General Combining Ability Estimates Research Articles

A method of parental selection and cross prediction using incomplete partial diallels

When a character has a large additive genetic component in its variance, general combining ability estimates may be used for predicting cross performance. Further, if emphasis is placed on the ranks of the general combining abilities in a diallel rather than on their numerical values, the incomplete partial diallel is a powerful tool for parental selection. In a self pollinating species, if general combining ability effects are equal to or greater than specific combining ability effects, 20% of the partial diallel is found to give enough information for accurate ranking of the parental general combining abilities. A generalised method for calculating general combining abilities from incomplete partial diallels is presented and tested by computer simulation over a large range of genetic population parameters.

Combining Ability in Cotton for Resistance to Pink Bollworm1

Seed damage by pink bollworm (PBW) (Pectinophora gossypiella Saunders), to cotton (Gossypium hirsutum L.) grown for 2 years at Tempe, Ariz. in insecticide‐f~ee environments was determined in six parents and in all of their hybrid and reciprocal combinations. The six parents included two cultivars, ‘Deltapine 61’ and ‘Stoneville 256’, three primitive race stocks, Texas 31 (T‐31), 55, and T‐167, and an upland breeding stock of complex parentage, designated AET‐5. The latter four p~rents had been selected for PBW resistance in earlier tests. Parents and hybrids grown in 1977 showed significant genetic variability only at the fourth of five harvest dates, whereas those grown in 1978 showed significant variability at all four hgrvest dates. For both years, at the only directly comparable harvest, general combining ability estimates (GCA) were significant for low seed damage in T‐167 and AET‐5 and significant for high seed damage in T‐55. Significant effects from specific combining ability (SCA) were shown for six of the hybrid combinations for at least one harvest date. The combinations of most interest, cultivar ✕ T‐167, cultivar ✕ AET‐5, and T‐167 ✕ AET‐5, showed only GCA effects. Maternal effects were not significant. Significant reciprocal effects at two harvest dates were confined to two hybrid combinations. On the basis of GCA estimates, T‐167 and AET‐5 should each combine well for low seed damage.

Quantitative Genetic Analysis of Ten Characteristics in Sweet Corn (Zea mays L.)1

Abstract Tassel date, silk date, plant height, ear height, shank length, husk extension, tip blanking, row number, ear length, and first ear weight were studied in a diallel involving 7 inbred sweet corn parents. Both general combining ability (GCA) and specific combining ability (SCA) were involved in the inheritance of all 10 characters. This was consistent for F1 crosses in 2 years and for F2 families. SCA variance (VSCA) was larger than GCA variance (VGCA) for ear length and first ear weight in the F1 and ratios of VSCA/VGCA for these characters were slightly larger than 1.0. VGCA was larger than VSCA all other characters in the F1. Ratios of VSCA/VGCA ranged from .05 for row no. to .57 for plant height. Variance ratios for most characters decreased in the F2. The failure of some ratios to decrease in the F2 was attributed to either differential interactions of GCA and SCA with environment or inadequate sampling of F2 families. Genotype × year interactions influenced the expression of most characters. A greater portion of the genotype × year interaction was contained in estimates of SCA than in estimates of GCA. Heritability estimates from parent-progeny regression were generally larger than those from variance components, although these estimates were generally in close agreement.

The effect of temperature on radiation-induced macromutants of Arachis Hypogaea L. and expression of heterosis in F 1 hybrid populations

Three separate experiments were conducted with cultivated peanuts to (a) study the effect of four controlled temperatures on the expression of seven radiation-induced macromutants and the mother line; (b) determine the responses of normal appearing F 1 hybrids involving four macromutants to three controlled temperature regimes and (c) evaluate the same macromutant, parental and F 1 hybrid populations (described in b) when grown for a full season under field conditions. Macromutant plant weights and flower production were generally lower than that of the mother line in all three experiments. The macromutants also tended to flower later than the mother line. The leaflet expression of two of the macromutants was drastically influenced by changes in temperature. Lupinus reached maximum leaflet curvature when grown at 34/30°C but appeared near normal when grown at 22/18°C. The reverse was true for the macromutant Recurved. The macromutant Flop contained maximum percentages of nitrogen and phosphorus in its vegetative parts when grown at the highest temperature (34/30°C). All other mutants and the mother line had highest proportions of these nutrients when grown at the lowest temperature regime (22/18°C). Expressions of heterosis were maximized when hybrids of macromutant parentage were grown at suboptimal temperatures. General combining ability estimates were higher than specific combining ability estimates with the macromutant Hedera (a dwarf type) making the greatest contribution to the general combining ability effects for peg (fruit-bearing structure) production and pegging efficiency. The same macromutant was found to make substantial contributions to general combining ability effects for fruit and seed weight when hybrids were grown under field conditions.

Variability of In Vitro Dry Matter Digestion in Diallel and Polycross Progenies of Intermediate Wheatgrass1

AbstractVariation in height, seed set, and in vitro dry matter digestion (IVDMD) within a diallel and a polycross nursery of intermediate wheatgrass, Agropyron intermedium (Host) Beauv., were studied. Significant differences in IVDMD of whole tillers occurred among diallel crosses, but did not occur among polycrosses, indicating greater precision of measurement in the diallel. Differences among diallel crosses for plant fraction (flag leaf, peduncle, and spike) IVDMD were also significant. Digestibility of the peduncle contributed the greatest effect to whole tiller digestibility. It was concluded, however, that digestibility of the upper part of the plant could not be used as an indicator of whole tiller digestibility. Correlations of height, seed weight for 10 heads, and seed set with IVDMD were low. Significant general combining ability, specific combining ability, and reciprocal effects were found for each character. General combining ability estimates were highest in one parent for almost all characters investigated. Since additive genetic effects were predominant, the variability within the diallel cross population should allow success in selection of a superior cultivar for the characters studied

Heterotic Performance and Combining Ability of Two‐Way F1 Soybean Hybrids1

Eight attributes were measured in spaced F1 soybean (Glycine max (L.) Merrill) hybrids and their parents. The F1 hybrids gave an average of 13.4% heterosis for seed yield over their respective high parent in the 85 crosses evaluated. Nearly 77% of the hybrids exceeded the high parent yield. Seed size in large‐seeded ✕ large‐seeded hybrids was nearly 4% smaller than the large parent, while in small‐seeded ✕ small‐seeded crosses, the F1's and the larger‐seeded parents had about the same average seed size. Thus, an increase in seed number was largely responsible for the increase in seed yield of the F1. Wholeplant dry weight was larger and harvest index was smaller in the hybrids as compared with the high parent, indicating that, while the F1's produced more seed than the parents, their nonseed portion was unproportionately larger than in the parents. The hybrids approximated the midparent average in maturity, were generally shorter than the taller parent, and were not significantly different from the midparent mean in protein and oil contents.Specific combining ability effects were significant for seed yield, maturity date, plant height, and oil content. Except for oil content, general combining ability estimates were significant and were two to six times larger than specific combining ability effects.

COMBINING ABILITY STUDIES OF GRAIN YIELD AND RELATED TRAITS IN PEARL MILLET

The present study was undertaken to explore the genetic architecture of pearl millet through combining ability analysis in a 5X5 diallel fashion. Both GCA and SCA mean squares were significant in grain yield, plant height, panicle length and days to flowering. However, these were non-significant for number of productive tillers and panicle girth. General combining ability estimates revealed that genotype MGP-322 was good general combiner for all the traits under study except for days to flowering for which MGP-335 and 13RBS-01 were good general combiners but these were poor general combiners for all other traits under study. The crosses MGP-322XMGP-328, MGP-322XMGP-335, MGP-328X13RBS-13, 13RBS-01X13RBS-13 and MGP-322X13RBS-01 were best specific combiners for grain yield and some other attributes respectively. All these crosses involved at least one good general combiner except MGP-328X13RBS-13. This suggested that good general combiners are the best tool in improving the crop yield by manipulating the genetic architecture. Combining ability variances revealed that although both GCA and SCA variances were important, however, SCA variances were higher than GCA variances suggesting that non additive type of gene action was more prominent in the inheritance of characters under study.