INHERITANCE OF PROTEIN CONTENT IN PEA. III. CORRELATION BETWEEN PROTEIN CONTENT AND SEED YIELD

52 RESEARCH REPORTS

PNL Volume 13

1981

Swiecicki, W. K., Plant Experiment Station, Wiatrowo, Poland

P. Blazczak, J. Hauke, and S. Mejza Agricultural Academy, Poznan, Poland

After several years of research work at Wiatrowo to breed cultivars with

a higher protein content, our progress has been less than expected. The basic

difficulty was the negative correlation between % protein content and seed

yield, a difficulty discussed also by Jermyn and Slinkard (Canad. J. Pl. Sci.,

1976, 56:427). To learn more about the problem we decided to subject

the results of breeding tests to statistical analysis. First a preliminary

analysis of correlation and regression was made. The analysis was based on

the observations, from 1973-76, of seed yield and % protein content in four

crosses: L 2813 x L 6003 (mean protein content 28.9%), L 3509 x L 2813 (30.6%),

L 2815 x L 2813 (29.4%), and L 2813 x L 4318 (30.9%). In the first stage

the significance of the coefficient of correlation between seed yield and

% protein content for particular hybrids and for particular years was studied.

There was a high, negative correlation always above (according to the absolute

value) -0.95 between these factors.

Next the coefficients of correlation and regression were analyzed over

all years. There was general lack of homoegeneity among the coefficients

of correlation, reflecting differences in some or all of the variables studied.

Crosses were also compared with respect to coefficients of correlation and

regression. Three of these crosses showed substantially different correlation

in all possible clusters of years whereas L 2813 x L 4318 showed a certain

regularity (homogeneity of coefficients of correlation) over years.

From a breeding point of view, it was of interest to know if the negative

correlation between seed yield and % protein content was equally strong at

different levels of protein content. In order to study this problem, the

cross L 3503 x L 2813 was chosen because the most data were available. Using

a computer, the data were searched for those instances in which higher seed

yield was not associated with lower protein content. This analysis showed

that when protein content was not more than 27% a larger seed yield did not

cause significant reduction of protein content. Since this conclusion was

based on only one cross, we checked for verification in following years.

Coefficients of correlation were analyzed and coefficients of equations of

regression were compared for other crosses in which protein content was not

more than 27% (1977 - 17 crosses, 1978 - 7 crosses, 1979 - 15 crosses). The

results from 1979 (Table 1) are given as examples verifying the conclusions

as stated.

The conclusions presented above show the possibilities of increasing

the protein yield in cultivars, either by improvement of yield when protein

content is not more that 27%, or by increase of protein content to the

threshold level of 27% in high-yielding cultivars. For example, some varieties

bred in Poland give a seed yield of about 3-4 tons/hectare, yet their protein

content is only 22%. If, according to the above hypothesis, the protein content

is increased to the theoretical 27%, protein yield would be greater by 150-200

kilos per hectare.

These observations demonstrate how difficulties faced in routine breeding

inspire more detailed investigations.