Inheritance of Aposporous Apomixis in Inter‐specific Hybrids Derived from Sexual Paspalum plicatulum and Apomictic Paspalum guenoarum

Abstract

Apomictic Paspalum plicatulum Michx. and P. guenoarum Arechav. are promising candidates for forage grass development in tropical regions. From a plant breeding perspective, apomixis provides a unique mechanism for developing superior cultivars and preserving them indefinitely. Therefore, analysis of its inheritance is of great interest in these apomictic species. The objective of this work was to analyze the inheritance and expressivity of apomixis in interspecific families derived from crosses between a sexual colchicine‐induced plant of P. plicatulum and an apomictic P. guenoarum plant. One F1, one F2, and three backcross (BC) populations were created. Amplified fragment‐length polymorphism (AFLP) markers confirmed the hybrid origin of the F1 descendants. Analysis of the reproductive mode of the F1 by flow cytometry seed screen (FCSS) showed a segregation ratio of 1.6:1 sexual vs. apomictic plants. The same analysis in F2 and BC populations showed that in selfing or crosses involving sexual genotypes all progeny reproduced by sexuality, while BC populations involving apomictic hybrids as pollen donors produced offspring that segregated for the reproductive mode. Apomixis can be transmitted by pollen from P. guenoarum to other species of the Plicatula group as a simplex (Aaaa) Mendelian dominant factor, and full sexual reproduction requires the homozygous recessive (nulliplex) condition (aaaa) for the apomixis determinant. Results provided here are of interest for breeding apomictic species of Plicatula and for basic research on the genetic determinants of apomixis. Also, the possibility of creating new apomictic cultivars by traditional breeding methods is presented.

How to Become an Apomixis Model: The Multifaceted Case of Paspalum

“…Inheritance studies in species of the Plicatula group using F 1 and F 2 generations and three backcross populations derived from an artificial tetraploid sexual clone of P. plicatulum and an apomictic P. guenoarum cv. Rojas plant confirmed the previous genetic model, with a single Mendelian dominant factor with altered transmission (1 apo:1.6 sex) [ 67 ]. Interestingly, high rates of distortion against apomixis were also found in interspecific crosses involving P. simplex x Paspalum malacophyllum (1:5) [ 77 ] and P. simplex x Paspalum procurrens (1:15.7) [ 69 ].…”

“…These genotypes became the female progenitors of segregating populations used in apomixis inheritance genetic dissection and breeding programs. Currently, a large number of well-characterized sexual tetraploid individuals, generated by chromosome doubling treatments (sometimes followed by experimental crosses) are available for the three species [ 33 , 50 , 51 , 53 , 67 , 68 ]. Moreover, several sexual genotypes of P. simplex and P. plicatulum were also used as female parents in interspecific crosses with different members of the Anachyris subgenus and the Plicatula group, respectively, widening the genetic studies to other species of the genus [ 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 ].…”

“…All genetic analyses in Paspalum showed a strict co-segregation between apospory, parthenogenesis, and unbalanced endosperm formation, suggesting that their relevant genetic determinants are located in the same low recombining chromosome area [ 23 , 67 , 79 ]. The parthenogenesis of reduced egg cells in the genus was never documented.…”

Reproductive Systems in Paspalum: Relevance for Germplasm Collection and Conservation, Breeding Techniques, and Adoption of Released Cultivars

“…Later, Martínez et al (2007) reported that apospory could not be transferred by monoploid male gametes ( n = x ), supporting the hypothesis postulated by Nogler (1984) that apomixis can only be transferred under heterozygous conditions. In addition, Aguilera et al (2015) reported distorted segregation in favor of sexual inter-specific hybrids of crosses between an induced sexual tetraploid P. plicatulum and an apomictic P. guenoarum . Interestingly, when back-crossing the induced sexual tetraploid plant of P. plicatulum with apomictic F 1 hybrids, no distortion was observed in the segregation patterns.…”

“…This technique was developed by Young et al (1979) and recently modified by Zilli et al (2015); it requires plants at flowering stage and provides reliable information about expressivity of apomixis (Ortiz et al, 1997) and also is inexpensive, rapid, and straightforward (Zilli et al, 2018). Flow cytometry on seeds was used in P. notatum (Urbani et al, 2017), P. simplex (Brugnoli et al, 2014), P. malacophyllum (Hojsgaard et al, 2016), P. rufum (Delgado et al, 2014), and in inter-specific hybrids of the Plicatula group of Paspalum (Aguilera et al, 2015). This technique provides similar information to embryo sac observation, but determining expressivity of apomixis at seed stage, though giving a more accurate approximation to what is expected in the progeny, comes at a higher cost in comparison to embryo sac observations.…”