Browsing by Author "Mateo Moncada, Rafael Arturo"
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Item Evaluation and heritability of ergot resistance derived from sorghum germplasm IS8525.(Texas A&M University, 2004-09-30) Mateo Moncada, Rafael ArturoSorghum (Sorghum bicolor [L.] Moench) is fifth among the major cereal crops in the world in terms of production area and total production. Grain sorghum can be successfully produced in a wide range of environments, its productivity is severely limited by pathogens, insects and abiotic stresses. One of these pathogens is Claviceps africana Frederickson Mantle & de Milliano, commonly known as ergot. As is the case with many sorghum diseases, the best long term approach to control ergot may be the use of genetic resistance. There is limited information about resistance to C. africana in sorghum, and the reported resistance in most lines is fertility-based. Dahlberg (1999) first reported the line IS8525 to have the most tolerance to ergot of any of the accessions screened in Puerto Rico. The specific objectives of this research are: (1) to confirm the presence of C. africana resistance in IS8525 germplasm, (2) to determine if the resistance in IS8525 is pollen mediated or ovule based, and (3) to determine if the resistance in IS8525 is heritable and stable across environments. Ergot vulnerability ratings were determined for two recombinant inbred line populations, IS8525D and IS8525J, in four locations during 2001. Also, ergot vulnerability ratings were evaluated in four test-cross populations (using as testers A3Tx623 and A3Tx623) in two locations. Evaluations of the original parents indicate that ergot tolerance in IS8525D parent was consistently better than that in IS8525J parent. As expected, neither parent provided complete resistance. The IS8525J recombinant inbred line population showed significantly more ergot susceptibility than the IS8525D recombinant inbred line population and this trend was consistent across environments. Variation for ergot vulnerability amo ng recombinant inbred lines for both populations was detected, but the amount of variability was environment dependent. In the testcross hybrids, all four populations were susceptible to ergot, primarily due to male sterility in the hybrids, confirming that the tolerance shown in IS8525 germplasm is mostly pollen mediated. However, a greater level of tolerance in the IS8525 hybrid checks confirmed the reports of tolerance by Dahlberg et al. (1998) and Reed et al. (2002).Item Genetic diversity and combining ability among sorghum conversion lines(Texas A&M University, 2007-04-25) Mateo Moncada, Rafael ArturoSorghum (Sorghum bicolor [L] Moench) was first introduced to the United States in the 1800s. These introductions consisted of tropical varieties with a short day photoperiod response that limited their use in temperate hybrid breeding programs. Commercial exploitation of F1 hybrids in grain sorghum started by the mid 1950s with the use of cytoplasmic male sterility system CMS (A1). Even though other CMS are available, most sorghum hybrid seed production still relies on the A1 system. Genetic gain in most agronomic crop species is limited by several factors. In the specific case of sorghum, the uniform use of the CMS (A1) system and the recent introduction of sorghum to the United States have resulted in a reduction of its genetic base. In order to create enough genetic variability, plant breeders might utilize exotic non adapted material, exotic adapted material or existing elite material as a source of new alleles that will protect and improve genetic gain through selection. This study provides an estimate of the genetic diversity existing in a set of sorghum conversion lines. The objectives of this study were: (1) to estimate the genetic diversity present among a set of 16 sorghum conversion lines???? (2) to classify this set of lines based on genetic similarities estimated using AFLP markers and (3) to estimate heterosis, general and specific combining ability for grain yield among the set of conversion lines. Genetic diversity was present in the set of conversion lines evaluated. For the lines included only in this study, Caudatum was the most homogenous race (average GS = 0.69), and this race was closely related to the Durra race (Average GS = 0.66). Two other homogenous races were Bicolor and Kafir with average GS of 0.67. Highest GCA effects were obtained from the Kafir and Caudatum races. Good heterotic responses were obtained from DurraKafir races and CaudatumKafir races. Estimation of SCA, MPH and BPH identified specific crosses that were numerically superior than those of the checks. The use of AFLP markers allowed the identification of five strong clusters through estimates of genetic similarities. This classification did not group the lines by either their genetic background or their fertility reaction. This study provides information to identify specific combinations that would help to understand heterotic relationships in sorghum, and support the suggestions made by Menz and Gabriel that races in sorghum are not well defined.