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Abstract

The roles of free and bound abscisic acid (ABA) in the breaking of dormancy in seeds of peach (Prunus persica (L.) Batsch) were investigated. Concentrations were consistently 10- to 100-fold higher in the embryonic axes of seeds than in the seed coats or cotyledons. Free and bound ABA declined 75 to 95% during stratification at both 5° and 20°C, yet only the 5° treatment broke dormancy. Extracts of chilled seeds were less inhibitory to germination of non-dormant seeds than were extracts of non-chilled seeds, but ABA content of the extracts was sufficient to account for only a small part of their biological activity.

Abstract

Watermelon [Citrullus lanatus (Schrad.) Matsum. & Nakai] seeds of the tetraploid ‘Alena’ and the diploid ‘Sugar Baby’ were subjected to one of several treatments prior to germination at 17°, 21°, and 25°C, including lateral splitting, soaking in H₂O (aerated or nonaerated), GA₄₊₇, or benzyladenine (BA) for 24 hr, or in KNO₃ for 5 days, followed by drying. These treatments were successful in increasing germination percentage of ‘Alena’ seeds. Soaking treatments increased ‘Alena’ embryo length. ‘Alena’ seeds possessed thicker seed coats, larger seed cavities, and absorbed more water than those of their diploid counterpart, ‘Sugar Baby’.

Abstract

Both physical and metabolic events were found important in the dormancy-regulating mechanism of seed of Elaeagnus umbellata Thunb. Covering structures offered mechanical resistance to germination, but they did not restrict the flow of water to the embryo. Oxygen concentrations from 60 to 100% increased germination, indicating that the endocarp and seed coat may restrict gaseous exchange by the dormant embryo. Restricted gaseous exchange may compliment a germination-inhibiting substance found in dormant seed. Gibberellic acid decreased the stratification period, but kinetin and potassium nitrate were ineffective.

Abstract

The seed influences rate of growth, size, shape and maturation of avocado fruits. Seeded fruits are 8-10 times larger than seedless ones and contain more and larger cells. The growth pattern of seeded and seedless fruits is similar from June until maturation, when growth rate of seeded fruits decreases. Fruit maturation is characterized by rapid accumulation of oil in the mesocarp, preceded by shriveling of the seed coats, and the discontinuation of the seeds’ influence on fruit growth. The role of the seed in the development of avocado fruit is discussed.

Abstract

Procedures are described to mechanize partially harvesting, cleaning, and pretreat-ment of guayule achenes. Achenes are harvested with a vacuum insect net and cleaned by a series of screening, threshing, and forced air separations, then treated to overcome seed coat impermeability in a semiautomatic system that presoaks, treats with 0.5% sodium hypochlorite, and rinses. Achenes may be sown immediately or dried for storage. Procedures outlined involve commercially available equipment with a minimum of custom construction and are adaptable to small or large operations.

A wide range of methodologies, ranging from Leonard jar to growth pouch have been used to investigate the nitrogen fixation process in leguminous crops. The effectiveness of most of these research methods have been questioned. Problems encountered vary from difficulty in root separation to water log conditions. This study was undertaken to determine the effect of different growing media on nodule development and harvestability. Black and Red seed coat kidney bean were surface sterilized and inoculated with the Rhizobium phaseoli strain UMR 1899. Seeds were planted in 8.5 cm diameter sterile clay pots containing the respective growing medium. These growing media were sand, Promix GM, Promix BX, and fritted clay. The black seed coat kidney bean had higher germination rate under all media for all dates recorded. Black kidney bean grown in sand and fritted clay had plant heights significantly greater than ones grown in the other media on the third harvest date. Nodule activities as measured by shoot dry weight and nodule number were significantly higher in both beans grown in fritted clay than in other media. Promix GM plants with dry weight of .45g for the black bean and .32g for the red beans were the lowest. Nodule separation from the growing media was easiest when plants were grown in sand, however, this was not significantly different from that of plants grown in fritted clay.

Experiments were conducted in the Dominican Republic to determine the effect of physical and chemical treatments on the germination of the ornamental palms Roystonea hispaniolana Bailey (Royal palm), Acrocomia quisqueyana Bailey (Corozo palm), Sabal umbraculifera Mart (Cana palm), Phoenix canariensis (Canary Islands date palm), Veitchia merrillii (Becc) Bailey (Manila palm), Chrysalidocarpus lutescens Wendl (Areca palm), and Caryota urens (Fishtail palm). Treatments were seed immersion in water or gibberellic acid 3 (GA₃) solution for 72 hours, immersion in concentrated nitric acid for 5 minutes, or cracking of the seed coat. Rate and percentage of emergence 90 days after treatment were measured. The best results for Roystonea, Phoenix, Veitchia, Caryota, and Chrysalidocarpus were obtained soaking the seeds in water or a 200-ppm gibberellic acid solution. Nitric acid and seed coat cracking significantly reduced the germination percentage in all the species, except Acrocomia guisqueyana and Sabal umbraculifera. Seeds of Acrocomia did not germinate as a response to any of the treatments tested. Sabal seeds germinated only after coat cracking or nitric acid treatment.

Triploid watermelon seed does not germinate in cold, wet soils as well as diploids; germination is slower due to reduced embryo size and thicker seed coat; fissures on the seed coat provide safe harbour for fungal spores; and triploid fruit set is later than most diploid cultivars. Because of these problems producers often transplant rather than direct-seed seedless watermelons. Seed priming has been shown to improve germination in other crops and would be an attractive method allowing for direct seeding of seedless watermelons. Seed from open-pollinated 4n × 2n crosses were primed in solutions of H₂O, polyethylene glycol 8000, KNO₃, or left untreated. Treatment times were 1, 3, or 6 days, and treated seed were subsequently dried for either 1 or 7 d. Seed were scored for germination in the laboratory and emergence under field conditions. Germination was better using H₂O than KNO₃ and PEG but not always better than the untreated control. Treatment time of 1 day was superior to 3 or 6 days, but length of drying time was insignificant. In the field trial, treatments did not differ in emergence.

Abstract

Capsicum annuum (‘Early Calwonder’) seeds germinated (radicle protrusion) in 8 days at 15°C and 4 days at 25°. The seeds have an endosperm 7 to 9 cells in thickness which lies directly in front of the radicle. The external appearance of the endosperm did not change until one day before radicle emergence, when the endosperm in front of the radicle enlarged and protruded outward. This change was accompanied by breakdown and loss of endosperm cellular integrity and reduction in endosperm thickness directly in front of the radicle, but not in other regions of the endosperm. Gibberellic acid (GA₄₊₇) decreased the time for appearance of the protruding endosperm and radicle protrusion through the seed coat by one day. Cell wall degrading activity was detectable during the early stages of germination and became extremely high after radicle emergence. Seeds treated with 100 ppm GA₄₊₇ showed slightly increased enzyme activity during early germination and differences became more pronounced as germination progressed. Cellulase activity was not found in the extracts, but seed enzyme preparations degraded a galactomannan substrate. The enzyme exhibited only endohydrolytic activity, indicating an enzyme which may participate in the weakening of cell wall. It was postulated that an endomannanase is needed for endosperm breakdown in front of the radicle in order for rapid germination of pepper to occur. A reduction in germination temperature from 25° to 15° reduced the rate of radicle movement through the seed coat by one half.

Southern seaoats (Uniola particulata) are difficult to propagate from seed due to low seed numbers produced and cold dormancy effects. To efficiently produce southern seaoats in the nursery industry the dormancy must be effectively broken to assure quick and even germination. 24 hr soaks in gibberillic acid (100 and 500 ppm) or scarification of the seed coat combined with GA soaks were compared. Seeds were planted in 50/50 peat/perlite medium 2.5 cm deep. 21 DAT both the 100 and 500 ppm GA soaks had higher germination rates. The 100 ppm GA was determined to he most effective (56% germination) with the seedlings being 3 cm in length. The 500 ppm treated seeds were 6 cm in length hut twisted from the GA causing excessive cell elongation.