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.
Fibrolytic enzymes and microbial inoculants have the potential to improve the value of sorghum feedstuff and feedstock. An experiment was conducted to determine nutritive value, ensiling characteristics, and in situ disappearance kinetics of 4 sorghum (Sorghum bicolor L.) silage varieties: Dairy Master BMR (DBMR; brown midrib; Richardson Seed, Vega, TX), PS 747 (PS; photoperiod sensitive; Pogue Seed, Kenedy, TX), Silo 700D (S700D; conventional forage type; Richardson Seed), and MMR 381/73 (MMR; conventional forage type; Richardson Seed) pretreated with fibrolytic enzyme (xylanase plus cellulase, XC; 50:50 mixture of Cellulase Plus and Xylanase Plus; Dyadic, Juniper, FL) or microbial [Promote ASB (Lactobacillus buchneri and Lactobacillus plantarum); Cargill Animal Nutrition, Indianapolis, IN; PRO] inoculants. The greatest yield was for cultivar PS and the least for MMR. Neutral detergent fiber (NDF) concentration was least for XC-treated silage, and acid detergent fiber (ADF) concentration was least for XC- and PRO-treated silage. When silage was treated with XC, concentrations of NDF concentrations decreased, on average, 4.81% across all cultivars and ADF concentrations decreased, on average, 3.23% in all cultivars except MMR. Inoculant PRO reduced the NDF concentration of DBMR by 6.47%. The ADF concentrations of DBMR and PS treated with PRO were decreased by 3.25%. Treating sorghum silage with XC or PRO reduced the NDF and ADF fractions, which increased cell wall degradability. In vitro true digestibility was greatest for PRO-treated DBMR, whereas acid detergent lignin was least for PRO-treated DBMR. Aerobic stability was not improved by PRO; however, aerobic stability of XC-treated MMR was 63 h greater than that of the control. Acetate concentrations were greatest for XC-treated MMR, which explains the 63-h improvement in aerobic stability due to the inhibition of fungi. However, inoculant PRO did not improve yeast and mold counts or aerobic stability of sorghum silage compared with the control, which may be due to the lesser acetate concentrations, especially of PRO-treated S700D silage. Generally, in situ disappearance kinetics were improved with the application of XC and PRO, and XC had the greatest effect on silage with greater NDF and ADF concentrations.
lecular markers within mapping populations (Wendel and Parks, 1984;Torres et al., 1985; Molecular tools have not identified the gene(s) governing apomixis Paterson et al., 1988Paterson et al., , 1991Saito et al., 1991; Lyt-nor have they been used to successfully transfer the trait to important, sexually reproducing food crops. Several molecular studies addressing tle, 1991;Schon et al., 1991; Zivy et al., 1992; Causse et apomixis in grasses have used interspecific and intergeneric hybrids. al., 1994; Chittenden et al., 1994). This loss of specific The failure to recover specific F 1 genotypes from these wide crosses genotypes from the progeny may be due to interactions can be caused by unfavorable interactions between the gametes, zybetween genes of the two species within gametes, zygote, embryo, endosperm, and/ or maternal tissue. These interactions gote, embryo, endosperm, or maternal tissue (Hadley can eliminate recombinant genotypes with valuable information toand Openshaw, 1980). Differential viability of offspring wards linkage analyses of the trait. Buffelgrass [Pennisetum ciliare because of allelic interactions has been reported in (L.) Link syn. Cenchrus ciliaris L.], a polymorphic species with intermaize (Zea mays L.)-Tripsacum hybrids (Maguire, fertile apomictic and sexual genotypes, offers an opportunity to genetically map apomixis by means of intraspecific hybrids with euploid 1963), tomato, Lycopersicon esculentum Mill. (Rick, genomes. This study reports a linkage map of the apospory region in 1966), wheat, Triticum aestivum L. (Manabe et al., 1999), buffelgrass. Apospory, classified by progeny testing and cytologically and rice,
While rhizome formation is intimately associated with perennialism and the derived benefit of sustainability, the introduction of this trait into temperate-zone adapted Sorghum cultivars requires precise knowledge of the genetics conditioning this trait in order to minimize the risk of weediness (e.g., Johnsongrass, S. halepense) while maximizing the productivity of perennial sorghum. As an incremental step towards dissecting the genetics of perennialism, a segregating F4 heterogeneous inbred family derived from a cross between S. bicolor and S. propinquum was phenotyped in both field and greenhouse environments for traits related to over-wintering and rhizome formation. An unseasonably cold winter in 2011 provided high selection pressure, and hence 74.8 % of the population did not survive. This severe selection pressure for cold tolerance allowed the resolution of two previously unidentified over-wintering quantitative trait locus (QTL) and more powerful correlation models than previously reported. Conflicting with previous reports, a maximum of 33 % of over-wintering variation could be explained by above-ground shoot formation from rhizomes; however, every over-wintering plant exhibited rhizome growth. Thus, while rhizome formation is required for over-wintering, other factors also determine survival in this interspecific population. The fine mapping of a previously reported rhizome QTL on sorghum chromosome SBI-01 was conducted by targeting this genomic region with additional simple sequence repeat markers. Fine mapping reduced the 2-LOD rhizome QTL interval from ~59 to ~14.5 Mb, which represents a 75 % reduction in physical distance and a 53 % reduction in the number of putative genes in the locus.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-012-9778-8) contains supplementary material, which is available to authorized users.
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