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The establishment of stands from directly sown seed may be a way to reduce the current high costs associated with guayule (Parthenium argentatum Gray) cultivation. These field studies were conducted to examine the combined effects of shade and fungicides on the survival of guayule seedlings established from directly sown seed. Soil in the experimental plot was a loam of pH 7.25. The following fungicides: a) Terraclor Super X, b) Ridomil 5G, c) Ridomil PC llG, d) Tilt 3.6E, e) Terracoat, and f) Vitavax + PCNB were tested alone and in combination with the nonwoven polyester shadecloth, Reemay, to identify treatments enhancing seed germination and seedling establishment. In all cases, seedling emergence in microplots covered with Reemay was significantly higher than in noncovered microplots. Terraclor Super X, Ridomil 5G, and Ridomil PC 1 lG were effective only when used in combination with the shadecloth. The long-term survival of guayule seedlings was strongly affected by severe climatic events. Since Reemay-protected seedlings were larger and more robust, they were more likely to survive the climatic extremes than unprotected seedlings. Two new guayule seedling pathogens were recorded -pythium dissotocum Drechsler and P. paroecandrum Drechsler. Chemical names used: 5-ethoxy-3-(trichloromethyl)-1,2,4-thiadiazole (Terrazole) + pen. tachloronitrobenzene (PCNB); N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-alamine methyl ester Ridomil + PCNB; 7. bromo-5-chloro-quinolin-8-yl-acrylate; Terrazole 5,6-dihydro-2-methyl-l,4 -oxathiin-3-carboxanilide + PCNB.
The reproductive biology of Schlumbergera truncata (Haworth) Moran and S. xbuckleyi (T. Moore) Tjaden was examined in a series of experiments. At anthesis, pollen grains are spherical, 54 to 62 μm in diameter, and tricellular. The receptive surface of the stigma is densely covered with elongated papillae and is devoid of exudate during the period of flower opening. When compatible pollen was applied to mature stigmas, germination occurred between 20 and 30 minutes after pollination and pollen tubes penetrated the stigma surface between 30 and 40 minutes after pollination. Pollen tubes exhibited a nonlinear pattern of growth in the upper two-thirds of the style, and the maximum rate of growth (≫1.9 mm·h-1) occurred between 12 and 18 hours after pollination. Full seed set was attained between 32 and 48 hours after pollination. Genotypic variation in the time required to achieve full seed set was partly attributable to differences in stylar length. Seeds were fully mature 6 months after pollination, but delaying fruit harvest until 8 months after pollination did not affect seed germination.
In a test to overcome poor seed germination and seedling vigor of sweet corn (Zea mays L.) seeds carrying the shrunken-2 (sh2) mutant endosperm, primed seeds of two sh2 sweet corn cultivars—Crisp N'Sweet 711 (CNS-711) and How Sweet It Is (HSII)—were redried at 15, 20, 30, or 40C and 25% relative humidity after solid matrix priming (SMP). The dehydration rate was significantly lower in `CNS-711' than `HSII' at all temperatures. In both cultivars, the drying temperature after SMP was critical for seed performance. Primed seeds with a higher dehydration rate (dried at 30 or 40C) had better seed vigor, greater field emergence and seedling vigor, lower leachate conductivity and imbibition rate, and a higher respiration rate and glutamic acid decarboxylase activity than primed seeds redried at the lower temperatures or control seeds. Increased incidence of pathogen growth was observed on seeds dried at 15 and 20C relative to those dried at 30 or 40C, probably as a consequence of greater leakage from the seeds at a lower redrying temperatures. Lack of tolerance to dehydration at 15 and 20C was another factor adversely affecting the seeds redried at low temperature. A more rapid dehydration rate at a higher temperature after priming sh2 sweet corn improved many of the physiological characteristics used to measure seed quality and the subsequent emergence and vigor of the seedlings under field conditions.
We determined whether the chilling process (endodormancy release) was similar in peach [Prunus persica (L.) Batch cv. Johnson Elberta] seeds, seedlings (near normal to physiologically dwarfed), and mature plants (cuttings) by comparing correlation coefficients of various growth measurements following similar chilling treatments. Seed germination (10 days after forcing at 20C) and seedling emergence (15 days after forcing in the greenhouse) correlated highly with leaf and shoot growth (56 days of growth) of seedlings and terminal shoot growth of cuttings (13 days after forcing). The correlations were higher for germination than for emergence. Initial (first season) seedling growth correlated poorly with germination, emergence, budbreak, and growth of seedlings (second season) and shoot growth of cuttings. Budbreak and growth of seedlings correlated highly with shoot growth of cuttings. The abnormal leaf problem, which can cause apex abortion (common with initial seedling growth), confounded correlations with initial seedling growth. Yet, the abnormal leaf problem did not hinder correlations with the second seasons growth. Good relationships between the chilling mechanisms that promoted germination, emergence, budbreak, and growth of seedlings and shoot growth of cuttings existed, but were dependent on what was measured and when the measurement was taken. Germination (forced at 20C) was the most accurate indicator of the seed chilling status for comparisons with the responses of the other propagules.
Presowing seed treatments were devised to improve emergence and crop uniformity of two sweet corn (Zea mays L.) cultivars [`Crisp N' Sweet 711' (CNS-711) and `How Sweet It Is' (HSII)] that carry shrunken-2 (sh2) mutant endosperm. The treatments included a fungicide combination, sodium hypochlorite (SH), solid matrix priming (SMP), and SMP combined with SH during treatment (SMPSH). Seed germination was tested in a laboratory cold test. Emergence percentage, emergence rate index (ERI), and seedling dry weight were calculated from field trials. CNS-711, in the cold test and field trials, had a higher germination rate, ERI, final emergence, and seedling dry weight than HSII. In both cultivars, SMPSH significantly improved germination in the cold test and final emergence and ERI in the field trials for HSII compared to nontreated seeds. There was no significant difference between the fungicide and SMPSH treatments regardless of cultivar. These results suggest that the combination of SMP and disinfection with SH can be an alternative seed treatment to fungicides to improve uniformity and stand establishment in sh2 sweet corns.
The reciprocal crosses between two citrus cultivars and Citropsis schweinfurthii (Engl.) Swing. & M. Kell. were conducted. The cross between `Nanpu' tangor {`Kiyomi' tangor (Citrus unshiu Marc. × C. sinensis Osbeck) × `Fairchild' tangerine-tangelo [clementine (C. clementina hort. ex Tanaka) × `Orlando' tangelo (C. paradisi Macf. × C. reticulata Blanco)]} and C. schweinfurthii produced some developed seeds with an average weight approximately 1/10 of that of the seeds obtained from open pollination in `Nanpu' tangor. These seeds germinated on Murashige and Tucker medium, and three and 28 seedlings were obtained from crosses using C. schweinfurthii as the female and the male parent, respectively. The absolute nuclear genome size of these seedlings [∼0.84 pg of DNA content per somatic nucleus (2C)] was intermediate of that of the `Nanpu' tangor (0.78 pg/2C) and C. schweinfurthii (0.90 pg/2C) seedlings. The chromosome counts of the young leaves revealed that they were diploids (2n = 2X = 18). Furthermore, the hybridity of the seedlings obtained from the reciprocal crosses between `Nanpu' tangor and C. schweinfurthii was confirmed by randomly amplified polymorphic DNA (RAPD) analysis and cleaved amplified polymorphic sequence (CAPS) analysis. These hybrids will be utilized as important materials for investigating the phylogenic relationships between these genera in the subfamily Aurantioideae.
The activities of catalase and of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH), the two key enzymes in the pentose phosphate pathway (ppp), were measured in the seeds of Prunus persica (L.) Batsch var. nectarina Maxim `Nectarine 7'. The seeds were subjected to three imbibition treatments: 1) continuous 24C; 2) continuous 4C; and 3) application of thiourea (TU)/gibberellic acid (GA) at various concentrations to seed held at 24C then subsequently chilled at 4C. Treatments of continuous 24 or 4C indicated that catalase, G6PDH, and 6PGDH exhibited significant activity increases only when the seeds obtained germination potential, which occurred in the seeds chilled for 7 weeks at 4C. Seeds held at 24C did not germinate and showed little change with time in G6PDH and 6PGDH activity. There was only a slight increase in catalase activity beginning 3 weeks following treatment initiation and a decrease in activity following 13 weeks of treatment. Thiourea treatment resulted in an inhibition of catalase activity and a stimulation of G6PDH, but had no effect on 6PGDH activity. However, no correlation between enzymic activity and seed germination was found. The results strongly questioned the role of the ppp and catalase activity in dormancy control as previously hypothesized.
Progenies from crosses among eight highbush (Vaccinium corymbosum L.), lowbush (V. angustifolium Ait.), and V. corymbosum/V. angustifolium hybrid-derivative parents were evaluated in vitro at low (5.0) and high (6.0) pH for vitality, height, and dry weight. Succinic acid and 2[N- morpholino]ethanesulfonic acid (Mes) effectively maintained pH in the medium and rhizosphere. The pH regime did not affect percent radicle emergence from seed or survival; however, percent seed germination was slightly lower at high pH. The parental general combining ability (GCA), reciprocal and maternal, but not the specific combining ability (SCA) variance components were significant for plant vitality, height, and dry weight. The GCA variance components were six to 26 times larger than the SCA variance components for the plant growth traits. Variation due to pH regime was significant for vitality and dry weight but not for plant height. The progenies of parents with high percent lowbush ancestry were taller at both pH levels than those with less such ancestry. Little variation was apparent for higher pH tolerance as measured by dry weight; however, the GCA effects suggested that the progenies of some parents performed better than others at high pH. Vaccinium angustifolium parents differed in the extent to which tolerance to high pH was transmitted. In vitro screening in concert with a traditional breeding program should be effective in improving blueberry tolerance to higher pH.
Vaccinium ashei (6x) /V. corymbosum (4x) pentaploid hybrids backcrossed to V. ashei yield aneuploid progeny ranging in chromosome number from 5x to 6x levels. Six backcross aneuploids having chromosome numbers of 2n = 61, 62, 64, 66, 68, and 70 were selected from this backcross and crossed in a complete diallel mating design and backcrossed (as female parents) to two V. ashei cultivars and an interspecific hexaploid hybrid. Fertility variables measured were percent fruit set, total seed per berry, developed seed per berry, percent developed seed per berry, percent seed germination, developed seed per pollination, and seedlings per pollination. A significant linear and positive relationship was found between chromosome number and all seven fertility variables. However, regression accounted for 30% or less of the variation among crosses. Diallel analysis revealed that general combining ability was the major contributing effect for all seven variables, followed by reciprocal effects. Specific combining ability was not significant. The second backcross to the hexaploid level suggested significant effects due to both the BC1 aneuploid and hexaploid genotypes and to a significant genotype × genotype interaction for three of the variables. All six aneuploids were either fully or partially self-sterile. The findings of this study substantiate earlier suggestions that pentaploids in blueberry can be used to facilitate bilateral transfer of characteristics between the tetraploid and hexaploid levels in blueberry.
Siberian C peach (Prunus persica L.) seeds were stratified at 5 and 20C. DWs and soluble protein content remained constant regardless of stratification temperature and duration. Seed extracts subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a decrease in the intensity of nine polypeptides in the cotyledons of seeds held at 5C during weeks 5 through 8, coinciding with an increase in germination capacity. These changes were confined to cotyledons held at 5C, and were observed only when the seeds were able to germinate. The effects of stratification and the imbibition degree on changes in the protein content of seeds of two additional peach biotypes (`Farouki' and `Maloussi') were also evaluated. Germination of fully imbibed seeds at 20C increased steadily as stratification time at 5C increased. Partially imbibed seeds (25 % or 50% of full imbibition) did not germinate regardless of stratification time. However, when these seeds were soaked in water after stratification, their germination paralleled that of fully imbibed seeds. Thus, dormancy was broken, even though the seeds could not germinate. Changes in protein profiles in fully imbibed seeds confirmed those previously reported for Siberian C seeds. Similar changes occurred in cotyledons of partially imbibed seeds during stratification at 5C, but at a slower rate. Those changes were, however, delayed by partial imbibition, whereas germination capacity (ability to germinate when fully imbibed) was not. Changes in cotyledon protein profiles were not affected by removing the embryonic axis before stratification, a result indicating that such changes are not controlled by the axis. Gibberellic acid (GA3 induced 35 % to 40% germination of nonchilled seeds. It hastened the loss of protein band intensity in `Farouki' but not in `Maloussi'. However, GA3-treated seeds germinated before any visible changes occurred in protein profiles. We conclude that the effects of chilling on breaking dormancy are independent of its effects on the protein changes observed in this study.