Positive General Combining Ability Effects Research Articles

Genetic analysis of quantitative characters in cigar and pipe tobacco, Nicotiana tabacum. III. Economic indices: grade index, yield, and crop revenue

A diallel cross of four cigar cultivars and one pipe tobacco (Nicotiana tabacum L.) cultivar was analyzed for the following parameters: grade index, yield, crop revenue or index, percentage of nicotine, percentage of total alkaloids, and susceptability to pole rot. The experiment was performed over 3 years. Analysis was done for general combining ability and specific combining ability. General combining ability was greater than specific combining ability for all variables although significant specific combining ability effects were also present for all parameters with the exception of nicotine and total alkaloids. Reciprocal effects were completely absent. The line Pennbel 69 showed a positive general combining ability effect for yield, crop index, and infestation by pole rot and a high negative general combining ability effect for grade index and percentage of nicotine and total alkaloids. Petit Havane showed a complete reverse of general combining ability effects for these parameters while the other three cultivars were intermediate. High positive specific combining ability effects for grade index, yield, and crop index and high negative specific combining ability effects for the percentage of pole rot were shown by crosses of Pennbel 69.

The Inheritance of N2 Fixation Efficiency in Crimson Clover1

Host plant genetics of N2 fixation efficiency in the crimson clover‐Rhizobium trifolii symbiosis was investigated using a diallel mating design and mass selection. Dinitrogen fixation was evaluated using the acetylene reduction assay. Plants were grown for 60 days prior to the assay in plastic pouches containing N free nutrient solution. Live plants were assayed using the plastic pouch to contain the gas mixture.Crosses differed significantly in acetylene reduction rate. In a combining ability analysis, both general and specific combining abillty were significant sources of variation. Only one of the six parental lines showed a significant, positive general combining ability effect. This line uniformly transmitted its high acetylene reducing ability to all but one of its progeny. In terms of variance components, specific combining ability was more important in determining the acetylene reduction rate than general combining ability for all lines tested. After one cyle of mass selection, acetylene reduction rate was increased 8%. The realized heritability of this trait was 63.1%.

A STUDY OF COMBINING ABILITY FOR GRAIN PROTEIN PERCENTAGE IN A DIALLEL CROSS OF FIVE SIX-ROW BARLEY CULTIVARS

Grain protein percentage was assessed in F1 and F2 populations in two experiments involving a complete diallel cross among the barley (Hordeum vulgare L.) cultivars Bonanza, Conquest, Olli, Galt and Jubilee. Heterosis was absent in all crosses and a Griffing combining ability analysis showed that specific combining ability was nonsignificant in both F1 and F2 populations. General combining ability (GCA) for protein percentage was highly significant in both generations, with Conquest and Olli having major positive GCA effects. Galt produced a large negative GCA effect, while Jubilee and Bonanza caused small negative GCA effects. Significant differences between the hybrids were found only in F1. Broad sense heritabilities for protein differences between the parents were 0.57 and 0.72 in the two experiments, and were significant at the 5 and 1% levels of significance, respectively. Conquest had significantly higher protein than Bonanza, with Olli being intermediate. Galt had lower protein than Jubilee, but this difference was significant in only one experiment. The differences among the five cultivars for mean grain protein percentage and general combining ability are significant in relation to breeding for malting and feed type barleys.

Influence of High Day and Variable Night Temperatures on Nitrate Reductase Activity of Young Corn (Zea mays L.) Plants1

Sixteen corn (Zea mays L.) genotypes (a four‐parent diallel cross) were grown from seed for a month in controlled‐environment rooms in the University of Wisconsin Biotron. A high day (35 C) and three night temperatures (24, 16, and 7 C) were provided to study the influence of high day and variable night temperatures on nitrate reductase (E.C. 1.6.6.1) activity (NRA) in these genotypes. A 15‐hour photoperiod at 35 klux was provided. Plants were grown in vermiculite with nutrient solution.Growth was fastest at a high night temperature of 24 C and slowest at 7 C, but NRA per g fresh wt (gfw) of leaf blades declined more rapidly at the high night temperature of 24 C than at 16 or 7 C and the decline was least rapid at 7 C. NRA per plant changed little at the 24 C night temperature during the first 21 days, but increased markedly thereafter. At 16 C, NRA per plant increased from 11 to 17 days, but decreased thereafter, whereas it increased at 7 C from 13 to 30 days in most genotypes.Significant genotypic differences were observed at all night temperatures and at 9 of 10 samplings. At 24 C, levels of NRA of each reciprocal cross generally were intermediate with respect to levels of NRA in the two parental inbreds. However, in a few cases, one or both reciprocal crosses were higher than the midparent with respect to NRA. At 16 C, additional crosses were higher than the midparent with respect to NRA per gfw and per plant, though a few were intermediate in NRA as compared with their parents. At 7 C, NRA per plant generally was higher in the hybrids than in either parent.Reciprocal effects were statistically significant in only 2 out of 10 samplings. General combining ability (GCA) effects were significant in eight samplings. In all samplings and at all temperature regimes, inbred ‘A632’ was the parent with most positive GCA effects.

Second Phase in the Evaluation of Synthetic Varieties of Maize for Yield1

The second phase of a sequential synthetic variety testing program for yield in maize (Zea mays L.) is reported. Four varieties selected from the tests of the first phase and five previously untested varieties were crossed in a diallel series and evaluated at three locations in each of two years.The yield level of the varieties included for the first time was generally higher than those selected from the first phase. Two‐ear Syn., Syn. AA, and Syn. BB were the highest‐yielding varieties, whereas S.S. Syn. and Purdue MJ yielded significantly lower than the other varieties. S.S. Syn. was outstanding in cross performance; it had the highest average yield in crosses and a significant, positive general combining ability effect. Two‐ear Syn. was high in both variety and cross performance and had the largest variety effect ( = 3.44**).Relative to the midparent and high parent, average heterosis for all crosses was 9.8 and 4.2%, respectively. Relative to the high parent, S.S. Syn., L.E. Syn., and C.B. Syn. #3 exhibited the most heterosis in crosses. S.S. Syn. ✕ Pa. Int. Syn. had a significant, specific heterosis effect ( = 5.51**) and an observed heterosis of 24.1% relative to the midparent. Very little heterosis was observed for the crosses involving Syn. AA and Syn. BB. Specific heterosis (s.c.a.) was significant (P < .05) in the combined analysis. The specific effects for only three crosses were larger than the standard error: S.S. Syn. ✕ Pa. Int. Syn. had a positive effect, and Syn. AA ✕ Pa. Int. Syn. and Syn. BB ✕ S.S. Syn. significant, negative effects. The cross, S.S. Syn. ✕ Pa. Int. Syn., was the highest yielding in both phases of testing.