Characterization and prediction of parents seeking tolerance to pre-harvest sprouting in wheat (Triticum aestivum L.)

As adversidades clim??ticas como temperaturas elevadas e precipita????o antes e durante o per??odo de colheita ocasionam o fen??meno da germina????o na pr??-colheita (Pre-harvest sprouting PHS) dos gr??os de trigo. Tal condu????o deprecia a qualidade da farinha por meio da atividade de enzimas respons??veis pela germina????o, que degradam o amido. Desta forma, o estudo teve o objetivo de analisar o comportamento do car??ter germina????o na pr??-colheita em gen??tipos de trigo hexapl??ide (Triticum aestivum L.), com base em distintos anos de avalia????o, gerando informa????o para a melhor indica????o de cultivares a regi??o sul do Brasil e na reposi????o de combina????es promissoras em blocos de cruzamentos em programas de melhoramento gen??tico do trigo. O experimento foi conduzido nos anos de 2010 e 2011, no Centro de Gen??mica e Fitomelhoramento, Faculdade de Agronomia Eliseu Maciel, Universidade Federal de Pelotas (CGF/FAEM/UFPel), situado no munic??pio do Cap??o do Le??o/RS, Brasil. O delineamento empregado foi de blocos ao acaso com tr??s repeti????es, foram analisados 33 gen??tipos de trigo a partir de caracteres agron??micos e relacionados a germina????o na pr??-colheita do trigo. Simultaneamente, no ano de 2010 foram obtidas 56 popula????es h??bridas F1 e F2 a partir de hibrida????es artificiais entre oito cultivares de trigo, com distinta toler??ncia a germina????o na espiga, seguindo o delineamento dial??lico completo, com os rec??procos. As popula????es e os respectivos genitores foram avaliados na safra agr??cola de 2011 em campo experimental, no munic??pio de Cap??o do Le??o, adotando o delineamento em blocos ao acaso, com tr??s repeti????es. Neste experimento foram avaliados os caracteres: percentual de gr??os germinados (GG) nas gera????es fixas F1 e genitores, e ??ndice de queda ??mido (IQU), nas gera????es fixas (F1 e genitores) e popula????es segregantes (F2). Na an??lise de intera????o gen??tipo x ano foi detectada interfer??ncia do ambiente sobre alguns gen??tipos. Os gen??tipos BIO 08228, RA??ZES, HORIZONTE e BRS 194 foram aqueles de menores valores de GG, e a cultivar GUAMIRIM com elevado IQ, para os dois anos de avalia????o, demonstrando a presen??a de genes de toler??ncia a PHS. Com base nos resultados da dissimilaridade gen??tica, foi obtida a predi????o de importantes genitores. Assim destacam-se TBIO ITAIP??, BIO 08228, RA??ZES, HORIZONTE, BRS 194, TBIO PIONEIRO, BIO 07367, RA??ZES, GUAMIRIM e FRONTANA para compor os blocos de cruzamento, visando ?? melhor complementaridade de alelos distintos de toler??ncia a PHS em trigo. No desempenho per se, a maioria dos gen??tipos apresentaram reduzida atividade de alfa-amilase que degradam o amido. Os gen??tipos TBIO PIONEIRO, MARFIM e TBIO TIBAGI, expressaram reduzida atividade da enzima alfa-amilase. Houve pronunciada herdabilidades para os caracteres em ambos os anos exceto para GG nos gen??tipos sens??veis em 2011. A toler??ncia a PHS ?? controlada por genes de efeitos aditivos evidenciados por elevadas capacidade geral de combina????o (CGC) e por genes de efeitos n??o aditivos evidenciado pela capacidade especifica de combina????o (CEC).Se destaca que os efeitos aditivos foram mais importantes sobre a vari??ncia gen??tica total. Neste experimento, as cultivares QUARTZO e FRONTANA apresentam o melhor potencial para o uso em blocos de cruzamentos para incremento da toler??ncia a PHS e redu????o da atividade da enzima alfa-amilase. Foram evidenciadas constitui????es gen??ticas transgressivas em F2 associadas com elevadas estimativas de heterose em F1 para ambas as caracter??sticas avaliadas no IQU e GG. Isto, conciliado a baixa perda de vigor por endogamia para IQU, evidenciando que as popula????es destas combina????es s??o potenciais fontes de recupera????o de indiv??duos superiores. Existe pronunciado efeito rec??proco para o car??ter toler??ncia a germina????o na pr??-colheita e aumento do ??ndice de queda.The climate adversities, such as high temperatures and rain before and during the harvesting period lead to a phenomenon called Pre-harvest sprouting (PHS) of wheat grain. This germination decreases the wheat flour quality through the activation of enzymes responsible for germination which degrade starch. Therefore, this study had as objective to analyse the character pre-harvest sprouting in hexaploid wheat genotypes (Triticum aestivum L.), in the Southern region of Brazil, based on distinct evaluation years. Also, the evaluations aim to indicate the most adapted cultivars for Southern Brazil and to select parental genotypes for breeding programs of wheat. The experiment was conducted in the years 2010 and 2011, in the Centro de Gen??mica e Fitomelhoramento, Faculdade de Agronomia Eliseu Maciel, Universidade Federal de Pelotas (CGF/FAEM/UFPel), located at Cap??o do Le??o County/RS, Brazil. The design used was random blocks with three replications. A total of 33 genotypes were phenotyped regarding agronomic and pre-harvest sprouting characters in wheat. Simultaneously, in 2010, 56 F1 and F2 hybrid populations obtained from artificial hybridizations between eight wheat cultivars, with different tolerance to sprouting according to a complete diallel design, with reciprocals. The populations and their parental genotypes were evaluated in the agricultural season of 2011. In this experiment, the following characters were evaluated: percentage of germinated grains (GG) in the fixed generations F1 and parents, falling number index (FNI) in the fixed generations F1 and parents, and segregant populations (F2). In the analysis of genotype x year, it was detected an interference of the environment on the results of some genotypes. The genotypes: BIO 08228, RA??ZES, HORIZONTE and BRS 194 with the lowest GG values, and the cultivar GUAMIRIM with high FNI, for both evaluation years, showing the presence of PHS tolerance alleles. Based on the genetic dissimilarity, was obtained from the prediction of important parents. Thus elite genotypes such as TBIO ITAIP??, BIO 08228, RA??ZES, HORIZONTE, BRS 194, TBIO PIONEIRO, BIO 07367, RA??ZES, GUAMIRIM and FRONTANA were obtained to form the crossing blocks, aiming to complement the distinct alleles for PHS. The majority of genotypes presented reduced alpha-amylase activity, which causes starch degradation. The genotypes TBIO PIONEIRO, MARFIM and TBIO TIBAGI, on the other hand, presented the lowest alpha-amylase activity. There was a high heritability for both characters in both years except for GG of susceptible genotypes in 2011. The PHS tolerance is controlled by additive effects of genes evidenced by high general combining ability and by non-additive effects of genes evidenced by the specific combining ability, but it was evident that the additive effects were more important. The cultivars QUARTZO and FRONTANA presented the best potential for the use in crossing blocks aiming to increase PHS tolerance and to reduce alpha-amylase activity. Transgressive segregation was observed with high heterosis estimates for both traits FNI and GG. This, added to the loss of vigor by inbreeding for FNI, this indicates that these combinations are potential sources of tolerance to PHS. There was a high reciprocal effect that should be taken into account when producing hybrid cultivars with tolerance to pre-harvest germination and high FNI