Interploid St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] hybrids recovered by embryo rescue

Abstract

St. Augustinegrass is one of the most important warm season turfgrasses in the southern United States because of its shade tolerance. Most cultivars are diploids (2n=2x=18) and are susceptible to various diseases and insects. Polyploid cultivars in the species have some resistance to pests, but most lack cold tolerance. In this study, eight polyploid genotypes were crossed with six diploid cultivars to transfer pest resistance to the diploids. Because interploid crosses often result in aborted seed, it was necessary to use in vitro techniques. Using embryo rescue, 268 plants were recovered from 2,463 emasculated and pollinated florets (10.88% crossability). Because of the heterogeneous nature of the species, these purported hybrids could not be verified by phenotype. DNA markers were used for hybrid identification. A subset of 25 plants from crosses between the aneuploid cultivar Floratam (2n= 4x=32) and five diploid cultivars were analyzed using 144 expressed sequence tags-simple sequence repeats (ESTSSRs) developed from buffelgrass cDNA sequence data. Chi-square tests for paternal-specific markers revealed that all analyzed progeny were true F 1 hybrids and none originated from self-fertilization or unintended outcrossing. In addition to identifying DNA polymorphism, the ESTSSRs revealed that genetic variation exists among all analyzed cultivars and is not partitioned between ploidy levels. The findings demonstrate that these embryo rescue techniques will enable the entire spectrum of St. Augustinegrass genetic variation to be better used through the recovery of interploid hybrids.

Registration of ‘DALSA 0605’ St. Augustinegrass

“…Following pollination by ‘Palmetto’ (Kirkland and Wagner, 1995; ‘Palmetto’ is a registered trademark of Sod Solutions, Inc.) (diploid pollen parent), enlarged ovules from TAES 5382 (African polyploidy, PI 291594) were dissected to recover developing embryos 14 to 21 d postpollination. Hybrid embryos with vestigial endosperm attached were transferred to the half‐strength Murashige and Skoog basal medium (Murashige and Skoog, 1962) containing 5% sucrose as a carbon source and osmoticum, and incubated at 25°C with an 18‐h photoperiod for 5 to 7 wk (Genovesi et al, 2009) before the DALSA 0605 plantlet was transplanted to the greenhouse. To determine the 2C DNA content of DALSA 0605 in comparison to its parental lines, young leaf tissue samples of DALSA 0605, TAES 5382 and Palmetto were sent to the Flow Cytometry and Imaging Core laboratory (Dr. K. Arumuganathan, Seattle, WA).…”

“…Until recently, the polyploid gene pool has not been readily available as a breeding resource due to sterility barriers resulting from differences in ploidy levels. Genovesi et al (2009) described a protocol whereby in vitro embryo rescue methods allowed for the recovery of viable hybrids (interploids) when polyploid females were crossed with diploid males. ‘DALSA 0605’ (Reg.…”

Comparison of screening methods to evaluate the response of St. Augustine grass to Magnaporthe oryzae

“…Difficulty in using conventional breeding methods to generate crosses between diploid and polyploids has slowed the development of breeding material with desirable turf quality and disease resistance. Recent advances (Genovesi et al. , 2009) have identified use of non‐conventional methods such as in vitro embryo rescue, which has been successful in producing F 1 interploid progeny from crosses between diploid lines and introduced African polyploid germplasm of St. Augustine grass.…”

Development of colchicine‐induced tetraploid St. Augustinegrass (Stenotaphrum secundatum) lines

“…Theoretically, crosses between diploid and polyploid germplasm could combine the best characteristics of both groups. However, the development of hybrids between ploidy levels has been hindered due to embryo abortion or poor seedling vigour related to unbalanced chromosome numbers (Genovesi, Jessup, Engelke, & Burson, ; Yang et al, ). Moreover, the prevalence of gamete sterility due to aneuploidy in publicly available Stenotaphrum polyploid germplasm has also hindered inter ploidy breeding efforts (Yang et al, ).…”

“…Theoretically, crosses between diploid and polyploid germplasm could combine the best characteristics of both groups. However, the development of hybrids between ploidy levels has been hindered due to embryo abortion or poor seedling vigour related to unbalanced chromosome numbers (Genovesi, Jessup, Engelke, & Burson, 2009;Yang et al, 2014).…”