Thesis (M.Sc. (Crop Science)) --University of Limpopo, 2008 / Stenocarpella ear rot caused by Stenocarpella maydis (Berck) Sutton is the most important disease of maize in South Africa. It is a sporadic disease which makes it difficult for farmers to prepare for its occurrence and consequently of the control measure. The objectives of this study were to genetically characterise the resistance of Stenocarpella maydis ear rot and to identify agronomically suitable Stenocarpella ear rot resistant inbred lines with good combining ability for grain yield. The experimental design was a randomised complete block design with three replications. Studies were conducted at Bethlehem, Cedara and Potchefstroom. To facilitate the comparison, separate trials were established for inbred lines and top cross hybrids. Fifty-four inbred lines were compared against four inbred lines vs. E739, DO620Y, H111 and Mo17 that are well adapted and stable yielders possessing variable resistance to Stenocarpella maydis ear rot. Fifty-four top crosses were compared against one open pollinated variety (SAM 1066), which was used as a tester line as well as three commercial hybrids vs. PAN 6124BT, PAN 6026 and CRN 3505. At Potchefstroom there was an inoculation trial using both inbreds and top crosses. The inbred and top cross materials were obtained from 2004/05 breeding nursery under natural infestation of Stenocarpella maydis at Agricultural Research Council-Grain Crops Institute, Potchefstroom. Data collected were number of days to 50% silking, plant and ear height in centimetres, husk cover, ear position, stand count, total number of ears, number of diseased ears and lodging resistance,. Entries 43 and 4 were the most stable inbred lines with a beta close to 1, while entries 9 and 25 had the smallest deviation from regression. Among the tested inbred lines entry 47 was superior over other inbred lines for grain yield followed by entry 4. Entry 47 showed grain yield of 2.84 tons ha-1 at Bethlehem and 4.42 tons ha-1 at Potchefstroom. While entry 4 had a grain yield of 2.19 tons ha-1 at Bethlehem and 4.58 tons ha-1at Potchefstroom. The two lines, however, are poor combiners for both grain yield and Stenocarpella maydis ear rot resistance. Using SAM 1066 as a tester the grain yield observed for top crosses at Bethlehem, Cedara and Potchefstroom were 5.94, 7,15 and 9.95 tons ha-1, respectively. Entries 57 and 14 were the most stable top cross hybrids with a beta close to one, while entries 46 and 47 had the smallest deviation from regression. Entries 56 and 28 were the most superior top cross hybrids. Entry 56 showed grain yield of 5.58 tons ha-1 at Bethlehem, at Cedara it showed the yield of 5.90 tons ha-1 and at Potchefstroom it was 9.95 tons ha-1 and for the average of three sites it was 7.14 tons ha-1. Entry 28 showed grain yield of 5.80 tons ha-1 at Bethlehem, at Cedara it was 5.80 and at Pothefstroom it was 9.35 tons ha-1 and the combined average was 6.98 tons ha-1. These values compared favourably with the commercial standards. The checks entries 58 and 57 had proved to be resistant over locations. The best combiners for Stenocarpella maydis resistance were entries 29 and 52. Stenocarpella maydis ear rot was found to be of polygenic resistance with additive genetic effects. / The government of Lesotho, Agricultural Research Council-Grain Crops Institute (ARC-GCI), and the Maize Trust

Made available in DSpace on 2016-12-08T16:44:43Z (GMT). No. of bitstreams: 1 PGPV13MA115.pdf: 363959 bytes, checksum: 6e95b30ef3170c9a81eb55320f07a3ed (MD5) Previous issue date: 2013-02-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The importance of pathogens that infect corn crop is a major obstacle to the continued increase in crop yield. Genetic resistance is a major strategy for disease control, however, in Brazil there is no information maize cultivars resistant to macrospora spot caused by the fungus Stenocarpella macrospora. With the objective to evaluate the resistance of different cultivars to macrospora spot, the impact of their occurrence on yield and quality of grain, get an ideal concentration of conidial S. macrospora to beused for inoculation of corn and investigate whether there are differences in disease severity from isolates of the fungus were developed four experiments. The first experiment tested six xoncentration: 0,60, 120, 180, 240 and 300 000 conidia mL-1 and the second tested isolates drom the regions of Vacaria, Passo Fundo, São Valentim, Campinas do Sul, state of Rio Grande do Sul, and Quilombo e Lages, Santa Catarina state, and Pato Branco, Paraná state. The inoculum concentration data were subjected to regression analysis (P <0.05) while data from different isolates were submitted to Tukey test (P <0.05). the third study was conducted in a greenhouse, in 2011, with 92 cultivars and three isolates of the fungus and mountainous regions west of the State of Santa Catarina (OSC and SSC) and Campos de Cima da Serra of the State of Rio Grande do Sul (CCSRS). It was used a completely randomized designs with five replicates. It was evaluated the severity of the macrospora spot 21 days after inoculation. Data were analyzed by ANOVA and means were compared by the Scott Knott test (P <0.05) and genotype groups responses being analyzed by orthogonal contrast (P <0.05). the fourth experiment was conducted in the field in Lages, SC, 2011/2012 season, with eigth genotypes: CD 393, NBX 920YG, TORK TL, AS 1565, DKB 240YG, SG 6304YG, P30F53YG and SCS 155 CATARINA under inoculating conidia of S. macrospora in different stages (V10, V12 and tasseling) and a control. It was evaluated the incidence of white rot cob, percentage of rot grains, thousand grain weigth and grain yield. Data were analyzed by analysis of variance and then by Tukey test (P <0.005). Dunnett s test was conducted to compare the stages of inoculation with control for each hybrid. The results in these experiments have revealed that there was infection and expression of symptoms in all cultivars, differing in severity. The hybrids showed uo for the three most resistant isolates, indicating that the gratest genetic variability of VPA and HD did not guarantee greater resistance to macrospora spot. It was also verified differneces in aggressiveness among isolates from different regions, being isolated from the Quilombo showed that on average greater disease severity, for this isolated significant difference between transgenic and conventional cultivars. It can be confirmed that was not detected complete resistance to S. macrospora. From the regression analysis it was determined that with 180.000 conidia ml-1 was reached maximum severity. Of the eighjt hybrids tested, five had decreased productivity when inoculated with S. macrospora. For all hybrids increased incidence of white rot cob and rot grains compared stages of inoculation with the witness (check) and as the stadium came from tasseling inoculation increased the percentage of rot cob and rot grain. It was demonstrated in this study that there is genetic variation for resistance to white rot cob caused by S. macrospora with inoculum derived from leaf lesions / A importância dos patógenos que infectam a cultura do milho constitui um dos principais entraves para o contínuo aumento na produtividade da cultura. A resistência genética é uma das principais estratégias de controle de doenças foliares, no entanto, no Brasil não há informações de cultivares de milho resistente à mancha de macrospora causada pelo fungo Stenocarpella macrospora. Com o objetivo de avaliar a resistência de diferentes cultivares comerciais à mancha de macrospora, o impacto da sua ocorrência na produtividade e qualidade de grãos, obter uma concentração ideal de conídios de S. macrospora a ser utilizada na inoculação do milho e investigar se há diferença na severidade da doença a partir de isolados do fungo foram desenvolvidos quatro experimentos. O primeiro experimento testou seis concentrações de conídios: 0, 60, 120, 180, 240 e 300 mil conídios mL-1 e o segundo testou isolados oriundos das regiões de Vacaria, Passo Fundo, São Valentim, Campinas do Sul, Estado do Rio Grande do Sul, Lages e Quilombo, Estado de Santa Catarina, e Pato Branco, Estado do Paraná. Os dados de concentração de inóculo foram submetidos à análise de regressão (P<0,05) enquanto os dados dos diferentes isolados foram submetidos ao teste de Tukey (P<0,05). O terceiro trabalho foi conduzido em casa de vegetação, no ano de 2011, com 92 cultivares e três isolados do fungo das regiões Oeste e Serrana do Estado de Santa Catarina (OSC e SSC) e Campos de Cima da Serra do Estado do Rio Grande do Sul (CCSRS). Utilizou-se delineamento experimental inteiramente casualizado com cinco repetições. Avaliou-se a severidade da mancha de macrospora aos 21 dias após a inoculação. Os dados foram submetidos à ANOVA e as médias comparadas pelo teste de Scott Knott (P<0,05), respostas ente grupos de genótipos analisadas por contraste ortogonal (P<0,05). O quarto experimento foi realizado a campo no município de Lages, SC, safra 2011/2012, com oito genótipos: CD 393, NBX 920YG, TORK TL, AS 1565, DKB 240YG, SG 6304YG, P30F53YG e SCS 155 CATARINA, sob inoculação de conídios de S. macrospora em diferentes estádios de (V10, V12 e Pendoamento) e uma testemunha. Avaliaram-se incidência de podridão branca de espiga, porcentagem de grãos ardidos, massa de mil grãos e rendimento de grãos. Os dados foram analisados por meio de análise de variância e posteriormente por teste de Tukey (P<0,05). Foi realizado teste de Dunnett para comparação dos estádios de inoculação com a testemunha, para cada híbrido. Os resultados obtidos em tais experimentos permitem afirmar que houve infecção e expressão de sintomas em todas cultivares avaliadas, diferindo no nível de severidade. Os híbridos simples demonstraram-se mais resistentes para os três isolados, demonstrando que a maior variabilidade genética da VPA e do HD não garantiu maior resistência à mancha de macrospora. Foi verificado também diferenças de agressividade entre os isolados de regiões diferentes, sendo o isolado de Quilombo o que apresentou na média maior severidade da doença. Para este isolado houve diferença significativa entre cultivares transgênicas e convencionais. Pode-se confirmar que não foi detectada resistência completa à S. macrospora. A partir da análise de regressão determinouse que com 180 mil conídios mL-1 foi alcançada máxima severidade. Dos oito híbridos avaliados, cinco apresentaram queda de produtividade quando foram inoculados com S. macrospora. Para todos os híbridos houve aumento de podridão branca da espiga e grãos ardidos quando comparados os estádios de inoculação com a testemunha e conforme o estádio de inoculação se aproximou do pendoamento aumentou espigas doentes e grãos ardidos. Ficou evidenciado neste estudo que existe variabilidade genética para resistência a podridão da espiga causada por S. macrospora com inóculo oriundo das lesões foliares

Diplodia ear rot (DER) of maize (Zea mays L.) caused by the fungus, Stenocarpella maydis (Berk.) Sutton has increased in incidence in localized fields over the past decade. My research focused on screening for resistance by examining the development of DER following inoculations prior to flowering, analyzing a diallel cross for DER resistance, and examining the genetic variability of the fungus from isolates collected from the U.S. and the Republic of South Africa. DER developed in maize following inoculations with a spore suspension prior to flowering in both greenhouse and field evaluations. A spore suspension gave a better differentiation of resistance responses than dried preparations of colonized millet, colonized ground popcorn, or kernels from a diseased maize ear, all applied in the whorl 10 to 15 days prior to flowering (V12 for inbreds), and natural occurrence of disease. General combining ability was significant for both 1994 and 1995 growing seasons in an analysis of the F₁ of the diallel cross, indicating that additive gene action may be responsible for resistance and could be introduced into commercial cultivars. Specific combining ability was significant in 1995 and indicates that dominant gene action or epistasis may play role in DER resistance. There were minimal numbers of isozyme polymorphisms found in my S. maydis collection. Two isolates were polymorphic for esterase, two isolates were polymorphic for hexokinase and malate dehydrogenase and one isolate was polymorphic for hexose kinase. Fungi that have limited isozyme polymorphisms often are biotrophs or fungi with formae speciales which are usually limited to one host. These groups of fungi usually have races and this may indicate that a gene-for-gene interaction exists. These findings suggest that i) the whorl inoculation separates genotypes into resistant, intermediate, and susceptible groupings; ii) additive gene action is predominant form of inheritance, and iii) there are few isozyme polymorphisms in the population of S. maydis sampled. / Ph. D.

This work evaluated the reaction of 140 corn hybrids from double-haploid inbred derived from a crossing of a resistant inbred line with and susceptible inbred line. Being that, crossed with a conventional susceptible line which were inoculated with Stenocarpella maydis and Stenocarpella macrospora .The hybrids were assessed in three locations in the Miner Triangle and three locations in Southern Brazil to evaluate the difference of hybrids reaction to S. macrospora and S. maydis. Two analysis were performed, one of the three locations in the Miner Triangle and one of the three locations in the South for the separation of five resistant hybrids, five average resistance and five susceptible to rot grain for the two locations. About the incidence of rot grain obtained from the hybrids, the quantification of S. macrospora, S.maydis and other fungi were done in the laboratory for the Miner Triangle and South of Brazil. In a joint analysis in the Miner Triangle it was found a frequency of 60% S. macrospora, 10% S.maydis and 30% other fungi. And in a joint analysis of South Brazil found 20% S. macrospora, 11% S.maydis and 69% of other fungi. The pathogen hybrid interaction showed the prevalence of S. macrospora in incidence of infected grains, with 60% in the Miner Triangle and 20% in the South, against S. maydis with 10% in the Miner Triangle and 11% in south of Brazil. These results showed that there were differences between the two places regarding the rotten grain caused by S. macrospora and S. maydis. Thus, positioning breeding programs in the pathosystem Stenocarpella-corn. / Neste trabalho, avaliou-se a reação de 140 híbridos de milho provenientes de uma linhagem duplo-haplóide derivada do cruzamento, entre uma linhagem resistente e uma linhagem suscetível, cruzada com uma linhagem convencional suscetível. Os híbridos quais foram inoculados com Stenocarpella maydis (Berkeley) Sacc e Stenocarpella macrospora (Earle) sendo avaliados em três locais no Triângulo Mineiro e Três locais no Sul do Brasil. O objetivo foi identificar genótipos resistentes à S. macrospora e S. maydis e a sua quantificação nas duas regiões. Efetuou-se duas análises conjuntas, uma com os três locais do Triângulo Mineiro e outra com três locais do Sul verificar a reação dos híbridos quanto a resistência à grãos ardidos. Na incidência de grãos ardidos obtidos dos híbridos, realizou-se a quantificação de S. macrospora, S. maydis e outros fungos, para o Triângulo Mineiro e Sul. Na análise conjunta do Triângulo Mineiro ocorreu uma freqüência de 60% de S. macrospora, 10% de S. maydis e 30% de outros fungos. A análise conjunta dos dados do Sul obteve-se 20% de S.macrospora, 11% de S.maydis e 69% de outros fungos. A interação híbrido patógeno mostrou a prevalência da S. macrospora na incidência dos grãos infectados, com 60% no Triângulo Mineiro e de 20% no Sul e S. maydis com 10% no Triângulo Mineiro e 11% no Sul do Brasil. Esses resultados mostram que existem diferenças entre os dois locais, quanto à reação à podridão de grãos de milho causado por S. macrospora e S. maydis. Com isso pode-se direcionar os programas de melhoramento no patossistema Stenocarpella-milho. / Doutor em Genética e Bioquímica