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The responses of 15 rice cultivars to low temperature during germination were studied in order to develop appropriate techniques to identify rice genotypes suitable for direct-wet seeding in the cooler <I>Boro</I> season. Most rice cultivars showed more than 90% final germination over a range of temperatures. When tested at 13.7°C, cultivars differed in their final germination and rate of germination. The rates of germination at higher temperatures were significantly related to the rates of germination at lower temperatures. Thermal times to 50% final germination also differed significantly. Artificial ageing for 48 hours clearly separated the cultivars which had different K_i<I> </I>(initial seed viability). Such measures of physiological age and their relationship with final germination suggested that low quality seed exhibited reduced low temperature germination. Differences in rates and final germination at lower temperature of unaged seed suggested genotypic differences between cultivars. Inconsistency in rates of seed deterioration was seen contrary to conventional theory. Storage of seeds up to 9 weeks in simulated Bangladeshi conditions showed reductions in final germination tested at 11°C but not at 20°C. The rates of chitting and germination were increased by pregermination hydration treatments. Emergence of rice cultivars from soil was greater in constant than in alternating temperatures. Higher final emergence was associated with faster emergence. Thermal time to 50% and 80% emergence differed between cultivars. Many of the seedling growth parameters were higher in constant temperatures where the rate of germination was faster. The outcome of these experiments is to highlight the potential for comparing rates of germination of large numbers of genotypes relatively rapidly at higher temperatures as a measure to predict germination at lower temperatures.

Vegetable soybean, also known as edamame, has become increasingly popular in the United States due to its excellent nutrition and health benefits. This rising demand has sparked the interest of local farmers in growing edamame. However, a significant problem in edamame production is the poor seedling emergence. This dissertation focuses on three key objectives: 1) exploring the physiological traits linked to the low emergence of edamame seeds; 2) enhancing edamame seedling emergence by identifying genotypes with high vigor and resistance to soil-borne diseases; and 3) determining the optimal temperature for edamame seedling emergence. The study includes newly developed edamame breeding lines from the soybean breeding programs at Virginia Tech and the University of Arkansas, and major edamame cultivars commonly used in the Mid-Atlantic region. The results have identified several genotypes that exhibit high seeding vigor, aging tolerance, and consistently achieve a plant stand of over 80% in both laboratory and field conditions. It is also clarified that edamame's larger seed size leads to lower germination rates and slower emergence, although this is not correlated to total emergence. Moreover, environmental factors, pathogens and temperature, impact emergence. The study highlights that current edamame genotypes are commonly affected by soilborne pathogens, including Rhizoctonia solani, Athelia rolfsii, and Pythium irregulare, leading to seed rot and seedling damping off. However, the research has successfully identified partially resistant varieties characterized by significantly low disease indexes (p<0.05). Furthermore, the optimal temperature range for edamame seedling emergence (25-32°C) was found to be lower than that of other types of soybeans such as grain-type soybeans (29-36°C). This research provides a scientific foundation to improve edamame production practices. / Doctor of Philosophy / Vegetable soybean, also known as edamame, commonly consumed as a healthy snack, is steadily gaining popularity in the United States. However, there are significant challenges in achieving successful edamame plant growth from seeds. This research focuses on three primary objectives: first, understanding the underlying factors contributing to poor seedling emergence in edamame; second, identifying edamame genotypes with exceptional vigor and resistance to soil-borne diseases; and third, determining the ideal temperature conditions for optimal edamame seedling development. To accomplish these goals, a comprehensive study was conducted, encompassing various edamame varieties, including those developed by Virginia Tech and the University of Arkansas. The research identified some edamame genotypes that exhibited exceptional seed vigor, aging tolerance, and consistently achieved plant stands of over 80% under both laboratory and field conditions. Additionally, we also learned that bigger edamame seeds take longer time to grow, but the seed size does not affect the total emergence. Furthermore, we found that some diseases in the soil can hurt edamame seedlings, but we identified a few genotypes that are more resistant to these diseases. Lastly, in terms of temperature, we found that edamame seedlings grow the best between 25-32°C, which is slightly lower than other types of soybeans. Overall, this research helps farmers grow better edamame and brings more delicious and healthy food to our tables.

Awarded second place in Biological Sciences for GPSC Student Showcase

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Orientador: Massanori Takaki / Banca: João Domingos Rodrigues / Banca: Silvio Moure Cícero / Banca: José Marcos Barbosa / Banca: Márcia Balistiero Figliolia / Resumo: Este estudo teve como objetivo avaliar a relação entre a massa e características morfométricas de frutos e sementes de Tecoma stans, bem como relacionar a massa das sementes a suas características morfológicas, utilizando paquímetro e imagens de raios X, e fisiológicas, através da germinação, emergência e desenvolvimento inicial de suas plântulas, sob duas condições de luminosidade . a pleno sol e sombra. Além disso, também foram avaliados os efeitos de diferentes condições de temperatura e luz constantes, em laboratório, e em ambiente natural no sol e na sombra na germinação e emergência das plântulas. A massa dos frutos apresentou relações lineares significativas e positivas com suas características morfológicas e de produção de sementes. As relações entre a massa das sementes e suas características morfológicas foram positivas e significativas, porém na forma de uma função potência, sendo esta relação mais evidente com a largura do embrião. A massa das sementes também esteve relacionada a determinadas anomalias do desenvolvimento embrionário, observadas nas imagens de raios X. A germinação, a emergência e o desenvolvimento inicial das plântulas foram significativamente afetados pela massa das sementes, porém somente durante os três primeiros meses de desenvolvimento no ambiente de sol. A temperatura apresentou efeito na germinação e suas sementes germinaram tanto na luz quanto no escuro, contudo a emergência e sobrevivência das plântulas no ambiente de sol foi superior em relação ao observado na sombra. / Abstract: This study had the objective to evaluate the relationship between the mass and the morphometric characteristics of Tecoma stans fruits and seeds, as well as to relate the seed mass with its morphometric characteristics, utilizing caliper and X-ray images, and physiological characteristics, thought germination, emergency and seedlings initial development, under two conditions of light - at the sun and shade. More than, also were evaluated the effects of different conditions of constant temperature and light, under laboratory, and natural environment under sun and shade in the germination and emergency of the seedlings. The fruit mass presented positive, significative linear relationship with his morphological characteristics and with its seed production characteristics. The relationship between seed mass and its morphological characteristics were positive and significative, nevertheless with the model (shape) of power function, being the relationship more clear with the embryo width. The seed mass also was related to determinate anomalies of the embryo development that could be observed in the X-ray images. The germination, the seedling emergence and the initial seedling development were significative affected by seed mass, but only in the firth three months of development at the sun environment. The temperature affected Tecoma stans seed germination in both light and darkness environment, however the seedlings emergency and survival was greater at the sun environment than shade. / Doutor

In about half of the angiosperm species the gamete chromosome number is a multiple of that found in some related species. This and the fact that polyploidy has such a pronounced effect on plant physiology and growth, as pointed out by Noggle, serve only to emphasize the importance of understanding more about polyploid genetics.

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We wanted to develop rapid and cost-effective drought tolerance screening methods for mass amounts of germplasm. In 2009 and 2010, we evaluated sixty-two maize inbred lines and their hybrid testcross progeny using seedling stress response and epicuticular wax accumulation as predictors of drought tolerance. The seedling screening method measured germination, survival and recovery percentages after a series of drought cycles in a greenhouse environment. Eight inbred lines had significantly (P < 0.05) lower germination than the mean estimate, but hybrid testcrosses were not significantly different. The second-to-last day of survival cycle and the second day of recovery cycle best explained genotypic differences for inbred lines and hybrid testcrosses respectively. One inbred line performed well as both an inbred line and hybrid testcross, but poor correlation over the sample set (R2 = 0.0097) was observed. Flag leaves taken at flowering from plants under full and limited irrigation regimes were sampled for epicuticular wax. Extracted wax weight for genotypes was compared as a percentage of leaf weight (percent wxlfwt) and leaf area (percent wxwta). Eleven genotypes had above average percent wxlfwt as both inbred lines and hybrid testcrosses. Thirteen genotypes had above average percent wxwta as either inbred lines or hybrid testcrosses. Irrigation treatment was not significant (P > 0.05). Heritability of percent wxlfwt was 0.17 (inbred lines) and 0.58 (hybrid testcrosses). Heritability of percent wxwta was 0.41 (inbred lines) and 0.59 (hybrid testcrosses). Correlations (R2) for percent wxlfwt and percent wxwta were 0.19 and 0.03, respectively. Heritability of grams of grain per ear and total grain yield was highest in hybrid testcrosses, with no correlation between inbreds and hybrids. The developed seedling screening method easily allowed visible drought tolerance observations in inbred lines and hybrid testcrosses but does not seem heritable in our germplasm. Epicuticular wax weight is not an ideal primary trait to evaluate for drought tolerance, but may be a good candidate to observe as a secondary trait in relation to grain yield production in hybrids. Results from this research best supports breeder selection of hybrid germplasm using seedling drought tolerance in conjunction with epicuticular wax.

Cotton seedling disease complex is caused by a number of pathogens inducing similar symptoms and can lead to thin, uneven stands that grow slowly and yield poorly. Preliminary work indicated that a set of high tannin cotton lines developed and released in 1989 by Texas A&M AgriLife Research, (Smith et al., 1990a, Smith et al., 1990b, Schuster et al., 1990) may possess increased resistance to disease. This evidence, along with additional studies that show a clear role of tannin in disease resistance, suggest that these high tannin cotton lines may prove useful in breeding for increased resistance to cotton seedling disease complex. High tannin cotton lines were screened for their resistance to Rhizoctonia solani and Pythium aphanidermatum. While no high tannin germplasm line was more resistant to R. solani than the resistant control, Tamcot SP 21, the potential for significant gains from selection was demonstrated. Fifteen high tannin lines expressed resistance to P. aphanidermatum equal to the resistant control, Tamcot Sphinx (El-Zik and Thaxton, 1996). This resistance was not shown to be correlated with tannin content, though it is still unclear whether or not this lack of correlation is real or due to limitations in measuring tannin in infected seedlings.