Occurrence of 2n microspore production in diploid interspecific hybrids between the wild parental species of peanut (Arachis hypogaea L., Leguminosae) and its relevance in the genetic origin of the cultigen

Abstract

Unreduced (2n) gametes are the driving force that leads to polyploidization of plants in nature and an important tool for ploidy breeding. Peanut (Arachis hypogaea L., Leguminosae) seems most likely to have originated by sexual polyploidization through interspecific hybridization between the wild diploid relatives—A. duranensis Krapov. & W.C. Greg. and A. ipaënsis Krapov. & W.C. Greg—and subsequent binding of the unreduced gametes in the hybrid. Therefore, aiming to contribute to understanding the event of polyploid origin of this important crop, we made diploid hybrids between A. duranensis and A. ipaënsis and then investigated the production of unreduced gametes in the hybrids by analyzing the size range of pollen, the constitution of the sporads, and the microsporogenesis process. The meiotic abnormalities found, such as persistent bridges, tripolar spindles, and cytomixis processes, would lead to the formation of restitution nuclei in both the first and second meiotic division. These failures in the regularity of meiosis lead to the formation of dyads and triads, and consequently to 2n pollen grains. These findings constitute the first evidence of the formation of unreduced gametes in intergenomic hybrids obtained between the wild progenitors of A. hypogaea and enable us to propose a model of origin of the crop through sexual polyploidization.