<p dir="ltr"><a href="" target="_blank">Shoot architecture in plants refers to the spatial layout of the above-ground organs, which develops through complicated networks of genetic and environmental interactions. Modification of shoot architecture has been a major driver of yield increases in many crop species, but knowledge of the genetic control of shoot architectural traits in soybeans remains incomplete. Chapter 1 provides an overview of soybean shoot architecture traits, encompassing stem growth habit, plant height, branch number, branch angle, petiole angle, leaf size, and leaf shape. The review not only delves into the genetic basis of these traits but also underscores their importance, identifies knowledge gaps, and outlines avenues for future research leveraging cutting-edge technologies in gene editing, phenomics, and genomics. Chapter 2 describes the identification and mapping of a novel locus modulating semideterminate and indeterminate stem growth habits, <i>dt3</i>, on chromosome 10. Allelic and haplotypic analysis of the USDA soybean germplasm collection was conducted to find semideterminate soybean accessions which did not carry known stem termination alleles at the <i>dt1</i> and <i>Dt2 </i>loci. Mapping populations were developed by crossing several of these accessions to indeterminate cultivars, and initial mapping revealed a region on chromosome 10 common to all populations. <i>dt3</i> is a recessive mutation resulting in semideterminate growth habits, and this locus displays a unique pattern of inheritance compared with known stem growth habit genes in soybean or other plant species. Chapter 3 describes the identification of <i>Dt4</i>, a novel semideterminacy allele of <i>FT5a</i> originating from wild soybean. <i>Dt4</i> was identified by quantitative trait locus (QTL) mapping using a population developed by crossing LD00-3309, an indeterminate cultivar with a semideterminate recombinant inbred line (RIL1890) originating from a cross between wild and domesticated soybean. A combination of fine mapping and candidate gene expression analysis pinpointed the allele of the floral inducer <i>FT5a</i> in RIL1890 as <i>Dt4 </i>for semideterminacy. Intriguingly, when the <i>Dt4 </i>allele was transformed into LD00-3309, it resulted in not only semideterminate stem growth habit but also narrowed leaf shape. Chapter 4 describes the identification and mapping of <i>GmBa1</i>, a novel locus specifying soybean branch angle, in which wide branch angle is completely dominant over narrow branch angle. This locus was identified in two distinct biparental mapping populations. The findings described in this dissertation deepen our understanding of genetic mechanisms underlying shoot architecture traits and provide a valuable resource for breeders looking to modify these traits for soybean improvement.</a></p>

Thesis (Ph.D)-University of KwaZulu-Natal, Pietermaritzburg, 2008. / Full text also available online. Scroll down for electronic link.

A introdução de genes Rht, oriundos principalmente de programas de melhoramento da Ásia, Europa, Estados Unidos e México permitiu o avanço da cultura do trigo (Triticum aestivum L.) para áreas consideradas marginais. Nesse contexto, este trabalho se propõe avaliar a capacidade de combinação, heterose e heterobeltiose em um dialelo 8x8 afim de verificar o efeito pleiotrópico (único gene controla diversas características do fenótipo), ou seja, além da estatura, quais os componentes de rendimento que estão sendo alterados quando cultivares de maior estatura são cruzados com as linhas anãs CD 0827, CD 0985 e UTF 0605 disponibilizadas por programas de melhoramento genético nacionais de trigo. O experimento foi conduzido em Pato Branco – PR, na safra agrícola de 2012, em delineamento experimental de blocos casualizados com três repetições. As hibridações foram realizadas com oito genitores, sendo três anões (CD 0827, CD 0985 e UTF 0605) e BRS Pardela, Safira, BRS Tangará, CD 111 e CD 108, escolhidos por apresentarem estatura de planta média à elevada, potencial produtivo e demais caracteres agronômicos de interesse. Os valores dos quadrados médios da capacidade geral de combinação (CGC) foram superiores à capacidade específica de combinação (CEC) para todos os caracteres estudados, demonstrando maior contribuição dos efeitos gênicos aditivos. A capacidade geral de combinação das linhagens anãs (CD 0827, CD 0985 e UTF 0605) indicou as maiores contribuições para a redução da estatura de planta, em ambas as gerações avaliadas, com destaque para a linhagem UTF 0605. A CGC também indica que os genitores UTF 0605, Safira e BRS Tangará maximizam o número de afilhos férteis por planta (AFPL) e CD 0985 e CD 111 se mostraram efetivos em aumentar o número de grãos por planta (NGE). Os genitores Safira, BRS Tangará, CD 108 e entre as anãs CD 0827 se destacaram com os mais elevados valores quanto a CGC para rendimento de grãos por planta (RGP). Os genitores anãos UTF 0605, CD 0985 e CD 0827 são fontes promissoras de genes aditivos para o desenvolvimento de progênies de menor estatura de planta e maior número de afilhos férteis por planta, grãos por espiga e massa de mil grãos. Os cruzamentos CD 0827 x Safira, UTF 0605 x Safira, CD 0985 x CD 111, CD 0985 x CD 108, UTF 0605 x CD 111, UTF 0605 x BRS Tangará destacaram-se com maiores valores de capacidade específica de combinação para rendimento de grãos, e os dois primeiros foram superiores quando se considera os valores de heterose e heterobeltiose e depressão endogâmica. Os resultados deste estudo demonstram a viabilidade de utilização de linhagens anãs em programas de melhoramento genético. / The introduction of Rht genes, mainly from breeding programs in Asia, Europe, United States and Mexico has allowed the advancement of wheat (Triticum aestivum L.) to marginal areas considered. In this context, this study aims to evaluate the combining ability, heterosis and heterosis in a 8x8 diallel order to verify the pleiotropic effect (single gene controls several features of the phenotype), in other words, beyond the stature which components of income that are being changed when taller cultivars are crossed with dwarf lines CD 0827, CD 0985 and UTF 0605 provided by national wheat breeding programs. The experiment was conducted in Pato Branco - PR in the 2012 harvest, in a randomized block design with three replications. Hybridizations were performed with eight parents, three of them dwarfs (CD 0827 , CD 0985 and UTF 0605), BRS Pardela, Safira , BRS Tangara, CD 111 and CD 108. The values of the mean squares for GCA were higher than SCA for all traits indicating higher contribution of additive genetic effects. The general combining ability of the dwarf lines (CD 0827 , CD 0985 and UTF 0605) indicated the greatest contributions to the reduction of plant height in both generations evaluated, highlighting the UTF 0605 lineage. The CGC also indicates that UTF 0605, Safira and BRS Tangará parents maximize the number of fertile tillers per plant (NFPP) and CD 0985 , CD 111 were effective in increasing the number of grains per spike (NGS). The Safira, BRS Tangará, CD 108 and CD 0827 between dwarf parents stood out with the highest values for GCA for grain yield per plant (GYP) . The dwarf parents UTF 0605, CD 0985 and CD 0827 are promising sources of additive genes for the development of progenies of lower plant height and increased number of fertile tillers per plant, grains per spike and thousand grain weight. The CD 0827 x Safira, UTF 0605 x Safira, CD 0985 x CD 111, CD 0985 x CD 108, UTF 0605 x CD 111, UTF 0605 x BRS Tangará stood out with higher values of specific combining ability for grain yield, and the first two were higher when considering the values of heterosis and heterosis and inbreeding depression. The results of this study demonstrate the feasibility of using plant population used in breeding programs.

A rainha é a progenitora de todos os integrantes da colônia de abelhas (Apis mellifera L.) através da qual são passadas as características hereditárias para seus descendentes, sendo de extrema importância nos programas de melhoramento genético apícola. A qualidade de uma rainha é determinada principalmente por fatores intimamente relacionados à sua estrutura reprodutiva, o que é refletido tanto no peso destas, como na atividade de postura e na sua longevidade. Por esse motivo, o objetivo deste trabalho foi avaliar a influência do peso ao nascer de rainhas de abelhas africanizadas sobre o os aspectos relacionados ao comportamento reprodutivo em rainhas fecundadas naturalmente e inseminadas instrumentalmente, bem como acompanhar o desenvolvimento e produtividade das colônias descendentes destas rainhas. Os experimentos foram realizados no Apiário Experimental do Departamento de Genética da Faculdade de Medicina de Ribeirão Preto USP, onde foram estabelecidas doze colônias de abelhas africanizadas divididas em quatro grupos: seis colônias com rainhas fecundadas naturalmente e seis inseminadas instrumentalmente, subdivididas em três colônias com rainhas leves (< 180 mg) e três com rainhas pesadas (> 200 mg), onde o peso foi registrado imediatamente após as rainhas emergirem. As rainhas leves e pesadas, fecundadas naturalmente, foram acompanhadas simultaneamente em colméias de observação, visando analisar o comportamento de acasalamento dos dois grupos, enquanto que as rainhas inseminadas instrumentalmente, de ambos os pesos, foram fecundadas com 6 l de sêmen. Após as fecundações, todas as rainhas foram estabelecidas em caixas tipo núcleo, montadas a partir biomassa semelhante. Vinte dias após a introdução das rainhas nos núcleos estas colônias foram avaliadas quinzenalmente, por meio de mapeamento dos quadros a fim de estimar a porcentagem de ovos, cria aberta, cria fechada e pólen estocado, assim como foram realizados teste de viabilidade de cria. O acompanhamento do tempo de expansão populacional foi estimado através do período necessário para transferência das colônias das caixas tipo núcleo (com três quadros e alimentador) para caixas tipo ninho (com nove quadros e alimentador). Na análise dos dados relacionados ao comportamento de acasalamento observouse que as rainhas leves realizaram maior quantidade de vôos nupciais que as rainhas pesadas, sendo que 56% das nove rainhas leves realizaram mais de um vôo nupcial, enquanto que apenas 33% das nove rainhas pesadas realizaram mais de um vôo nupcial, embora esta diferença não tenha sido estatisticamente significante. Constatamos ainda diferença de um dia na idade de realização de vôos de acasalamento, sendo que as rainhas leves saíram um dia antes, com idade média de 6,11 ± 1,53 dias, enquanto que para as rainhas pesadas essa média foi de 7, 09 ± 4,59 dias. Esta diferença também foi observada na idade em que as rainhas iniciaram a ovoposição, que foi de 7,77 ± 1,86 dias para rainhas leves e 9,88 ± 3,02 dias para rainhas pesadas. Com relação à duração dos vôos nupciais e horário em que foram realizados, ambos ii os grupos tiveram resultados muito semelhantes. As comparações das médias dos dados gerados pelos mapeamentos realizados em colônias com rainhas fecundadas naturalmente e inseminada instrumentalmente, mostraram diferenças estatisticamente significantes relacionada área de postura de ovos (P = 0,117) e área de cria fechada (P = 0,003), onde as colônias descendentes de rainhas pesadas apresentaram desempenho superior em relação as colônias com rainhas leves. Este melhor desempenho é representado ainda pela maior taxa de viabilidade de cria das colônias com rainhas pesadas, dado estatisticamente significante. Atrelado a este fato, as colônias com rainhas pesadas mostraram-se ainda mais rápidas na expansão populacional, que colônias com rainhas leves, onde foi verificada uma diferença média de 24 dias a menos, pelas colônias descendentes de rainhas pesadas, para a transferência para caixas maiores tipo ninho. Quando comparamos as rainhas fecundadas naturalmente e inseminadas instrumentalmente, foi observada diferença média de um dia na idade em que iniciaram a ovoposição, sendo que as rainhas fecundadas naturalmente iniciaram com 9,31 ± 2,49 dias e as rainhas inseminadas instrumentalmente com 10,43 ± 0,51 dias. Observou-se também diferença estatisticamente significante apenas para a variável área de postura (P = 0,004), onde as colônias com rainhas fecundadas naturalmente apresentaram médias superiores, muito embora esta diferença não tenha afetado o desenvolvimento geral das colônias com rainhas inseminadas instrumentalmente, o que foi representado pelo tempo de expansão populacional, igual entre as colônias com rainhas de ambos os tipos de fecundação. Conclui-se que a utilização da técnica de inseminação instrumental de abelhas é uma metodologia viável para a aplicação em programas de melhoramento apícola, uma vez que não encontramos diferenças no desenvolvimento entre colônias descendentes de rainhas inseminadas instrumentalmente e descendentes de rainhas fecundadas naturalmente. Tomando-se por base os principais resultados obtidos no presente trabalho concluímos que a utilização da característica fenotípica peso da rainha acima de 200mg como uma característica importante a ser adotada em programas de seleção e melhoramento de abelhas / The queen is the progenitor of all the honey bee colony members. The quality of a queen is determined mainly by factors closely related to her reproductive structure, including weight, egg-laying activity and longevity. We evaluated the influence of adult eclosion weight on the reproductive behavior of naturally mated and instrumentally inseminated Africanized queens, and we monitored the development and productivity of colonies headed by these queens. Twelve colonies of Africanized honey bees were divided into two groups: six colonies with naturally mated queens and six with instrumentally inseminated queens; there were three light queens (<180 mg) and three heavy queens (> 200 mg) in each mating type group; queen weight was recorded immediately after the virgin queens emerged. The virgin queens in the naturally mated queens group were introduced into observation hives, to compare the mating behavior of the light and heavy queens. The other six queens were artificially inseminated with 6 l semen. After the inseminations, all of the artificially inseminated queens were introduced into four standard Langstroth frame nuclei, which were established with similar numbers of bees and brood area. Beginning 20 days after the introduction of these queens, the colonies were evaluated twice per month, by mapping combs to estimate the areas containing eggs, open and closed brood and stored pollen; the viability of the brood was also investigated. We observed the time it took to outgrow the nucleus boxes (three combs plus an internal frame-size feeder); the colonies were then transferred to 10 frame hives (with nine combs and a feeder). We observed that the light queens made more nuptial flights than heavy queens; five of the nine light queens made more than one nuptial flight, whereas only three of the nine heavy queens took more than a nuptial flight, though this difference was not significant. We also observed a one day difference in the age of queen when she made her mating flights; the light queens went on their first mating flights at a mean age of 6.11 ± 1.53 days, while for the heavy queens the mean was 7.09 ± 4.59 days. A similar tendency was observed in the age at which the queens started oviposition, which was 7.77 ± 1.86 days for light queens and 9.88 ± 3.02 days for heavy queens. The two types of queens had similar duration and time of day of nuptial flights. Heavy queens (both artificially and naturally inseminated) produced significantly more eggs (P = 0.117) and more sealed brood (P = 0.003) than did light queens. Brood viability was significantly greater in the colonies headed by heavy queens. Colony expansion was also faster in colonies with heavy queens. It took an average of 24 days less for the heavy-queen colonies to expand to a point that they needed to be transferred from the four-frame nucleus hives to the 10-frame standard hives. Oviposition by the naturally mated queens began earlier (9.31 ± 2.49 days) than by instrumentally inseminated queens (10.43 ± 0.51 days). Naturally mated queens laid significantly more eggs (P = 0.004), although this difference did not affect the rate of colony population expansion. We concluded that the use of instrumental iv insemination of honey bees is a viable methodology for use in bee breeding programs, since we found no differences in development between colonies with artificially versus naturally inseminated queens. We also concluded that queen weight above 200 mg is a useful characteristic to select for in Africanized honey bees.

Les plantations d’hévéa (Hevea brasiliensis) s’étendent vers des zones non traditionnelles de production en Thaïlande où des conditions plus sèches ont pu conduire à une diminution de la croissance des arbres et de la production de latex. Des paramètres physiologiques utiles pour sélectionner des génotypes adaptés sont nécessaires, comme l’efficience d’utilisation de l’eau (WUE). La discrimination isotopique du carbone est largement utilisée comme proxy pour WUE et peut être aisément utilisée dans des programmes de sélection pour la tolérance à la sécheresse. δ13C des feuilles et les échanges gazeux foliaires ont été mesurés sur de jeunes plants de dix clones d’hévéa cultivés en pot dans une pépinière. La gamme de δ13C des feuilles entre ces dix clones était restreinte et la corrélation entre δ13C et WUEi était significative que sous fort déficit de pression de vapeur saturante, ce qui signifie que la prédiction de WUE par δ13C serait peu précise. Il y avait une large gamme de δ13C entre les génotypes dans une collection de 49 génotypes sauvages d’hévéa cultivés dans le nord-est de la Thaïlande en saison sèche et en saison des pluies. δ13C était relativement stable avec une bonne corrélation entre les saisons. Cette étude montre que la variabilité génétique de δ13C est prometteuse pour des futurs programmes de sélections si une bonne corrélation entre δ13C et WUE peut être établie. L’absence de corrélation entre de δ13C du latex (δ13C-L) et des composés solubles extraits des feuilles (δ13C-S) prélevées sur des arbres saignés et non saignés âgés de 20 ans suggère que photosynthétats récemment produits se mélangent à un stock important d’hydrate de carbone impliqués dans la régénération du latex après la saignée. Donc, δ13C du latex n’est pas un indicateur pertinent de WUE / The rubber (Hevea brasiliensis) plantations extend to non-traditional area in Thailand where dryer conditions has been reported to impair the growth of rubber trees and latex production. Physiological parameters helpful for breeding adapted genotypes are required, such as water use efficiency (WUE). Carbon isotope discrimination is widely used as a proxy for WUE that can easily be used for selection and breeding programs for drought tolerance. Leaf δ13C and leaf gas exchange were measured on young saplings of 10 rubber clones growing in pot in a common garden. The range of leaf δ13C among 10 clones was narrow and the correlation between δ13C and WUEi was significant under high vapour pressure deficit only, which means the prediction of WUE by δ13C would have low precision. There were large δ13C variations among the genotypes at all seasons in a collection of 49 wild genotypes of rubber in Northeastern Thailand. δ13C was rather stable with a good correlation between rainy and dry season. The genetic variability of δ13C is promising for breeding if a good correlation between δ13C of leaf and WUE can be established. The lack of correlation between δ13C of latex (δ13C-L) and of leaf soluble compounds (δ13C-S) collected from tapped and untapped 20 year-old rubber trees suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping. Thus δ13C of latex is not a relevant indicator of WUE of rubber trees

A rainha é a progenitora de todos os integrantes da colônia de abelhas (Apis mellifera L.) através da qual são passadas as características hereditárias para seus descendentes, sendo de extrema importância nos programas de melhoramento genético apícola. A qualidade de uma rainha é determinada principalmente por fatores intimamente relacionados à sua estrutura reprodutiva, o que é refletido tanto no peso destas, como na atividade de postura e na sua longevidade. Por esse motivo, o objetivo deste trabalho foi avaliar a influência do peso ao nascer de rainhas de abelhas africanizadas sobre o os aspectos relacionados ao comportamento reprodutivo em rainhas fecundadas naturalmente e inseminadas instrumentalmente, bem como acompanhar o desenvolvimento e produtividade das colônias descendentes destas rainhas. Os experimentos foram realizados no Apiário Experimental do Departamento de Genética da Faculdade de Medicina de Ribeirão Preto USP, onde foram estabelecidas doze colônias de abelhas africanizadas divididas em quatro grupos: seis colônias com rainhas fecundadas naturalmente e seis inseminadas instrumentalmente, subdivididas em três colônias com rainhas leves (< 180 mg) e três com rainhas pesadas (> 200 mg), onde o peso foi registrado imediatamente após as rainhas emergirem. As rainhas leves e pesadas, fecundadas naturalmente, foram acompanhadas simultaneamente em colméias de observação, visando analisar o comportamento de acasalamento dos dois grupos, enquanto que as rainhas inseminadas instrumentalmente, de ambos os pesos, foram fecundadas com 6 l de sêmen. Após as fecundações, todas as rainhas foram estabelecidas em caixas tipo núcleo, montadas a partir biomassa semelhante. Vinte dias após a introdução das rainhas nos núcleos estas colônias foram avaliadas quinzenalmente, por meio de mapeamento dos quadros a fim de estimar a porcentagem de ovos, cria aberta, cria fechada e pólen estocado, assim como foram realizados teste de viabilidade de cria. O acompanhamento do tempo de expansão populacional foi estimado através do período necessário para transferência das colônias das caixas tipo núcleo (com três quadros e alimentador) para caixas tipo ninho (com nove quadros e alimentador). Na análise dos dados relacionados ao comportamento de acasalamento observouse que as rainhas leves realizaram maior quantidade de vôos nupciais que as rainhas pesadas, sendo que 56% das nove rainhas leves realizaram mais de um vôo nupcial, enquanto que apenas 33% das nove rainhas pesadas realizaram mais de um vôo nupcial, embora esta diferença não tenha sido estatisticamente significante. Constatamos ainda diferença de um dia na idade de realização de vôos de acasalamento, sendo que as rainhas leves saíram um dia antes, com idade média de 6,11 ± 1,53 dias, enquanto que para as rainhas pesadas essa média foi de 7, 09 ± 4,59 dias. Esta diferença também foi observada na idade em que as rainhas iniciaram a ovoposição, que foi de 7,77 ± 1,86 dias para rainhas leves e 9,88 ± 3,02 dias para rainhas pesadas. Com relação à duração dos vôos nupciais e horário em que foram realizados, ambos ii os grupos tiveram resultados muito semelhantes. As comparações das médias dos dados gerados pelos mapeamentos realizados em colônias com rainhas fecundadas naturalmente e inseminada instrumentalmente, mostraram diferenças estatisticamente significantes relacionada área de postura de ovos (P = 0,117) e área de cria fechada (P = 0,003), onde as colônias descendentes de rainhas pesadas apresentaram desempenho superior em relação as colônias com rainhas leves. Este melhor desempenho é representado ainda pela maior taxa de viabilidade de cria das colônias com rainhas pesadas, dado estatisticamente significante. Atrelado a este fato, as colônias com rainhas pesadas mostraram-se ainda mais rápidas na expansão populacional, que colônias com rainhas leves, onde foi verificada uma diferença média de 24 dias a menos, pelas colônias descendentes de rainhas pesadas, para a transferência para caixas maiores tipo ninho. Quando comparamos as rainhas fecundadas naturalmente e inseminadas instrumentalmente, foi observada diferença média de um dia na idade em que iniciaram a ovoposição, sendo que as rainhas fecundadas naturalmente iniciaram com 9,31 ± 2,49 dias e as rainhas inseminadas instrumentalmente com 10,43 ± 0,51 dias. Observou-se também diferença estatisticamente significante apenas para a variável área de postura (P = 0,004), onde as colônias com rainhas fecundadas naturalmente apresentaram médias superiores, muito embora esta diferença não tenha afetado o desenvolvimento geral das colônias com rainhas inseminadas instrumentalmente, o que foi representado pelo tempo de expansão populacional, igual entre as colônias com rainhas de ambos os tipos de fecundação. Conclui-se que a utilização da técnica de inseminação instrumental de abelhas é uma metodologia viável para a aplicação em programas de melhoramento apícola, uma vez que não encontramos diferenças no desenvolvimento entre colônias descendentes de rainhas inseminadas instrumentalmente e descendentes de rainhas fecundadas naturalmente. Tomando-se por base os principais resultados obtidos no presente trabalho concluímos que a utilização da característica fenotípica peso da rainha acima de 200mg como uma característica importante a ser adotada em programas de seleção e melhoramento de abelhas / The queen is the progenitor of all the honey bee colony members. The quality of a queen is determined mainly by factors closely related to her reproductive structure, including weight, egg-laying activity and longevity. We evaluated the influence of adult eclosion weight on the reproductive behavior of naturally mated and instrumentally inseminated Africanized queens, and we monitored the development and productivity of colonies headed by these queens. Twelve colonies of Africanized honey bees were divided into two groups: six colonies with naturally mated queens and six with instrumentally inseminated queens; there were three light queens (<180 mg) and three heavy queens (> 200 mg) in each mating type group; queen weight was recorded immediately after the virgin queens emerged. The virgin queens in the naturally mated queens group were introduced into observation hives, to compare the mating behavior of the light and heavy queens. The other six queens were artificially inseminated with 6 l semen. After the inseminations, all of the artificially inseminated queens were introduced into four standard Langstroth frame nuclei, which were established with similar numbers of bees and brood area. Beginning 20 days after the introduction of these queens, the colonies were evaluated twice per month, by mapping combs to estimate the areas containing eggs, open and closed brood and stored pollen; the viability of the brood was also investigated. We observed the time it took to outgrow the nucleus boxes (three combs plus an internal frame-size feeder); the colonies were then transferred to 10 frame hives (with nine combs and a feeder). We observed that the light queens made more nuptial flights than heavy queens; five of the nine light queens made more than one nuptial flight, whereas only three of the nine heavy queens took more than a nuptial flight, though this difference was not significant. We also observed a one day difference in the age of queen when she made her mating flights; the light queens went on their first mating flights at a mean age of 6.11 ± 1.53 days, while for the heavy queens the mean was 7.09 ± 4.59 days. A similar tendency was observed in the age at which the queens started oviposition, which was 7.77 ± 1.86 days for light queens and 9.88 ± 3.02 days for heavy queens. The two types of queens had similar duration and time of day of nuptial flights. Heavy queens (both artificially and naturally inseminated) produced significantly more eggs (P = 0.117) and more sealed brood (P = 0.003) than did light queens. Brood viability was significantly greater in the colonies headed by heavy queens. Colony expansion was also faster in colonies with heavy queens. It took an average of 24 days less for the heavy-queen colonies to expand to a point that they needed to be transferred from the four-frame nucleus hives to the 10-frame standard hives. Oviposition by the naturally mated queens began earlier (9.31 ± 2.49 days) than by instrumentally inseminated queens (10.43 ± 0.51 days). Naturally mated queens laid significantly more eggs (P = 0.004), although this difference did not affect the rate of colony population expansion. We concluded that the use of instrumental iv insemination of honey bees is a viable methodology for use in bee breeding programs, since we found no differences in development between colonies with artificially versus naturally inseminated queens. We also concluded that queen weight above 200 mg is a useful characteristic to select for in Africanized honey bees.

<div>Drought is the leading cause of crop loss globally. Breeding for drought tolerance is difficult due to the polygenetic nature of the trait and low heritability of yield under drought. Plant relative water content is a secondary trait that may advance drought breeding programs.</div><div><br></div><div>The LeafSpec, a newly developed hyperspectral leaf scanner, was used to test the hypothesis that distribution of hyperspectral information across the leaf can be used to improve prediction of leaf relative water content. Data was collected across two experiments from five different maize genotypes representing temperate and tropical hybrids with varying levels of drought tolerance and inbreds with varying stomatal densities. The hyperspectral intensity averaged across the entire leaf was used to predict relative water content with an R2Prediction of 0.7989. Model performance was tested using additional predictors that quantify:</div><div><br></div><div>• Spectral information from multiple regions in the leaf (e.g. base, middle, tip).</div><div>• Spectral information from regions segmented by tissue type.</div><div>• The distribution of hyperspectral intensity in a cross section parallel to the midrib or in a cross-section perpendicular to the midrib.</div><div>• A contour pattern of hyperspectral intensity from the outside edge of the leaf to the midrib.</div><div>• Texture features extracted from each wavelength.</div><div><br></div><div>The mean spectrum model outperformed previously reported results, potentially due to the elimination of sources of noise and higher quality data produced by the LeafSpec. None of the models with expanded feature sets outperformed the mean spectrum model at a statistically significant level. The hyperspectral signal from the green tissue a third of the way from the base of the leaf and half way between the midrib and edge was the most correlated with relative water content. Models without midrib and vein tissue signals had increased performance. Distribution of the Water Index visually showed improved ability to discriminate leaf RWC as compared to individual wavelengths but this did not translate to improved model performance.</div><div><br></div><div>For future work, more data should be collected to improve model robustness and hyperspectral imaging should include SWIR wavelengths that have previously been found useful for predicting relative water content. Exploring indices composed from current spectral bands may lead to improved prediction performance.</div>

<p dir="ltr">Communication between the male gametophyte (the tip-growing pollen tube) and the female gametophyte (the synergid cells) is crucial for sexual reproduction in flowering plants. The reception of the pollen tube (PT) depends on its recognition and sensitivity to the signals from the synergid cells for its rupture, sperm release, and double fertilization. Mutations in genes regulating communication between the synergid cells and pollen tube lead to PT overgrowth. Despite significant advances in understanding the molecular mechanism of pollen tube reception in Arabidopsis, there remains a need for more comprehensive information on the impact of natural variations on physiological traits related to pollen tube and synergid signals in pollen tube reception. This research investigates the effects of natural variation on pollen tube sensitivity to synergid signals mediated by NORTIA. In <i>nortia</i> homozygous mutants, PT-synergid communication is disrupted due to lower levels of calcium signals in the synergid cells, resulting in PT overgrowth. Using the Aniline blue staining procedure, this study identified twelve ecotypes of Arabidopsis thaliana out of the twenty-four ecotypes that could suppress the PT overgrowth phenotype of <i>nta-1</i>. I observed that the suppressor ecotypes exhibit characteristics like the Columbia (Col-0) ecotype, while non-suppressor ecotypes resemble the Ws-2 ecotype. Comparing the impact of the Columbia (Col-0) and Wassilewskija (Ws-2) ecotypes on PT overgrowth in the <i>nta-2</i> mutant revealed that Columbia (Col-0) effectively suppressed PT overgrowth compared to Wassilewskija (Ws-2). We investigated the sensitivity of PT integrity mutants to synergid signals. Our results showed that compromised PT integrity mutant genes (<i>mlo1mlo15</i>) partially suppressed PT overgrowth in <i>nta-1</i>. I propose that suppressor ecotypes and mutants may exhibit a heightened sensitivity to synergid signals, that help them to regulate their response to synergid signals finely.</p>

<p>Dissecting the soybean grain yield (GY) to approach it as a sum of its associated processes seems a viable approach to explore this trait considering its complex multigenic nature. Monteith (1972, 1977) first defined potential yield as the result of three physiological efficiencies: light interception (Ei), radiation use efficiency (RUE) and harvest index (HI). Though this rationality is not recent, few works assessing these three efficiencies as strategies to improve crops have been carried out. This thesis approaches yield from the perspective of Ei, RUE, and HI to better understand yield as the result of genetic and physiological processes. This study reveals the phenotypic variation, heritability, genetic architecture, and genetic relationships for Ei, RUE, and HI and their relationships with GY and other physiological and phenological variables. Similarly, genomic prediction is presented as a viable strategy to partially overcome the tedious phenotyping of these traits. A large panel of 383 soybean recombinant inbred lines (RIL) with significant yield variation but shrinkage maturity was evaluated in three field environments. Ground measurements of dry matter, photosynthesis (A), transpiration (E), water use efficiency (WUE), stomatal conductance (gs), leaf area index (LAI) and phenology (R1, R5, R8) were measured. Likewise, RGB imagery from an unmanned aircraft system (UAS) were collected with high frequency (~12 days) to estimate the canopy dynamic through the canopy coverage (CC). Light interception was modeled through a logistic curve using CC as a proxy and later compared with the seasonal cumulative solar radiation collected from weather stations to calculate Ei. The total above ground biomass collected during the growing season and its respective cumulative light intercepted were used to derive RUE through linear models fitting, while apparent HI was calculated through the ratio seeds dry matter vs total above-ground dry matter. Additive-genetic correlations, genome wide association (GWA) and whole genome regressions (WGR) were performed to determine the relationship between traits, their association with genomic regions, and the feasibility of predicting these efficiencies through genomic information. Our results revealed moderate to high phenotypic variation for Ei, RUE, and HI. Additive-genetic correlation showed a strong relationship of GY with HI and moderate with RUE and Ei when the whole data set was considered, but negligible contribution of HI on GY when just the top 100 yielding RILs were analyzed. High genetic correlation to grain yield (GY) was also observed for A (0.87) and E (0.67), suggesting increase in GY can be achieved through the improvement of A or E. The GWA analyses showed that Ei is associated with three SNPs; two of them located on chromosome 7 and one on chromosome 11 with no previous quantitative trait loci (QTLs) reported for these regions. RUE is associated with four SNPs on chromosomes 1, 7, 11, and 18. Some of these QTLs are novel, while others are previously documented for plant architecture and chlorophyll content. Two SNPs positioned on chromosome 13 and 15 with previous QTLs reported for plant height and seed set, weight and abortion were associated with HI. WGR showed high predictive ability for Ei, RUE, and HI with maximum correlation ranging between 0.75 to 0.80. Both directed and undirected multivariate explanatory models indicate that HI has a strong relationship with A, average growth rate of canopy coverage for the first 40 days after planting (AGR40), seed-filling (SFL), and reproductive length (RL). According to the path analysis, increase in one standard unit of HI promotes changes in 0.5 standard units of GY, while changes in the same standard unit of RUE, and Ei produce increases on GY of 0.20 and 0.19 standard units. This study presents novel genetic knowledge for Ei, RUE, HI and GY along with a set of tools that may contribute to the development of new cultivars with enhanced light interception, light conversion and optimized dry matter partitioning in soybean. This work not only complements the physiological knowledge already available with the genetic control of traits directly associated with yield, but also represents a pioneer attempt to integrate traditional physiological traits into the breeding process in the context of physiological breeding<br></p>

There are few maize varieties that are drought tolerant in semi-arid eastern Kenya and farmer perceptions of drought tolerant maize cultivars have not been studied in this region. Farmers in this region use maize landraces that have not been studied for their potential future hybridization. The main objectives of this study were therefore to: (i) study farmer perceptions of drought and preference for maize varieties, (ii) improve drought tolerance in maize populations in the semi-arid eastern Kenya using S1 family recurrent selection, and (iii) classify maize landraces according to their heterotic patterns. A participatory rural appraisal (PRA) was conducted in Machakos and Makueni districts in semi-arid eastern Kenya. A total of 175 farmers were involved in focus group discussions. An open ended questionnaire and a checklist were used to guide the farmers during the discussion sessions. Scoring and ranking techniques were used to assess farmers’ preferences of maize varieties and constraints to maize production. The farmers grew maize as their major crop followed by beans. Nearly 60% of the farmers grew local maize landraces, whose seed they recycled from season to season; 40% grew improved varieties, but mainly composites rather than hybrids. The key farmers’ criteria for choosing a maize variety in order of importance were drought tolerance, early maturity, high yield, and disease resistance. The major constraints to maize production were drought, lack of technical know-how, pests, poor soils, and inadequate seed supply. Maize traits preferred by farmers in a drought tolerant variety included high yield, recovery after a dry spell and the stay green characteristic. Two maize landrace populations MKS and KTU from semi-arid eastern Kenya and three CIMMYT populations V032, ZM423, and ZM523 were subjected to two cycles of S1 progeny recurrent selection for drought tolerance in yield and traits indicative of drought tolerance were measured during flowering and grain filling from February 2005 to September 2007. Evaluation to determine selection gains was done in one trial replicated five times. It was laid out as a 4x4 lattice design and drought was imposed at reproductive stage by withholding irrigation one week before flowering and resumed during grain filling. The trial was repeated under well-watered conditions which served as a control experiment. After two cycles of selection under drought stress conditions, KTU population had a realized gain in yield of 0.2 t ha-1, MKS population 1.2 t ha-1 and ZM423 0.4 t ha-1, whereas in V032 and ZM523, grain yield reduced by 1.1 t ha-1 and 0.6 t ha-1, respectively. Under well watered conditions, the realized gains in grain yield were positive in all the populations except V032, where there was a reduction of 0.1 t ha-1. Selection increased the genetic variability and heritability estimates for yield in S1 lines of MKS and ZM423 populations, but decreased in KTU, V032 and ZM523 populations. The research to identify heterotic patterns was undertaken using ten maize landraces from the semi-arid eastern Kenya, six maize landraces from coastal Kenya, and three maize populations from CIMMYT. These populations were planted at Kiboko Research Farm during the short rains of October-December 2005 and crossed to two population testers, Embu 11 and Embu 12. The evaluation of the test crosses was done during the long rains of March-June 2006. Percentage heterosis for yield ranged from -17.7% to 397.4%, -79.4 to 22.2% for anthesis-silking interval, -23.9% to 29.2% for ear height, -0.1 to 1.1 for ear diameter, -7.1 to 21.2% for ear length and -5.9% to 30.3% for plant height. iii General combining ability (GCA) effects were significant (p=0.05) for all the traits, while specific combining ability (SCA) effects were not significant (p>0.05), implying that variation among these crosses was mainly due to additive rather than nonadditive gene effects. Since SCA was not significant (p>0.05) for yield, maize populations were classified based on percentage heterosis for yield alone. The maize populations therefore, were grouped into three different heterotic groups P, Q and R. Twelve landrace populations and two CIMMYT populations showed heterosis with Embu 11 and no heterosis with Embu 12 were put in one group P. Two landrace populations that showed no heterosis with either tester were put in group Q. Two landrace populations and one CIMMYT population showed heterosis with both testers were put in group R. None of the populations showed heterosis only with Embu 12 and no heterosis with Embu 11. The main constraint to maize production was drought and the farmers preferred their landraces whose seed they recycled season to season. After two cycles of recurrent selection, the landrace populations showed improved progress in yield. Thus, further selection will be beneficial in the populations where genetic variability increased. Therefore, these populations can further be improved per se and released as varieties and/or incorporated into the existing maize germplasm to broaden their genetic base, given that their heterotic patterns have been identified. Considering that farmers recycle seed, breeding should be towards the development of open-pollinated varieties which are drought tolerant. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.