Estimates of heterosis and combining ability were made using 15 hybrid combinations grown under field conditions. The hybrids were produced by crossing in diallel six peanut (Arachis hypogaea L.) lines collected from three geographic areas of South America.Of 17 characters, estimates of specific combining ability were significant for 16 and estimates of general combining ability were significant for 8. Specific combining ability was greater for yield and for most fruit characters.Several of the crosses showed considerable heterosis when compared with mid‐parent means. Crosses of Virginia × Valencia type parents gave greater heterosis than other crosses for vegetative plant characters. However crosses of Valencia × Spanish type parents gave greatest heterosis for yield and fruit characters.Comparison of field results with results obtained previously in a controlled environment indicated that the controlled environment may have limited use in predicting field performance of peanut hybrids.

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The stability or shelf-life of peanut (Armhis hypogaea L.) oil is related to the fatty acid content of the oil, with the major factor being the ratio of oleic (C18:l) to linoleic (C18:2) acid (OK ratio).To obtain information needed for development of cultivars with improved oil quality, eight parents representing a range in oleic and linoleic content were crossed in diallel. Individual F, seeds (F, embryos) from the greenhouse and F, bulk seed from the 56 crosses grown in the field were analyzed to determine levels of the eight major fatty acids. General combining ability (GCA) was consistently more important than specific combining ability (SCA) in both generations, suggesting that additive effects are important in the inheritance of fatty acid composition. Maternal effects were significant in the F, but dissipated in the F,; thus the differences in the environment provided by the maternal parent was more critical to oil composition than heritable extranuclear factors. Reciprocal effects were significant in both generations suggesting an interaction between nuclear and extranuclear factors. Correlations between GCA effects and self means for O/L ratio were nonsignificant. Since no significant correlations were found between percent oil and any of the fatty acids or related variables, selection for improved fatty acid composition should not affect the oil content of seed. Of The stability, or shelf-life, of peanut (Armhis hypogaea L.) oil is measured by the number of days before the onset of oxidative rancidity, a process which is generally induced in either the whole peanut or peanut oil by exposure to heat and air (5,17,22). Oxygen reacts with the double bonds of unsaturated fatty acids to form products that have undesirable flavor and odor. Linoleic acid (C18:2) is more susceptible to this process than the monounsaturate, oleic acid (C18:l) or other saturated fatty acids (5,15). Eight major fatty acids account for 98% of the total fatty acids in peanut oil (19,25), but of these oleic and linoleic together make up 75-80% of the total (13,21), ranging from 36-80% and from 2-43%, respectively (5,16,21). There is a negative correlation between the percentage of oleic and linoleic acids (l0,21), since linoleic acid is produced from the conversion of oleic acid. Since the seed of most peanut cultivars are composed of approximately 50% oil (3,13,21), quality of a peanut product can be greatly affected by oil stability. The iodine value (Iod), which provides a measure of the degree of oil unsaturation, has been commonly used as a means of predicting shelf-life. The ratio of oleic to linoleic acid (O/L ratio) is also a measure of oil stability (23,24,26). Selection

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A study was conducted to determine the extent of and genetic basis for heterosis in crosses between 27 exotic peanut (Arachis hypogaea L.) cultivars and an adapted virginia breeding line. Because their subspecific taxonomy was not always clear, principal components were used to cluster the exotic parents into five morphologically distinct groups roughly corresponding to the botanical divisions of the species. Heterosis (measured as the deviation of F~ performance from the midparent) was observed for pod yield, pod size parameters, seed yield and other traits. Heterosis up to 19% above the higher parent occurred for pod size and length. A significant portion (27 to 68%) of the variability in heterotic effects was attributable to difference among the parental groups with generally higher levels expressed in intersubspecificcrosses. Heterotic deviations were broken into two components reflecting the relative contributions of dominance and epistasis to nonadditive genetic variation. For pod and seed yield and pod length, dominance was the more important source while epistasis was more important for pod and seed number and meat content. The two sources made approximately equal contributions to heterosis for pod and seed size. The degree of genetic divergence between exotic parents and the adapted line was estimated by a Euclidean distance based on the vegetative and reproductive characters used in the principal component analysis. For characters exhibiting more dominance, the relationship of heterosis to divergence between parents was linear and increasing. The relationship was curvilinear for traits largely influenced by epistasis. An optimum level of divergence was detected for pod number only.

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Effect of temperature and photoperiod and their interaction on plant growth and partitioning of dry matter to pods was examined in three selected groundnut genotypes uiz., TMV 2, NC Ac 17090 and VA 81B. The genotypes were grown in six walk-in growth chambers which were programmed to simulate three temperature regimes (22/18"C, 26/22"C and 30/26"C day/night) each under long (12 h) and short (9 h) photoperiods. The plant growth rates and partitioning of dry matter to pods were estimated on a thermal time basis.Plant growth rate (PLGR) was significantly influenced by temperature, photoperiod and genotype, whereas pod growth rate (PDGR) was influenced primarily by temperature and genotype. The interaction of genotype with photoperiod and with temperature was significant for both PLGR and PDGR. For example, at the 22/18"C temperature regime, VA 81B had a high PDGR. while NC Ac 17090 did not even initiate pod growth. The partitioning of dry matter to pods (Pf) was also significantly influenced by photoperiod, temperature and genotype, and significant interactions were found. Photoperiod did not significantly affect Pf under the low temperature regime, but at higher temperatures, partitioning to pods was significantly greater under short days. Pf of VA 81B was relatively insensitive to photoperiod compared with the other two genotypes. The study provided evidence of genotypic variability for photoperiod x temperature interactions which could influence adaptation of groundnut genotypes to new environments.