Sources of Variation in Shelling Percentage in Peanut Germplasm and Crop Improvement for Calcium Deficiency-Prone Soils1

Abstract Calcium (Ca) deficiency causes peanut pegs and pods to abort, resulting in decreased shelling percentages and yields. Environmental factors influencing calcium availability include soil Ca content and soil moisture. Genetic attributes that influence the sensitivity of cultivars to soil Ca supply include pod size, soil volume per pod (varied by plant growth habit), and pod wall attributes. Where Ca fertilization is not possible, genetic solutions to Ca deficiency are important, and breeders need information on the relative importance of these attributes. The objective of this research was to quantify the relative importance of these three sources of variation. Data from three trials were used to evaluate the relative importance of these attributes. The trials, sited on Ca-deficient alfisols, used between four and 12 germplasm lines with varied Ca sensitivity- determining attributes. Lines differed in growth habit (spreading or bunch), pod volume, pod yield, shelling percentage, and seed yield. The trial treatments and environments (sites and seasons) also varied Ca supply through soil type, fertilization, and water supply. Assuming that Ca supply has little impact on crop growth rates (CGR), a physiological model was used to set aside the contributions of CGR to yield differences between treatments. The three trials were analyzed separately and then combined for further regression analysis by defining each site and treatment combination as an environment. Within trials, variations in shelling percentage accounted for up to half the variations in seed yield between lines. In the combined analysis, easily selected attributes—pod volume (58% of germplasm sums of squares) and plant habit (8%) and their interaction (14%)—accounted for much of the variation in shelling percentage. The interaction was due to shelling percentage being less influenced by pod volume in spreading than in the bunch types. Thus, in Ca-limiting situations, the spreading growth habit allowed larger seeded peanuts to be grown than the bunch growth habit because of the greater pod dispersal of this type. Assuming that the lines tested typified peanuts for their relation between attributes and Ca deficiency-based shelling percentage variations, breeders should place the greatest emphasis on small pod size to decrease peanut sensitivity to Ca deficiency. Increased soil available to each pod by pod dispersal decreases the need for small pods to decrease sensitivity to Ca-deficient soils.