Genetic relationships and evolution in Cucurbita pepo (pumpkin, squash, gourd) as revealed by simple sequence repeat polymorphisms

Genetic relationships among 104 accessions of Cucurbita pepo were assessed from polymorphisms in 134 SSR (microsatellite) and four SCAR loci, yielding a total of 418 alleles, distributed among all 20 linkage groups. Genetic distance values were calculated, a dendrogram constructed, and principal coordinate analyses conducted. The results showed 100 of the accessions as distributed among three clusters representing each of the recognized subspecies, pepo, texana, and fraterna. The remaining four accessions, all having very small, round, striped fruits, assumed central positions between the two cultivated subspecies, pepo and texana, suggesting that they are relicts of undescribed wild ancestors of the two domesticated subspecies. In both, subsp. texana and subsp. pepo, accessions belonging to the same cultivar-group (fruit shape) associated with one another. Within subsp. pepo, accessions grown for their seeds or that are generalists, used for both seed and fruit consumption, assumed central positions. Specialized accessions, grown exclusively for consumption of their young fruits, or their mature fruit flesh, or seed oil extraction, tended to assume outlying positions, and the different specializations radiated outward from the center in different directions. Accessions of the longest-fruited cultivar-group, Cocozelle, radiated bidirectionally, indicating independent selection events for long fruits in subsp. pepo probably driven by a common desire to consume the young fruits. Among the accessions tested, there was no evidence for crossing between subspecies after domestication

Seed research for improved technologies Pesquisa para o aprimoramento de tecnologia de sementes

The production of high-quality seed is the basis for a durable a profitable agriculture. After production, seed is processed, conditioned, stored, shipped and germinated. For quality assurance, seed quality has to be controlled at all steps of the production chain. Seed functioning is accompanied by programmed transitions from cell proliferation to quiescence upon maturation and from quiescence to reinitiation of cellular metabolism upon imbibition. Despite the obvious importance of these control mechanisms, very little information is available at the molecular level concerning those elements that regulate seed germination. In the present study, the induction of cell cycle activity and the regulation of ß-tubulin expression is related to the water content and other physical properties of the seed.<br>A produção de sementes de alta qualidade é a base para uma agricultura produtiva. Após a colheita, a semente é beneficiada, embalada, armazenada, transportada e semeada. Para maior segurança, tanto dos produtores como dos consumidores, a qualidade da semente deve ser mantida sob controle em todas as fases do processo de produção. O desempenho da semente é resultado de transições programadas desde a divisão celular até a quiescência, durante a maturação, e da quiescência até o reinicio do metabolismo celular, durante a embebição. Apesar da importância destes mecanismos de controle, há pouca informação disponível, a nível molecular, no que diz respeito aos elementos que regulam a germinação da semente. No presente trabalho, a indução do ciclo de atividade celular e a regulação da expressão de ß-tubulina são relacionadas ao grau de umidade e a outras propriedades físicas da semente