Auxin test induces parthenogenesis and aposporous-like embryo sacs in Paspalum notatum

VEGA MS; SIENA LA; VEGA JM; PESSINO SC; LEBLANC O; ORTIZ JPA

Rosario

Congreso; RAFV Conference 2023 XXXIV Argentinian Meeting of Plant Physiology; 2023

Sociedad Argentina de Fisiología Vegetal

Auxin plays an essential role in plant development. The 'auxin test' (the spraying of immature inflorescences with a dilute auxin solution) is used in some grass species to identify individuals with parthenogenesis. P. notatum is a subtropical fodder grass that forms a multiploid complex. The common form (2n=4x=40) reproduces by pseudogamous aposporous apomixis and is self-fertile. Apomixis involves the formation of unreduced aposporous embryo sacs (AES), the development of maternal embryos by parthenogenesis, and the formation of endosperm after fertilisation of polar nuclei. In AES parthenogenesis often begins before anthesis. Fully sexual tetraploid plants have never been found in nature, but can be produced artificially by colchicine treatment of diploids. The aim of this study was to evaluate the effect of the auxin test on the reproductive development of apomictic and sexual plants. Inflorescences were sprayed with an aqueous solution of 2,4-D (80mg/l + Tween 20) 10 to 3 days before anthesis. Inflorescences treated with distilled water served as controls. The experiments were carried out during the flowering seasons of the years 2021 and 2022. The effect of auxin was assessed by observation of ovules at anthesis. Auxin-treated inflorescences of apomictic plants showed a significant increase in the proportion of ovules with parthenogenetic embryos compared to controls (average 24% vs 11%, p=0.03 year 2021 and 23% vs 8%, p=0.02 year 2022). Proembryos, were also detected in meiotic embryo sacs (up to 14%). In sexual plants, auxin application resulted in an average of 7 and 12% of ovules bearing aposporous-like embryo sacs compared to 0% of controls, and up to 4% of ovules with double meiotic embryo sacs. No parthenogenetic embryos were observed. Our results indicate that external auxin application significantly increases the proportion of parthenogenetic embryos in apomictic genotypes and induces the formation of aposporous-like embryo sacs in sexual genotypes