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Dennis Ray, Steven Smith, and Mark Hurlburt

Lettuce (Lactuca Sativa L.) seeds imbibe water but most fail to germinate, This phenomenon now termed “thermodormancy” is prevalent in arid and semiarid climates like the southwest desert regions, Inheritance studies of thermodormancy were performed in two lettuce cultivars, Dabora (Dutch butterhead) and PI 251245 (a plant introduction from Egypt). Dabora will germinate up to 27 C and PI 251245 up to 36C. Reciprocal crosses were made. Pericarp color was used as a marker to determine successful crosses. Dabora X PI 251245 was used to estimate the heritability of thermodormancy by germinating seed from 10 F3 families and 160 F4 families at “high” temperatures.

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Anwar A Khan

Fluridone (FL), a catotenoid biosynthesis inhibitory herbicide, prevented supraoptimal temperatures from inducing thermodormancy in seeds and permitted seedling emergence in several lettuce cultivars. A 48-h dark soak at 35C with 23 μM FL completely prevented the induction of thermodormancy in `Mesa 659' and `Emperor' lettuce seeds as more than 90% of the seeds germinated on transfer to water in darkness at 25C. Abscisic acid (100 μM) applied with FL did not prevent FL from acting. Dormancy was released completely in the naturally dormant `Garnet' and `Grand Rapids' lettuce seeds at 25C in darkness by 1 μM FL. FL applied following thermodormancy induction at 35C in `Mesa 659' lettuce seeds had little effect on releasing the induced dormancy. A 2-h presoak of `Mesa 659' lettuce seeds with 0.47 μM FL followed by washing, drying, and sowing in a peatlite mix at 25C/35C (12 h/12 h), permitted 80% seedling emergence. Higher concentrations resulted in the emergence of albino seedlings. Similar results were obtained with seeds of other lettuce cultivars (`Prizehead', `Emperor', `Ithaca', and `Empress'). A 6-h matriconditioning (MC) (A.A. Khan, Hort. Rev. 13:131–181, 92) of `Mesa 659' lettuce seeds in 7.5 μM FL enhanced the emergence to a greater extent than by MC alone at 25C/35C. The FL procedure in alleviating high-temperature stress in lettuce and other seeds is being tested further.

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Yu Sung, Daniel J. Cantliffe, Russell T. Nagata, and Warley M. Nascimento

micropylar cap before radicle protrusion ( Dutta et al., 1997 ; Nascimento et al., 2000 , 2001 ), and 7) the ability of seed priming to completely circumvent thermodormancy and the buildup of endo-β-mannanase during the priming process ( Bonina et al., 2007

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Anne K. Carter and Charles S. Vavrina

The germination of five commercial cultivars of jalapeño and cayenne pepper were tested to determine cultivar response of Capsicum annuum L. to supra-optimal temperatures. Two seedlots of `Cayenne, Large Red Thick', `Ole', `Jalapeño M', `Mitla', and `Tam Veracruz' were evaluated on a thermogradient table at temperatures of 20, 25, 30, 35, and 40 °C. Percent germination and time to 50% of final germination (T50) were calculated. All cultivars exhibited thermodormancy, but the degree of inhibition varied within temperature and cultivar. No cultivar had >1.0% germination at 40 °C. Generally, the T50 varied among cultivars, but not among temperatures within a cultivar (T50 at 40 °C was not measured). Cultivar selection should be considered when growing fall transplants in Florida.

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Abbas Lafta and Beiquan Mou

results in yield and quality losses ( Jenni, 2005 ; Jenni and Yan, 2009 ). At high temperatures, lettuce seed germination is inhibited (thermoinhibition) and the seeds became dormant, which is called thermodormancy ( Gonai et al., 2004 ; Negm et al

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D.J. Cantliffe

When lettuce seeds are imbibed and subjected to high temperature for periods of 72 h or more, dormancy known as thermodormaney is induced. Priming of three cultivars of lettuce (Lactuca sativa L.) seeds in 1% (w/v) K3 P O4 for 20 h in the dark reduced thermodormaney. Addition of 100 mg 6-benzyladenine (BA)/liter to the priming solution increased germination in petri dishes at 35C in `Green Lakes' from 65% in seeds that were primed without BA, to 92% when BA was added to the priming solution. In `South Bay' these percentages were 24% and 86%, respectively. Seedling emergence was improved in other lots of `Green Lakes' and `Montello' using soilless mix.

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Warley M. Nascimento, Daniel J. Cantliffe, and Donald J. Huber

Weakening of the endosperm tissue around the radicle tip before radicle protrusion and a potential role of endo-β-mannanase during germination of lettuce seeds (Lactuca sativa L.) at high temperature (35 °C) were investigated. Seeds from the thermotolerant genotypes `Everglades' and PI 251245 had greater endo-β-mannanase activity before radicle protrusion at 35 °C than the thermosensitive genotypes `Dark Green Boston', `Valmaine' and `Floricos 83'. Thermotolerant genotypes also generated more ethylene at high temperature. At 35 °C, germination of `Dark Green Boston' and `Everglades' seeds produced at days/nights of 20/10 °C was 10% and 32%, respectively, whereas germination of seeds produced at days/nights of 30/20 °C was 67% and 83%, respectively. Higher endo-β-mannanase activity was observed before radicle protrusion in `Dark Green Boston' seeds produced at 30/20 °C compared with those produced at 20/10 °C. A relationship between seed germination at high temperature, ethylene production, and an increase in endo-β-mannanase activity before radicle protrusion was confirmed.

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Tim D. Davis, Daksha Sankhla, N. Sankhla, A. Upadhyaya, J.M. Parsons, and S.W. George

Seeds of Aquilegia chrysantha Gray were germinated under a variety of temperature regimes. Germination was nearly 90% under a day/night cycle of 25/20C, but was reduced to ≤ 40% under constant 25C or a 25/10C day/night cycle. With days between 25 and 29C (night = 20C), germination percentage dropped gradually to ≈ 60% with increasing temperature. With days >29C, germination declined dramatically such that no germination occurred at 31C. Neither kinetin (4.6 to 46 μm) nor ethephon (6.9 to 207 μm) was able to reverse the inhibitory effects of 33C days. Our results indicate that germination of A. chrysantha seed is sensitive to temperature and that germination ≈ 75% can be obtained under a 25 to 27C day/20C night regime. Chemical names used: 2-chloroethylphosphonic acid (ethephon); 6-furfurylaminopurine (kinetin).

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Anne K. Carter and Roseann Stevens

`Jalapeño M' pepper (Capsicum annuum L.) seeds were soaked for 40 h in solutions of 0.0, 0.5, 1.0, 2.0, or 3.0 mM GA3 (using Release, 10% GA3) and 0.0, 1.75, 3.5, 7.0, or 10.5 mM ethephon in all combinations in petri dishes at 25 °C. The seeds were rinsed, dried for 24 hours, then germinated at either 25 or 40 °C. Thermoinhibition was induced at 40 °C, as nontreated seeds failed to germinate, but 99% of the seeds germinated at 25 °C after 7 days. Pretreatment with H2O alone partially alleviated thermoinhibition at 40 °C (41% germination). Pretreatment with ethephon alone resulted in up to 50% germination and with GA3 alone up to 79% germination. The effects of the GA3 and ethephon were additive, as the highest germination percentage (91%) at 40 °C was obtained with 3.5 mM ethephon + 3.0 mM GA3. The percentage of abnormal radicles was <1% in all treatments. Chemicals used: (2-chloroethyl) phosphonic acid (ethephon); gibberellic acid (GA3).

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Iwanka Kozarewa, Daniel J. Cantliffe, Russell T. Nagata, and Peter J. Stoffella

Ethylene synthesis and sensitivity, and their relation to germination at supraoptimal temperatures, were investigated in lettuce (Lactuca sativa L.) seeds matured at 30/20 °C [12-h day/night, high temperature matured (HTM)] or 20/10 °C [12-h day/night, low temperature matured (LTM)]. HTM seeds of both thermosensitive `Dark Green Boston' (DGB) and thermotolerant `Everglades' (EVE) had greater germination at a supraoptimal temperature (36 °C), in both light or dark, than LTM seeds of DGB and EVE. HTM seeds of DGB and EVE produced more ethylene during germination than LTM seeds, regardless of imbibition conditions. The ethylene action inhibitor, silver thiosulfate, led to reduced germination in both cultivars. The ethylene precursor, 1-aminocyclopropane-1-carboxylic acid at 10 mm increased germination of both cultivars at supraoptimal temperatures, whereas germination of HTM seeds was greater than that of LTM seeds. No differences in ethylene perception were detected between HTM and LTM germinating seeds using a triple response bioassay. This study demonstrated that at least one method through which seed maturation temperature influences lettuce germination is by affecting ethylene production.