Characteristics of a novel male–female sterile watermelon (Citrullus lanatus) mutant

A novel male–female sterile (MFS) watermelon mutant was discovered as a progeny of the F1-hybrid cultivar Chunlei, which was irradiated twice with gamma rays. The present study aimed to characterise the primary mechanism responsible for the sterility of the MFS watermelons. Morphological characteristics of male and female gametophyte development were investigated using acetocarmine staining, pollen germination, and paraffin methods. Genetic analyses were conducted using heterozygote fertility reciprocal crossing with one normal line, M134. The most meiotic pollen mother cells (PMCs) showed variable chromosome behaviours such as incomplete synapsis, chromosome lagging, univalents, and bridges, which led to the formation of multiple nuclei and non-viable male gametes with only 0.58% stainability and zero germination rate. Embryo-sac mother cells (EMCs) were also shown to be abnormal. As a result, 0.31% of the ovules had complete embryo sacs and 99.8% of the seeds per fruit were empty. Fertility segregation was observed in the heterozygote, with a fertile-to-sterile plant ratio of 3:1. Findings of this study indicate that the male–female sterility of the watermelons, which was controlled by a single recessive gene, can be attributed to abnormal meiosis in PMCs and EMCs.

► We model a novel male–female sterile (MFS) watermelon mutant which set seedless fruits.
► Incomplete synapsis and abnormal separation of chromatids result in male–female sterility.
► Sterility of MFS plants is controlled by the single-recessive-gene-related meiosis.