crop Plants. Philadelphia. 1917. 



3 Pope, M. N. The Mode of Pollination in Some Farm Crops. Jour. Ainer. Soc. 

 Agron., Vol. 8. 1916, pp. 209-227. 



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