Anatomical characteristics correlated to peg strength in Arachis

Wild, diploid Arachis species are a great source of biotic and abiotic stress resistances and tolerances for peanut breeding programs; however, these species also have undesirable characteristics such as small seed size, low yield, and weak peg strength. Peg strength has been shown to have a positive, linear relationship with yield in cultivated peanut. Therefore, the weak peg strength of wild Arachis species could be detrimental to yield and needs to be selected against when introgressing useful alleles from wild species into elite germplasm. To enable breeders to effectively utilize these wild species, we sought to characterize peg strength and anatomical characteristics correlated with peg strength in seven diploid Arachis species, as well as four allotetraploids, six (cultivated peanut lines x allotetraploid) F1 hybrids, and two cultivated peanut breeding lines. For each genotype, five mature pegs were tested for peg strength and cross-sections for three of the five pegs were subsequently taken and analyzed for peg anatomical characteristics including total peg cross-section area, mean bundle cap area, total bundle cap area, bundle cap as a percentage of peg area, bundle cap number, mean distance between bundle caps, total distance between bundle caps, and tannin cell count. Genotype was a significant indicator for peg strength and all the anatomical characterization parameters (P < 0.05). Peg strength was positively and highly correlated with peg area, mean bundle cap area, total bundle cap area, and bundle cap number. Peg strength comparable to that of peanut breeding lines was recovered in the F1 hybrids. Because weak peg strength in the wild species appears to be recessive, strong pegs can likely be easily selected during the process of introgression.