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  • Author or Editor: David Rhodes x
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Desiccation tolerance of somatic embryos is a key factor for production of dry synthetic seeds. In celery (Apium graveolens L.) desiccation tolerance can be enhanced by optimization of culture duration, ABA application, or sucrose concentration in the embryo production medium. Morphologically mature embryos cultured for 10 days have shown higher desiccation tolerance then those cultured for 8 days, indicating that biochemical changes occur without any noticeable morphological changes. Application of ABA (1 μM) for the last two days of the embryo production cycle was critical for inducing desiccation tolerance; ABA application for the last four days had some additional beneficial effect. Desiccation tolerance was further enhanced by increasing the sucrose concentration of the embryo production media from 3% to 7% for the last two days. Increased desiccation tolerance achieved with optimal harvest timing and ABA application were associated with increased endogenous proline and aminobutyrate, and reduced glutamine.

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Tolerance to partial desiccation and amino acid composition of celery (Apium graveolens L. cv. SB 12) somatic embryos were investigated under various culture durations and with exogenous application of 1 μm ABA, proline, and/or γ -aminobutyrate (GABA). ABA consistently increased tolerance to partial desiccation and elevated proline and GABA content of embryos. The changes in tolerance to partial desiccation associated with changes in culture duration (optimum 9 to 10 days) correlated with embryo proline content. Exogenous proline increased embryo proline content and tolerance to partial desiccation. Exogenous GABA increased embryo GABA content and tolerance to partial desiccation only when applied in combination with proline. Chemical name used: abscisic acid (ABA).

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Field studies were conducted in 1983 and 1984 to evaluate the feasibility of growing fresh-market tomatoes (Lycopersicon esculentum Mill. ‘Floradade’) in no-tillage or conventional tillage systems and to evaluate the efficacy of postemergence herbicides under both tillage systems. In 1983, marketable fruit yields in no-tillage were nearly twice those from conventional tillage. In 1984, there were no statistical differences in marketable yields among herbicide treatments or between tillage systems. Yields were higher in 1984 than in 1983, largely due to more favorable growing conditions. In both years, metribuzin provided good broadleaf weed control. In 1983, annual grasses were better controlled in no-tillage with a sequential metribuzin application for fluazifop following metribuzin than with a single metribuzin application. Marketable yields were highest in plots where annual grasses were adequately controlled. Sequential metribuzin applications provided good broadleaf weed control and postemergence grass herbicides each provided excellent annual grass control in 1984. Chemical names used: (±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid (fluazifop); 4-amino-6-(1,1-diemthylethyl)-3-(methyIthio)-1,2,4-triazin-5(4H)-one (metribuzin).

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Gibberellins (GAs) are phytohormones that regulate plant height and flowering time in plants. Plants with reduced GA or disrupted in GA signaling exhibit a dwarf phenotype. DELLA proteins are transcriptional repressors that attenuate GA-mediated promotion of plant growth. Alleles in which the eponymous DELLA motif in these proteins is disrupted result in constitutive repression of GA signaling and a dominantly inherited dwarf phenotype. We found that the dwarf Helianthus annuus (sunflower) cultivar Sunspot is hyposensitive to GA3 as compared with the tall cultivar Mammoth Grey. Sequencing of the HaDella1 gene indicates that ‘Sunspot’ has a single nucleotide polymorphism resulting in a missense mutation in the DELLA motif as compared with ‘Mammoth Grey’ and the reference sequence. Helianthus annuus has five genes encoding DELLA proteins, including HaDella1. We propose that the DELLA motif alteration in the HaDella1 gene results in a dominant mutation in ‘Sunspot’ and is the cause of its dwarf phenotype.

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