GrainGenes

II. 17. Heterosis for ear and grain size in F1 and F2 six-row x two-row hybrids.

P. T. Gymer, Rothwell Plant Breeders Limited, Rothwell, Lincoln LN7 6UT, United Kingdom.

Last year we reported yield component studies on two F1 barley hybrids (six-row x two-row and six row x deficiens) (Gymer, 1976). In 1976 we followed this by looking at the F2 generation. The plants were grown as spaced individuals in soil under glass. In addition to the F2 of the two crosses, the F1 and parents were also grown. At harvest, the four leading ears of each plant were taken; the number of central grains per ear was recorded, and the thousand grain weight was calculated from the weights of these grains.

The F2 were also classified according to their lateral floret type. Large-lateralled two-rows (VVII from the six-row x two-row cross, and V^t_v VII and perhaps V^t_v Ii Ii from the six-row x deficiens cross) were recorded separately, but their ear and grain size were almost identical to those of normal two-rows (VVii and V^t_v Ii respectively), and so the data was combined; the classification is thus according to the V^tVv genotype.

Table 1 shows that both crosses gave the same result. For number of grains per ear, the F1 hybrids were significantly better than their parents and better than the heterozygous F2's (p<0.1%). There was no significant difference between the two-row (or deficiens) F2's and the heterozygous F2's; nor were the F2's significantly different from the two-row (or deficiens) parent. Thus the heterosis in the F1 was complete]y absent in the F2

Table 1. Yield components of parent, F1 and F2 plants

For grain weight, the F1's showed very marked heterosis, as in previous studies (in fact, 25 to 30% above better parent). They were significantly better than their parents (p<0.1%), and better than the heterozygous F2's (p<1%) though these were nearer the F1 value than the parental value. Indeed there was a significant difference between the two-row (or deficiens) F2's and their parents (p 0.1%). In fact, the average grain size of the F2's was still about 20% higher than in the two-row or deficiens parent.

From the present data we cannot attribute any appreciable part of the heterosis for grain size to heterozygosity at the V^tVv locus (see Gymer, 1976). Nor can any be attributed here to compensation for grain number per ear. Linear regression analysis of the two characters within each category showed a positive relationship, sometimes significant instead of the expected negative one. This may have been due to compensation by both ear and grain size for variations in tillering, which of course was not measured on the individual spaced plants.

Since much of the heterosis for grain size was still present in the F2 (unlike the heterosis for grain number), it seems likely that the six-row parent contributed genes for large grains; this may enable us to obtain pure-breeding two-row or deficiens lines with increased grain size, as was found by Elliot and Poehlman (1976). To this end, we shall be growing F3 progenies from the best F2 plants in the field in 1977.

The six rows deserve brief mention. Although the grain size of the six row F2's was higher than that of the six-row parent, the ear size was smaller. This may imply that it is difficult to improve the yield components of six-rows by crossing with two-rows. Nevertheless, we shall be growing a few six-row F3 progenies in 1977.

References:

Elliot, W. A. and J. M. Poehlman. 1976. Inheritance of kernel weight in sixrowed by two-rowed barley crosses. Proc. 3rd Int. Barley Genetics Symposium (1975), 678-685.

Gymer, P. T. 1976. Heterosis for grain size in six-row x two-row F hybrids. BGN 6:30-33. 1

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